CN101873502B - Color space converting circuit and method - Google Patents

Abstract

The present invention relates to a color space conversion circuit and method, which can compress the part beyond the sRGB color space into the sRGB color space with a simplified circuit design when performing the conversion from the xvYcc color space to the sRGB color space, so as to improve vision Effect. The color space conversion circuit includes a conversion unit. The conversion unit can convert a pixel signal from the xvYcc color space to the sRGB color space. During the conversion process, the conversion unit generates pixel components of the pixel signal in each color space dimension of the sRGB color space. When any pixel component is in the compression range, the conversion unit compresses the pixel component to output a compressed pixel component. The compressed pixel components do not exceed the coverage range of the sRGB color space on the corresponding color space dimension.

Description

Color space conversion circuit and method

technical field

The present invention relates to color space conversion, especially to a color space conversion circuit and method.

Background technique

YCbCr and sRGB (standard RGB) are commonly used standard color spaces. In practical applications, for example, imaging devices (such as digital cameras or DVD players, etc.) can output video signals in YCbCr format to display devices (such as digital TVs, etc.) ), the display device converts it to sRGB format for display. In the CCIR Recommendation 601 specification, Y (brightness), Cb and Cr (chroma) are each coded with 8 bits, where the range of Y is 16-235, and the range of Cb and Cr is 16-240. When converting the YCbCr color space to the sRGB color space, use the following conversion formula:

$\left[\begin{array}{c}{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; \&prime;</span>}\\ {\mathrm{<span\; class="notranslate">\; G</span>}}^{<span\; class="notranslate">\; \&prime;</span>}\\ {\mathrm{<span\; class="notranslate">\; B</span>}}^{<span\; class="notranslate">\; \&prime;</span>}\end{array}\right]<span\; class="notranslate">\; =</span>\left[\begin{array}{ccc}\mathrm{<span\; class="notranslate">\; 0.00456621</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; .</span>& \mathrm{<span\; class="notranslate">\; 0.00625893</span>}\\ \mathrm{<span\; class="notranslate">\; 0.00456621</span>}& <span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 0.00153632</span>}& <span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 0.00318811</span>}\\ \mathrm{<span\; class="notranslate">\; 0.00456621</span>}& \mathrm{<span\; class="notranslate">\; 0.00791071</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; .</span>\end{array}\right]<span\; class="notranslate">\; =</span>\left(\begin{array}{c}\left[\begin{array}{c}{\mathrm{<span\; class="notranslate">\; Y</span>}}_{\mathrm{<span\; class="notranslate">\; 601</span>}}^{<span\; class="notranslate">\; \&prime;</span>}\\ {\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; B</span>}}\\ {\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}\end{array}\right]<span\; class="notranslate">\; -</span>\left[\begin{array}{c}\mathrm{<span\; class="notranslate">\; 16</span>}\\ \mathrm{<span\; class="notranslate">\; 128</span>}\\ \mathrm{<span\; class="notranslate">\; 128</span>}\end{array}\right]\end{array}\right)$

It can be known that the red (R), green (G), and blue (B) components range from 0 to 1, respectively, and represent a range of 0 to 255 with 8 bits.

Due to the increasing demand of consumers for visual effects, the YCbCr color space is gradually insufficient. Therefore, in recent years, based on the YCbCr color space, the xvYcc (eXtended Video YCC, or x.v.Color) color space has been developed. Its color gamut It is approximately 1.8 times larger than the original YCbCr color space to provide richer color performance. In the xvYcc color space, if it is also coded with 8 bits, the ranges of Y, Cb and Cr can be expanded to 1-254. If the expanded range is converted according to the aforementioned conversion formula, the ranges of the R, G, and B components are also expanded to -17.46~277, as shown in Figure 1. However, the part beyond 0 to 255, that is, the part of -17.46 to 0 and 255 to 277, cannot be represented by 8 bits. The traditional technology system discards the part from -17.46 to 0 as 0, and discards the part from 255 to 277 as 255, so that the wide color gamut of the xvYcc color space cannot be fully expressed in the sRGB color space and cannot be improved. Visual effect.

Contents of the invention

In view of this, an object of the present invention is to provide a color space conversion circuit and method, which can compress the part beyond the sRGB color space with a simplified circuit design when performing the conversion from the xvYcc color space to the sRGB color space. into the sRGB color space for enhanced visuals.

The invention provides a color space conversion circuit for converting a pixel signal from a first color space to a second color space, and the second color space has at least one color space dimension. The color space conversion circuit includes: a conversion unit, which is used to generate a pixel component of the pixel signal on the dimension of the color space, and compress the pixel component to output a compressed pixel component when the pixel component is in a compression interval; wherein, the compressed pixel The components do not exceed the range covered by the second color space in the color space dimension.

The present invention also provides a color space conversion method, comprising the following steps: receiving a pixel signal belonging to a first color space; generating a pixel component of the pixel signal in the color space dimension of the second color space; and when the pixel component is located in a compressed During interval, the pixel components are compressed to output the compressed pixel components, wherein the compressed pixel components do not exceed the range covered by the second color space in its color space dimension.

Description of drawings

FIG. 1 is a schematic diagram showing the relative sizes of the YCbCr color space and the xvYcc color space.

FIG. 2 is a block diagram of an embodiment of the color space conversion circuit of the present invention.

FIG. 3 is a schematic diagram showing how the conversion unit in FIG. 2 performs compression.

FIG. 4 is a flowchart of an embodiment of the color space conversion method of the present invention.

In the figure, 20 is a color space conversion circuit, 21 and 22 are registers, 23 is a conversion unit, 24 is a buffer unit, 41-45 are process steps of an embodiment of a color space conversion method.

Detailed ways

FIG. 2 is a block diagram of an embodiment of the color space conversion circuit 20 of the present invention, including a buffer unit 24 and a conversion unit 23 . The color space conversion circuit 20 can perform conversion from the xvYcc color space (hereinafter referred to as xvYcc) to the sRGB color space (hereinafter referred to as sRGB). sRGB has three color space dimensions, namely red, green, and blue dimensions. sRGB has a coverage range in each dimension, and the coverage range has a lower limit value and an upper limit value (hereinafter respectively referred to as the first lower limit value and the first upper limit value), if represented by 8 bits, they are 0 with 255. When converting xvYcc to sRGB, xvYcc also has a lower limit and an upper limit in the red, green and blue dimensions (referred to below as the second lower limit and the second upper limit respectively), if 8 Bit representation, respectively -17.46 and 277. Therefore, the second lower limit value is smaller than the first lower limit value, and the second upper limit value is greater than the first upper limit value.

The buffer unit 24 may include registers 21 and 22 . The register 21 stores the first critical value and the first slope, the register 22 stores the second critical value and the second slope, and the first critical value is greater than the second critical value. These parameters stored in the registers 21 and 22 can be adjusted according to actual needs. The conversion unit 23 is coupled to the registers 21 and 22, and can convert an input pixel signal belonging to xvYcc into an output pixel signal belonging to sRGB according to the parameter values stored in the registers 21 and 22, and then output it. In this conversion process, the conversion unit 23 first converts the input pixel signal into pixel components in each color space dimension of sRGB, namely red component, green component and blue component. Next, the conversion unit 23 judges whether the size of each pixel component is in the compression range, and if so, performs compression; otherwise, does not perform compression. In other words, the compressed range represents the range of pixel values to be compressed. In this embodiment, the compression interval includes: a pixel value interval whose lower limit and upper limit are respectively the first critical value and a second upper limit value, and a pixel value interval whose lower limit and upper limit are respectively the second lower limit value and the second critical value . Therefore, the size of the compressed interval can be adjusted by changing the first threshold or the second threshold. When any pixel component (such as the red component) is greater than the first critical value and not greater than the second upper limit (such as the upper limit of xvYcc on the red dimension), the conversion unit 23 performs the first compression operation on the pixel component to Output the first compressed pixel component, so that the first compressed pixel component is not higher than the first upper limit (such as the upper limit of sRGB on the red dimension), and the first compressed pixel component and the pixel component have a first slope linear relationship; when any pixel component is less than the second critical value and not less than the second lower limit value, the conversion unit 23 performs the second compression operation on the pixel component to output the second compressed pixel component, so that the second compressed pixel component is not lower than the first lower limit value, and the second compressed pixel component and the pixel component have a linear relationship with a second slope; If there is a pixel component, no compression is performed, and the pixel component is directly output. Therefore, in the output pixel signal output by the converting unit 23, the red, green and blue components are all within the sRGB color gamut.

Fig. 3 is a schematic diagram showing how the conversion unit 23 performs the compression operation, wherein the input pixel component is one of the red, green and blue components converted from the input pixel signal in Fig. 2, and the output pixel component is the output pixel signal in Fig. 2 One of the red, green and blue components included. In FIG. 3, when the input pixel component is greater than the first critical value and not greater than the second upper limit value, or less than the second critical value and not less than the second lower limit value, it will be compressed to generate an output pixel component, so , the pixel components that originally exceeded the sRGB color gamut can be compressed within the sRGB color gamut to display colors of different levels, and will not be treated as the same color. For example, the red components of 260 and 270 (both exceeding the upper limit of 255) will present different levels of red after being compressed, and will not be displayed as red of 255. Figure 3 shows two compression methods, in this embodiment, one is curve compression and the other is linear compression. Preferably, the curve compression is generated according to the Gamma curve to conform to human vision. Alternatively, in the color space conversion circuit 20 of the present invention, linear compression is used to approach curve compression, which can reduce circuit cost and achieve a visual effect very similar to curve compression.

In this embodiment, the slope of the slope between the first critical value and the second upper limit is the first slope, and the aforementioned first compression action performs linear compression according to the first slope, that is:

Output pixel component (that is, the first compressed pixel component) = (input pixel component - first critical value) × first slope + first critical value Formula (1)

The slope of the slope between the second critical value and the second lower limit is the second slope, and the aforementioned second compression action performs linear compression according to the second slope, that is:

Output pixel component (i.e. the second compressed pixel component)=(input pixel component-second critical value)×second slope+second critical value Formula (2)

Formula (1) can be regarded as performing linear interpolation between the first critical value and the second upper limit value, and formula (2) can be regarded as performing linear interpolation between the second critical value and the second lower limit value . Preferably, the conversion circuit 23 includes an interpolation circuit (not shown in the figure) for performing the linear interpolation operation of the formula (1) and the formula (2).

In formula (1), when the input pixel component and the first compressed pixel component are respectively the second upper limit and the first upper limit, if the first critical value is known, then the first slope can be obtained by taking the first The critical value, the first upper limit value and the second upper limit value are substituted into formula (1) and derived; if the first slope is known, then the first critical value can be obtained by combining the first slope, the first upper limit value and The second upper limit is derived by substituting into formula (1). Similarly, in formula (2), when the input pixel component and the second compressed pixel component are the second lower limit value and the first lower limit value respectively, if the second critical value is known, the second slope can be obtained by Substituting the second critical value, the first lower limit value and the second lower limit value into formula (2) and deriving; if the second slope is known, the second critical value can be obtained by taking the second slope, the first lower limit The limit value and the second lower limit value are substituted into formula (2) and derived. Therefore, in this case, the register 21 only needs to store one of the first critical value and the first slope, and the register 22 only needs to store one of the second critical value and the second slope. Can be generated by derivation, which saves memory space.

In another specific embodiment, the conversion unit 23 includes a lookup table (not shown in the figure) for storing the input pixel component and the corresponding output pixel component, wherein, when the input pixel component is greater than the first critical value and not When it is greater than the second upper limit value, the corresponding output pixel component is the first compressed pixel component; when the input pixel component is less than the second critical value and not less than the second lower limit value, the corresponding output pixel component is the second compressed pixel component ; When the input pixel component is between the first critical value and the second critical value, the corresponding output pixel component is the original input pixel component. Therefore, the conversion unit 23 can quickly perform the first compression action and the second compression action according to the lookup table.

Preferably, for the red, green and blue components generated by converting the input pixel signal of xvYcc, the conversion unit 23 can respectively use different thresholds and slopes to perform the aforementioned linear compression. These different thresholds and slopes can be stored in the registers 21 , 22 .

Since the high-definition multimedia interface (High-definition Multimedia Interface, HDMI) started to support xvYcc in its version 1.3 specification, the color space conversion circuit 20 of the present invention can be applied to an HDMI receiver to convert the color received by the HDMI receiver Signals in xvYcc format are converted into signals in sRGB format and displayed on a display device such as a digital TV.

FIG. 4 is a flowchart of an embodiment of the color space conversion method of the present invention, which is used for conversion from the first color space to the second color space. The method comprises the following steps:

Step 41: Receive a pixel signal belonging to the first color space.

Step 42: Generate pixel components of the pixel signal in each color space dimension of the second color space.

Step 43: When the pixel component on any color space dimension is greater than the first critical value and not greater than the upper limit value of the pixel component, perform the first compression operation on the pixel component to output the first compressed pixel component, wherein the first The compressed pixel component is not higher than the upper limit value of the second color space on the color space dimension, and the first compressed pixel component and the pixel component have a linear relationship with a first slope.

Step 44: When the pixel component on any color space dimension is less than the second critical value and not less than the lower limit value of the pixel component, perform the second compression operation on the pixel component to output the second compressed pixel component, wherein the second The compressed pixel component is not lower than the lower limit value of the second color space on the dimension of the color space, and the second compressed pixel component and the pixel component have a linear relationship with a second slope.

Step 45: When the pixel component in any color space dimension is between the first critical value and the second critical value, directly output the pixel component.

In the aforementioned steps, the first critical value is greater than the second critical value; the upper limit value of the pixel component on any color space dimension is greater than the upper limit value of the second color space on the color space dimension; the upper limit value on any color space dimension The lower limit value of the pixel component is smaller than the lower limit value of the second color space on the color space dimension.

Preferably, the first color space is xvYcc color space, and the second color space is sRGB color space, which includes three color space dimensions of red, green and blue. The color space conversion method of FIG. 4 can be applied to HDMI receivers.

Preferably, steps 43-45 are performed according to a lookup table. The look-up table pre-stores the pixel components of different sizes generated in step 42 and the corresponding output pixel components of steps 43-45, that is, the first compressed pixel component, the second compressed pixel component or the uncompressed original pixel component, so that Speed up the execution speed of steps 43-45.

The above description is to illustrate the present invention with preferred embodiments, but not to limit the scope of the present invention. Those who are familiar with this art can understand that many possible changes can be made according to the disclosure of the above embodiments without departing from the spirit and scope of the present invention.

Claims (15)

1. a color space converting circuit, is characterized in that, comprises:

One converting unit, in order to a pixel signal is converted to one second color space from one first color space, this second color space has at least one color space dimensions, wherein, this first color space is xvYcc color space, and this second color space is sRGB color space;

Wherein, this converting unit produces this pixel signal pixel component one of on this color space dimensions, and when this pixel component is positioned between a compressional zone, compress to export a packed pixel component to this pixel component, making this packed pixel component not exceed this second color space covering scope one of on this color space dimensions, is a linear relationship between this packed pixel component and this pixel component;

Between described compressional zone, lower limit and the upper limit are respectively one of one first critical value and this pixel component higher limit for it, and this packed pixel component is not higher than one of this covering scope higher limit, and now, the linear relationship between this packed pixel component and this pixel component is:

Packed pixel component=(pixel component-the first critical value) × first slope+the first critical value, wherein, the first slope is the slope of one of the first critical value and this pixel component higher limit; Or the upper limit between described compressional zone and lower limit are respectively one of one second critical value and this pixel component lower limit, this packed pixel component is not less than one of this covering scope lower limit, and now, the linear relationship between this packed pixel component and this pixel component is:

Packed pixel component=(pixel component-the second critical value) × second slope+the second critical value, wherein, the second slope is the slope of one of the second critical value and this pixel component lower limit;

Described first critical value is greater than described second critical value;

Described converting unit directly exports the arbitrary pixel component between described first critical value and described second critical value.

2. color space converting circuit according to claim 1, is characterized in that, when this pixel component is positioned at outer between this compressional zone, this converting unit directly exports this pixel component.

3. color space converting circuit according to claim 1, is characterized in that, this converting unit comprises a question blank, in order to store this packed pixel component of this pixel component and correspondence; This converting unit is compressed this pixel component according to this question blank.

4. color space converting circuit according to claim 1, is characterized in that, more comprises:

One buffer unit, is coupled to this converting unit, in order to store one of this linear relationship slope.

5. color space converting circuit according to claim 1, is characterized in that, this higher limit of this pixel component is greater than this higher limit of this covering scope.

6. color space converting circuit according to claim 1, is characterized in that, this packed pixel component system is according to this pixel component, one of this first critical value and this linear relationship slope and determining.

7. color space converting circuit according to claim 1, is characterized in that, more comprises:

One buffer unit, is coupled to this converting unit, in order to store this first critical value.

8. color space converting circuit according to claim 1, is characterized in that, one of this linear relationship slope system determines according to this higher limit of this first critical value, this pixel component and this higher limit of this covering scope.

9. color space converting circuit according to claim 1, is characterized in that, this lower limit of this pixel component is less than this lower limit of this covering scope.

10. color space converting circuit according to claim 1, is characterized in that, this packed pixel component system is according to this pixel component, one of this second critical value and this linear relationship slope and determining.

11. color space converting circuits according to claim 1, is characterized in that, more comprise:

One buffer unit, is coupled to this converting unit, in order to store this second critical value.

12. color space converting circuits according to claim 1, is characterized in that, one of this linear relationship slope system determines according to this lower limit of this second critical value, this pixel component and this lower limit of this covering scope.

13. color space converting circuits according to claim 1, is characterized in that, this color space converting circuit system is implemented in a HDMI (High Definition Multimedia Interface) (HDMI) receiver.

14. 1 kinds of color space changover methods, is characterized in that, comprise:

Receive the pixel signal that belongs to one first color space;

This pixel signal is converted to one second color space one of to produce one of this second color space color space dimensions pixel component from this first color space, wherein, this first color space is xvYcc color space, and this second color space is sRGB color space; And

When this pixel component is positioned between a compressional zone, compress to export a packed pixel component to this pixel component, making this packed pixel component not exceed this second color space covering scope one of on this color space dimensions, is a linear relationship between this packed pixel component and this pixel component;

Wherein, the lower limit between described compressional zone and the upper limit are respectively one of one first critical value and this pixel component higher limit, and this packed pixel component is not higher than one of this covering scope higher limit, and now, the linear relationship between this packed pixel component and this pixel component is:

Packed pixel component=(pixel component-the first critical value) × first slope+the first critical value, wherein, the first slope is the slope of one of the first critical value and this pixel component higher limit;

Or the upper limit between described compressional zone and lower limit are respectively one of one second critical value and this pixel component lower limit, this packed pixel component is not less than one of this covering scope lower limit

, now, the linear relationship between this packed pixel component and this pixel component is:

Packed pixel component=(pixel component-the second critical value) × second slope+the second critical value, wherein, the second slope is the slope of one of the second critical value and this pixel component lower limit;

Described first critical value is greater than described second critical value;

When this pixel component is between described first critical value and described second critical value, directly export this pixel component.

15. color space changover methods according to claim 14, is characterized in that, this compression step system performs according to a question blank, and wherein this question blank stores this packed pixel component of this pixel component and correspondence.