JP4998145B2 - Image processing apparatus, image processing method, image processing program, recording medium storing image processing program, and image display apparatus - Google Patents

Description

  The present invention relates to a technical field of an image processing apparatus that performs processing on image data, an image processing method, an image processing program, a recording medium that records the image processing program, and an image display apparatus.

  Conventionally, processing for converting the color space of image data has been performed in image processing apparatuses. For example, Patent Document 1 describes a technique for reproducing an image by performing color space conversion based on a color space at the time of camera shooting. Patent Document 2 describes a technique for converting a color space in consideration of the color space of an output device (display device).

JP 2002-152544 A JP 2005-341500 A

  However, when the circuit for converting the color space described in Patent Document 1 or 2 (hereinafter referred to as “color conversion circuit”) is realized as hardware, the display device is considered in consideration of the color space of the display device. In some cases, the color conversion circuit must be changed when the optical characteristics of the color change. Changing the circuit as hardware in this way requires a lot of time and cost, and thus can be said to impair convenience when designing a display device.

  The present invention has been made in view of the above points, and is an image processing apparatus, an image processing method, and an image processing program capable of performing color space conversion on a general basis without depending on the optical characteristics of the display unit. And a recording medium on which an image processing program is recorded, and an image display device.

In one aspect of the present invention, an image processing apparatus that performs a process of converting the color space of image data receives first wide color gamut image data, and the first wide color gamut image data is converted into a second wide color gamut image. A first color conversion unit for converting to data; a second color conversion unit for receiving the second wide color gamut image data and converting the second wide color gamut image data to image data of a standard wide color gamut space; Means for transmitting the image data converted by the second color conversion unit to a display unit capable of displaying the image data of the standard wide color gamut space, and the first color conversion unit receives a luminance color difference signal. When input, the luminance color difference signal is treated as the first wide color gamut image data and converted into the second wide color gamut image data. When the wide color gamut RGB signal is input, the wide color gamut RGB signal is input. Are directly output as the second wide color gamut image data.

The above-described image processing apparatus is suitably used for performing processing for converting the color space of image data. The first color conversion unit receives the first wide color gamut image data and converts the first wide color gamut image data into the second wide color gamut image data, and the second color conversion unit converts the second wide color gamut image data. Data is input, and the second wide color gamut image data is converted into image data of a standard wide color gamut space. Then, the converted image data of the standard wide color gamut space is transmitted to the display unit and displayed. As a result, it is possible to perform a process for converting the color space in a general manner regardless of the optical characteristics of the display unit. Therefore, even when the display unit is changed, it is almost unnecessary to change the circuit for performing color conversion as hardware, so that the image display apparatus can be designed quickly and the convenience of the designer can be improved.
In addition, when a luminance color difference signal is input , the first color conversion unit treats the luminance color difference signal as first wide color gamut image data and converts it into second wide color gamut image data. When input, the wide color gamut RGB signal is output as it is as second wide color gamut image data. As a result, processing corresponding to various types of wide color gamut image data can be appropriately performed, and these can be correctly reproduced. That is, the color space information of the image can be accurately reproduced in response to the input of various wide color gamut image data.

Preferably, the standard wide color gamut space can be represented by AdobeRGB. AdobeRGB is widely used as a wide color gamut as a standard, and is an appropriate setting when, for example, an input image from a digital still camera is handled.
Preferably, the second color conversion unit performs a first gamma conversion on the second wide color gamut image data and performs a second gamma conversion on the image data in the standard wide color gamut space. .

  More preferably, the xy chromaticity in the standard wide color gamut space is set such that Red is (0.64, 0.33), Green is (0.21, 0.71), and Blue is (0.15, 0.06).

In another aspect of the present invention, an image display device includes a display unit that displays the image data of the standard wide color gamut space transmitted from the image processing device according to any one of claims 1 to 5 . Since the image processing apparatus can perform color space conversion processing for general purposes regardless of the optical characteristics of the display unit, it is not necessary to change the color conversion circuit as hardware. It becomes possible to design quickly.

  In a preferred example, the display unit performs display using four colors, and is a liquid crystal display configured to include Red, Yellow-Green, Blue, and Emerald-Green color filters, and a white LED backlight. Can do.

  In another preferred example, the display unit can perform display using three colors.

In another aspect of the present invention, an image processing method for performing a process of converting a color space of image data acquires first wide color gamut image data, and the first wide color gamut image data is converted into a second wide color gamut image. A first color conversion step of converting to data; a second color conversion step of acquiring the second wide color gamut image data and converting the second wide color gamut image data into image data of a standard wide color gamut space; Transmitting the image data converted in the second color conversion step to a display unit capable of displaying the image data of the standard wide color gamut space, and the first color conversion step includes a luminance color difference signal. When input, the luminance color difference signal is treated as the first wide color gamut image data and converted into the second wide color gamut image data. When the wide color gamut RGB signal is input, the wide color gamut RGB signal is input. Are directly output as the second wide color gamut image data.

In still another aspect of the present invention, an image processing program for performing a process of converting a color space of image data acquires a first wide color gamut image data from a computer, and the first wide color gamut image data is obtained. A first color converting means for converting to second wide color gamut image data; a second color for obtaining the second wide color gamut image data; and converting the second wide color gamut image data into image data of a standard wide color gamut space. The color conversion means, the image data converted by the second color conversion means, function as means for transmitting to the display unit capable of displaying the image data of the standard wide color gamut space, and the first color conversion means When a luminance color difference signal is input , the luminance color difference signal is treated as the first wide color gamut image data and converted into the second wide color gamut image data. When a wide color gamut RGB signal is input, The wide color gamut RGB signal is converted into the second wide color gamut. It is output as it is as the image data.

  By executing the above-described image processing method and image processing program, it is possible to perform a process for converting the color space in a general manner regardless of the optical characteristics of the display unit.

  As the recording medium on which the image processing program is recorded, various computer-readable media such as a flexible disk, a CD-ROM, and an IC card can be used.

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

[First Embodiment]
First, a first embodiment of the present invention will be described.

(overall structure)
FIG. 1 is a block diagram illustrating a schematic configuration of an image display apparatus 100 according to the first embodiment. The image display apparatus 100 includes an image processing unit 10 that acquires image data and a control command from the outside and performs image processing on the image data, and a display unit 20 that displays the image data processed by the image processing unit 10. Is provided. Note that the image display device 100 is configured to be able to display an image using multiple colors (hereinafter, a basic color used when displaying an image is referred to as a “primary color”). Specifically, the image display apparatus 100 includes four primary colors of Red, Yellow-Green, Blue, and Emerald-Green (hereinafter, also simply referred to as “R”, “YG”, “B”, and “EG”). Is configured to be displayable.

  The image processing unit 10 includes an I / F control circuit 11, a color conversion circuit 12, a VRAM (Video RAM) 13, an address control circuit 14, a table storage memory 15, and a γ correction circuit 16. The image data input to the image processing unit 10 is a signal of three primary colors as a standard signal (a signal corresponding to wide color gamut image data, and is also referred to as a “standard three primary color signal” below). It is expressed as

  The I / F control circuit 11 acquires image data and a control command from the outside (for example, a camera) and supplies the image data d1 to the color conversion circuit 12. The color conversion circuit 12 processes the acquired image data d1 together with the color space information. Further, the color conversion circuit 12 performs processing for converting the image data obtained by this processing from three primary colors to four primary colors. For example, the color conversion circuit 12 includes a circuit that performs color conversion based on a three-dimensional lookup table format, and can perform conversion from three primary colors to four primary colors using this circuit. Thus, the color conversion circuit 12 corresponds to the image processing apparatus according to the present invention. Specifically, the color conversion circuit 12 functions as a color conversion unit. Details of the processing in the color conversion circuit 12 will be described later.

  The image data d2 subjected to image processing by the color conversion circuit 12 is written in the VRAM 13. The image data d2 written in the VRAM 13 is read as image data d3 by the γ correction circuit 16 based on the control signal d21 from the address control circuit 14. At the same time, the address signal d4 corresponding to the pre-display data is supplied to the scanning line driving circuit 22 in the display unit 20. As a result, the data line driving circuit 21 and the scanning line driving circuit 22 can drive the display panel 23 in synchronization. The γ correction circuit 16 performs γ correction on the acquired image data d3 based on the correction data stored in the table storage memory 15. Then, the γ correction circuit 16 supplies the image data d5 after γ correction to the data line driving circuit 21 in the display unit 20.

  The display unit 20 includes a data line driving circuit 21, a scanning line driving circuit 22, and a display panel 23. The data line driving circuit 21 supplies data line driving signals X1 to X960 to 960 data lines, and the scanning line driving circuit 22 supplies scanning line driving signals Y1 to Y320 to 320 scanning lines. To do. Specifically, the scanning line driving circuit 22 selects a horizontal pixel column at a constant cycle, and the data line driving circuit 21 outputs a driving signal corresponding to each of the pixel columns selected in the scanning line driving circuit 22. Supply. In this case, the data line driving circuit 21 and the scanning line driving circuit 22 drive the display panel 23 in synchronization. The display panel 23 is composed of a liquid crystal (LCD) or the like, and displays images such as characters and video to be displayed by applying voltages to the scanning lines and the data lines. The display panel 23 is configured to be able to display the four primary colors R-YG-B-EG described above.

  The VRAM 13 described above is an effective means for reducing power consumption when the same display data is repeatedly displayed. However, if the power consumption is not concerned, the image display apparatus 100 is configured without using the VRAM 13. Is also possible. In that case, the address control circuit 14 and the scanning line driving circuit 22 are directly connected, and the scanning line driving circuit 22 and the data line driving circuit 21 are synchronized to perform display.

  In the above, an example in which the display unit 20 is configured using an LCD has been described. However, any display device other than the LCD can be used for the display unit that performs multi-primary color display. For example, in addition to devices that perform flat display such as CRT, PDP, OLED, and FED, display devices that perform projection such as LCP and PTV can be used.

Next, the color gamut in the xy chromaticity diagram will be described with reference to FIG. A triangle denoted by reference numeral 61 is an “sRGB” color gamut widely used as a standard color space (hereinafter, R, G, and B in sRGB are also expressed as “R _S , G _S , and B _S ”. ). A triangle denoted by reference numeral 62 is a color reproduction gamut of “AdobeRGB” that is used as a wide color gamut (hereinafter, R, G, B in AdobeRGB are also referred to as “R _A , G _A , B _A ”. write). Note that Adobe RGB corresponds to a standard wide color gamut space.

In the above-described image display device 100, the four primary colors R-YG-B-EG can be used to reproduce the internal color of the rectangle indicated by reference numeral 63 (hereinafter, the image display device 100 uses 4). the primary color is denoted _{"R D, YG D, EG D} , B D " also). FIG. 2 shows that the color gamut using the four primary colors is wider than the standard sRGB color gamut. Therefore, according to the image display apparatus 100, it is possible to reproduce colors that are brighter than sRGB in emerald green colors. FIG. 3 shows the xy chromaticity in “R _S , G _S , B _S ”, “R _A , G _A , B _A ” and “R _D , YG _D , EG _D , B _D ” described above. Specific numerical values are shown.

  Here, in the present embodiment, the image processing unit 10 in the image display apparatus 100 is set to circuit so as to reproduce the Adobe RGB color reproduction range. Specifically, the color conversion circuit 12 of the image processing unit 10 converts the input standard three primary color signals (corresponding to wide color gamut image data) to AdobeRGB data (corresponding to image data in the standard wide color gamut space). Perform the conversion process. Furthermore, the color conversion circuit 12 also performs processing for converting AdobeRGB obtained by the above processing from three primary color signals to four primary color signals.

  The fact that the color conversion circuit 12 is set so as to reproduce the color gamut of AdobeRGB as described above will be described with reference to FIGS.

  FIG. 4 is a diagram showing spectral characteristics such as a color filter in each pixel. FIG. 4A shows the wavelength on the horizontal axis and the transmittance on the vertical axis, and the characteristics of the color filter are collectively shown in the R-YG-B-EG pixel portion. FIG. 4B shows the spectral characteristics of the white LED backlight (blue LED + phosphor), with the horizontal axis indicating the wavelength and the vertical axis indicating the relative luminance. FIG. 4C is a diagram in which the horizontal axis indicates the wavelength, the vertical axis indicates the transmittance, and the spectral characteristics during light emission are collectively shown in the R-YG-B-EG pixel unit. FIG. 4D is a diagram illustrating the xy chromaticity characteristics in sRGB and the xy chromaticity characteristics in the four primary color LCD. The xy chromaticity characteristics of the four primary color LCDs are plotted by calculating the xy chromaticity based on the spectral characteristics of the R-YG-B-EG pixels during light emission.

FIG. 5 is a graph plotting the xy chromaticity of the four primary color LCD and the xy chromaticity of the color reproduced by the four primary color LCD when Adobe RGB is input. In this case, color conversion from the three primary colors to the four primary colors is executed by the color conversion circuit 12. For example, by performing color conversion in a three-dimensional lookup table format, the three primary color signals as AdobeRGB can be converted and reproduced as colors inside the four primary color LCD. 2 and 3, the rectangles represented by R _D , YG _D , EG _D , and B _D (squares denoted by reference numeral 63) are the colors after the four-primary color LCD conversion shown in FIG. 5. It becomes four representative points.

  Incidentally, the color near the green vertex of AdobeRGB is outside the color reproduction range of the four primary color LCD and cannot be reproduced as it is. About such a color, by appropriately setting the color conversion circuit 12, it is possible to reproduce the color inside the four-primary-color LCD without any sense of incongruity. Conversely, the colors of the vertices of Yellow-Green and Emerald-Green of the four primary colors LCD are outside the color reproduction range of AdobeRGB. Since these colors do not exist as input AdobeRGB, they are not reproduced after color conversion.

  The reason why the color reproduction characteristics of the four primary color LCDs can be approximated to the color reproduction range of AdobeRGB is based on the design of the spectral characteristics of the color filter and the backlight. That is, the xy chromaticity (especially Red and Blue) calculated from the pixel portion emission characteristics is brought close to AdobeRGB by designing the spectral characteristics. The reason for referring to AdobeRGB is that AdobeRGB is recognized as a wide color gamut and is widely used as a standard.

  As described above, in this embodiment, the color conversion circuit 12 in the image processing unit 10 performs color conversion of AdobeRGB data from three primary colors to four primary colors. Therefore, before performing such color conversion, the color conversion circuit 12 first performs processing for converting the input standard three primary color signals into Adobe RGB. Hereinafter, the process of converting the standard three primary color signals to AdobeRGB performed by the color conversion circuit 12 will be described in detail.

(Processing in the color conversion circuit)
Next, processing in the color conversion circuit 12 in this embodiment will be specifically described.

  FIG. 6 is a block diagram showing a schematic configuration of the color conversion circuit 12. The color conversion circuit 12 includes a YCbCr → RGB conversion unit 12a and an RGB → RGB conversion unit 12b. The color conversion circuit 12 receives YCbCr data (8 bits) expressed by Y (luminance) and Cb, Cr (color difference). Specifically, the YCbCr data is a video signal defined by “ITU-R BT.601”. FIG. 6 illustrates only a processing unit for converting input image data into Adobe RGB data in the color conversion circuit 12, and illustrates a processing unit for converting image data from three primary color signals to four primary color signals. Not shown.

  The YCbCr → RGB conversion unit 12a mainly performs processing for converting input YCbCr data into RGB data. Specifically, the YCbCr → RGB conversion unit 12a uses the coefficient (hereinafter also referred to as “matrix coefficient”) represented by 10 bits (sign part 1 bit, integer part 2 bits, decimal part 7 bits) to convert the YCbCr data. Performs conversion to RGB data. Thereby, RGB data in which each of R, G, and B data is 10 bits (sign part 1 bit, integer part 1 bit, decimal part 8 bits) is obtained. The YCbCr → RGB conversion unit 12a supplies the RGB data thus obtained to the RGB → RGB conversion unit 12b. Note that data equivalent to sRGB is obtained by the processing by the YCbCr → RGB conversion unit 12a.

  The RGB → RGB conversion unit 12b mainly performs a process of converting the RGB data acquired from the YCbCr → RGB conversion unit 12a into AdobeRGB. That is, the RGB → RGB conversion unit 12b performs processing for converting data equivalent to sRGB obtained by the conversion by the YCbCr → RGB conversion unit 12a into AdobeRGB data having a wide color gamut. Specifically, the RGB → RGB conversion unit 12b first performs gamma conversion (hereinafter, this gamma conversion is referred to as “previous gamma conversion”), and then performs matrix calculation (specifically, RGB → RGB conversion). Finally, gamma conversion (hereinafter, this gamma conversion is referred to as “post-stage gamma conversion”) is performed. The reason for the gamma conversion is that the data after YCbCr → RGB conversion is subjected to gamma conversion.

  Specifically, 13-bit data (sign part 1 bit, integer part 2 bits, decimal part 10 bits) can be obtained by performing pre-stage gamma conversion. Next, RGB → RGB conversion is performed on the data subjected to the previous stage gamma conversion using a matrix coefficient represented by 8 bits (integer part 1 bit, decimal part 7 bits), that is, matrix calculation is performed. This calculation is a process of converting data equivalent to sRGB into AdobeRGB. Data of 10 bits (decimal part 10 bits) is obtained by RGB → RGB conversion. Next, 8-bit (decimal part 8 bits) data is obtained by performing post-stage gamma conversion on the RGB → RGB converted data. In this manner, 8-bit RGB data (specifically, AdobeRGB data) is output from the RGB → RGB conversion unit 12b. Thereafter, color conversion from the three primary colors to the four primary colors is performed in a circuit (not shown) in the color conversion circuit 12.

  Hereinafter, the processing in the YCbCr → RGB conversion unit 12a and the RGB → RGB conversion unit 12b will be described in detail.

<YCbCr → RGB conversion>
In the present embodiment, the YCbCr → RGB conversion unit 12a performs the above-described conversion by generally performed YCbCr → RGB conversion (in other words, YCbCr → RGB conversion based on the “ITU-R BT.601 standard”).

  Here, YCbCr → RGB conversion generally performed will be described. In the “ITU-R BT.601 standard”, conversion from a YCbCr signal to an RGB signal is performed using the following equation (1). In this case, the matrix coefficient is expressed as shown in Expression (2).

式(１)において左側の行列は、「ITU-R BT.601」で規定されているＲＧＢ→ＹＣｂＣｒ変換行列の逆行列である（ＹＣｂＣｒ→ＲＧＢ変換を行うからである）。また、右側の行列は、「ITU-R BT.601」では輝度Ｙ及び色差Ｃｂ、Ｃｒがそれぞれ「１６〜２３５」、「１６〜２４０」で表されるため、これらの信号の範囲を「０〜２５５」に復元するために用いられる行列である。なお、式（１）中の「Ｒ１、Ｇ１、Ｂ１」はＹＣｂＣｒ→ＲＧＢ変換後のＲＧＢデータを示し、「Ｙ_８、Ｃｂ_８、Ｃｒ_８」はＹＣｂＣｒ→ＲＧＢ変換の対象となっているＹＣｂＣｒデータを示す。以下、同様に扱うものとする。

The matrix on the left side in Equation (1) is an inverse matrix of the RGB → YCbCr conversion matrix defined in “ITU-R BT.601” (because YCbCr → RGB conversion is performed). In the right matrix, the luminance Y and the color differences Cb and Cr are represented by “16 to 235” and “16 to 240”, respectively, in “ITU-R BT.601”. The matrix used to restore to “˜255”. In the equation (1), “R1, G1, B1” indicates RGB data after YCbCr → RGB conversion, and “Y ₈ , Cb ₈ , Cr ₈ ” indicates YCbCr data that is the target of YCbCr → RGB conversion. Indicates. The same shall apply hereinafter.

<RGB → RGB conversion>
Next, RGB → RGB conversion performed by the RGB → RGB conversion unit 12b will be described. In this RGB → RGB conversion, data corresponding to sRGB (see FIGS. 2 and 3) obtained by the above-described YCbCr → RGB conversion is converted into AdobeRGB data having a wider color gamut.

  Such RGB → RGB conversion can be explained using the concept of primary conversion. Here, description will be made by taking an example of primary conversion in a two-dimensional space (the color space is a three-dimensional space, but the idea is the same, so a two-dimensional space is taken as an example for ease of explanation).

  FIG. 7 is a diagram for explaining color space conversion by primary conversion. Here, a case will be described in which a point 70 indicated by a black dot is linearly transformed in a two-dimensional space. Specifically, the black dot 70 is represented by (a, b) in the coordinate axis (i, j), and when the coordinate axis is converted to (i ′, j ′) by the primary conversion, (a ′, b) Represented as'). The RGB → RGB conversion can be considered as a concept of performing coordinate conversion in this way. That is, although it is the same as a color, it corresponds to expressing the data represented by sRGB by AdobeRGB.

  Further, when attention is paid to the coordinate a, the coordinate axis (i, j) before the primary conversion is “a <0” and is a negative value, but the coordinate axis (i ′, j ′) after the primary conversion is “ a ′> 0 ”, which is a positive value. That is, a negative value is converted into a positive value by the primary conversion. In this example, it is shown that the coordinates expressed as a negative value are expressed as a positive value depending on how the coordinate axes are selected. This can also be applied to colors. Pixels (= coordinates) expressed as negative values before color space conversion (= before the primary conversion of coordinate axes) are converted into color space (= coordinate axes). Can be expressed as positive pixels (= coordinates).

  In other words, although the color space is sRGB after YCbCr → RGB conversion, a value smaller than “0” and a value larger than “1” are held as numerical values in order to hold information of a wide color space. In this embodiment, as described above, the YCbCr → RGB conversion unit 12a inputs 10-bit data (sRGB data) of the decimal part 8 bits, the integer part 1 bit, and the code part 1 bit to the RGB → RGB conversion unit 12b, and RGB → The RGB conversion unit 12b performs processing for conversion to Adobe RGB in a wider color space while retaining the information.

  Here, the RGB → RGB conversion is a linear operation, but the data after YCbCr → RGB conversion is subjected to gamma conversion. Therefore, the RGB → RGB conversion unit 12b performs the above-described pre-stage gamma conversion, matrix calculation (RGB → RGB conversion), and post-stage gamma conversion.

  In the pre-stage gamma conversion, conversion represented by the following equation (3) is performed. In Expression (3), “R2” indicates R data after the previous stage gamma conversion, and “R1” indicates the R data after YCbCr → RGB conversion described above. Since the conversion formula is the same for RGB, only R is shown here as a representative.

この場合、回路上は、式（３）で示す変換式をＲＯＭのテーブル（以下、「前段ガンマテーブル」と呼ぶ。）として構成することができる（正負対称なので正のみ構成）。図８に、前段ガンマテーブルを示す。図８は、横軸に入力値（In-Data）を示し、縦軸に前段ガンマ変換による出力値（Out-Data）を示す。前段ガンマテーブルの入力は、ＹＣｂＣｒ→ＲＧＢ変換後の小数部８ｂｉｔ、整数部１ｂｉｔに対応する９ｂｉｔのデータとなる。前段ガンマ変換による出力については、変換特性が下に凸であり、かつ指数関数として増加することを考慮して、小数部１０ｂｉｔ、整数部２ｂｉｔとしている（符号部１ｂｉｔと合わせて計１３ｂｉｔで表現される）。

In this case, on the circuit, the conversion equation represented by Equation (3) can be configured as a ROM table (hereinafter referred to as “previous gamma table”) (only positive and negative because it is symmetrical). FIG. 8 shows a pre-stage gamma table. In FIG. 8, the horizontal axis represents the input value (In-Data), and the vertical axis represents the output value (Out-Data) obtained by the previous stage gamma conversion. The input of the previous stage gamma table is 9-bit data corresponding to the decimal part 8 bits and the integer part 1 bit after YCbCr → RGB conversion. In consideration of the fact that the conversion characteristic is convex downward and increases as an exponential function, the output by the pre-stage gamma conversion has a decimal part of 10 bits and an integer part of 2 bits (represented by 13 bits in total including the sign part of 1 bit). )

  Next, in the RGB → RGB conversion, the matrix calculation shown in the following equation (4) is performed. In this case, the matrix coefficient is represented by a small part number of 7 bits and an integer part of 1 bit as shown in Expression (5). In the equation (4), “R3, G3, B3” indicates RGB data after RGB → RGB conversion, and “R2, G2, B2” indicates RGB data after the previous stage gamma conversion.

次に、後段ガンマ変換では、以下の式(６)で表される変換を行う。なお、式（６）中の「Ｒ４」は後段ガンマ変換後のＲのデータを示し、「Ｒ３」は前述したＲＧＢ→ＲＧＢ変換後のＲのデータを示している。また、変換式はＲＧＢにおいて同一であるため、ここではＲのみを代表して示す。

Next, in the subsequent stage gamma conversion, conversion represented by the following equation (6) is performed. In Expression (6), “R4” indicates R data after the subsequent gamma conversion, and “R3” indicates R data after the RGB → RGB conversion described above. Since the conversion formula is the same for RGB, only R is shown here as a representative.

前段ガンマテーブルと同じく、回路上は、式（６）で示す変換式をＲＯＭのテーブル（以下、「後段ガンマテーブル」と呼ぶ。）として構成することができる（後段ガンマ変換の出力は正のみ）。図９に、後段ガンマテーブルを示す。図９は、横軸に入力値（In-Data）を示し、縦軸に後段ガンマ変換による出力値（Out-Data）を示す。後段ガンマテーブルの入力は、負および整数のビットを丸めて、小数１０ｂｉｔとする。そして、後段ガンマ変換による出力は、小数８ｂｉｔとなる。この後、後段ガンマ変換が行われた８ｂｉｔのデータ（ＡｄｏｂｅＲＧＢのデータ）は、色変換回路１２内の図示しない回路において、３原色から４原色への色変換が行われる。

Similar to the pre-stage gamma table, on the circuit, the conversion equation represented by equation (6) can be configured as a ROM table (hereinafter referred to as “post-stage gamma table”) (the output of the post-stage gamma conversion is only positive). . FIG. 9 shows a post-stage gamma table. In FIG. 9, the horizontal axis indicates an input value (In-Data), and the vertical axis indicates an output value (Out-Data) obtained by post-stage gamma conversion. The input of the post-stage gamma table is rounded off to the negative and integer bits to a decimal number of 10 bits. The output by the subsequent stage gamma conversion is a decimal 8 bits. Thereafter, the 8-bit data (Adobe RGB data) subjected to the post-stage gamma conversion is subjected to color conversion from three primary colors to four primary colors in a circuit (not shown) in the color conversion circuit 12.

  As described above, in the first embodiment, the input standard three primary color signals are converted to AdobeRGB, and AdobeRGB obtained by the conversion is color-converted from the three primary colors to the four primary colors. As a result, the YCbCr → RGB conversion unit 12a and the RGB → RGB conversion unit 12b in the color conversion circuit 12 can perform color space conversion processing for general purposes regardless of the optical characteristics of the image display device 100. . In addition, AdobeRGB obtained by color space conversion processing is widely used as a wide color gamut as a standard, and is an appropriate setting when handling an input image from a digital still camera, for example. If such a configuration is used, even if the display unit 20 is changed, the color conversion circuit 12 hardly needs to be changed as hardware, so that the image display apparatus can be designed quickly, and the convenience of the designer. Can be increased.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. In the first embodiment described above, YCbCr data as standard three primary color signals (specifically, a video signal defined in “ITU-R BT.601”, hereinafter referred to as “extended color gamut YCbCr”). The second embodiment differs from the first embodiment in that the processing is performed on several types of standard three primary color signals. Specifically, in the second embodiment, a total of four types of standard three primary color signals including the extended color gamut YCbCr described above are input to the color conversion circuit, and YCbCr → RGB conversion and RGB → RGB conversion are performed on these signals. I do. Specifically, four types of signals of standard YCbCr, extended color gamut YCbCr, standard RGB, and option RGB are input to the color conversion circuit as standard three primary color signals. In this case, standard RGB corresponds to sRGB, and option RGB corresponds to AdobeRGB. In the color conversion circuit according to the second embodiment, any one of the standard three primary color signals is input, and the process is switched according to the type of the standard three primary color signals to be input, and YCbCr → RGB conversion and RGB → RGB conversion is performed.

  FIG. 10 is a block diagram of the color conversion circuit 12x according to the second embodiment of the present invention. The color conversion circuit 12x is applied in place of the color conversion circuit 12 in the image processing unit 10 (see FIG. 1).

  The color conversion circuit 12x includes a YCbCr → RGB conversion unit 12xa and an RGB → RGB conversion unit 12xb. The YCbCr → RGB conversion unit 12xa and the RGB → RGB conversion unit 12xb perform substantially the same processing as the YCbCr → RGB conversion unit 12a and the RGB → RGB conversion unit 12b in the color conversion circuit 12 described above. However, the YCbCr → RGB conversion unit 12xa and the RGB → RGB conversion unit 12xb switch processing to be executed in accordance with the type of standard three primary color signals that are input. In this case, the YCbCr → RGB conversion unit 12xa and the RGB → RGB conversion unit 12xb are each switched between processes by being supplied with a control command from, for example, a CPU in the main system (not shown). In the following, processing executed according to the types of standard three primary color signals will be described.

  When the extended color gamut YCbCr corresponding to “ITU-R BT.601” is input, the YCbCr → RGB conversion unit 12xa performs the same calculation as the above-described calculation (see Expression (1) and Expression (2)). . On the other hand, when standard YCbCr is input, the YCbCr → RGB conversion unit 12xa performs conversion from the YCbCr signal to the RGB signal using the following equation (7).

式(７)の行列は、式(１)における右辺の左側の行列と同じものである。

The matrix of equation (7) is the same as the matrix on the left side of the right side in equation (1).

  Further, when standard RGB and option RGB are input, the YCbCr → RGB conversion unit 12xa does not perform arithmetic processing (that is, through arithmetic processing). This is because there is no need to convert YCbCr to RGB data since it is originally RGB data. Note that processing switching in the YCbCr → RGB conversion unit 12xa is performed based on the control command described above.

  After the above YCbCr → RGB conversion, the RGB → RGB conversion unit 12xb performs RGB → RGB conversion. Specifically, when standard YCbCr, extended color gamut YCbCr, and standard RGB are input to the YCbCr → RGB converter 12xa, they are converted into a color space equivalent to sRGB by YCbCr → RGB conversion, so that RGB → RGB The conversion unit 12xb performs conversion to AdobeRGB by performing the same arithmetic processing as the above-described equations (3) to (6). On the other hand, when the option RGB is input to the YCbCr → RGB conversion unit 12xa, since the option RGB is originally AdobeRGB, the RGB → RGB conversion unit 12xb does not perform the calculation process (that is, passes through the calculation process). Note that such switching of processing in the RGB → RGB conversion unit 12xb is performed based on the control command described above.

  Next, in the color conversion circuit 12x according to the second embodiment, it was verified whether the standard YCbCr, the extended color gamut YCbCr, the standard RGB, and the option RGB were correctly color-converted. In the verification, tristimulus values XYZ of 33 colors were defined, and data based on standard YCbCr, extended color gamut YCbCr, and option RGB were calculated. FIG. 11 shows a list of calculation results. Note that the above 33 colors are set based on the option RGB and include vivid colors that cannot be expressed in standard RGB, and therefore data in standard RGB is excluded in FIG.

  Further, when the data shown in FIG. 11 was processed by the color conversion circuit 12x, the display color when the processed data was displayed on the display unit 20 was measured by a measuring instrument. FIG. 12 shows the u′v ′ chromaticity plot of the input data (target) and the u′v ′ chromaticity plot in measured values when using standard YCbCr, option RGB, and extended color gamut YCbCr. FIG. 12A shows measured values in standard YCbCr, FIG. 12B shows measured values in option RGB, and FIG. 12C shows measured values in extended color gamut YCbCr.

  From FIG. 12, it can be seen that the standard YCbCr, the option RGB, and the extended color gamut YCbCr all have the measured values almost overlapped with the input data, and are reproduced with a practically satisfactory accuracy. In particular, it can be seen that the standard YCbCr, the option RGB, and the extended color gamut YCbCr are all properly reproduced with respect to the color (near Green) outside the sRGB color reproduction range (shown by a broken line).

  As described above, according to the second embodiment, since processing according to various standard three primary color signals can be appropriately performed, these can be correctly reproduced. That is, the color space information of the image can be accurately reproduced in response to various standard three primary color signal inputs.

[Third Embodiment]
Next, a third embodiment of the present invention will be described. In the first embodiment and the second embodiment described above, the display unit 20 that performs the display of the four primary colors is used. However, in the third embodiment, the display unit that performs the display of the three primary colors is used. Different. That is, the third embodiment is an embodiment in which the configuration according to the above-described embodiment is applied to a configuration using a display unit that displays three primary colors.

  Specifically, in the third embodiment, the display unit displays an image using RGB (Red, Green, Blue). Basically, the configuration of the image display device in the third embodiment is substantially the same as the configuration of the image display device 100 (see FIG. 1), and the color conversion circuit is also substantially the same as the configuration of the color conversion circuit 12. However, in the third embodiment, the color conversion circuit does not perform color conversion from the three primary colors to the four primary colors (that is, the color conversion circuit has only the YCbCr → RGB conversion unit 12a and the RGB → RGB conversion unit 12b, The display unit performs the display of the three primary colors without a circuit that performs color conversion from the three primary colors to the four primary colors. That is, the image display apparatus according to the third embodiment executes only YCbCr → RGB conversion and RGB → RGB conversion in the color conversion circuit, and displays the converted data (data of three primary colors of AdobeRGB) on the display unit. The YCbCr → RGB conversion is performed using the above-described equations (1) and (2), and the RGB → RGB conversion is performed using the above-described equations (3) to (6).

FIG. 13 is a diagram comparing the color gamuts in the xy chromaticity diagram in the third embodiment. A triangle denoted by reference numeral 61 (the triangle formed by R _S , G _S , and B _S described above) is an sRGB color reproduction region, and a triangle denoted by reference numeral 62 (formed by R _A , G _A , and B _A described above). Is a color gamut of AdobeRGB. The display unit in the third embodiment can reproduce the color inside the triangle denoted by reference numeral 65 by using the three primary colors RGB (hereinafter, the image in the third embodiment will be described below). (The three primary colors that can be displayed by the display device are also expressed as “R _E , G _E , B _E ”). As is apparent from FIG. 13, the image display device according to the third embodiment has a color reproduction range wider than that of standard sRGB, and can reproduce colors that are brighter than sRGB in emerald green colors. Become. FIG. 14 shows specific xy chromaticities in “R _S , G _S , B _S ”, “R _A , G _A , B _A ” and “R _E , G _E , B _E ” described above. Indicates a numerical value.

  Here, also in the third embodiment, the color conversion circuit is set so as to reproduce the color gamut of AdobeRGB. That is, the color conversion circuit converts the input standard three primary color signals into AdobeRGB. The display unit is set to reproduce the AdobeRGB data wp after processing by the color conversion circuit.

  The fact that the color conversion circuit is set to reproduce the AdobeRGB color reproduction range will be described with reference to FIGS. 15 and 16. FIG.

  FIG. 15 is a diagram illustrating spectral characteristics and the like in each pixel unit. FIG. 15A shows the wavelength on the horizontal axis, the relative luminance on the vertical axis, and the spectral characteristics during light emission are collectively shown in the RGB pixel unit. FIG. 15B is a diagram showing the xy chromaticity characteristics in sRGB and the xy chromaticity characteristics in the three primary color LCD. The xy chromaticity characteristics in the three primary color LCDs are plotted by calculating the xy chromaticity based on the spectral characteristics of each RGB pixel during light emission.

FIG. 16 is a diagram plotting the xy chromaticity of the three primary color LCD and the xy chromaticity of the color reproduced by the three primary color LCD when Adobe RGB is input. In FIG. 13 and FIG. 14, the triangles represented by R _E , G _E , and B _E (triangles indicated by reference numeral 65) are representative of the reproduction colors in the three primary color LCD shown in FIG. 3 points.

  As described above, in the third embodiment, the standard three primary color signals input to the color conversion circuit are converted into Adobe RGB, and the converted data is displayed on the display unit that displays the three primary colors. Therefore, according to the third embodiment, it is possible to perform color space conversion processing for a display unit that displays three primary colors in a general manner. If such a configuration is used, even when a display unit that performs three primary colors is used, the circuit hardly needs to be changed as hardware, so that the image display device can be designed quickly, and the convenience of the designer can be improved. Can be increased.

  The configuration according to the third embodiment and the configuration according to the second embodiment described above may be combined. That is, even when various standard three primary color signals (standard YCbCr, extended color gamut YCbCr, standard RGB, and option RGB) are input even by the configuration according to the third embodiment, the standard three primary colors that are input are input. Processing according to the signal is performed, and the data obtained thereby can be displayed on the display unit that displays the three primary colors. In this case as well, the color conversion circuit does not perform color conversion from the three primary colors to the four primary colors.

[Modification]
In the above, an example is shown in which the color conversion circuits 12 and 12x are configured as circuits that perform fixed-point arithmetic, but the number of bits in the fixed-point is not limited to the above. Further, the color conversion circuits 12 and 12x may be configured as a circuit that performs floating-point arithmetic.

  In addition, the chromaticity in the display unit 20 that performs 4-primary color display and the display unit that performs 3-primary color display is not limited to that shown in the above example (see FIGS. 3, 14, and the like). The color conversion circuits 12 and 12x shown in the above embodiment can be applied to other chromaticities.

  Furthermore, although the example of “ITU-R BT.601” is shown as the matrix for performing YCbCr → RGB conversion for the extended color gamut YCbCr, the matrix can also be applied to the case of “ITU-R BT.709”. Here, both define the transmission standard of the digital video signal, “ITU-R BT.601” is SDTV (Standard Definition Television) with 525 scanning lines, and “ITU-R BT.709” is scanning. This is a standard for HDTV (High Definition Television) with 1125 lines.

  Furthermore, although it is assumed that the operation performed in the above-described conversion is basically performed by a circuit, the operation may be performed by software processing. For example, the functions of the color conversion circuit 12 and the like can be realized by an image processing program that is executed by a CPU (computer). The image processing program may be stored in advance in a hard disk or ROM, or may be supplied from the outside by a computer-readable recording medium such as a CD-ROM and read by a CD-ROM drive. The program may be stored on a hard disk.

1 is a block diagram illustrating a schematic configuration of an image display device according to a first embodiment. It is a figure which shows the color reproduction range in xy chromaticity diagram. In a 1st embodiment, it is a figure showing a concrete numerical value as xy chromaticity. It is the figure which showed the spectral characteristics, such as a color filter, in each pixel. It is the figure which plotted xy chromaticity of 4 primary color LCD, and xy chromaticity of the color reproduced by 4 primary color LCD when AdobeRGB is input. 1 is a block diagram illustrating a schematic configuration of a color conversion circuit according to a first embodiment. It is a figure for demonstrating the color space conversion by primary conversion. It is a figure which shows a front | former stage gamma table. It is a figure which shows a back | latter stage gamma table. It is a block diagram which shows schematic structure of the color conversion circuit which concerns on 2nd Embodiment. When the tristimulus values XYZ of 33 colors are defined, data calculated from various standard three primary color signals are shown. The u'v 'chromaticity plot of the input data and the u'v' chromaticity plot based on the measured values of various standard three primary color signals are shown. In 3rd Embodiment, it is a figure which shows the color gamut in an xy chromaticity diagram. In a 3rd embodiment, it is a figure showing a concrete numerical value as xy chromaticity. It is the figure which showed the spectral characteristic etc. in each pixel part. It is the figure which plotted xy chromaticity of 3 primary color LCD, and xy chromaticity of the color reproduced by 3 primary color LCD when AdobeRGB is input.

Explanation of symbols

  10 image processing unit, 11 I / F control circuit, 12, 12x color conversion circuit, 12a, 12xa YCbCr → RGB conversion unit, 12b, 12xb RGB → RGB conversion unit, 13 VRAM, 14 address control circuit, 15 table storage memory, 16 γ correction circuit, 20 display unit, 23 display panel, 100 image display device

Claims (10)

In an image processing apparatus that performs processing for converting the color space of image data,
A first color conversion unit that receives first wide color gamut image data and converts the first wide color gamut image data into second wide color gamut image data;
A second color conversion unit that receives the second wide color gamut image data and converts the second wide color gamut image data into image data of a standard wide color gamut space;
Means for transmitting the image data converted by the second color conversion unit to a display unit capable of displaying the image data of the standard wide color gamut space;
The first color converter is
When a luminance color difference signal is input, the luminance color difference signal is treated as the first wide color gamut image data and converted into the second wide color gamut image data;
When a wide color gamut RGB signal is input , the image processing apparatus outputs the wide color gamut RGB signal as it is as the second wide color gamut image data .   The image processing apparatus according to claim 1, wherein the standard wide color gamut space is represented by AdobeRGB. The second color converter is
Performing a first gamma conversion on the second wide color gamut image data;
The image processing apparatus according to claim 1, wherein second gamma conversion is performed on the image data in the standard wide color gamut space.   Regarding the xy chromaticity in the standard wide color gamut space, Red is (0.64, 0.33), Green is (0.21, 0.71), and Blue is (0.15, 0.06). 4. The image processing apparatus according to claim 1, wherein the image processing apparatus is an image processing apparatus.   An image display apparatus comprising: a display unit configured to display image data of the standard wide color gamut space transmitted from the image processing apparatus according to claim 1.   The display unit is a liquid crystal display that performs display using four colors and includes a red, yellow-green, blue, and emerald-green color filter, and a white LED backlight. Item 6. The image display device according to Item 5.   The image display apparatus according to claim 5, wherein the display unit performs display using three colors. In an image processing method for performing a process of converting a color space of image data,
A first color conversion step of acquiring first wide color gamut image data and converting the first wide color gamut image data into second wide color gamut image data;
A second color conversion step of acquiring the second wide color gamut image data and converting the second wide color gamut image data into image data of a standard wide color gamut space;
Transmitting the image data converted in the second color conversion step to a display unit capable of displaying the image data of the standard wide color gamut space,
The first color conversion step includes
When a luminance color difference signal is input, the luminance color difference signal is treated as the first wide color gamut image data and converted into the second wide color gamut image data;
When a wide color gamut RGB signal is input, the wide color gamut RGB signal is directly output as the second wide color gamut image data . In an image processing program for performing processing for converting the color space of image data,
Computer
First color conversion means for acquiring first wide color gamut image data and converting the first wide color gamut image data into second wide color gamut image data;
Second color conversion means for acquiring the second wide color gamut image data and converting the second wide color gamut image data into image data of a standard wide color gamut space;
The image data converted by the second color conversion means functions as a means for transmitting to the display unit capable of displaying the image data of the standard wide color gamut space,
The first color conversion means includes
When a luminance color difference signal is input, the luminance color difference signal is treated as the first wide color gamut image data and converted into the second wide color gamut image data;
When a wide color gamut RGB signal is input , the image processing program outputs the wide color gamut RGB signal as it is as the second wide color gamut image data .   A computer-readable recording medium on which the image processing program according to claim 9 is recorded.

Images