JP5057053B2 - Gamma switching device and method - Google Patents

Description

  The present invention relates to a display device that displays natural images such as video images and computer images such as characters and graphics, and in particular, can switch a gamma characteristic indicating a relative relationship between luminance of an input image signal and the display image. The present invention relates to a display device.

  In a display device used for an information processing device such as a personal computer, not only computer images such as characters and graphics but also natural images such as video images are displayed.

  Since natural images place importance on halftones, it is desirable that the gamma characteristic of the display device be a characteristic that emphasizes halftones. On the other hand, since a computer image has few halftones, when the halftone is emphasized, a display image with a sense of incongruity is obtained. For this reason, it is necessary to switch the gamma characteristic between when displaying a natural image and when displaying a computer image.

Patent Document 1 discloses a liquid crystal display device capable of switching gamma characteristics. In this liquid crystal display device, first gamma characteristic data optimum for displaying a natural image and second gamma characteristic data optimum for displaying a computer image are given in advance. When displaying a natural image, luminance correction is performed on the input image signal based on the first gamma characteristic data. When a computer image is displayed, brightness correction based on the second gamma characteristic data is performed. In the luminance correction based on the first gamma characteristic data, the gamma characteristic can be further adjusted.
Japanese Patent Laid-Open No. 10-11025

  However, in the above-described display device, the user himself needs to perform a gamma characteristic switching operation according to the display image. Such a switching operation is troublesome.

  An object of the present invention is to provide a gamma switching device that can automatically select an optimal gamma characteristic according to an input image signal.

In order to achieve the above object, the gamma switching device of the present invention provides:
A gamma correction unit that holds gamma characteristic data indicating a relative relationship of luminance between an input image signal and a display image displayed based on the input image signal, and corrects the input image signal according to the gamma characteristic data; ,
Based on the input image signal, the number of different colors among the colors constituting the display image is counted, and a color number counting unit that determines whether the count value is equal to or greater than a threshold value;
First and second gamma characteristic data having different characteristics are given in advance, and the gamma characteristic data held in the gamma correction unit is changed to the first and second gamma correction data according to the determination result in the color number counting unit. have a, and a control unit for switching between the gamma characteristic data,
When the count value is equal to or greater than the threshold value, the control unit recognizes the image as a natural image and causes the gamma correction unit to hold the first gamma characteristic data, and when the count value is less than the threshold value. , Recognizing that the computer image has fewer colors than the natural image and holding the second gamma characteristic data in the gamma correction unit,
The input image signal includes first to third image signals corresponding to the respective color components of the three primary colors,
The number-of-colors counting unit obtains an added value of each color component for each of a plurality of pixels constituting the display image based on the first to third image signals, and detects the pixels having different added values. Count the number as the number of different colors .

  The number of colors in a natural image is much larger than that in a computer image. According to the present invention, the gamma characteristic data can be automatically switched between the case where the count value (the number of colors of the image) is greater than or equal to the threshold value and the case where the count value is less than the threshold value. Therefore, by appropriately setting the threshold value, gamma characteristic data can be automatically switched between displaying a natural image and displaying a computer image, and the user does not need to switch the gamma characteristic. is there. Since the gamma characteristic can be automatically switched in this way, the user can view an image with the optimum gamma characteristic without being aware of the gamma characteristic at all.

  Next, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a block diagram showing the configuration of the gamma switching device according to the first embodiment of the present invention.

  Referring to FIG. 1, the gamma switching device is applied to a display device that displays a natural image such as a video image or a computer image such as a character or a figure, and its main part is a control unit (CPU). : Central Processing Unit) 1, a color number counting circuit 2, and a lookup table 3 which is a gamma correction unit.

  Specifically, the display device is used for an information processing device such as a personal computer. The basic configuration of the information processing device is a storage device that stores programs, input devices such as keyboards and mice, display devices such as CRT (Cathode Ray Tube) and LCD (Liquid Crystal Display), modems that communicate with the outside, etc. The communication device, an output device such as a printer, and a control device that operates according to a program stored in the storage device, receives input from the input device, and controls the operation of the communication device, output device, and display device. The gamma switching device may be used for a display device that is one of the basic components of the information processing device. The gamma switching device may be used for an external display device such as a projector or a liquid crystal display connected to the information processing device.

  The gamma switching device has an input terminal 101 to which an image signal of a computer image or a natural image is supplied, an input terminal 102 to which a synchronization signal is supplied, an input terminal 103 to which a time setting value is supplied, and a threshold level setting value. Input terminal 104 to be supplied.

  The image signal and the synchronization signal are, for example, signals that are synchronized and separated from the video signal, and are supplied from a video signal processing circuit mounted on the display device or the information processing device. The time setting value and the threshold level setting value are supplied from the control unit on the information processing apparatus side. Here, the computer image is, for example, an image such as a character or a graphic created by the user using the information processing apparatus. Natural images are, for example, video data stored in a storage device in an information processing device, video data provided on a recording medium such as a DVD (Digital Versatile Disk), or an external video supply device represented by a video camera or recorder. Video data to be provided.

  The image signal includes image signals of respective color components of R (red), G (green), and B (blue). The image signal of each color component of RGB is, for example, an 8-bit digital signal. An image of one frame is composed of a plurality of dots, and the color at each dot is expressed by an image signal of each color component of RGB. When the image signal of each RGB color component is an 8-bit digital signal, each RGB color component is expressed by 256 gradations, and the combination of these color components represents the dot color.

  The synchronization signal includes a horizontal synchronization signal, a vertical synchronization signal, and a dot clock. These horizontal synchronization signal, vertical synchronization signal, and dot clock are used to acquire the value of each color component of RGB in dot units from the image signal supplied in frame units.

  The time setting value is for setting the retention time of the gamma characteristic data in the lookup table 3. The threshold level setting value is a threshold level serving as a criterion for discrimination between a natural image and a computer image. The user can freely set the time set value and the threshold level through the operation unit of the information processing device or the display device.

  The image signal supplied to the input terminal 101 is supplied to the color number counting circuit 2 and the lookup table 3. The synchronization signal supplied to the input terminal 102, the threshold level setting value supplied to the input terminal 103, and the time setting value supplied to the input terminal 104 are supplied to the color number counting circuit 2, respectively.

  The look-up table 3 holds gamma characteristic data of the display device, and performs luminance correction based on the held gamma characteristic data for the image signal supplied from the input terminal 101.

  The color number counting circuit 2 simply counts the number of colors included in the image signal supplied from the input terminal 101. Here, the number of colors is the number of colors included in one frame image. That is, the number of colors indicates how many colors are included in one frame image. When the image signal of each RGB color component is an 8-bit signal, there are 16,777,216 (= 256 × 256 × 256) types of image colors.

  The color number counting circuit 2 compares the color number count value with the threshold level setting value. Generally, the number of colors of a natural image is about several hundred thousand to several million, and the number of colors of a computer image is 256 or less. As described above, since the number of colors of a natural image is extremely larger than that of a computer image, it is possible to determine whether the input image is a natural image or a computer image if the approximate number of colors of one frame image is known. Can do.

  When the count value of the number of colors is equal to or greater than the threshold level setting value, the color number counting circuit 2 outputs a determination result (high level signal) indicating that the image signal is a natural image. When the count value of the number of colors is less than the threshold level setting value, the color number count circuit 2 outputs a determination result (low level signal) indicating that the image signal is a computer image. The threshold level setting value is, for example, 256. The determination result output from the color number counting circuit 2 is supplied to the control unit 1.

  The control unit 1 rewrites the gamma characteristic data held in the lookup table 3 according to the determination result supplied from the color number counting circuit 2. When the determination result indicating that the image signal is a natural image is received from the color count circuit 2, the control unit 1 writes gamma characteristic data optimal for displaying the natural image in the lookup table 3. When the determination result indicating that the image signal is a computer image is received from the color number counting circuit 2, the control unit 1 writes gamma characteristic data optimum for displaying the computer image in the lookup table 3.

  In the gamma switching device, the color number counting circuit 2 simply counts the number of colors of the input image signal for each frame, and compares the count value with the threshold level setting value so that the input image becomes a natural image and a computer. It is determined which of the images. Then, the control unit 1 writes optimum gamma characteristic data to the lookup table 3 according to the determination result.

  In the color count circuit 2, when a high level signal is output, the output state is maintained for the time (period) specified by the time setting value supplied from the input terminal 104. Thus, after the gamma characteristic data optimum for displaying the natural image is written in the lookup table 3, the gamma characteristic data is held in the lookup table 3 during the period specified by the time setting value.

  The configuration and operation of the color number counting circuit 2 will be specifically described below. In the following description, it is assumed that the image signal of each RGB color component is an 8-bit digital signal.

  In the case of a full color image, about 16 million colors are used. When counting the number of colors included in an image of one frame for a full-color image, about 16 million calculations are required, and the count processing time increases. Since the color count process needs to be completed during the vertical blanking period, it is preferable that the time required for the count process is short. In order to shorten the count processing time, the color number counting circuit 2 simply counts the number of colors of one frame image.

  FIG. 2 shows the configuration of the color number counting circuit 2. Referring to FIG. 2, the color number counting circuit 2 includes a memory 200, an adder 201, a timing generation circuit 202, a readout counter 203, a color number counter 204, a comparator 205, a delay circuit 206, and an OR circuit 207.

  A synchronization signal is supplied from the input terminal 102 to the timing generation circuit 202. The timing generation circuit 202 generates a timing signal for counting the number of colors based on the synchronization signal. The timing signal is supplied from the timing generation circuit 202 to the adder 201.

  FIG. 3 shows the relationship between the timing signal and the synchronization signal. The vertical synchronization signal is a signal that defines one frame period. The horizontal synchronization signal is a signal that defines a period of one line. The timing signal is synchronized with the horizontal synchronization signal.

  A region to be counted for the number of colors in an image of one frame is determined according to how long (time length) the high level period of the timing signal is set with respect to the high level period of the horizontal synchronization signal.

  If the high-level period of the timing signal and the horizontal synchronization signal are both the same length, the area for counting the number of colors is the entire image of one frame. When the high-level period of the timing signal is shorter than the high-level period of the horizontal synchronization signal, the region for counting the number of colors in one frame image is also reduced by the shortening of the high-level period. In the case of counting the number of colors for the region of the central portion of the image of one frame, the high level period of the timing signal is set only for the central portion of the horizontal synchronization signal shown in FIG. In this way, it is possible to set a region to be counted for the number of colors for one frame image.

  The adder 201 adds RGB components representing the color of the dot for each dot of the image signal supplied from the input terminal 101 in units of frames. Since the image signal of each color component of RGB is an 8-bit digital signal, the minimum value of the addition value of each color component of RGB is given by 0 and the maximum value is given by 767.

  The memory 205 is used to count the number of colors included in an image for one frame. The memory 200 is composed of 768 words × 1 bit. The adder 201 writes 1 to the address of the memory 200 corresponding to the added value of each color component obtained for each dot. When 1 is already written in the address corresponding to the added value of the color component, 1 is held as it is. Addition of the color component data by the adder 201 and writing to the memory are performed in synchronization with the timing signal shown in FIG. Note that every address value in the memory 200 is initialized to “0” before the start of writing by the adder 201 for each frame period.

  FIG. 4 shows a procedure for writing data into the memory 200 by the adder 201. First, the address of the memory 200 is defined by a one-dimensional array of Buf [768], and all address values are initialized to 0 (step 401). Next, for each dot of the image signal input in units of frames, the RGB color components are sequentially acquired, and 1 is written to Buf [R + G + B], which is an address corresponding to the added value of each color component. (Step 402). For example, if the values (R, G, B) of RGB color components of the first dot are (16, 63, 128), 1 is written to Buf [207].

  It is determined whether or not the writing process in step 402 has been performed for all the dots of the image of one frame (step 403). If there is a dot that has not yet been written, the writing process of step 402 is performed for that dot.

  According to the above data writing process, the number of addresses in which 1 is written out of the addresses 0 to 767 of the memory 200 can be regarded as the approximate number of colors of one frame image.

  The read counter 203 is a counter for designating an address from which data is read. According to the count value of the read counter 203, the data at the corresponding address is read from the memory 200. The count value of the read counter 203 starts from 0 and is incremented by 1 for each step. An address from 0 to 767 is designated by the read counter 203.

  Data read from the memory 200 is supplied to the color number counter 204. The color number counter 204 counts the number of 1 data among the data of addresses 0 to 767 read from the memory 200. This count value is the number of colors of one frame image. The color number counter 204 supplies the count value to the comparator 205.

  The comparator 205 compares the count value supplied from the color number counter 204 as the number of colors of the image of one frame with the threshold level setting value supplied from the input terminal 103. When the count value is greater than or equal to the threshold level setting value, the comparator 205 outputs a high level signal. When the count value is less than the threshold level setting value, the comparator 205 outputs a low level signal.

  FIG. 5 shows the procedure for counting the number of colors. First, both the count value x of the reading counter 203 and the count value y of the color number counter 204 are initialized to 0 (step 501). Here, the count value X of the read counter 203 indicates an address to be read.

  When the count value of the read counter 203 is set to 0, data at an address corresponding to Buf [0] in the memory 200 is read. If the read data is 1, the count value y of the color number counter 204 is incremented by 1 (step 502).

  After the data is read, the count value x of the read counter 203 is incremented by 1, and it is determined whether or not the count value x has reached 767 (step 503). If the count value x has not reached 767, the process returns to step 502.

  When the count value x reaches 767, it is determined whether or not the count value y is greater than or equal to the threshold level setting value (step 504). If the count value y is greater than or equal to the threshold level setting value, a high level signal is output (step 505). If the count value y is less than the threshold level setting value, a low level signal is output (step 506).

  In the simple counting of the number of colors by the number-of-colors counting circuit 2, when the image signals of the respective RGB color components are 8-bit digital signals, the number of colors of the natural image of one frame is as close as possible to 768. Value. On the other hand, the number of colors of one frame of the computer image is at most about 256. Therefore, it is desirable to set the threshold level setting value to about 256.

  In the color number counting circuit 2 shown in FIG. 2, the output signal of the comparator 205 is supplied to one input of the OR circuit 207 and the delay circuit 206. The delay circuit 206 delays the signal supplied from the comparator 205 by a time specified by the time setting value supplied from the input terminal 104. The output signal of the comparator 205 given a delay by the delay circuit 206 is supplied to the other input of the OR circuit 207.

  The OR circuit 207 calculates the logical sum of the output signal of the comparator 205 and the output signal of the delay circuit 206 (a signal obtained by delaying the output signal of the comparator 205). The output of the OR circuit 207 is the output signal of the color number counting circuit 2.

  When the output signal of the color number counting circuit 2 is switched from the high level to the low level, the control unit 1 writes gamma characteristic data 701 having a flat characteristic as shown in FIG. When the output signal of the color count circuit 2 is switched from the low level to the high level, the control unit 1 writes the gamma characteristic data 702 having the characteristic of producing a contrast feeling as shown in FIG. The gamma characteristic data 702 has such characteristics that the relationship between input and output is indicated by an S-shaped curve. The gamma characteristic data 702 has a characteristic that emphasizes halftones by suppressing the luminance of the low luminance part and increasing the luminance of the high luminance part.

  In the gamma switching device according to the present embodiment, the color number counting circuit 2 simply counts the number of colors of one frame image, and compares the count value with the threshold level setting value, thereby making the input image a natural image. The computer image is determined. Then, the control unit 1 writes optimum gamma characteristic data to the lookup table 3 according to the determination result. As described above, since the gamma characteristic can be automatically switched according to the input image, the user does not need to switch the gamma characteristic. Therefore, the user can always see the image with the optimum gamma characteristic without being aware of the gamma characteristic at all.

  In the case of accurately counting the number of colors of one frame image, the number of colors of [256] × [256] × [256] when the image signals of RGB color components are 8-bit digital signals respectively. Will count. On the other hand, in the present embodiment, the dot color is determined by the added value (R + G + B) of each RGB color component, and the number of colors of one frame image is simply counted. That is, the number of colors of [256] + [256] + [256] is counted. With this simple color count process, the color count process time can be shortened.

  By adjusting the relationship of the timing signal shown in FIG. 3 with the horizontal synchronization signal in the high level period, it is possible to limit the area (number of dots) that is the object of counting the number of colors in one frame image. By limiting the area (number of dots) to be counted for the number of colors to the center portion of the image, the counting process time for the number of colors can be further shortened.

  When displaying a moving image of a natural image, for example, when a blue sky scene is displayed for a moment, the number of colors changes suddenly before and after the blue sky scene. The number of colors of an image of a blue sky scene is often lower than a threshold level setting value. For this reason, the gamma characteristic is switched before and after the blue sky scene. If the gamma characteristics are switched before and after the blue sky scene in this way, the display image becomes uncomfortable and the display quality deteriorates. According to the gamma switching device of the present embodiment, when the output signal of the comparator 206 is switched from the low level to the high level by the delay circuit 206 and the OR circuit 207, the high level period is designated by the time setting value. Continues for hours. Therefore, when a blue sky scene is displayed for a moment, the gamma characteristic data used before the display of the blue sky scene is continuously used for a specified time. This suppresses the display image from being uncomfortable. When a blue sky scene is displayed for a certain period of time, even if the gamma characteristic is switched, the display image does not feel strange.

  Further, the gamma switching device of the present embodiment may be configured to perform function setting using an on-screen display. FIG. 8 shows an example of a function setting menu screen using an on-screen display. Referring to FIG. 8, the menu screen is composed of two columns, a gamma select 801 and a holding time setting 802. In the field of the gamma select 801, check boxes for “auto”, “computer”, and “video” are provided. In the holding time setting 802 column, check boxes of “0.5 seconds”, “1 second”, “1.5 seconds”, and “2 seconds” are provided.

  Input information for checking the check boxes in the respective fields of the gamma select 801 and the holding time setting 802 is supplied to the gamma switching device 1 from the control device on the information processing device side. When the “auto” check box in the gamma select 801 column is checked, automatic gamma characteristic switching processing by the gamma switching device is executed. The time when the check box is checked in the holding time setting 802 field is used as a time setting value supplied to the input terminal 103.

  When manually switching gamma characteristics, check the “PC” and “Video” check boxes in the Gamma Select 801 column. When the “PC” check box is checked, the gamma characteristic data shown in FIG. 6 is written and held in the lookup table 3. When the video check box is checked, the gamma characteristic data shown in FIG. 7 is written and held in the lookup table 3.

(Second Embodiment)
Natural images include video (cinema) and the like in addition to video images. There are many dark scenes in images such as movies. For this reason, it is desirable to switch the gamma characteristic between when displaying an image including a dark scene such as a movie (cinema) and when displaying other video images. Here, in addition to switching the gamma characteristic between the display of the natural image and the display of the computer image, in the display of the natural image, the gamma characteristic between the display of the video including the dark scene and the display of the other video video is displayed. A mode in which switching is enabled will be described.

  FIG. 9 is a block diagram showing the configuration of the gamma switching device according to the second embodiment of the present invention.

  Referring to FIG. 9, the gamma switching device is applied to a display device that displays a natural image such as a movie (cinema) or a video image, or a computer image such as a character or a figure. It consists of a control unit (CPU) 10, an image acquisition unit 11, a memory 12 and a lookup table 13. The display device is used in the information processing apparatus as described above.

  In addition to the input terminals 101 to 104 shown in FIG. 1, the gamma switching device includes an input terminal 105 to which a dark part comparison value is supplied and an input terminal 106 to which a dark part level setting value is supplied. The image signal, the synchronization signal, the time setting value, and the threshold level setting value are the same as those described in the first embodiment.

  The dark part comparison value indicates the upper limit of the brightness for determining the dark part of the natural image. That is, the dark part comparison value is a value for determining which brightness level of the natural image is a dark part, and is set to 100, for example. The dark part level setting value is a value for determining whether or not the natural image is a video (movie) including a dark scene. The dark part comparison value and the dark part level setting value are supplied from the control unit of the information processing device or the display device to the control unit 10 of the gamma switching device. The user can freely set the dark part comparison value and the dark part level setting value through the operation unit of the information processing device or the display device.

  The image signal supplied to the input terminal 101 is supplied to the image acquisition unit 11 and the lookup table 13. The synchronization signal supplied to the input terminal 102 is supplied to the image acquisition unit 11. The threshold level setting value supplied to the input terminal 103, the time setting value supplied to the input terminal 104, the dark part comparison value supplied to the input terminal 105, and the dark part level setting value supplied to the input terminal 105 are respectively controlled. Supplied to the unit 10.

  The look-up table 13 holds gamma characteristic data of the display device, and performs luminance correction on the image signal supplied from the input terminal 101 based on the held gamma characteristic data. The image acquisition unit 11 holds the image signal supplied from the input terminal 101 in units of frames. The image acquisition unit 11 passes the held image signal to the control unit 10 in units of dots. The image acquisition unit 11 uses a horizontal synchronization signal, a vertical synchronization signal, and a dot clock in order to provide the image signal for one frame to the control unit 10 in units of dots.

  The control unit 10 includes a first count processing unit that counts the number of colors of an image of one frame, a second count processing unit that counts the number of colors of a dark portion of an image when the input image is a natural image, and a look And an LUT control unit that controls writing of gamma characteristic data to the up table 13.

  A memory 12 is used to count the number of colors. When the RGB color component image signals are 8-bit digital signals, the image colors are 16,777,216 (= 256 × 256 × 256) types. In the first embodiment, the storage area of the memory 200 is defined by a one-dimensional array of Buf [756]. However, in this embodiment, the storage area of the memory 12 is defined as 3 of Buf [256] [256] [256]. It is defined by an array of dimensions. Since Buf [R] [G] [B] may be 1 bit, if the RGB color component image signal is an 8-bit digital signal, the memory area required for counting the number of colors in the memory 12 is 96 ( = 256 × 3 ÷ 8) bytes.

  The first count processing unit uses the memory 12 to count the number of colors of the image signal held by the image acquisition unit 11. FIG. 10 shows the procedure of the color count process using the memory 12 by the first count processor.

  Referring to FIG. 10, first, the address of the memory 12 is defined by a three-dimensional array of Buf [256] [256] [256], and all address values are initialized to 0 (step 901).

  Next, for each dot of the image signal held by the image acquisition unit 11, RGB color components are sequentially acquired, and Buf [Rdata] [Gdata] [Bdata] which is an address corresponding to the value of each color component 1 is written in (step 902). For example, if the values (R, G, B) of RGB color components of the first dot are (16, 63, 128), 1 is written to Buf [16] [63] [128].

  Next, it is determined whether or not the writing process in step 902 has been performed for all the dots in the image of one frame (step 903). If there is a dot that has not yet been written, the writing process of step 902 is performed for that dot.

  After the writing process of step 902 is performed for all dots, the number of addresses to which 1 is written out of all addresses in the memory 12 is acquired, and the acquired number (number of colors) and the threshold value supplied from the input terminal 103 are acquired. The level setting value is compared (step 904). If the number of colors is equal to or greater than the threshold level setting value, a determination result (high level flag output) indicating that the input image is a natural image is output (step 905). If the number of colors is less than the threshold level setting value, a determination result (low level flag output) indicating that the input image is a computer image is output (step 906). In the following description, the determination result (flag output) is referred to as a color information flag.

  The color information flag is supplied from the first count processing unit to the second count processing unit and the LUT control unit. The second count processing unit counts the number of colors in the dark portion of the input image when a color information flag indicating that the input image is a natural image is supplied from the first count processing unit. FIG. 11 shows a procedure for counting the number of colors in the dark area by the second count processor.

  Referring to FIG. 11, first, the value of the dark part color number counter for counting the number of colors in the dark part is initialized to 0 (step 1001). Next, for the memory 12 after the processing shown in FIG. 10 is executed, data is read from the address specified by Buf [Rdata] [Gdata] [Bdata], and if the data at the read address is 1, The count value of the dark part color number counter is incremented by one (steps 1002 and 1003).

  The designation of addresses by Buf [Rdata] [Gdata] [Bdata] is designated in order within the address range from Buf [0] [0] [0] to Buf [x] [x] [x]. Here, x is a dark part comparison value supplied from the input terminal 105 and is smaller than 255. For example, x is set to 100. It is determined whether the address designation by Buf [Rdata] [Gdata] [Bdata] has reached the address of Buf [x] [x] [x] (step 1003). If Buf [x] [x] [x] has not been reached, the processing returns to Step 1002.

  When the address designation by Buf [Rdata] [Gdata] [Bdata] reaches the address of Buf [x] [x] [x], the number of dark color numbers, which is the count value of the dark color number counter, is subsequently determined. The ratio (dark part ratio) with respect to the number of colors (total number of colors) of the image of one frame obtained by the processing shown in FIG.

Dark portion ratio = (dark portion count value / total color number count value) × 100 (Expression 1)
Then, the dark portion ratio is compared with the dark portion level set value supplied from the input terminal 106 (step 1004).

  When the dark portion ratio is equal to or higher than the dark portion level setting value, a determination result (high level flag output) indicating that the natural image is a video (movie mode) including a dark scene is output (step 1005). If the dark portion ratio is less than the dark portion level setting value, a determination result (low level flag output) indicating that the natural image is a video image other than the movie mode is output (step 1006). In the following description, this determination result (flag output) is referred to as a dark part flag.

  The dark part flag is supplied from the second count processing unit to the LUT control unit. The LUT control unit determines gamma characteristic data to be written in the lookup table 13 based on the color information flag supplied from the first count processing unit and the dark part flag supplied from the second count processing unit.

  The gamma characteristic data selection method based on the color information flag and the dark part flag performed by the LUT control unit will be specifically described below.

  (1) When the color information flag is L, the input image is recognized as a computer image and gamma characteristic data (gamma characteristic data shown in FIG. 6) optimal for the computer image is written into the lookup table 13. .

  (2) When the color information flag is H and the dark part flag is L, the input image is recognized as a video image, and the optimum gamma characteristic data (gamma characteristic data shown in FIG. 7) for the video image is obtained. Write to the lookup table 13.

  (3) When the color information flag is H and the dark portion flag is H, the input image is recognized as an image including a dark scene (movie mode), and the dark portion has high brightness as shown in FIG. Such gamma characteristic data is written in the lookup table 13.

  Also in the gamma switching device of the present embodiment, as in the first embodiment, the gamma characteristics can be automatically switched according to the input image, so that the user does not need to switch the gamma characteristics. Therefore, the user can always see the image with the optimum gamma characteristic without being aware of the gamma characteristic at all.

  In addition, in the gamma switching device according to the present embodiment, when displaying a natural image, the gamma characteristic can be switched between display of an image with many dark scenes such as a movie (cinema) and display of other video images. Therefore, the quality of the display image is higher than that of the first embodiment.

  As described above, when the number of colors changes suddenly (for example, when a blue sky scene is displayed for a moment), if the gamma characteristic is frequently switched, a display image with a sense of incongruity is obtained. Also in the gamma switching device of the present embodiment, in order to prevent the gamma characteristic from being frequently switched, the LUT control unit writes the gamma characteristic data in the lookup table 13 and then within the time specified by the time setting value, Even if the color information flag and the dark part flag change, the gamma characteristic is not rewritten. The control unit 10 may generate a dummy code and determine the waiting time based on the dummy code. When a real-time clock (video signal processing clock) is built in the control unit 10, the waiting time may be determined using the real-time clock.

  Also in the gamma switching device of the present embodiment, as in the first embodiment, the first color number counting unit obtains the color of the pixels in at least a partial area of the image of the frame from the input image signal. May be. For example, the first color number counting unit may count the number of colors for the central portion of the image. Thereby, the amount of calculation by the first color number counting unit is reduced.

  Also, the gamma switching device of the present embodiment may be configured to perform function setting using an on-screen display, as in the first embodiment. FIG. 13 shows an example of a function setting menu screen using an on-screen display. Referring to FIG. 13, the menu screen includes two columns, a gamma select 803 and a holding time setting 804. In the field of gamma select 803, check boxes for “Auto”, “PC”, “Video”, and “Cinema” are provided. In the holding time setting 804 column, check boxes of “0.5 seconds”, “1 second”, “1.5 seconds”, and “2 seconds” are provided.

  Input information for checking the check boxes in the respective fields of the gamma select 803 and the holding time setting 804 is supplied from the control device on the information processing apparatus side to the gamma switching device. When the “auto” check box in the gamma select 803 column is checked, automatic switching processing of gamma characteristics by the gamma switching device is executed. In the column of holding time setting 804, the time when the check box is checked is used as a time setting value supplied to the input terminal 103.

  To manually switch the gamma characteristics, check the “PC”, “Video”, and “Cinema” check boxes in the gamma select 803 column. When the “PC” check box is checked, the gamma characteristic data shown in FIG. 6 is written and held in the lookup table 13. When the video check box is checked, the gamma characteristic data shown in FIG. 7 is written and held in the lookup table 13. When the cinema check box is checked, the gamma characteristic data shown in FIG. 12 is written and held in the lookup table 13.

  The automatic switching process of the gamma characteristic by the gamma switching device of the present invention described above may be executed when a video signal is supplied to a display device equipped with the gamma switching device. In a display device having a plurality of video signal input systems, automatic switching processing of gamma characteristics by the gamma switching device may be performed at the timing when the input system is switched. Further, when the synchronization signal is interrupted, automatic switching processing of gamma characteristics by the gamma switching device may be performed.

  The gamma switching device of each embodiment described above is an example of the present invention, and the configuration and operation thereof can be changed as appropriate without departing from the spirit of the invention. For example, although gamma correction using a lookup table is performed on the input image signal, gamma correction by a multiplier may be performed instead.

  In each embodiment, the image signal is in units of frames, but may be in units of fields. When an image signal is input in field units, the number of colors is counted in field units.

  The gamma switching device of the present invention can be applied to all display devices such as projectors, liquid crystal displays, and plasma displays.

  As an example, a display device including the gamma switching device of the present invention will be described below.

  FIG. 14 shows a configuration of a display device to which the gamma switching device of the present invention is applied. Referring to FIG. 14, the display device includes a display device 144 that is illuminated with a light beam from a lamp 143, a lens 145 for projecting image light formed by the display device 144 on a screen (not shown), and an input. A video signal processing circuit 140 that performs video signal processing on the signal, a gamma switching circuit 141, and a display device drive circuit 142 for driving the display device 144 are included. The gamma switching circuit 141 is the gamma switching device of the present invention, and other configurations are existing.

  In this display device, an image signal is supplied from the video signal processing circuit 140 to the gamma switching circuit 141, and the gamma switching circuit 141 performs gamma correction processing on the input image signal. Then, the display device driving circuit 142 drives the display device 144 based on the corrected image signal from the gamma switching circuit 141. The display device 144 displays an image based on the image signal that has been subjected to gamma correction.

It is a block diagram which shows the structure of the gamma switching apparatus which is the 1st Embodiment of this invention. FIG. 2 is a block diagram showing a configuration of a color number counting circuit of the gamma switching device shown in FIG. 1. It is a figure for demonstrating the relationship between a timing signal and a synchronizing signal. 3 is a flowchart showing a procedure for writing data into a memory by an adder of the color number counting circuit shown in FIG. 2. 3 is a flowchart showing a color number counting process procedure by a color number counting circuit shown in FIG. 2. It is a characteristic view which shows an example of the gamma characteristic data used for a computer image. It is a characteristic view which shows an example of the gamma characteristic data used for a natural image. It is a schematic diagram which shows an example of the menu screen for a function setting using an on-screen display applied to the gamma switching apparatus shown in FIG. It is a block diagram which shows the structure of the gamma switching apparatus which is the 2nd Embodiment of this invention. 10 is a flowchart illustrating a procedure of a color count process using a memory by a control unit of the gamma switching device illustrated in FIG. 9. 10 is a flowchart illustrating a procedure for counting the number of colors in a dark area by the control unit of the gamma switching device illustrated in FIG. 9. It is a characteristic view which shows an example of the gamma characteristic data used for the natural image of a movie mode. It is a schematic diagram which shows an example of the menu screen for a function setting using an on-screen display applied to the gamma switching apparatus shown in FIG. It is a block diagram which shows the structure of the display apparatus with which the gamma switching apparatus of this invention is applied.

Explanation of symbols

1 Control unit 2 Color count circuit 3 Look-up table

Claims (5)

A gamma correction unit that holds gamma characteristic data indicating a relative relationship of luminance between an input image signal and a display image displayed based on the input image signal, and corrects the input image signal according to the gamma characteristic data; ,
Based on the input image signal, the number of different colors among the colors constituting the display image is counted, and a color number counting unit that determines whether the count value is equal to or greater than a threshold value;
First and second gamma characteristic data having different characteristics are given in advance, and the gamma characteristic data held in the gamma correction unit is changed to the first and second gamma correction data according to the determination result in the color number counting unit. have a, and a control unit for switching between the gamma characteristic data,
When the count value is equal to or greater than the threshold value, the control unit recognizes the image as a natural image and causes the gamma correction unit to hold the first gamma characteristic data, and when the count value is less than the threshold value. , Recognizing that the computer image has fewer colors than the natural image and holding the second gamma characteristic data in the gamma correction unit,
The input image signal includes first to third image signals corresponding to the respective color components of the three primary colors,
The number-of-colors counting unit obtains an added value of each color component for each of a plurality of pixels constituting the display image based on the first to third image signals, and detects the pixels having different added values. A gamma switching device that counts the number of different colors . Wherein, when said first gamma characteristic data is held in the gamma correction unit to continue for only a predetermined time of the holding state, the gamma switching device according to claim 1. The color number counting unit acquires the color of the pixel of at least a partial area of the display image from the input image signal, the gamma switching device according to claim 1 or 2. Holding gamma characteristic data indicating a relative relationship of luminance between an input image signal and a display image displayed based on the input image signal, and correcting the input image signal according to the gamma characteristic data;
Counting the number of different colors among the colors constituting the display image based on the input image signal, and determining whether the count value is greater than or equal to a threshold value;
First and second gamma characteristic data having different characteristics are given in advance, and switching the gamma characteristic data between the first and second gamma characteristic data according to the result of the determination, and A gamma switching method comprising :
When the count value is greater than or equal to the threshold value, the image is recognized as a natural image and the first gamma characteristic data is used as the gamma characteristic data. When the count value is less than the threshold value, the color is greater than the natural image. Using the second gamma characteristic data as the gamma characteristic data by recognizing that the computer image has a small number of
The input image signal includes first to third image signals corresponding to the respective color components of the three primary colors, and each of the plurality of pixels constituting the display image based on the first to third image signals. Obtaining a sum value of each color component, and counting the number of pixels having different sum values as the number of different colors . A gamma switching device according to any one of claims 1 to 3 ,
And a display unit that displays an image based on an image signal supplied from the gamma switching device.

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