JP2008258662A - Image pickup device, image processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To simply create an encoding table used when reversible compression of image information is carried out. <P>SOLUTION: Master CCD-RAW data acquired by a master photosensitive section PD1 and slave CCD-RAW data acquired by a slave photosensitive section PD2 are respectively and individually memorized in an internal memory 32. A Huffman coding-decoding section 42A of a master photosensitive section compression/expansion processing section 30A creates a master Huffman table corresponding to the master CCD-RAW data, and a Huffman coding-decoding section 42B of a master photosensitive section compression/expansion processing section 30B creates a slave Huffman table corresponding to the slave CCD-RAW data based on the master Huffman table. The master CCD-RAW data are carried out reversible compression using the master Huffman table, and the slave CCD-RAW data are carried out reversible compression using the slave Huffman table. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an imaging apparatus and an image processing method, and in particular, performs image processing on image information acquired by a plurality of types of light receiving elements having different sensitivities and image information acquired by a plurality of types of light receiving elements having different sensitivities. The present invention relates to an image processing method to be performed.

  In recent years, in an imaging apparatus such as a digital electronic still camera (hereinafter referred to as a digital camera), with the increase in the number of pixels of a solid-state imaging device such as a CCD (Charge Coupled Device) area sensor or a CMOS (Complementary Metal Oxide Semiconductor) image sensor. The data size of image information obtained by photographing has also increased. For this reason, in this type of imaging apparatus, generally, image information is compressed by a lossy compression method such as a jpeg format with high compression efficiency and stored in a storage medium.

  There is also an imaging apparatus having a function of storing image information in a storage medium in the form of so-called CCD-RAW data, which is raw data in which no image processing is performed on the image information. Since CCD-RAW data is not subjected to image processing, there is an advantage that the user can freely perform image processing.

  Incidentally, since the CCD-RAW data generally has a large data size, it is required to increase the capacity of the storage medium. For this reason, it is conceivable to compress the CCD-RAW data by irreversible compression with high compression efficiency. However, in this case, the compressed image information cannot be decoded and returned to the original CCD-RAW data. -Image quality deteriorates compared to RAW data. Therefore, it is considered that the CCD-RAW data is subjected to reversible compression that is lower in compression efficiency than lossy compression but does not cause deterioration in image quality, and is stored.

  As a technique for reversibly compressing image information, for example, there is a technique in which pixel information constituting image information is converted into a difference value with adjacent pixel information by DPCM conversion or the like, and Huffman coding is performed. Huffman coding is a technique for compressing image information by assigning a code with a small amount of information to the pixel information converted into the difference value in descending order of occurrence frequency of the difference value.

  This Huffman coding may be performed using a typical Huffman table designed for an average statistic of many natural images. As a technique for realizing higher compression efficiency, Patent Document 1 Discloses a technique for creating an optimum Huffman table for each piece of image information without using a typical Huffman table and compressing the image information using the Huffman table.

  On the other hand, in recent years, in order to obtain a clear subject image, there has been a demand for an imaging apparatus that has a wide dynamic range of image information acquired by photographing.

  In order to realize this wide dynamic range, Patent Document 2 discloses a technique for obtaining image information with a wide dynamic range by providing each pixel with a main photosensitive portion and a secondary photosensitive portion. According to this technique, the main photosensitive part is a light receiving element having a high sensitivity to the exposure amount, while the sub photosensitive part is a light receiving element having a lower sensitivity to the exposure amount than the main photosensitive part. Even in an exposure condition where the signal is saturated, the sub-photosensitive portion can acquire information such as the contrast of the subject, and as a result, image information with a wide dynamic range is obtained.

By applying the technique disclosed in Patent Document 1 to this technique, both the image information obtained by the main photosensitive part and the image information obtained by the secondary photosensitive part can be compressed with high compression efficiency. it can.
JP 2000-125295 A JP 2004-304246 A

  However, in this technique, it is necessary to create a Huffman table optimized for each image information, and thus there is a problem that it takes much time to create the Huffman table.

  This problem is not limited to the one using the Huffman table, and can occur in the technique of lossless compression using some kind of encoding table.

  The present invention has been made to solve the above-described problems, and it is an object of the present invention to provide an imaging apparatus and an image processing method that can easily create an encoding table used when reversibly compressing image information. is there.

  In order to achieve the above object, the invention of claim 1 is characterized in that an image of a subject is picked up by a plurality of types of light receiving elements having different sensitivities, and image information indicating a subject image is acquired individually, and acquired by the image pickup means. Storage means for storing the image information by type of the light receiving element, and a plurality of high sensitivity image information obtained by the light receiving element having the highest sensitivity among the image information stored by the storage means. An encoding table for assigning codes with a small amount of information in order of increasing occurrence frequency to information corresponding to pixel information is created as one corresponding to the high-sensitivity image information, and the highest sensitivity based on the encoding table Table creation means for creating an encoding table corresponding to the image information obtained by the light receiving element excluding the light receiving element, and each image information using the corresponding encoding table Having a compression means for decompressing.

  According to the imaging apparatus of the first aspect, image information is acquired by an imaging unit that images a subject with a plurality of types of light receiving elements having different sensitivities, and the acquired image information is stored by a storage unit for each type of light receiving element. The

  Here, according to the present invention, information corresponding to a plurality of pieces of pixel information constituting the high-sensitivity image information obtained by the light-sensitive element having the highest sensitivity among the image information stored by the storage unit by the table creation unit. A code corresponding to image information obtained by a light receiving element excluding the light receiving element with the highest sensitivity is created based on the coding table after a coding table for assigning codes with a small amount of information is created in descending order of occurrence frequency. Table is created. Then, each image information is reversibly compressed by the compression means using the corresponding encoding table.

  Thus, according to the imaging device of claim 1, the light receiving elements excluding the light receiving element with the highest sensitivity based on the encoding table corresponding to the high sensitivity image information obtained by the light receiving element with the highest sensitivity. Since the encoding table corresponding to the image information obtained by the above is generated, the encoding table used when the image information is reversibly compressed can be easily generated.

  According to the present invention, as in the invention described in claim 2, the table creation unit converts each piece of pixel information constituting the high-sensitivity image information into a difference value from adjacent pixel information. As an encoding table corresponding to the high-sensitivity image information as a table in which a code with a small amount of information is assigned to a plurality of groups for each bit number of the difference value, and a code with a small amount of information is assigned to the group in which the difference value is frequently generated. Good. Thereby, image information can be compressed with higher compression efficiency.

  In particular, the invention according to claim 2 is the encoding according to the image information obtained by the light receiving element excluding the light receiving element having the highest sensitivity, wherein the table creating means is the same as the invention according to claim 3. The code assignment target assigned to each group in the coding table corresponding to the high-sensitivity image information is changed according to the difference in the number of bits between the table and the pixel information constituting the high-sensitivity image information. You may make it create by. Thereby, the encoding table corresponding to all the image information can be created more easily.

  Further, according to the present invention, as in the invention described in claim 4, the compression unit performs Huffman coding using the corresponding coding table created by the table creation unit after the image information is DPCM converted. Thus, the lossless compression may be performed. As a result, the image information can be reversibly compressed with higher compression efficiency.

  The present invention may further include decompression means for decompressing the image information reversibly compressed by the compression means, as in the fifth aspect of the invention. Thereby, the image information after lossless compression can be returned to the image information before compression.

  In particular, the invention according to claim 5 corresponds to the image information created by the table creation means, the decompression means reversibly compressed by the compression means, as in the invention according to claim 6. The decompression may be performed by inverse DPCM conversion after Huffman decoding using an encoding table. Thereby, the image information after lossless compression can be simply and reliably returned to the image information before compression.

  On the other hand, in order to achieve the above-mentioned object, the invention of claim 7 captures a subject with a plurality of types of light receiving elements having different sensitivities, individually acquires image information indicating a subject image, and acquires the acquired image information. Stored by the storage means for each type of the light receiving element, and among the image information stored by the storage means, information corresponding to a plurality of pixel information constituting the high sensitivity image information obtained by the light receiving element having the highest sensitivity. On the other hand, an encoding table for assigning codes with a small amount of information in the order of occurrence frequency is created as one corresponding to the high-sensitivity image information, and the highest sensitivity is obtained based on the encoding table corresponding to the high-sensitivity image information. A coding table corresponding to image information obtained by a light receiving element excluding the light receiving element is created, and each image information is reversibly compressed using the corresponding coding table. To.

  Therefore, according to the image processing method of the seventh aspect, since it operates in the same manner as the first aspect of the invention, the code used when the image information is reversibly compressed as in the first aspect of the invention. Table can be created easily.

  As described above, according to the present invention, there is an excellent effect that a coding table used when reversibly compressing image information can be easily created.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Here, an example of a case where the present invention is applied to a digital camera that captures a still image will be described.
(First embodiment)
FIG. 1 is a block diagram showing a schematic configuration of the digital camera 10 according to the first embodiment.

  As shown in FIG. 1, the digital camera 10 includes a CPU (central processing unit) 12 that controls the entire digital camera 10, and the CPU 12 is connected to an imaging unit 14.

  The imaging unit 14 includes a lens unit 16 configured as a zoom lens having a plurality of lenses and capable of changing (magnifying) the focal length, and an object image is formed by the lens unit 16. .

  A CCD area sensor 18 that is a solid-state imaging device is provided behind the optical axis of the lens unit 16. The CCD area sensor 18 photoelectrically converts an optical signal indicating a subject image formed by the lens unit 16 and outputs it as an analog signal.

  Here, the structure of the CCD area sensor 18 according to the present embodiment will be described. As the CCD area sensor 18, a honeycomb CCD as shown in FIG.

  The CCD area sensor 18 includes a plurality of main photosensitive portions PD1 as light receiving elements. The main photosensitive portion PD1 is two-dimensionally arranged with a predetermined arrangement pitch (horizontal arrangement pitch = Ph (μm), vertical arrangement pitch = Pv (μm)) and is shifted in the vertical and horizontal directions from the adjacent main photosensitive portion PD1. Is done. The CCD area sensor 18 includes a vertical transfer electrode VEL and a horizontal transfer electrode HEL. The vertical transfer electrode VEL is arranged so as to bypass the opening AP formed on the front surface of the main photosensitive portion PD1, and takes out a signal (charge) from the main photosensitive portion PD1 and transfers it in the vertical direction. The horizontal transfer electrode HEL is arranged on the lower side in the vertical direction of the vertical transfer electrode VEL positioned at the lowest in the vertical direction, and transfers the signal transferred from the vertical transfer electrode VEL to the outside. In the example shown in the figure, the opening AP is formed in an octagonal honeycomb shape.

  Here, each of the vertical transfer electrode groups constituted by a plurality of vertical transfer electrodes VEL arranged in a straight line in the horizontal direction has one of the vertical transfer drive signals V1, V2,. Can be applied simultaneously. In the example shown in the figure, the vertical transfer drive signal V3 is applied to the first-stage vertical transfer electrode group, and the vertical transfer drive signal V4 is applied to the second-stage vertical transfer electrode group. The vertical transfer drive signal V5 for the transfer electrode group, the vertical transfer drive signal V6 for the fourth vertical transfer electrode group, and the vertical transfer drive signal V7 for the fifth vertical transfer electrode group are 6 The vertical transfer drive signal V8 for the vertical transfer electrode group at the stage, the vertical transfer drive signal V1 for the vertical transfer electrode group at the seventh stage, and the vertical transfer drive signal for the vertical transfer electrode group at the eighth stage. V2 can be applied to each.

  Each main photosensitive portion PD1 is configured to be electrically connected to one adjacent vertical transfer electrode VEL via a transfer gate TG. In the example shown in the figure, each main photosensitive portion PD1 is connected to the vertical transfer electrode VEL adjacent to the lower right via a transfer gate TG.

  The CCD area sensor 18 further includes a secondary photosensitive portion PD2 which is a light receiving element having a low sensitivity with respect to the exposure amount as compared with the above-described main photosensitive portion PD1. The main photosensitive portion PD1 and the secondary photosensitive portion PD2 constitute a set of pixels. As shown in FIG. 2, the secondary photosensitive portion PD2 is provided between a plurality of primary photosensitive portions PD1, and the secondary photosensitive portion PD2 is electrically connected to one adjacent vertical transfer electrode VEL by a transfer gate TG. Yes. Note that the electrode to which the transfer gate TG of the secondary photosensitive portion PD2 is connected is provided differently from the electrode to which the transfer gate TG of the adjacent main photosensitive portion PD1 is connected. Further, the secondary photosensitive portion PD2 also has an opening AP as in the main photosensitive portion PD1. The opening AP of the secondary photosensitive portion PD2 has a smaller area than the opening of the main photosensitive portion PD1. For this reason, the secondary photosensitive portion PD2 is less sensitive than the main photosensitive portion PD1.

  Next, FIG. 3 shows an example of a graph showing the sensitivity states of the main photosensitive portion PD1 and the secondary photosensitive portion PD2 with respect to the exposure amount.

  A line A in FIG. 3 shows the sensitivity of the main photosensitive portion PD1 with respect to the exposure amount, and a line B in FIG. 3 shows the sensitivity of the secondary photosensitive portion PD2 with respect to the exposure amount. The main photosensitive portion PD1 is more sensitive to the exposure amount than the slave photosensitive portion PD2, and outputs a high signal level even when the signal range m is wide and the exposure amount is small. However, on the other hand, the signal level of the main photosensitive portion PD1 reaches saturation with a lower exposure amount than that of the secondary photosensitive portion PD2. On the other hand, the secondary photosensitive portion PD2 has a narrower signal range n than the main photosensitive portion PD1 and a low signal level for the same exposure amount. However, the signal level does not saturate until a relatively high exposure amount is reached. That is, the main photosensitive portion PD1 is suitable for photographing a subject having a relatively small difference in brightness and the sub-photosensitive portion PD2 is suitable for photographing a subject having a relatively large difference in brightness. Therefore, by using a combination of the signal levels obtained by the main photosensitive portion PD1 and the secondary photosensitive portion PD2, the CCD area sensor 18 realizes a wide dynamic range as compared with the case where the main photosensitive portion PD1 alone is configured. be able to.

  Since the signal range m of the main photosensitive portion PD1 and the signal range n of the secondary photosensitive portion PD2 are different as described above, the number of bits of the pixel information obtained by the primary photosensitive portion PD1 and the pixels obtained by the secondary photosensitive portion PD2 are different. The number of bits of information is also different, and the number of bits of pixel information obtained by the main photosensitive portion PD1 is larger than the number of bits of pixel information obtained by the secondary photosensitive portion PD2. Hereinafter, in the present embodiment, as an example, the number of bits of pixel information of the primary photosensitive portion PD1 is 14 bits, and the number of bits of pixel information of the secondary photosensitive portion PD2 is 12 bits.

  As shown in FIG. 1, the output end of the CCD area sensor 18 is connected to an analog signal processing unit 20, and an analog signal indicating a subject image generated by photoelectric conversion by the CCD area sensor 18 is an analog signal processing unit 20. Sent to.

  The analog signal processing unit 20 includes a correlated double sampling circuit (hereinafter referred to as “CDS”) (not shown). The correlated double sampling process by the CDS is performed in order to reduce noise included in the output signal of the CCD area sensor 18, and the feedthrough component level and the pixel signal included in the output signal for each pixel of the CCD area sensor 18. This is processing for obtaining accurate pixel information by taking the difference from the component level. An output end of the analog signal processing unit 20 is connected to an input end of an analog / digital converter (hereinafter referred to as “ADC”) 22. The analog signal subjected to the correlated double sampling process by the CDS is transmitted to the ADC 22.

  The ADC 22 converts the transmitted analog signal into image information that is a digital signal, and an output end thereof is connected to an input end of the digital signal processing unit 24.

  The digital signal processing unit 24 has a built-in line buffer having a predetermined capacity and performs control to directly store input image information in a predetermined area of an internal memory 32 to be described later, and performs various image processing on the image information. Do. The digital camera 10 according to the present embodiment has a function of storing image information in the form of so-called CCD-RAW data, which is raw data that is not subjected to image processing at all, and executes the function. In this case, the digital signal processing unit 24 does not perform any image processing on the image information input from the ADC 22.

  The CPU 12 is connected to a memory control unit 28, a main photosensitive unit compression / expansion processing unit 30A, and a secondary photosensitive unit compression / decompression processing unit 30B via a system bus 26.

  The memory control unit 28 controls access to the internal memory 32 and the external memory 34. The memory control unit 28 includes a main / subordinate determination unit 36.

  The master / slave discriminating unit 36 discriminates whether the pixel information constituting the CCD-RAW data is acquired by the main photosensitive unit PD1 or the secondary photosensitive unit PD2. Specifically, since the arrangement state of the main photosensitive portion PD1 and the secondary photosensitive portion PD2 is known in the CCD area sensor 18, pixel information output from the CCD area sensor 18 is distributed according to this arrangement state.

  The internal memory 32 temporarily stores image information acquired mainly by imaging. The image information includes image information after digital signal processing by the digital signal processing unit 24, CCD-RAW data, image information after reversibly compressing the CCD-RAW data, and the like. Various data related to the control of the digital camera 10 are also stored.

  Furthermore, the external memory 34 is a portable nonvolatile storage medium that stores image information obtained by photographing.

  On the other hand, the compression / decompression processing unit 30A for the main photosensitive portion has the number of bits of pixel information constituting the main CCD-RAW data with respect to the main CCD-RAW data which is the CCD-RAW data acquired by the main photosensitive portion PD1. Compression / decompression processing is performed according to (14 bits in this embodiment). Further, the secondary photosensitive unit compression / decompression processing unit 30B has the number of bits of pixel information constituting the secondary CCD-RAW data with respect to the secondary CCD-RAW data which is the CCD-RAW data acquired by the secondary photosensitive unit PD2. Compression / decompression processing is performed according to (in this embodiment, 12 bits).

  The compression / decompression processing unit 30A for the primary photosensitive unit includes a DPCM conversion unit 40A and a Huffman encoding / decoding unit 42A, and the compression / decompression processing unit 30B for the secondary photosensitive unit includes a DPCM conversion unit 40B and a Huffman encoding / decoding unit 42B. It has.

  The DPCM converters 40A and B DPCD-convert the CCD-RAW data, and inverse DPCM convert the DPCM-converted CCD-RAW data to return it to the CCD-RAW data before DPCM conversion.

  Here, DPCM conversion for CCD-RAW data will be described with reference to FIG.

  In the DPCM conversion, pixel information to be converted ('x' in the example shown in FIG. 4A, hereinafter referred to as “conversion target pixel information”) is converted into pixel information of an adjacent pixel (for example, FIG. A predicted value is obtained by prediction from a), b, and c) of A), and pixel information to be converted is converted into an error (difference value) between the predicted value and actual pixel information. Therefore, the smaller the error is, the smaller the converted value is, and it becomes possible to obtain high compression efficiency by Huffman coding, which will be described later, performed after DPCM conversion.

  Further, the conversion target image information x in FIG. 4A may be simply converted into a value (difference value) obtained by dividing the pixel information x by the value of the pixel information c.

  Here, in the CCD area sensor 18 according to the present embodiment, as shown in FIG. 2, the main photosensitive portion PD1 and the secondary photosensitive portion PD2 are alternately arranged. Therefore, as shown in FIG. 4B as an example, the CCD-RAW data includes pixel information sequences A, B, C... Corresponding to the main photosensitive portion PD1, and pixel information corresponding to the secondary photosensitive portion PD2. It has a structure in which the rows A2, B2, C2,. If the DPCM conversion is performed as it is, the difference in signal level between the pixel information of the primary photosensitive portion PD1 and the pixel information of the secondary photosensitive portion PD2 is large over the entire exposure amount range, as is apparent from FIG. Even if the conversion target pixel information is converted with this difference value, it is difficult to obtain high compression efficiency in the subsequent Huffman coding.

  Therefore, in the digital camera 10 according to the present embodiment, the main / subordinate determining unit 36 acquires each pixel information constituting the CCD-RAW data in either the main photosensitive unit PD1 or the secondary photosensitive unit PD2. It is determined whether it has been done. Then, the pixel information acquired by the main photosensitive portion PD1 as shown in FIG. 4C is set as main CCD-RAW data, and the pixel information acquired by the follower photosensitive portion PD2 as shown in FIG. 4D. Are stored in the internal memory 32 as slave CCD-RAW data.

  The DPCM conversion unit 40A included in the main photosensitive unit compression / expansion processing unit 30A performs DPCM conversion on the main CCD-RAW data, and the DPCM conversion unit included in the sub photosensitive unit compression / expansion processing unit 30B. 40B performs DPCM conversion on slave CCD-RAW data.

  Note that the DPCM converters 40A and 40B perform inverse DPCM conversion in addition to the above DPCM conversion. The inverse DPCM conversion is a process for returning the CCD-RAW data after the DPCM conversion to the CCD-RAW data before the DPCM conversion by performing the reverse process of the DPCM conversion.

  Further, the Huffman encoding / decoding unit 42A included in the compression / decompression processing unit 30A for the main photosensitive unit and the Huffman encoding / decoding unit 42B included in the compression / decompression processing unit 30B for the secondary photosensitive unit are the CCDs after DPCM conversion. -Reversibly compress the CCD-RAW data by Huffman encoding the RAW data. The Huffman coding referred to here is a process of assigning an optimum code (Huffman code) to each pixel information based on the frequency of occurrence of a difference value obtained by converting each pixel information by DPCM conversion.

  The Huffman coding / decoding units 42A and 42B can perform Huffman decoding in addition to such Huffman coding. The Huffman decoding is a process for returning the Huffman-encoded CCD-RAW data to the CCD-RAW data before the Huffman encoding.

  Here, the Huffman coding according to the present embodiment will be described in detail.

  When reversibly compressing CCD-RAW data, first, the CCD-RAW data is DPCM converted, and the converted pixel information (difference values) is divided into a plurality of groups as shown in FIG. For example, group 0 is a group having a difference value of 0, group 1 is a group having a difference value of −1, 1, group 2 is a group having a difference value of −3, −2, 2, 3, The last group 14 is a group having a difference value in the range of −16383 to −8192 and in the range of 8192 to 16383. Thus, in the Huffman encoding / decoding unit 42A according to the present embodiment, the main CCD-RAW data that is 14-bit data is divided into 15 groups according to the number of bits of the difference value.

  Then, the occurrence frequency of the difference value is obtained for each group, and a code with a small amount of information (short), that is, a Huffman code is assigned to the group with the highest occurrence frequency. For example, when the frequency of occurrence of the difference value of group 0 is the highest and the frequency of occurrence decreases as the group number increases, 00 as the Huffman code for group 0, 010 for group 1, 011 for group 2, and group 14 Is assigned 1111111111110. Note that the difference values in each group are distinguished by additional bits. For example, in the case of group 1, one bit is sufficient as an additional bit to distinguish between -1 and 1, and similarly, group 2 has 2 bits as an additional bit to distinguish -3, -2, 2, 3 14 may be 14 bits as additional bits.

  In this way, the Huffman code / decoding unit 42A creates a Huffman table in which short codes are assigned in the order of groups in which the generation frequency of the difference value of the main CCD-RAW data is high, and the main CCD-RAW data is generated using the Huffman table. Is reversibly compressed.

  Here, an example in which the occurrence frequency when the difference value obtained by DPCM conversion of the main CCD-RAW data is divided from group 0 to group 14 is statistically expressed for each color (R, G, B). Is shown in FIG. In FIG. 6A, the frequency of occurrence increases as the group number increases within the range from group 0 to group 7, the frequency of occurrence of group 8 is the highest, and the group number within the range from group 9 to group 14 As the value increases, the frequency of occurrence decreases.

  By the way, it is considered that the frequency of occurrence of the difference value obtained by DPCM conversion of the sub CCD-RAW data has the same tendency as the main CCD-RAW data. This is because the primary photosensitive portion PD1 and the secondary photosensitive portion PD2 are alternately arranged as shown in FIG. 2, and the adjacent primary photosensitive portion PD1 and secondary photosensitive portion PD2 have an exposure amount per the same light receiving area. Is considered to be substantially the same.

  Here, since the slave CCD-RAW data according to the present embodiment is 12 bits, in the digital camera 10 according to the present embodiment, the difference value of the pixel information of the main CCD-RAW data is divided for each number of bits. Of the groups, the remaining 12 bits from which the groups of the lower 2 bits (group 0 and group 1) are deleted are regarded as slave CCD-RAW data groups. FIG. 6B is a diagram in which group 0 and group 1 in FIG. 6A are deleted, and group 2 to group 14 of the main CCD-RAW data are changed to group 0 to group 12 of the sub CCD-RAW data. is there.

  In this way, since the frequency of occurrence of the difference value constituting the sub CCD-RAW data can be obtained based on the frequency of occurrence of the difference value constituting the main CCD-RAW data, the Huffman code / decoding unit 42B A secondary Huffman table is created based on the primary Huffman table, and the secondary CCD-RAW data is Huffman encoded.

  The created main Huffman table is stored in the main Huffman table storage unit 44A of the internal memory 32, and the subordinate Huffman table is stored in the subordinate Huffman table storage unit 44B of the internal memory 32.

  Next, the operation of the digital camera 10 according to the present embodiment will be described.

  First, with reference to FIG. 7, a flow when the CCD-RAW data is compressed by the digital camera 10 according to the present embodiment will be briefly described.

  As shown in FIG. 7, the CCD-RAW data acquired by the main photosensitive portion PD1 and the secondary photosensitive portion PD2 is divided into the main CCD-RAW data and the secondary CCD-RAW data by the main / subordinate discrimination portion 36. It is done. Then, the main Huffman table corresponding to the 14-bit main CCD-RAW data is used to compress the main CCD-RAW data, and in parallel with this, the slave CCD-RAW data corresponding to the 12-bit sub CCD-RAW data is compressed. The slave CCD-RAW data is compressed using the Huffman table.

  FIG. 8 is a diagram for explaining a case where a secondary Huffman table is created from the primary Huffman table. FIG. 8 corresponds to the frequency of occurrence of the difference value of the pixel information constituting the main CCD-RAW data shown in FIG.

  The “occurrence frequency order in the main CCD-RAW data” in FIG. 8 is obtained from the occurrence frequency of the difference values shown in FIG. Further, the “occurrence frequency order in the sub CCD-RAW data” in FIG. 8 is based on the “occurrence frequency order in the main CCD-RAW data” to the “pixel code step 1 of the sub CCD-RAW data” to the sub CCD- The Huffman code corresponding to the “occurrence frequency order in the subordinate CCD-RAW data” is assigned to each group and a subordinate Huffman table is created.

  The “pixel information code of the main CCD-RAW data” in FIG. 8 is an abbreviation of the Huffman code assigned to each group of the main CCD-RAW data, and the relationship between the Huffman code and the abbreviation is shown in FIG. Shown in According to FIG. 9, 00 is assigned as the Huffman code to the group number where the difference value occurs with the highest frequency, and the abbreviated name of the Huffman code is code 1. Similarly, 010 is assigned as the Huffman code to the group number in which the difference value occurs at the second highest frequency, and the abbreviated name of this Huffman code is code 2. 1111111111110 is assigned as the Huffman code to the group number in which the difference value occurs at the lowest frequency, and the abbreviated name of this Huffman code is code 15.

  Here, FIG. 10 shows the flow of processing of the CCD-RAW data compression processing program.

  FIG. 10 is a flowchart showing a flow of processing executed by the CPU 12 when image information acquired by the digital camera 10 capturing a subject image is stored as CCD-RAW data. The program according to this flow is stored in advance in a predetermined area of the internal memory 32.

  First, at step 100, the main CCD-RAW data, which is discriminated by the main / subordinate discrimination unit 36 and stored separately in the internal memory 32, is sent to the compression / decompression processing unit 30A for the main photosensitive unit, and the sub CCD-RAW data is subordinated. The data is transmitted to the compression / decompression processing unit 30B for the photosensitive unit.

  Next, in step 102, the DPCM conversion unit 40A included in the main photosensitive unit compression / decompression processing unit 30A is instructed to execute DPCM conversion processing. Upon receiving this instruction, the DPCM conversion unit 40A performs DPCM conversion on the main CCD-RAW data.

  In step 104, the DPCM conversion unit 40B included in the secondary photosensitive unit compression / decompression processing unit 30B is instructed to execute DPCM conversion processing. Upon receiving this instruction, the DPCM conversion unit 40B performs DPCM conversion on the slave CCD-RAW data.

  Next, in step 106, the Huffman encoding / decoding unit 42A included in the main photosensitive unit compression / decompression processing unit 30A is instructed to execute a main Huffman table creation process. In response to this instruction, the Huffman encoding / decoding unit 42A creates a main Huffman table based on the pixel information (difference value) of the main CCD-RAW data after DPCM conversion. The created main Huffman table is stored in the main Huffman table storage unit 44A of the internal memory 32.

  Next, in step 108, the Huffman encoding / decoding unit 42A included in the main photosensitive unit compression / decompression processing unit 30A is instructed to execute the Huffman encoding process. In response to this instruction, the Huffman encoding / decoding unit 42A executes Huffman encoding of the main CCD-RAW data subjected to DPCM conversion using the main Huffman table, and stores the main CCD-RAW data compressed in a lossless manner in the internal memory. 32 or stored in the external memory 34.

  Next, in step 110, the Huffman encoding / decoding unit 42B included in the secondary photosensitive unit compression / decompression processing unit 30B is instructed to execute the secondary Huffman table creation processing. In response to this instruction, the Huffman encoding / decoding unit 42B creates a slave Huffman table based on the master Huffman table. The created slave Huffman table is stored in the slave Huffman table storage unit 44B of the internal memory 32.

  Next, in step 112, the Huffman encoding / decoding unit 42B included in the secondary photosensitive unit compression / decompression processing unit 30B is instructed to execute the Huffman encoding processing. In response to this instruction, the Huffman encoder / decoder 42B performs Huffman encoding of the slave CCD-RAW data that has been DPCM converted using the slave Huffman table, and stores the slave CCD-RAW data that has been reversibly compressed into the internal memory. 32 or stored in the external memory 34. Then, this program is terminated.

  Note that step 104 may be processed in parallel with step 102.

  Steps 110 and 112 may be processed in parallel with step 108.

  Next, the flow of processing of the slave Huffman table creation processing program executed when creating the slave Huffman table based on the master Huffman table will be described using the flowchart of FIG. This program is executed by the Huffman encoding / decoding unit 42B included in the secondary photosensitive unit compression / decompression processing unit 30B in accordance with an instruction from the CPU 12. The program according to this flow is stored in advance in a predetermined area of the internal memory 32.

  First, in step 200, codes indicating the Huffman codes of groups 2 to 14 of the main CCD-RAW data are temporarily placed as codes of groups 0 to 12 of the sub CCD-RAW data. This corresponds to “pixel information code step1 of slave CCD-RAW data” in FIG.

  Next, in step 202, it is determined whether or not there is a code 14 that is not used in the subordinate Huffman table in the temporary code. Since the slave CCD-RAW data is 12 bits, there is no group to which the code 14 is assigned. If there is a code 14 in the temporary placement code, it is determined affirmative and the routine proceeds to step 204. On the other hand, if there is no code 14 in the temporary placement code, it is determined as negative and the process proceeds to step 214.

  In step 204, it is determined whether there is a code 15 that is not used in the subordinate Huffman table in the temporary code. Since the slave CCD-RAW data is 12 bits, there is no group to which the code 15 is assigned. If there is a code 15 in the temporary placement code, it is determined as affirmative and the routine proceeds to step 206. On the other hand, if there is no code 14 in the temporary placement code, it is determined as negative and the process proceeds to step 222.

  In step 206, codes that are not used among the temporary codes among the codes 1 to 13 are selected as codes N and M (N <M). In “pixel information code step 1 of slave CCD-RAW data” in FIG. 8, since code 10 and code 11 are not used, N = 10 and M = 11 are selected.

  Next, in step 208, the code 14 in the temporary code is replaced with the code 12, and the code 15 is replaced with the code 13. This is because the codes 14 and 15 are unused code numbers as described above. In FIG. 8, this corresponds to “pixel information code step 2 of slave CCD-RAW data”.

  Next, in step 210, all codes other than the code replaced in step 208 but not less than code (N + 1) and less than code M are replaced with code numbers obtained by dividing 1 from the code number. In FIG. 8, codes of code 12 or more and codes less than 12 are targeted, but such codes do not exist. Therefore, there is no code replacement in this step.

  Next, in step 212, all codes other than the code replaced in step 208 are replaced with codes obtained by dividing 2 from the code number. In FIG. 8, a code of code 12 or more is a target. That is, in the “subordinate CCD-RAW data pixel information code step 2”, the codes of the groups 9 and 10 are targeted. Therefore, the code 12 of the group 9 is replaced with the code 10, and the code 13 of the group 10 is replaced with the code 11. The result is the “subordinate CCD-RAW data pixel information code step 3” in FIG. 8, and a code, that is, a Huffman code is assigned to each group of the sub-CCD-RAW data by the above processing. Exit.

  Step 214 is a case where it is determined in step 202 that there is no code 14 in the temporary code, and it is further determined whether there is a code 15 that is not used in the secondary Huffman table in the temporary code. To do. If there is a code 15 in the temporary placement code, it is determined as affirmative and the routine proceeds to step 216. On the other hand, if there is no code 15 in the temporary placement code, it is determined to be negative and there is no need to replace the code, so the secondary Huffman table creation processing program is terminated.

  In step 216, among the codes 1 to 13, a code that is not used in the temporary placement code is selected as a code N.

  Next, in step 218, the code 15 in the temporary placement code is replaced with the code 13.

  Next, in step 220, all codes other than the code replaced in step 218 are replaced with code numbers obtained by dividing 1 from the code number. Through the above processing, a code, that is, a Huffman code is assigned to each group of slave CCD-RAW data, and the slave Huffman table creation processing program is terminated.

  Step 222 is a case where it is determined in step 204 that there is no code 15 in the temporary code, and a code that is not used in the temporary code among the codes 1 to 13 is selected as a code N. To do.

  Next, in step 224, the code 14 in the temporary placement code is replaced with the code 13.

  Next, in step 226, all codes other than the code replaced in step 224 are replaced with code numbers obtained by dividing 1 from the code number. Through the above processing, a code, that is, a Huffman code is assigned to each group of slave CCD-RAW data, and the slave Huffman table creation processing program is terminated.

  Next, the lossless compression CCD-RAW data decompression executed by the CPU 12 when decompressing the CCD-RAW data reversibly compressed by the CCD-RAW data compression processing program shown in FIG. A processing flow of the processing program will be described. A program relating to this flow is stored in a predetermined area of the internal memory 32 in advance.

  First, in step 300, the reversible compressed main CCD-RAW data is compressed from the internal memory 32 or the external memory 34 to the main photosensitive unit compression / expansion processing unit 30A, and the reversible compressed sub CCD-RAW data is compressed / expanded to the sub photosensitive unit. Transmit to the processing unit 30B.

  Next, in step 302, the Huffman encoding / decoding unit 42A included in the main photosensitive unit compression / decompression processing unit 30A is instructed to execute the Huffman decoding process. In response to this instruction, the Huffman coding / decoding unit 42A executes Huffman decoding on the lossless compressed main CCD-RAW data using the main Huffman table stored in the main Huffman table storage unit 44. . As a result, the reversible compression main CCD-RAW data becomes the state of the main CCD-RAW data after DPCM conversion.

  Next, in step 304, the DPCM conversion unit 40A is instructed to execute an inverse DPCM conversion process. In response to this instruction, the DPCM conversion unit 40A performs inverse DPCM conversion on the main CCD-RAW data after the DPCM conversion, completes the expansion of the lossless compression main CCD-RAW data, and expands the main CCD-RAW data. CCD-RAW data is stored in the internal memory 32 or the external memory 34.

  Next, in step 306, the Huffman encoding / decoding unit 42B is instructed to execute the Huffman decoding process. In response to this instruction, the Huffman coding / decoding unit 42B performs Huffman decoding on the lossless-compressed slave CCD-RAW data using the slave Huffman table stored in the slave Huffman table storage unit 44. Execute. As a result, the slave CCD-RAW data is in a state after DPCM conversion.

  Next, in step 308, the DPCM conversion unit 40B is instructed to execute reverse DPCM conversion processing. Upon receiving this instruction, the DPCM conversion unit 40B performs inverse DPCM conversion on the slave CCD-RAW data in the DPCM-converted state, completes decompression of the lossless compression slave CCD-RAW data, and decompresses the slave slave. The CCD-RAW data is stored in the internal memory 32 or the external memory 34, and this program is terminated.

  Note that steps 306 and 308 may be processed in parallel with steps 302 and 304.

  As described above, according to the first embodiment, the main CCD-RAW data acquired by the main photosensitive unit PD1 and the sub CCD-RAW data acquired by the sub photosensitive unit PD2 are individually stored in the internal memory. 32. The Huffman code / decoding unit 42A of the main photosensitive unit compression / expansion processing unit 30A creates a main Huffman table corresponding to the main CCD-RAW data, and the Huffman code / decoding unit 30B of the main photosensitive unit compression / decompression processing unit 30B. The decoding unit 42B creates a slave Huffman table corresponding to the slave CCD-RAW data based on the master Huffman table. Then, the main CCD-RAW data is reversibly compressed using the main Huffman table, and the sub CCD-RAW data is reversibly compressed using the sub Huffman table.

In this way, since the slave Huffman table is created based on the master Huffman table, it is not necessary to take statistics of the difference values of the pixel information constituting the slave CCD-RAW data. Therefore, the Huffman table can be created more easily than in the case of obtaining statistics of the difference values of the pixel information of the main CCD-RAW data and the sub CCD-RAW data. Furthermore, the time required for the compression processing of the main CCD-RAW data and the sub CCD-RAW data can be shortened.
(Second Embodiment)
In the second embodiment, an example in which the digital camera 10 ′ creates the main Huffman table and the subordinate Huffman table with the same compression / decompression processing unit will be described.

  First, the configuration of a digital camera 10 'according to the second embodiment will be described with reference to FIG. In FIG. 13, the same components as those in FIG. 1 are denoted by the same reference numerals as those in FIG.

  As shown in FIG. 13, the digital camera 10 ′ according to the present embodiment includes a compression / decompression processing unit 30.

  The compression / decompression processing unit 30 includes a processing switching unit 46, a DPCM conversion unit 40, and a Huffman code / decoding unit 42.

  When the main CCD-RAW data is transmitted to the compression / decompression processing unit 30, the processing switching unit 46 compresses / decompresses the number of bits of the pixel information constituting the main CCD-RAW data. When the processing unit 30 is switched to perform processing corresponding to 14 bits and CCD-RAW data is transmitted according to the compression / decompression processing unit 30, the number of bits of pixel information constituting the sub-CCD-RAW data Since it is 12 bits, the compression / decompression processing unit 30 is switched so as to perform processing corresponding to 12 bits.

  The DPCM conversion unit 40 performs DPCM conversion on the CCD-RAW data and inverse DPCM conversion on the CCD-RAW data that has been subjected to DPCM conversion.

  The Huffman encoding / decoding unit 42 reversibly compresses the CCD-RAW data by performing Huffman encoding on the CCD-RAW data after DPCM conversion. Also, Huffman decoding is performed on the reversibly compressed CCD-RAW data.

  Next, the operation of the digital camera 10 'according to the second embodiment will be described.

  FIG. 14 shows CCD-RAW data compression executed by the CPU 12 when image information acquired by the digital camera 10 ′ according to the second embodiment capturing a subject image is stored as CCD-RAW data. It is a flowchart which shows the flow of a process of a processing program. The program according to this flow is stored in advance in a predetermined area of the internal memory 32.

  First, in step 500, the main CCD-RAW data discriminated by the main / subordinate discriminating unit 36 and separately stored in the internal memory 32 is transmitted to the compression / decompression processing unit 30.

  Next, in step 502, the DPCM conversion unit 40 is instructed to execute DPCM conversion processing. In response to this instruction, the DPCM conversion unit 40 performs DPCM conversion on the main CCD-RAW data.

  Next, in step 504, the Huffman encoding / decoding unit 42 is instructed to execute a main Huffman table creation process. In response to this instruction, the Huffman encoding / decoding unit 42 creates a main Huffman table based on the pixel information (difference value) of the main CCD-RAW data after DPCM conversion. The created main Huffman table is stored in the main Huffman table storage unit 44A of the internal memory 32.

  Next, in step 506, the Huffman encoding / decoding unit 42 is instructed to execute the Huffman encoding process. In response to this instruction, the Huffman encoder / decoder 42 executes Huffman encoding of the main CCD-RAW data that has been DPCM converted using the main Huffman table, and stores the reversibly compressed main CCD-RAW data in the internal memory. 32 or stored in the external memory 34.

  Next, in step 508, the process switching unit 46 is instructed to switch processes. In response to this instruction, the processing switching unit 46 switches the compression / decompression processing unit 30 from processing corresponding to 14-bit pixel information to processing corresponding to 12-bit pixel information.

  Next, in step 510, the sub CCD-RAW data discriminated by the main / sub discriminator 36 and separately stored in the internal memory 32 is transmitted to the compression / decompression processor 30.

  Next, in step 512, the DPCM conversion unit 40 is instructed to execute DPCM conversion processing. In response to this instruction, the DPCM conversion unit 40 performs DPCM conversion on the slave CCD-RAW data.

  Next, in step 514, the Huffman encoding / decoding unit 42 is instructed to execute a secondary Huffman table creation process. In response to this instruction, the Huffman encoder / decoder 42 creates a slave Huffman table based on the master Huffman table. The created slave Huffman table is stored in the slave Huffman table storage unit 44B of the internal memory 32.

  Next, in step 516, the Huffman encoding / decoding unit 42 is instructed to execute the Huffman encoding process. In response to this instruction, the Huffman encoder / decoder 42 performs Huffman encoding of the slave CCD-RAW data that has been DPCM converted using the slave Huffman table, and stores the slave CCD-RAW data that has been reversibly compressed into the internal memory. 32 or stored in the external memory 34. Then, this program is terminated.

  Next, the lossless compression CCD-RAW data decompression executed by the CPU 12 when decompressing the CCD-RAW data reversibly compressed by the CCD-RAW data compression processing program shown in FIG. A processing flow of the processing program will be described. The program according to this flow is stored in advance in a predetermined area of the internal memory 32.

  First, in step 600, the main CCD-RAW data subjected to lossless compression is transmitted to the compression / decompression processing unit 30.

  Next, in step 602, the Huffman encoding / decoding unit 42 is instructed to execute the Huffman decoding process. In response to this instruction, the Huffman encoding / decoding unit 42 performs Huffman decoding on the lossless compressed main CCD-RAW data using the main Huffman table stored in the main Huffman table storage unit 44A. . As a result, the main CCD-RAW data is returned to the DPCM-converted state.

  Next, in step 604, the DPCM conversion unit 40 is instructed to execute an inverse DPCM conversion process. In response to this instruction, the DPCM conversion unit 40 performs inverse DPCM conversion on the main CCD-RAW data in the DPCM-converted state, completes the expansion of the lossless compression main CCD-RAW data, and expands the expanded main CCD-RAW data. CCD-RAW data is stored in the internal memory 32 or the external memory 34.

  Next, in step 606, the process switching unit 46 is instructed to switch processes. In response to this instruction, the processing switching unit 46 switches the compression / decompression processing unit 30 from processing corresponding to 14-bit pixel information to processing corresponding to 12-bit pixel information.

  Next, in step 608, the reversible compressed slave CCD-RAW data is transmitted to the compression / expansion processing unit 30.

  Next, in step 610, the Huffman encoding / decoding unit 42 is instructed to execute the Huffman decoding process. In response to this instruction, the Huffman encoding / decoding unit 42 performs Huffman decoding on the lossless compressed secondary CCD-RAW data using the secondary Huffman table stored in the secondary Huffman table storage unit 44B. . As a result, the slave CCD-RAW data is returned to the DPCM-converted state.

  Next, in step 612, the DPCM conversion unit 40 is instructed to execute an inverse DPCM conversion process. In response to this instruction, the DPCM conversion unit 40 performs inverse DPCM conversion on the slave CCD-RAW data that has undergone DPCM conversion, completes decompression of the lossless compression slave CCD-RAW data, and decompresses the slave CCD-RAW that has been decompressed. RAW data is stored in the internal memory 32 or the external memory 34.

  As described above, according to the second embodiment, by providing the compression / decompression processing unit 30 with the processing switching unit 46, it is possible to perform processing according to image information of different numbers of bits, and the main CCD-RAW. The configuration of the digital camera 10 ′ that creates the master Huffman table corresponding to the data and the slave Huffman table corresponding to the slave CCD-RAW data can be simplified.

  In each of the above-described embodiments, the case where the CCD area sensor 18 in which the main photosensitive portion PD1 and the secondary photosensitive portion PD2 are alternately arranged has been described, but as an example, as shown in FIG. In addition, the light receiving region of one light receiving element PD is divided into a high sensitivity light receiving region 92 having a large light receiving area for receiving light with high sensitivity by a channel stopper 94 and a low sensitivity light receiving region 90 having a small light receiving area for receiving low sensitivity light. However, a CCD area sensor 18 that can obtain a high-sensitivity signal and a low-sensitivity signal in each region may be applied. Since each light receiving element PD is provided with a channel stopper 94, a signal received with high sensitivity and a signal received with low sensitivity are not mixed, and both signals can be received separately. it can.

  In each of the above-described embodiments, the case where one sub-photosensitive part PD2 is provided for one main photosensitive part PD1 has been described. However, the present invention is not limited to this. The secondary photosensitive portion may be provided. The plurality of sub-photosensitive portions have different sensitivities with respect to the exposure amount. In this case, CCD-RAW data is stored in the internal memory 32 for each type of light receiving element, and a Huffman table is created for each CCD-RAW data. Note that when the CCD area sensor 18 shown in FIG. 16 is applied as an example, a plurality of low-sensitivity light receiving regions 90 may be provided.

  Further, in each of the above embodiments, the CCD area sensor 18 includes the main photosensitive portion PD1 and the secondary photosensitive portion PD2, but the digital camera 10 includes the CCD area sensor and the secondary photosensitive portion PD1. Two types of CCD area sensors including only the photosensitive portion PD2 may be provided.

  In each of the above embodiments, the case where the CCD area sensor is applied as the imaging means of the present invention has been described. However, the present invention is not limited to this, and other individual imaging elements such as a CMOS image sensor may be applied. .

  In each of the above embodiments, image information to be subjected to compression processing has been described as CCD-RAW data. However, the present invention is not limited to this, and image information subjected to image processing by the digital signal processing unit 24 is to be subjected to compression processing. Also good.

It is a block diagram which shows schematic structure of the digital camera which concerns on 1st Embodiment. It is a schematic plan view which shows the structure of the CCD area sensor applied with the digital camera which concerns on 1st Embodiment. It is a graph which shows an example of the difference in the sensitivity with respect to the exposure amount of the main photosensitive part of the CCD area sensor which concerns on 1st Embodiment, and a secondary photosensitive part. It is a figure with which it uses for description of DPCM conversion which concerns on 1st Embodiment, and description of the data structure of CCD-RAW data. It is a schematic diagram which shows the example of a grouping of the pixel information (difference value) after carrying out DPCM conversion of the CCD-RAW data acquired in the main photosensitive part which concerns on 1st Embodiment. It is the figure showing the occurrence frequency of the difference value of the pixel information of CCD-RAW data concerning a 1st embodiment for every group. It is a figure where it uses for description of the flow of the process which concerns on 1st Embodiment. It is a figure with which it uses for description in the case of producing a subordinate Huffman table from the main Huffman table which concerns on 1st Embodiment. It is a figure which shows the relationship between the Huffman code | cord | chord which concerns on 1st Embodiment, and the code which is the abbreviation. It is a flowchart which shows the flow of the process of the program which concerns on the CCD-RAW data lossless compression process which concerns on 1st Embodiment. It is a flowchart which shows the flow of the process of the program which concerns on the subordinate Huffman table creation process which concerns on 1st Embodiment. It is a flowchart which shows the flow of the process of the program which concerns on the reversible compression CCD-RAW data expansion | extension process which concerns on 1st Embodiment. It is a block diagram which shows schematic structure of the digital camera which concerns on 2nd Embodiment. It is a flowchart which shows the flow of the process of the program which concerns on the CCD-RAW data lossless compression process which concerns on 2nd Embodiment. It is a flowchart which shows the flow of the process of the program which concerns on the reversible compression CCD-RAW data expansion | extension process which concerns on 2nd Embodiment. It is the schematic which shows the structural example of the CCD area sensor provided with the light receiving element which can receive both a high sensitivity and a low sensitivity signal.

Explanation of symbols

10 Digital camera 18 CCD area sensor (imaging means)
30A Main photosensitive section compression / expansion processing section (compression means, expansion means)
30B Secondary photosensitive section compression / expansion processing section (compression means, expansion means)
32 Internal memory (storage means)
42A Huffman encoder / decoder (table creation means)
42B Huffman coding / decoding unit (table creation means)

Claims (7)

Imaging means for imaging a subject with a plurality of types of light receiving elements having different sensitivities, and acquiring image information indicating a subject image individually;
Storage means for storing the image information acquired by the imaging means for each type of the light receiving element;
Out of the image information stored by the storage means, the information corresponding to a plurality of pieces of pixel information constituting the high-sensitivity image information obtained by the light-sensitive element having the highest sensitivity is smaller in the amount of information in descending order of occurrence frequency. A coding table for assigning a code is created as one corresponding to the high-sensitivity image information, and based on the coding table, a coding table corresponding to image information obtained by a light receiving element excluding the light receiving element with the highest sensitivity A table creation means for creating
Compression means for reversibly compressing each piece of image information using a corresponding encoding table;
An imaging apparatus having   The table creating means converts each piece of pixel information constituting the high-sensitivity image information into a difference value from adjacent pixel information, and then divides the difference information into a plurality of groups for each bit number of the difference value. The imaging apparatus according to claim 1, wherein an encoding table corresponding to the high-sensitivity image information is created as a table to which codes with a small amount of information are assigned in order of a group having a high occurrence frequency.   The table creating means converts the encoding table corresponding to the image information obtained by the light receiving element excluding the light receiving element having the highest sensitivity to the difference in the number of bits from the pixel information constituting the high sensitivity image information. The imaging apparatus according to claim 2, wherein the imaging apparatus is created by changing a code allocation target allocated to each group in an encoding table corresponding to the high-sensitivity image information.   The compression means performs the lossless compression by performing Huffman coding using a corresponding coding table created by the table creation means after DPCM conversion of the image information. The imaging device according to claim 3.   5. The imaging apparatus according to claim 1, further comprising a decompression unit that decompresses the image information that has been reversibly compressed by the compression unit.   The decompression means performs the decompression by performing inverse DPCM conversion after Huffman decoding the image information compressed losslessly by the compression means using the corresponding encoding table created by the table creation means. The imaging apparatus according to claim 5. Captures a subject with multiple types of light receiving elements with different sensitivities and acquires image information indicating the subject image individually,
The acquired image information is stored by storage means for each type of the light receiving element,
Among the image information stored by the storage means, codes corresponding to a plurality of pieces of pixel information constituting the high-sensitivity image information obtained by the light-sensitive element having the highest sensitivity, and codes having a small amount of information in descending order of occurrence frequency A coding table for assigning is created as corresponding to the high-sensitivity image information,
Based on the encoding table corresponding to the high-sensitivity image information, create an encoding table corresponding to the image information obtained by the light receiving element excluding the light receiving element with the highest sensitivity,
An image processing method for reversibly compressing each piece of image information using a corresponding encoding table.

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