JP4883057B2 - Image processing program, image processing apparatus, and image processing method - Google Patents

Description

  The present invention relates to an image processing program for performing image processing on image data to be processed, an image processing apparatus, and an image processing method.

To output image data generated by an imaging device such as an electronic camera to an output device such as a CRT monitor or a printer, a gradation conversion process using a gradation curve corresponding to the output device in order to improve the appearance. Has been done. If such gradation conversion processing is not performed, it will be difficult to see due to flare of the output device, black float, external light reflection, and the like. In the gradation conversion process, a so-called S-shaped gradation curve is used in addition to the gradation curve corresponding to the output device. By adjusting the contrast with this S-shaped gradation curve, a sharp output image can be obtained in the output device (see, for example, Patent Document 1).
JP 2004-222076 A

  In the gradation conversion process using the S-shaped gradation curve described above, the contrast can be enhanced, while the contrast of the bright gradation is lowered or the dark gradation is crushed darkly. was there.

  The present invention has been made in view of the above problems, and an object of the present invention is to perform image processing capable of improving bright part gradation and dark part gradation while maintaining apparent contrast.

  An image processing program of the present invention is an image processing program for realizing image processing on image data to be processed by a computer, an acquisition step for acquiring the image data, and input / output characteristics used for gradation conversion processing. A determination step in which a degree of emphasis at the time of performing correction for emphasizing a local contrast indicating a contrast in a local region of the image is determined and a gradation conversion process is performed on the image data according to the input / output characteristics. A computer that realizes a gradation conversion processing step to be performed and a correction step of performing correction for enhancing the local contrast on the image data subjected to the gradation conversion processing based on the enhancement degree. It is characterized by.

  The input / output characteristic may have a characteristic that takes into account the characteristic of weakening the contrast at an intermediate part of the gradation.

  The input / output characteristics are defined by a gradation curve having normal characteristics and a gradation curve having characteristics that weaken the contrast, or the characteristics that weaken the contrast are added to the normal characteristics. It may be defined by one gradation curve.

  Further, in the determination step, the degree of enhancement may be determined to be larger as the degree of weakening the contrast is larger, and the degree of enhancement may be determined to be smaller as the degree of weakening the contrast is smaller.

  In addition, a configuration obtained by converting the configuration related to the above invention into an image processing apparatus and an image processing method for performing image processing on image data to be processed is also effective as a specific aspect of the present invention.

  According to the present invention, it is possible to perform image processing capable of improving the bright part gradation and the dark part gradation while maintaining the apparent contrast.

<First Embodiment>
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. In the first embodiment, a single-lens reflex type electronic camera to which the image processing program of the present invention is applied will be described as an example.

  FIG. 1 is a diagram illustrating a configuration of an electronic camera 1 according to the first embodiment. As shown in FIG. 1, an electronic camera 1 includes a photographing lens 2, an aperture 3, a quick return mirror 4, a sub mirror 5, a diffusion screen 6, a condenser lens 7, a pentaprism 8, a beam splitter 9, an eyepiece lens 10, and an imaging lens. 11, a photometric sensor 12, a shutter 13, an image sensor 14, and a focus detection unit 15.

  The photometric sensor 12 is, for example, a five-part photometric sensor. The imaging element 14 is a semiconductor device such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor). For example, the focus detection unit 15 detects a focus state of the photographic lens 2 by performing phase difference type focus detection. The electronic camera 1 detects the focus state of the photographic lens 2 by performing contrast-type focus detection based on the luminance detected by the photometric sensor 12.

  The electronic camera 1 further includes a monitor 16 such as a liquid crystal monitor that displays an image generated by imaging, and a control unit 17 that controls each unit. The control unit 17 includes a memory (not shown) therein, and records a program for controlling each unit in advance.

  When not photographing, that is, when photographing is not performed, the quick return mirror 4 is disposed at an angle of 45 ° as shown in FIG. The light beam that has passed through the photographing lens 2 and the diaphragm 3 is reflected by the quick return mirror 4 and guided to the eyepiece lens 10 through the diffusion screen 6, the condenser lens 7, the pentaprism 8, and the beam splitter 9. The user confirms the composition by viewing the subject image through the eyepiece 10. On the other hand, the light beam split upward by the beam splitter 9 is re-imaged on the imaging surface of the photometric sensor 12 via the imaging lens 11. Further, the light beam transmitted through the quick return mirror 4 is guided to the focus detection unit 15 via the sub mirror 5.

  On the other hand, at the time of photographing, the quick return mirror 4 is retracted to the position indicated by the broken line, the shutter 13 is opened, and the light flux from the photographing lens 2 is guided to the image sensor 14.

  FIG. 2 is a functional block diagram of the electronic camera 1 according to the first embodiment. 2, the electronic camera 1 includes a timing generator 20, a signal processing unit 21, an A / D conversion unit 22, a buffer memory 23, a bus 24, a card interface 25, and a compression / decompression unit in addition to the configuration of FIG. 26, each part of the image display unit 27 is provided. The timing generator 20 supplies output pulses to the image sensor 14. The image data generated by the image sensor 14 is temporarily stored in the buffer memory 23 via the signal processing unit 21 (including a gain adjustment unit corresponding to the imaging sensitivity) and the A / D conversion unit 22. The buffer memory 23 is connected to the bus 24. The bus 24 is connected to the card interface 25, the control unit 17, the compression / decompression unit 26, and the image display unit 27 described in FIG. The card interface 25 is connected to a removable memory card 28 and records image data on the memory card 28. The control unit 17 is connected to a switch group 29 (including a release button (not shown)) of the electronic camera 1, a timing generator 20, and a photometric sensor 12. Further, the image display unit 27 displays an image or the like on the monitor 16 provided on the back surface of the electronic camera 1.

  The operation at the time of photographing of the electronic camera 1 having the above-described configuration will be described using the flowchart shown in FIG.

  In step S <b> 1, the control unit 17 determines whether or not the user has instructed to start shooting via the switch group 29. If the control unit 17 determines that an instruction to start photographing is given, the process proceeds to step S2.

  In step S <b> 2, the control unit 17 controls each unit and captures a subject image with the image sensor 14 to generate image data. Image data generated by the imaging device 14 is temporarily stored in the buffer memory 23 via the signal processing unit 21 and the A / D conversion unit 22.

  In step S3, the control unit 17 reads the image data from the buffer memory 23 and performs normal image processing. Normal image processing includes white balance adjustment, interpolation processing, color tone correction processing, and the like. Since the specific method of each process is the same as that of a well-known technique, description is abbreviate | omitted.

  In step S4, the control unit 17 selects the gradation curve G1. The gradation curve G1 is used for gradation conversion processing performed in step S5 described later, and is a gradation curve having a known S-shaped characteristic in a gradation curve corresponding to an output device such as a CRT. is there. The control unit 17 records in advance two types of gradation curves (G1, G2) shown in FIGS. 4 and 5 in an internal memory (not shown).

  In step S5, the control unit 17 performs gradation conversion processing on the image data subjected to image processing in step S3 according to the gradation curve G1 selected in step S4. The details of the gradation conversion process are the same as those of the known technique, and thus description thereof is omitted.

  In step S6, the control unit 17 selects the gradation curve G2. As shown in FIG. 5, the gradation curve G2 has a characteristic of weakening the contrast in the middle portion of the gradation as compared with the 1: 1 input / output (see the dotted line in FIG. 5).

  In step S7, the control unit 17 performs the second gradation conversion process on the image data that has been subjected to the first gradation conversion process in step S5, according to the gradation curve G2 selected in step S6. The details of the gradation conversion process are the same as those of the known technique, and thus description thereof is omitted. Note that the gradation is softened in the middle portion of the gradation by performing the gradation conversion processing according to the gradation curve G2 described above.

  In step S8, the control unit 17 performs local contrast enhancement processing on the image data that has been subjected to the second gradation conversion processing in step S7. The local contrast is a contrast in a local region of an image.

  The local contrast enhancement calculation in each pixel R [x, y], G [x, y], B [x, y] is performed by the following equations 1 to 6.

式１中のＹは、注目画素の輝度値を示す。また、式１中のｋｒ，ｋｇ，ｋｂは所定の係数である。また、式２中のＬｐｗは、注目画素周りのローパスフィルタであり、このローパスフィルタは、図６に示す特性を有する。このローパスフィルタは、半値幅（図６中ｄ）が画像の短辺の１／１００以上の広い幅のローパスフィルタである。したがって、式２のＹｌｐは、輝度値Ｙにローパス処理を施したローパス値に相当する。また、式３のｇａｉｎは、強調演算時のゲインであり、式３中のＫｄｉｆは、所定の調整係数である。

Y in Equation 1 indicates the luminance value of the target pixel. Further, kr, kg, and kb in Equation 1 are predetermined coefficients. Lpw in Equation 2 is a low-pass filter around the pixel of interest, and this low-pass filter has the characteristics shown in FIG. This low-pass filter is a wide-width low-pass filter whose half-value width (d in FIG. 6) is 1/100 or more of the short side of the image. Therefore, Ylp in Equation 2 corresponds to a low-pass value obtained by performing low-pass processing on the luminance value Y. Further, “gain” in Expression 3 is a gain at the time of emphasis calculation, and “Kdif” in Expression 3 is a predetermined adjustment coefficient.

  The adjustment coefficient Kdif is an adjustment coefficient for adjusting the local contrast. As apparent from Equation 3, when the adjustment coefficient Kdif changes, the weight for combining the luminance value of the target pixel and the low-pass value around the target pixel changes. For example, when the adjustment coefficient Kdif = 0, the local contrast is not enhanced, as is apparent from Equation 3. As a tendency, the degree of local contrast enhancement increases as the adjustment coefficient Kdif increases. As described in step S7, the gradation is softened by performing the gradation conversion processing according to the gradation curve G2, so that the local contrast is adjusted by appropriately setting the adjustment coefficient Kdif. The visual contrast can be maintained. The adjustment coefficient Kdif may be a fixed value or a fluctuation value. Here, for example, it is assumed that Kdif = a fixed value of about 0.1.

  In step S9, the control unit 17 records the image data subjected to the local contrast enhancement process in step S8 on the memory card 28 via the card interface 25, and ends the series of processes. Note that before the image data is recorded on the memory card 28, an image compression process (such as a JPEG compression process) may be performed as necessary via the compression / decompression unit 26.

  As described above, according to the first embodiment, gradation conversion processing is performed on image data to be processed in accordance with predetermined input / output characteristics, and image data subjected to gradation conversion processing is processed. Then, based on a predetermined enhancement degree according to the input characteristics, correction for enhancing the local contrast is performed. Therefore, it is possible to improve the bright part gradation and the dark part gradation while maintaining the contrast. Furthermore, according to the first embodiment, the hue of each of the bright part gradation, the intermediate part gradation, and the dark part gradation is obtained by the gradation conversion process using the S-shaped gradation curve as in the related art. The phenomenon of changing can also be reduced.

  Further, according to the first embodiment, the correction for emphasizing the local contrast using the low-pass filter having the wide width at half maximum (d in FIG. 6) of 1/100 or more of the short side of the image illustrated in FIG. Thus, correction can be performed based on the medium frequency component. This correction is different from the correction based on the super-high frequency component such as edge enhancement usually performed for each pixel, and corrects the local contrast to improve the bright part gradation and the dark part gradation while maintaining the contrast. be able to.

Second Embodiment
The second embodiment of the present invention will be described below with reference to the drawings. Since the second embodiment is a modification of the first embodiment, only portions different from the first embodiment will be described.

  The configuration of the electronic camera of the second embodiment is the same as that of the electronic camera 1 of the first embodiment. Therefore, the following description will be made using the same reference numerals as in the first embodiment.

  In the first embodiment, the case where the gradation curve G2 that is the gradation curve used for the second gradation conversion processing and the adjustment coefficient Kdif for adjusting the local contrast are fixed is described as an example. However, in the second embodiment, the gradation curve G2 and the adjustment coefficient Kdif are changed in conjunction with each other. As described in the first embodiment, the degree of enhancement of local contrast increases as the adjustment coefficient Kdif increases. Therefore, the control unit 17 may set the gradation curve G2 so that the contrast is weakened in the middle part of the gradation as the adjustment coefficient Kdif increases.

  The flowchart of FIG. 7 shows the operation at the time of photographing of the electronic camera 1 of the second embodiment.

  In step S21 to step S25, the control unit 17 performs the same processing as in step S1 to step S5 of the flowchart of FIG.

  In step S26, the control unit 17 selects the gradation curve G2 and determines the adjustment coefficient Kdif.

  The control unit 17 may be configured to perform the selection of the gradation curve G2 and the determination of the adjustment coefficient Kdif according to the shooting mode (for example, “portrait mode”, “landscape mode”, etc.), or the contrast of the image It is good also as a structure performed according to strength, and it is good also as a structure performed according to the adjustment mode of an image. Further, the gradation curve G2 may be selected and the adjustment coefficient Kdif may be determined according to the image determination result by scene analysis or face recognition. Thus, by appropriately selecting the gradation curve G2 and determining the adjustment coefficient Kdif, it is possible to perform gradation conversion processing and local contrast enhancement processing optimized for an image.

  In addition, the control unit 17 may select the gradation curve G2 and determine the adjustment coefficient Kdif based on a user operation via the switch group 29. For example, the control unit 17 displays a designation screen for designating characteristics at the time of image processing as shown in FIG. 8 on the image display unit 27. The user moves the slide bar via the switch group 29 and designates characteristics at the time of image processing. In the example of FIG. 8, the words “hard” or “natural” are used, but this is an example, and the words indicating the characteristics at the time of image processing according to the gradation curve G2 and the adjustment coefficient Kdif described above. Anything can be used. Then, the control unit 17 performs correction to enhance the input / output characteristics used for the gradation conversion process and the local contrast indicating the contrast in the local area of the image according to the characteristics at the time of image processing specified by the user. It is determined in association with the degree of emphasis. For example, in the example of FIG. 8, as the characteristic specified by the user is closer to “natural”, the value of the adjustment coefficient Kdif is determined to be larger, and as the characteristic specified to the user is closer to “hard”, the adjustment coefficient is increased. Decrease the value of Kdif. Further, the closer the characteristic specified by the user is to “natural”, the greater the degree of softening by the gradation curve G2, and the closer the characteristic specified by the user to “hard”, Reduce the degree of softening. In the case where the user designates characteristics at the time of image processing, a preview screen may be provided as shown in FIG. 8 so that the user can confirm the result of image processing according to the designated characteristics.

  FIG. 9 shows an example of the relationship between the gradation curve G2 and the value of the adjustment coefficient Kdif. The control unit 17 may record a plurality of gradation curves as shown in FIG. 9 in advance, select one of the gradation curves, and use the gradation curve as appropriate. It is good also as composition to do.

  In step S27, the control unit 17 performs the first gradation conversion process in step S25 on the image data that has been subjected to the first gradation conversion process in step S25 in accordance with the gradation curve G2 selected in step S26. A second gradation conversion process is performed.

  In step S28, the control unit 17 performs local processing on the image data that has been subjected to the second gradation conversion process in step S27 in accordance with the adjustment coefficient Kdif determined in step S26, as in step S8 of the flowchart of FIG. Contrast enhancement processing is performed.

  In step S29, the control unit 17 records the image data subjected to the local contrast enhancement processing in step S28 on the memory card 28 via the card interface 25, as in step S9 of the flowchart of FIG. The process ends. Note that before the image data is recorded on the memory card 28, an image compression process (such as a JPEG compression process) may be performed as necessary via the compression / decompression unit 26.

  As described above, according to the second embodiment, the input / output characteristics used for the gradation conversion process are associated with the degree of enhancement when performing correction for enhancing the local contrast indicating the contrast in the local region of the image. decide. Therefore, in addition to the effects of the first embodiment, it is possible to determine optimal factors in a well-balanced manner in order to improve the bright part gradation and the dark part gradation while maintaining the apparent contrast. This effect can be obtained because in human vision, it is local to perceive contrast.

<Third Embodiment>
The third embodiment of the present invention will be described below with reference to the drawings. Since the third embodiment is a modification of the first embodiment, only parts different from the first embodiment will be described.

  The configuration of the electronic camera of the third embodiment is the same as that of the electronic camera 1 of the first embodiment. Therefore, the following description will be made using the same reference numerals as in the first embodiment.

  The flowchart of FIG. 10 shows the operation at the time of shooting of the electronic camera 1 of the third embodiment.

  In step S41 to step S43, the control unit 17 performs the same processing as in step S1 to step S3 in the flowchart of FIG.

  In step S44, the control unit 17 selects the gradation curve G3. As shown in FIG. 11, the gradation curve G3 is a gradation curve having both the characteristics of the gradation curve G1 and the characteristics of the gradation curve G2 described using the flowchart of FIG.

  In step S45, the control unit 17 performs gradation conversion processing on the image data subjected to image processing in step S43 according to the gradation curve G3 selected in step S44. That is, the control unit 17 performs the gradation conversion process only once using one gradation curve in which a characteristic (corresponding to G2) that weakens contrast is added to a normal characteristic (corresponding to G1).

  In step S46 to step S47, the control unit 17 performs the same processing as in step S8 to step S9 in the flowchart of FIG. By adopting such a configuration, the same effect as that of the first embodiment can be obtained.

  In each of the above-described embodiments, the example in which the technique of the present invention is realized in the electronic camera 1 has been described. However, the present invention is not limited to this. For example, the present invention can be similarly applied to a compact type electronic camera, a movie camera for taking a moving image, and the like.

  Further, the image processing apparatus described in each of the above-described embodiments may be realized by software using a computer and an image processing program. In this case, what is necessary is just to make it the structure which implement | achieves part or all of the process after step S4 demonstrated with the flowchart of FIG. 3 with a computer. Or what is necessary is just to set it as the structure which implement | achieves one part or all part of the process after step S24 demonstrated with the flowchart of FIG. 7 with a computer. Or what is necessary is just to set it as the structure which implement | achieves a part or all of the process after step S44 demonstrated with the flowchart of FIG. 10 with a computer.

  In addition, the present invention can be similarly applied when the image to be processed is an image after the gradation conversion process using the gradation curve G1 described in each of the above-described embodiments. In this case, what is necessary is just to make it the structure which implement | achieves part or all of the process after step S6 demonstrated with the flowchart of FIG. 3 with a computer. Or what is necessary is just to set it as the structure which implement | achieves a part or all of the process after step S26 demonstrated with the flowchart of FIG. 7 with a computer.

  The present invention can be implemented in various other forms without departing from the spirit or main features thereof. For this reason, the above-described embodiments are merely examples in all respects and should not be interpreted in a limited manner. The scope of the present invention is indicated by the scope of claims, and is not restricted by the text of the specification. Further, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

It is a figure which shows the structure of the electronic camera 1 of 1st Embodiment. It is a functional block diagram of electronic camera 1 of a 1st embodiment. It is a flowchart which shows the operation | movement at the time of imaging | photography of the electronic camera 1 of 1st Embodiment. It is a figure explaining a gradation curve. It is another figure explaining a gradation curve. It is a figure explaining a low pass filter. It is a flowchart which shows the operation | movement at the time of imaging | photography of the electronic camera 1 of 2nd Embodiment. It is a figure explaining selection of the gradation curve G2, and determination of the adjustment coefficient Kdif. It is another figure explaining a gradation curve. It is another flowchart about the operation | movement at the time of imaging | photography of the electronic camera 1 of 3rd Embodiment. It is another figure explaining a gradation curve.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electronic camera, 2 ... Shooting lens, 14 ... Image sensor, 17 ... Control part

Claims (6)

An image processing program for realizing image processing on image data to be processed by a computer,
An acquisition step of acquiring the image data;
A determination step that correlates and determines input / output characteristics used for gradation conversion processing and an enhancement degree when performing correction for enhancing local contrast indicating contrast in a local region of an image;
A gradation conversion processing step for performing gradation conversion processing on the image data according to the input / output characteristics;
A computer-implemented image processing program for performing a correction step for correcting the local contrast based on the degree of enhancement on the image data subjected to the gradation conversion processing. In the image processing program according to claim 1,
The image processing program characterized in that the input / output characteristic has a characteristic in consideration of a characteristic of weakening the contrast in an intermediate part of gradation. The image processing program according to claim 2,
The input / output characteristic is defined by a gradation curve having a normal characteristic and a gradation curve having a characteristic that weakens the contrast, or one of the normal characteristic and a characteristic that weakens the contrast. An image processing program characterized by being defined by a gradation curve. The image processing program according to claim 2,
In the determining step, the degree of enhancement is determined to be larger as the degree of weakening the contrast is larger, and the degree of enhancement is determined to be smaller as the degree of weakening the contrast is smaller. An acquisition unit for acquiring image data to be processed;
A determination unit that associates and determines input / output characteristics used for gradation conversion processing and an enhancement degree when performing correction for enhancing local contrast indicating contrast in a local region of an image;
A gradation conversion processing unit that performs gradation conversion processing on the image data according to the input / output characteristics;
An image processing apparatus comprising: a correction unit configured to perform correction for enhancing the local contrast based on the enhancement degree with respect to the image data subjected to the gradation conversion process. An acquisition step of acquiring image data to be processed;
A determination step for determining the input / output characteristics used for the gradation conversion processing in association with the degree of enhancement when performing correction for enhancing the local contrast indicating the contrast in the local region of the image;
A gradation conversion processing step for performing gradation conversion processing on the image data according to the input / output characteristics;
An image processing method comprising: a correction step of performing correction for enhancing the local contrast on the image data subjected to the gradation conversion processing based on the enhancement degree.

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