WO2021043164A1 - 一种色域映射方法及系统 - Google Patents

一种色域映射方法及系统 Download PDF

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WO2021043164A1
WO2021043164A1 PCT/CN2020/113021 CN2020113021W WO2021043164A1 WO 2021043164 A1 WO2021043164 A1 WO 2021043164A1 CN 2020113021 W CN2020113021 W CN 2020113021W WO 2021043164 A1 WO2021043164 A1 WO 2021043164A1
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dimensional
color gamut
coordinates
display
brightness
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PCT/CN2020/113021
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English (en)
French (fr)
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张晓东
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深圳Tcl新技术有限公司
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Priority to US17/753,460 priority Critical patent/US20220345675A1/en
Priority to EP20861491.7A priority patent/EP4027641A4/en
Publication of WO2021043164A1 publication Critical patent/WO2021043164A1/zh

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N9/00—Details of colour television systems
    • H04N9/64—Circuits for processing colour signals
    • H04N9/67—Circuits for processing colour signals for matrixing
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G5/00—Control arrangements or circuits for visual indicators common to cathode-ray tube indicators and other visual indicators
    • G09G5/02—Control arrangements or circuits for visual indicators common to cathode-ray tube indicators and other visual indicators characterised by the way in which colour is displayed
    • G09G5/06—Control arrangements or circuits for visual indicators common to cathode-ray tube indicators and other visual indicators characterised by the way in which colour is displayed using colour palettes, e.g. look-up tables
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G5/00—Control arrangements or circuits for visual indicators common to cathode-ray tube indicators and other visual indicators
    • G09G5/10—Intensity circuits
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2320/00—Control of display operating conditions
    • G09G2320/06—Adjustment of display parameters
    • G09G2320/0626—Adjustment of display parameters for control of overall brightness
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2340/00—Aspects of display data processing
    • G09G2340/06—Colour space transformation
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2360/00—Aspects of the architecture of display systems
    • G09G2360/16—Calculation or use of calculated indices related to luminance levels in display data
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/46—Colour picture communication systems
    • H04N1/56—Processing of colour picture signals
    • H04N1/60—Colour correction or control
    • H04N1/6058—Reduction of colour to a range of reproducible colours, e.g. to ink- reproducible colour gamut

Definitions

  • the present disclosure relates to the field of image processing technology, and in particular to a color gamut mapping method and system.
  • Broadcast TV receivers often encounter the problem of inconsistency between the transmission color gamut (that is, the color gamut transmitted by the broadcast TV system, the source color gamut) and the display color gamut (that is, the color gamut that the display can cover) when performing color restoration. This problem will cause the reproduced color to be unable to be truly restored, and even color distortion will occur.
  • the transmission color gamut of the broadcast and television system includes BT601 (standard definition), BT709 (high definition) and so on.
  • BT601 standard definition
  • BT709 high definition
  • the display color gamut continues to expand.
  • the display color gamut LCD liquid crystal display
  • the transmission color gamut BT601, BT709
  • the display color gamut usually cannot completely include the transmission color gamut, and the two do not overlap each other.
  • the current approach is to realize the mapping from the transmission color gamut to the display color gamut through a 3 ⁇ 3 matrix.
  • the mapping and matching of the transmission color gamut to the display color gamut is achieved through a 3 ⁇ 3 matrix, which is not very accurate, only a rough matching can be done, and distortion and errors will be generated.
  • the color gamut extension or mapping disclosed in the prior art is often designed based on the (x, y) two-dimensional surface of CIE1931, as shown in Figure 1, which are schematic diagrams of two-dimensional transmission color gamut and two-dimensional display color gamut, respectively.
  • the area enclosed by the smaller triangle is the transmission color gamut (BT709) to be transmitted by the broadcast television system
  • the area enclosed by the larger triangle is the display color gamut of the terminal broadcast TV.
  • the display color gamut is larger than the transmission color gamut (BT709).
  • the real color gamut is three-dimensional, reflecting the three dimensions of brightness, chroma and hue, not just the (x, y) two-dimensional surface .
  • the present disclosure provides a color gamut mapping method and system to solve at least one of the above-mentioned technical problems.
  • this embodiment provides a color gamut mapping method, which includes:
  • the method before the step of acquiring the brightness value of each sampling point corresponding to the image data of the transmitting end based on the three-dimensional mapping table, the method further includes the following steps:
  • the three-dimensional color gamut model of the transmission end and the three-dimensional color gamut model of the display end are established respectively.
  • the step of establishing a three-dimensional color gamut model of the transmission end includes:
  • the three-dimensional color gamut model of the transmitting end is constructed according to the three-dimensional color gamut coordinates converted to the Yxy color model.
  • the step of linearizing the acquired image data includes:
  • the value range of the acquired image data is converted from 0-(2 n -1) to a value range of 0-1.
  • the step of establishing a three-dimensional color gamut model of the display terminal includes:
  • a three-dimensional color gamut model of the display color gamut is constructed.
  • the step of performing iso-brightness cutting on the three-dimensional color gamut model of the transmission end and the three-dimensional color gamut model of the display end based on the brightness value of each sampling point to form the corresponding iso-brightness two-dimensional surface includes:
  • the three-dimensional color gamut model of the transmission terminal and the three-dimensional color gamut model of the display terminal are respectively subjected to isoluminance cutting according to the brightness values contained in the transmission three-dimensional color gamut coordinates to obtain a series of two-dimensional planes with equal brightness.
  • the step of calculating the transmission three-dimensional color gamut coordinates in the three-dimensional color gamut model of the transmitting end based on the pixel value of each of the sampling points includes:
  • the linear RGB coordinates of each of the sampling points are determined to be converted to the transmission three-dimensional color gamut coordinates of the Yxy color model.
  • the step of performing color mapping based on the formed isoluminance two-dimensional surface, and outputting the mapping data includes:
  • the RGB coordinate value of each sampling point of the transmission end is mapped to the isoluminance two-dimensional surface of the display end.
  • the mapping relationship between the RGB coordinates of each sampling point on the isoluminance two-dimensional surface of the transmission end and the RGB coordinates of each sampling point on the isoluminance two-dimensional surface of the display end is established based on the isoluminance value
  • the steps include:
  • mapping relationship between the RGB coordinates of each sampling point on the iso-brightness two-dimensional surface of the transmission end and the RGB coordinates of each sampling point on the iso-brightness two-dimensional surface of the display end is:
  • x AO (x Ai -x w )*(x F -x w )/(x E -x w )
  • y AO (y Ai -y w )*(y F -y w )/(y E -y w )
  • the step of mapping the RGB coordinate value of each sampling point of the transmission end to the isoluminosity two-dimensional surface of the display end according to the mapping relationship includes:
  • the white point is connected to each The intersection coordinates of the connecting line between the sampling points and the iso-brightness two-dimensional surface of the transmission end and the iso-brightness two-dimensional surface of the display end, and the relational expression of the mapping relationship, calculate the iso-brightness of the transmission end
  • the linear RGB coordinates of each sampling point on the two-dimensional surface are mapped to the linear RGB coordinates on the iso-brightness two-dimensional surface of the display end;
  • the step of combining the linear RGB coordinates of each sampling point on the iso-brightness two-dimensional surface of the display end with the brightness value, converting it into mapping data, and outputting and displaying includes:
  • the three-dimensional RGB value of the target color gamut is obtained;
  • the three-dimensional RGB value of the target color gamut is converted from the three-dimensional color gamut coordinates of the Yxy color model to the three-dimensional color gamut coordinates of the XYZ color model;
  • the output image data is calculated according to the three-dimensional color gamut coordinates of the target color gamut converted to the XYZ color model and the display parameter matrix of the preset display.
  • the step of combining the linear RGB coordinates of each sampling point on the iso-brightness two-dimensional surface of the display end with the brightness value, converting it into mapping data, and outputting and displaying includes:
  • mapping data is filled by linear interpolation, and the filled mapping data is output and displayed.
  • the method before the step of acquiring the brightness value of each sampling point corresponding to the image data of the transmitting end based on the three-dimensional mapping table, the method further includes the following steps:
  • the preset display parameter matrix is calculated.
  • this embodiment also discloses a color gamut mapping system, which includes:
  • the brightness value obtaining module is used to obtain the brightness value of each sampling point corresponding to the image data of the transmission terminal based on the three-dimensional mapping table;
  • the iso-brightness cutting module is used to perform iso-brightness cutting on the three-dimensional color gamut model of the transmission end and the three-dimensional color gamut model of the display end based on the brightness value of each sampling point to form a corresponding equal-brightness two-dimensional surface;
  • the output data conversion module is used to perform color mapping based on the formed isoluminance two-dimensional surface and output the mapping data.
  • the brightness value of each sampling point corresponding to the image data of the transmission end is obtained based on a three-dimensional mapping table; the brightness value of each sampling point is used to determine the three-dimensional color gamut model of the transmission end and the display end respectively.
  • the three-dimensional color gamut model performs equal-brightness cutting to form a corresponding equal-brightness two-dimensional surface; performs color mapping based on the formed equal-brightness two-dimensional surface, and outputs the mapping data.
  • Fig. 1 is a two-dimensional schematic diagram of the transmission end color gamut and display color gamut in the prior art
  • FIG. 2 is a flowchart of steps of a color gamut mapping method in an embodiment of the present disclosure
  • FIG. 3 is a schematic diagram of the principle steps of a color gamut mapping method in an embodiment of the present disclosure
  • FIG. 4 is a schematic structural diagram of a three-dimensional color gamut model in an embodiment of the present disclosure
  • Fig. 5 is a flow chart of establishing a three-dimensional color gamut model of the signal source in an embodiment of the present disclosure
  • Fig. 6 is a flow chart of establishing a three-dimensional color gamut model of the display in an embodiment of the present disclosure
  • FIG. 7 is a flowchart of brightness calculation of a medium-brightness two-dimensional surface in an embodiment of the present disclosure
  • Fig. 8 is a flow chart of calculating 3D LUT output image data in an embodiment of the present disclosure
  • Fig. 9 is a schematic diagram of generating equivalent 3D LUT output image data in an embodiment of the present disclosure.
  • Fig. 10 is a block diagram of the principle structure of the color gamut mapping system in an embodiment of the present disclosure.
  • This embodiment provides a color gamut mapping method, as shown in Figure 2, including:
  • Step S1 Obtain the brightness value of each sampling point corresponding to the image data of the transmission terminal based on the three-dimensional mapping table.
  • the problem to be solved by the method of this embodiment is how to accurately map the color gamut space where the image data of the transmission end is located to the color gamut space of the display end, so as to achieve accurate restoration of the colors contained in the image data.
  • the transmission image data in the transmission color gamut space is acquired, and the transmission image data is sampled based on each sampling point in the pre-generated three-dimensional mapping table, and the brightness value of each sampling point is obtained.
  • the three-dimensional mapping table is a 3D LUT table (Look-Up-Table, display look-up table), which is essentially a RAM. Whenever a signal is input, the address will be input once to look up the table to find out the content corresponding to the address and output it. Play the role of color space conversion for the display.
  • the function of the LUT is to convert each set of RGB input values into output values, convert the RGB values of the input sampling data, and perform non-linear properties in the sampling data, such as color crosstalk, hue, saturation, and brightness. Correction, so that the converted sample data can be controlled more accurately after the conversion of the three-dimensional mapping table and its display calibration.
  • the three-dimensional mapping table contains all the pixel data to be transmitted, the amount of data is relatively large. Therefore, when the image data is transmitted, the data of limited sampling points is generally used. According to the number of sampling points, There are 17 ⁇ 17 ⁇ 17, 24 ⁇ 24 ⁇ 24, etc., so there are multiple sampling points in the three-dimensional mapping table. In the specific color gamut mapping step, only the color coordinates corresponding to the multiple limited sampling points Map to the display color gamut to realize the transmission of image data.
  • Step S2 based on the brightness value of each sampling point, perform iso-brightness cutting on the three-dimensional color gamut model of the transmission end and the three-dimensional color gamut model of the display end to form a corresponding two-dimensional surface of equal brightness.
  • the three-dimensional color gamut model of the transmission end reflects the color to be transmitted by the signal end; the three-dimensional color gamut model of the display end reflects the color capability of the display.
  • the step of obtaining the image data of the transmission color gamut it further includes:
  • the three-dimensional color gamut model of the transmission end and the three-dimensional color gamut model of the display end are established respectively.
  • the three-dimensional color gamut model of the transmission color gamut and the three-dimensional color gamut model of the display color gamut are respectively established.
  • Figure 4 it is a schematic diagram of the three-dimensional color gamut model.
  • the three-dimensional color gamut model reflects each sampling point.
  • the three-dimensional structure composed of three-dimensional color coordinates in the present reflects the coordinate values in three color gamut dimensions.
  • the brightness value of each sampling point needs to be extracted, and each sampling point is extracted
  • the step of establishing a three-dimensional color gamut model of the transmission terminal includes:
  • Step S211 Perform linearization processing on the acquired image data to obtain linear RGB coordinates of each pixel in the image data after linearization processing.
  • the received transmission image data is non-linear, it needs to be linearized first, so that the linearized image data is within a preset range, which is convenient for transmission control.
  • the image data of the BT709 signal source as an example, its value range is 0-(2 n -1) (n is the number of data bits), so after linearization or normalization, the image data is taken Set the range within 0-1 to get linear RGB coordinates.
  • Step S212 using the preset matrix parameters and the linear RGB coordinates of each pixel to determine the three-dimensional color coordinates of the linear RGB coordinates converted to the XYZ color space.
  • the preset matrix parameters are preset constants, which are related to the color coordinates of the signal source at the transmission end.
  • the color coordinates of the R, G, and B vertices (x, y) of the BT709 signal source are (0.640, 0.330), ( 0.300, 0.600), (0.150, 0.060), the white point (x, y) coordinates are (0.3127, 0.3290), and the preset matrix parameters are obtained according to the coordinates of the vertices of the known signal source and the white point.
  • the specific steps of obtaining the matrix parameters please refer to the relevant content in Chapter 1.4.2 of the Fourth Edition of "Principles of Television" et al.
  • the linear RGB coordinates are converted to the three-dimensional color coordinates of the XYZ color space through coordinate conversion.
  • Step S213 Determine the three-dimensional color gamut coordinates of the linear RGB coordinates converted to the Yxy color space according to the three-dimensional color gamut coordinates converted to the XYZ color space.
  • the linear RGB coordinates obtained in the above steps are converted to the three-dimensional color gamut coordinates of the XYZ color space, and the coordinate transformation is again converted to the Yxy color space to obtain the three-dimensional color gamut coordinates of the linear RGB coordinates in the Yxy color space.
  • Step S214 Construct a three-dimensional color gamut model of the transmission color gamut according to the three-dimensional color gamut coordinates converted to the Yxy color space.
  • the three-dimensional color gamut model of the transmission color gamut is constructed, that is, the linear RGB values corresponding to the three-dimensional color gamut coordinates of the Yxy color space are sequentially filled into the Yxy color space
  • a three-dimensional color gamut model of the transmission color gamut is obtained, that is, a three-dimensional three-dimensional model composed of its color coordinates.
  • the steps of establishing a three-dimensional color gamut model of the display terminal include:
  • Step S221 Obtain display image data corresponding to the display setting parameters on the display, and perform normalization processing on the display image data to obtain linear RGB coordinates of each pixel in the display image data after linearization processing.
  • the display image data corresponding to the display setting parameters obtained on the display are all non-linear, it needs to be linearized first, so that the linearized image data is within the preset range, which is convenient for transmission control. After linearization or normalization is performed on it, the value range of its image data is set within 0-1 to obtain linear RGB coordinates.
  • Step S222 Determine the three-dimensional color gamut coordinates of the linear RGB coordinates converted to the XYZ color space according to the pre-stored display parameter matrix and the linear RGB coordinates of each display pixel.
  • the preset display parameter matrix is determined based on the RGB vertex color coordinates and white point coordinates of the display on the display side.
  • the preset display parameters are calculated by the RGB vertex color coordinates and white point coordinates of the display.
  • Matrix based on the obtained preset display parameter matrix and linear RGB coordinates, calculate the three-dimensional color gamut coordinates converted to the XYZ color space.
  • Step S223 Determine, according to the three-dimensional color gamut coordinates converted to the XYZ color space, the linear RGB coordinates of each display pixel to be converted to the three-dimensional color gamut coordinates of the Yxy color space.
  • Step S224 Construct a three-dimensional color gamut model of the display terminal according to the three-dimensional color gamut coordinates converted to the Yxy color space.
  • the brightness value is extracted, and the iso-brightness region in the three-dimensional color gamut model is segmented according to the extracted brightness value. Since the coordinate value of each sampling point in the three-dimensional color gamut model corresponds to the brightness value, chroma and hue, the sampling points with the same brightness value are in a two-dimensional color gamut plane, so based on the same brightness value, three-dimensional colors can be divided Moderately bright areas of the domain model.
  • the step of segmenting the three-dimensional color gamut model of the transmission end and the three-dimensional color gamut model of the display end based on the brightness value includes:
  • the three-dimensional color gamut model of the transmission terminal and the three-dimensional color gamut model of the display terminal are respectively subjected to isoluminance cutting according to the brightness values contained in the transmission three-dimensional color gamut coordinates to obtain a series of two-dimensional planes with equal brightness.
  • the step of calculating the transmission three-dimensional color gamut coordinates of each of the sampling points in the three-dimensional color gamut model of the transmitting end includes:
  • Step S231 Perform linearization processing on each of the sampling points to obtain linear RGB coordinates of each sampling point after the linearization processing;
  • Step S232 Determine the linear RGB coordinates of each sampling point to convert to the three-dimensional color gamut coordinates of the XYZ color model according to the preset matrix parameters and the linear RGB coordinates corresponding to each sampling point;
  • Step S233 Determine, according to the three-dimensional color gamut coordinates converted to the XYZ color model, the linear RGB coordinates of each sampling point to be converted to the transmission three-dimensional color gamut coordinates of the Yxy color model.
  • the linear RGB coordinates are gradually converted to the XYZ color space, and then converted from the XYZ color space to the Yxy color space, and the obtained is transferred to the all the sampling points on the Yxy color space.
  • the step of converting the linear RGB coordinates of each sampling point to the brightness value in the three-dimensional color gamut coordinates on the Yxy color space to perform the isoluminance region segmentation of the three-dimensional color gamut model of the transmission color gamut includes:
  • the three-dimensional color gamut model of the transmission terminal and the three-dimensional color gamut model of the display terminal are respectively subjected to isoluminance cutting according to the brightness values contained in the transmission three-dimensional color gamut coordinates to obtain a series of two-dimensional planes with equal brightness.
  • Step S3 Perform color mapping based on the formed isoluminance two-dimensional surface, and output the mapping data.
  • mapping relationship between the RGB coordinates of each sampling point on the isoluminance two-dimensional surface of the transmission end and the RGB coordinates of each sampling point on the isoluminance two-dimensional surface of the display end is established by the isoluminance value, according to the The mapping relationship maps the RGB coordinate value of each sampling point of the transmission end to the isoluminance two-dimensional surface of the display end.
  • the mapping data is image data that maps the RGB coordinate value of each sampling point of the transmission end to the isoluminance two-dimensional surface of the display end.
  • This step specifically includes the following:
  • Step S31 Obtain the two-dimensional color gamut plane of the transmission color gamut and the two-dimensional plane of the display color gamut with equal brightness respectively;
  • Step S32 According to the pre-stored RGB coordinates of the white point corresponding to the transmission end, the RGB coordinates of the white point corresponding to the display end, and the linear RGB coordinates of each sampling point in the isoluminance two-dimensional plane, the white point is equal to each One of the intersection coordinates of the connecting line between the sampling points and the iso-brightness two-dimensional surface of the transmission end and the iso-brightness two-dimensional surface of the display end respectively, and calculate each of the two-dimensional iso-brightness surface of the transmission end.
  • the linear RGB coordinates of the sampling points are mapped to the linear RGB coordinates on the isoluminosity two-dimensional surface of the display end;
  • the horizontal axis is the chromaticity coordinate x
  • the vertical axis is the chromaticity coordinate y.
  • the triangle with a smaller area in the figure is a two-dimensional transmission color gamut plane, where the corresponding brightness value is the brightness Y of a pixel in the 17 ⁇ 17 ⁇ 17 data input by the 3D LUT.
  • W(x w ,y w ) is the white point of the BT709 and the display.
  • a i (x Ai , y Ai ) is a certain known pixel of one of 17 ⁇ 17 ⁇ 17 data. Connect W and A i , extend them, and intersect two triangles at points E(x E ,y E ) and F(x F ,y F ) respectively.
  • the dots on WF have the same ratio of x and y, so they are all equal tones.
  • a o is the target point.
  • x AO (x Ai -x w )*(x F -x w )/(x E -x w )
  • y AO (y Ai -y w )*(y F -y w )/(y E -y w )
  • W (x w, y w ), A i (x Ai, y Ai) are known.
  • the points E(x E ,y E ) and F(x F ,y F ) can be found in the three-dimensional color gamut. Therefore, x AO and y AO can be found.
  • Step S33 Combine the linear RGB coordinates of each sampling point on the iso-brightness two-dimensional surface of the display end with the brightness value, convert it into mapping data, and output and display it.
  • the two-dimensional coordinates on the iso-brightness two-dimensional surface of the transmission end in the above step S3 are mapped to the iso-brightness two-dimensional surface of the display end for each sampling point, there is no brightness value, so in this step, the two-dimensional coordinates need to be added. Its corresponding brightness value.
  • the three-dimensional color gamut coordinates of the added brightness value are the color coordinates in the Yxy color space, in order to display normally, it needs to be converted into the display color gamut space where the display is obtained, so as to obtain the output data of the three-dimensional mapping table.
  • the steps of combining the linear RGB coordinates of each sampling point on the iso-brightness two-dimensional surface of the display end with the brightness value, converting it into mapping data, and outputting and displaying include:
  • the three-dimensional RGB value of the target color gamut is obtained;
  • the three-dimensional RGB value of the target color gamut is converted from the three-dimensional color gamut coordinates of the Yxy color model to the three-dimensional color gamut coordinates of the XYZ color model;
  • the output image data is calculated according to the three-dimensional color gamut coordinates of the target color gamut converted to the XYZ color model and the display parameter matrix of the preset display.
  • the step of obtaining display image data according to the output data of the three-dimensional mapping table includes:
  • the output data of the three-dimensional mapping table is filled by linear interpolation to obtain display image data.
  • the linear interpolation method is used to expand the output data of the three-dimensional mapping table, so that the pixel value of the display image data meets the high-definition display condition or meets the requirements of other higher or lower display pixels, thereby obtaining the display image data.
  • the color space Yxy uses BT709 as the signal source and a 3D LUT of 17 ⁇ 17 ⁇ 17 as an example.
  • the signal source can be of other types, such as BT601, and the three-dimensional mapping table can also be in the form of 24 ⁇ 24 ⁇ 24.
  • FIG. 5 is a flow chart of the three-dimensional color gamut establishment at the transmitting end.
  • the processing flow is as follows:
  • BT709 image data input is non-linear R, G, B image data.
  • the value range is 0-(2 n -1) (n is the number of data bits).
  • the normalization/linearization module is to normalize the maximum value of non-linear R, G, and B image data.
  • the value range of the normalized image data is 0-1.
  • R 1 R/(2 n -1)
  • G 1 G/(2 n -1)
  • the linearization module linearizes non-linear data. Get linear R ′ , G ′ , B ′ data.
  • the color coordinates of the R, G, and B vertices (x, y) of the BT709 source are (0.640, 0.330), (0.300, 0.600), (0.150, 0.060), and the white point (x, y) coordinates are (0.3127, 0.3290) ). Then the conversion from R′G′B′ to XYZ is as follows:
  • Figure 6 is the process of establishing a three-dimensional color gamut on the display.
  • the matrix used is determined by the R, G, B vertex color coordinates and white point coordinates of the display. which is:
  • the matrix coefficients b10, b11...b32 are determined by the physical parameters of the display, that is, the color coordinates of the R, G, and B vertices and the white point coordinates.
  • the 256 ⁇ 256 ⁇ 256 groups of R, G, B BT709 input data are normalized/linearized, and 256 ⁇ 256 ⁇ 256 groups of linear R′, G′, B′ data are obtained, of which 17 ⁇ 17 ⁇ 17 groups of R′, G′, and B′ are used as 3D LUT sampling data, that is, the input data R i ′, G i ′, and B i ′ of the 3D LUT.
  • the input data R i ′, G i ′, and B i ′ of the 3D LUT are converted into XYZ according to the matrix coefficient of formula 1, and then XYZ is converted into Yxy.
  • the Y values corresponding to R i ′, G i ′, and B i ′ are obtained.
  • Y is the brightness value of the next two-dimensional surface with constant brightness.
  • the three-dimensional color gamut is subjected to iso-brightness tangent to obtain 17 ⁇ 17 ⁇ 17 iso-brightness two-dimensional planes.
  • the color mapping based on iso-brightness and iso-tone in Fig. 7 is performed on the 17 ⁇ 17 ⁇ 17 ⁇ 2 iso-brightness two-dimensional planes of the transmission end and the display end.
  • Figure 8 shows the 3D LUT output calculation process.
  • the 3D LUT output calculation process in Fig. 8 is a process of converting this corresponding Yxy value into a R o ′G o ′B o ′ value, that is, the process of calculating the output data of the 3D LUT.
  • the matrix coefficients c10, c11...c32 are determined by the physical parameters of the display, that is, the color coordinates of the R, G, and B vertices and the white point coordinates.
  • Ro'Go'Bo' is the output data of the 3D LUT.
  • each set of R i ′G i ′B i ′ values of 17 ⁇ 17 ⁇ 17 in the 3D LUT has a set of Ro according to the color mapping of equal brightness and equal tones.
  • the value of'Go'Bo' corresponds to it. That is, the color mapping of iso-brightness and iso-tone based on 3D LUT is completed.
  • Figure 9 is an equivalent diagram of a 3D LUT.
  • This embodiment also provides a color gamut mapping system, as shown in FIG. 10, including:
  • the brightness value obtaining module 110 is configured to obtain the brightness value of each sampling point corresponding to the image data of the transmission terminal based on the three-dimensional mapping table;
  • the iso-brightness cutting module 120 is configured to perform iso-brightness cutting on the three-dimensional color gamut model of the transmission end and the three-dimensional color gamut model of the display end based on the brightness value of each sampling point to form a corresponding iso-brightness two-dimensional surface;
  • the output data conversion module 130 is used to perform color mapping based on the formed isoluminance two-dimensional surface, and output the mapping data.
  • the system provided in the embodiment of the present disclosure calculates the brightness value of each sampling point in the three-dimensional mapping table according to the input image data; based on the brightness value of each sampling point, the three-dimensional color gamut model and the three-dimensional color gamut model and The three-dimensional color gamut model of the display end is divided into equal-brightness regions to obtain the two-dimensional surface of the medium-brightness of the transmission end and the two-dimensional surface of the display end; the two-dimensional surface of the transmission end and the two-dimensional surface of the display end are equalized and equal Color mapping, calculating the two-dimensional pixel value of the target color gamut; combining the two-dimensional pixel value of the target color gamut with the brightness value, and converting it into output image data.

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Abstract

本公开提供了一种色域映射方法及系统，根据本公开实施方式提供的方法，通过基于三维映射表获取传输端的图像数据对应的每一采样点的亮度值；基于每一所述采样点的亮度值分别对传输端的三维色域模型和显示端的三维色域模型进行等亮度切割，形成对应的等亮度二维面；基于所形成的等亮度二维面进行色彩映射，输出映射数据。可见，本公开所述方法在进行色域映射时，保持亮度和色调不变，实现传输色域到显示色域的三维色域映射的精确匹配，避免了因为传输色域到显示色域之间映射不匹配，而导致的图像失真或显示错误等问题。

Description

一种色域映射方法及系统
优先权
本公开要求申请日为2019年09月03日提交中国专利局、申请号为“201910828423.5”、申请名称为“一种色域映射方法及系统”的中国专利申请的优先权，其全部内容通过引用结合在本公开中。
技术领域
本公开涉及图像处理技术领域，尤其涉及的是一种色域映射方法及系统。
背景技术
广播电视接收机，在进行色彩还原时，往往会遇到传输色域(即广播电视系统传输的色域，源色域)与显示色域(即显示器所能覆盖的色域)不一致的问题，而该问题将会造成重显色彩无法真实还原，甚至会出现彩色失真的问题。
目前广播电视系统的传输色域有BT601(标清)，BT709(高清)等。而随着显示器技术的发展，显示色域范围不断扩大。目前的情况，通常显示色域(LCD液晶显示器)要大于传输色域(BT601，BT709)。并且，显示色域通常不能完全包含传输色域，二者有互不重合部分。
如何将传输色域的色彩不失真的在显示器中呈现，并尽可能利用显示色域的能力，这里涉及到一个从传输色域到显示色域的扩展或映射的问题。
对于上述问题，当前的做法是，通过3×3矩阵来实现传输色域到显示色域的映射。通过3×3矩阵来实现传输色域到显示色域的映射匹配，不是很精准，只能做粗略的匹配，并且会产生失真及错误。
现有技术中所公开的色域扩展或映射，往往是基于CIE1931的(x，y)二维面进行设计，如图1所示，分别是二维传输色域与二维显示色域示意图，其中，稍小的三角形所围成的区域，是广播电视系统所要传输的传输色域(BT709)，而稍大的三角形所围成的区域，则是终端广播电视机的显示色域。显示色域要大于传输色域(BT709)，而实际的情况，真实的色域是三维的，所反映的是亮度，色度和色相三个维度，并不只是(x，y)二维面。
因此，现有技术有待于进一步的改进。
发明内容
鉴于上述现有技术中的不足之处，本公开提供了一种色域映射方法及系统，以解决上述至少一个技术问题。
第一方面，本实施例提供了一种色域映射方法，其中，包括：
基于三维映射表获取传输端的图像数据对应的每一采样点的亮度值；
基于每一所述采样点的亮度值分别对传输端的三维色域模型和显示端的三维色域模型进行等亮度切割，形成对应的等亮度二维面；
基于所形成的等亮度二维面进行色彩映射，输出映射数据。
可选的，所述基于三维映射表获取传输端的图像数据对应的每一采样点的亮度值的步骤之前，还包括步骤：
分别建立传输端的三维色域模型和显示端的三维色域模型。
可选的，所述建立传输端的三维色域模型的步骤包括：
对获取到的所述图像数据进行线性化处理，得到线性化处理后所述图像数据中各个像素点的线性RGB坐标；
利用预设矩阵参数和各个像素点的线性RGB坐标确定所述线性RGB坐标转换到XYZ颜色模型的三维色域坐标；
根据转换到所述XYZ颜色模型的三维色域坐标确定所述线性RGB坐标转换到Yxy颜色模型的三维色域坐标；
根据转换到所述Yxy颜色模型上的三维色域坐标构建传输端的三维色域模型。
可选的，所述对获取到的所述图像数据进行线性化处理的步骤包括：
将获取到的所述图像数据的取值范围由0-(2 n-1)转换成取值范围为0-1以内。
可选的，所述建立显示器端的三维色域模型的步骤包括：
获取显示器上的与显示设置参数相对应的显示图像数据，并对所述显示图像数据进行归一化处理，得到线性化处理后所述显示图像数据中各个像素点的线性RGB坐标；
根据预存储的显示参数矩阵和各个显示图像数据中各个像素点的线性RGB坐标确定所述显示图像数据中各个像素点的所述线性RGB坐标转换到XYZ颜色模型的三维色域坐标；
根据转换到所述XYZ颜色模型的三维色域坐标确定所述显示图像数据中各个像素 点的线性RGB坐标转换到Yxy颜色模型的三维色域坐标；
根据转换到Yxy颜色模型上的三维色域坐标构建显示端显示色域的三维色域模型。
可选的，所述基于每一所述采样点的亮度值分别对传输端的三维色域模型和显示端的三维色域模型进行等亮度切割，形成对应的等亮度二维面的步骤包括：
基于所述每一所述采样点的像素值，计算出所述每一所述采样点处于所述传输端的三维色域模型中的传输三维色域坐标；
根据所述传输三维色域坐标中所含的亮度值分别对所述传输端的三维色域模型和显示端的三维色域模型进行等亮度切割，得到一系列等亮度的二维面。
可选的，所述基于所述每一所述采样点的像素值，计算出所述每一所述采样点处于所述传输端的三维色域模型中的传输三维色域坐标的步骤包括：
对所述每一所述采样点进行线性化处理，得到线性化处理后的每一所述采样点的线性RGB坐标；
根据所述预设矩阵参数和每一所述采样点所对应的线性RGB坐标确定每一所述采样点的所述线性RGB坐标转换到XYZ颜色模型的三维色域坐标；
根据转换到XYZ颜色模型的三维色域坐标确定所述每一所述采样点的线性RGB坐标转换到Yxy颜色模型的传输三维色域坐标。
可选的，所述基于所形成的等亮度二维面进行色彩映射，输出映射数据的步骤包括：
基于等亮度值建立传输端的等亮度二维面上的每个采样点的RGB坐标与显示端的等亮度二维面上的每个采样点的RGB坐标之间的映射关系；
根据所述映射关系，将传输端的每个采样点的RGB坐标值映射到显示端的等亮度二维面上。
可选的，所述基于等亮度值建立传输端的等亮度二维面上的每个采样点的RGB坐标与显示端的等亮度二维面上的每个采样点的RGB坐标之间的映射关系的步骤包括：
分别获取等亮度的所述传输色域的二维色域平面和所述显示色域的二维平面；
根据预存储的传输端所对应白点的RGB坐标、显示端所对应白点的RGB坐标、等亮度二维面内每一所述采样点的线性RGB坐标，所述白点与每一所述采样点之间的连接线分别与所述传输端的等亮度二维面和所述显示端的等亮度二维面的交点坐标，建立传输端的等亮度二维面上的每个采样点的RGB坐标与显示端的等亮度二维面上的每个采样点的RGB坐标之间的映射关系。
可选的，所述传输端的等亮度二维面上的每个采样点的RGB坐标与显示端的等亮 度二维面上的每个采样点的RGB坐标之间的映射关系的关系式为：
WA i/WE＝WA O/WF
x AO＝(x Ai-x w)*(x F-x w)/(x E-x w)
y AO＝(y Ai-y w)*(y F-y w)/(y E-y w)
其中，W(x w,y w)为预存储的传输端所对应白点的RGB坐标，A i(x Ai,y Ai)为已知采样点的线性RGB坐标，E(x E,y E)，F(x F,y F)点分别为W(x w,y w)和A i(x Ai,y Ai)的连接线分别与所述传输端的等亮度二维面和所述显示端的等亮度二维面的交点坐标，WA i为W(x w,y w)与A i(x Ai,y Ai)两点组成的直线，WE为W(x w,y w)与E(x E,y E)两点组成的直线，WA O为W(x w,y w)与A o(x AO,y AO)两点组成的直线，WF为W(x w,y w)与F(x F,y F)两点组成的直线。
可选的，所述根据所述映射关系，将传输端的每个采样点的RGB坐标值映射到显示端的等亮度二维面上的步骤包括：
根据预存储的传输端所对应白点的RGB坐标、显示端所对应白点的RGB坐标、等亮度二维面内中每一所述采样点的线性RGB坐标，所述白点与每一所述采样点之间的连接线分别与所述传输端的等亮度二维面和所述显示端的等亮度二维面的交点坐标，以及所述映射关系的关系式，计算出所述传输端的等亮度二维面上每个所述采样点的线性RGB坐标映射到所述显示端的等亮度二维面上的线性RGB坐标；
将每个所述采样点在所述显示端的等亮度二维面上的线性RGB坐标与亮度值相结合，转换成映射数据，并输出显示。
可选的，所述将每个所述采样点在所述显示端的等亮度二维面上的线性RGB坐标与亮度值相结合，转换成映射数据，并输出显示的步骤包括：
根据目标色域的二维像素值与其亮度值相结合，得到目标色域的三维RGB值；
根据XYZ颜色模型的RGB值与Yxy颜色模型的RGB值之间的转换公式，将所述目标色域的三维RGB值由Yxy颜色模型的三维色域坐标转换到XYZ颜色模型的三维色域坐标；
根据转换到XYZ颜色模型的目标色域的三维色域坐标、预设显示器的显示参数矩阵，计算出输出图像数据。
可选的，所述将每个所述采样点在所述显示端的等亮度二维面上的线性RGB坐标与亮度值相结合，转换成映射数据，并输出显示的步骤包括：
利用线性内插法对所述映射数据进行填充，并将填充后的所述映射数据进行输出显 示。
可选的，所述基于三维映射表获取传输端的图像数据对应的每一采样点的亮度值的步骤之前，还包括步骤：
根据信号源端RGB顶点色坐标和白点坐标的二维坐标值，计算得到所述预矩阵参数；
根据显示端RGB顶点色坐标及白点坐标的二维坐标值，计算得到预设显示参数矩阵。
第二方面，本实施例还公开了一种色域映射系统，其中，包括：
亮度值获取模块，用于基于三维映射表获取传输端的图像数据对应的每一采样点的亮度值；
等亮度切割模块，用于基于每一所述采样点的亮度值分别对传输端的三维色域模型和显示端的三维色域模型进行等亮度切割，形成对应的等亮度二维面；
输出数据转换模块，用于基于所形成的等亮度二维面进行色彩映射，输出映射数据。
与现有技术相比，本公开实施例具有以下优点：
根据本公开实施方式提供的方法，通过基于三维映射表获取传输端的图像数据对应的每一采样点的亮度值；基于每一所述采样点的亮度值分别对传输端的三维色域模型和显示端的三维色域模型进行等亮度切割，形成对应的等亮度二维面；基于所形成的等亮度二维面进行色彩映射，输出映射数据。可见，本公开所述方法在进行色域映射时，保持亮度和色调不变，实现传输色域到显示色域的三维色域映射的精确匹配，避免了因为传输色域到显示色域之间映射不匹配，而导致的图像失真或显示错误等问题。
附图说明
为了更清楚地说明本公开实施例或现有技术中的技术方案，下面将对实施例或现有技术描述中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图仅仅是本公开中记载的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据这些附图获得其他的附图。
图1是现有技术中传输端色域和显示色域的二维平面示意图；
图2中本公开实施例中一种色域映射方法的步骤流程图；
图3是本公开实施例中色域映射方法的原理步骤示意图；
图4是本公开实施例中三维色域模型的结构示意图；
图5是本公开实施例中信号源端三维色域模型的建立流程图；
图6是本公开实施例中显示器端三维色域模型的建立流程图；
图7是本公开实施例中等亮度二维面的亮度计算流程图；
图8是本公开实施例中3D LUT输出图像数据计算流程图；
图9是本公开实施例中等效3D LUT输出图像数据的生成示意图；
图10是本公开实施例中所述色域映射系统的原理结构框图。
具体实施方式
为使本公开的目的、技术方案及优点更加清楚、明确，以下参照附图并举实施例对本公开进一步详细说明。应当理解，此处所描述的具体实施例仅仅用于解释本公开，并不用于限定本公开。
本领域技术人员在考虑说明书及实践这里公开的发明后，将容易想到本公开的其它实施方案。本公开旨在涵盖本公开的任何变型、用途或者适应性变化，这些变型、用途或者适应性变化遵循本公开的一般性原理并包括本公开未公开的本技术领域中的公知常识或惯用技术手段。
实施例1
本实施例提供了一种色域映射方法，如图2，包括：
步骤S1、基于三维映射表获取传输端的图像数据对应的每一采样点的亮度值。
结合图3所述，本实施例所述方法所要解决的问题是如何将传输端的所述图像数据所在色域空间准确映射到显示端的色域空间，实现图像数据所含色彩的准确还原。
获取传输色域空间内的传输图像数据，并基于预先生成的三维映射表中的各个采样点对所述传输图像数据进行采样，获取每一采样点的亮度值。
所述三维映射表为3D LUT表(Look-Up-Table，显示查找表)，其本质是一个RAM，每当输入一个信号就会输入一次地址进行查表，找出地址对应的内容并输出，对显示器来说起到颜色空间转换的作用。LUT的作用就是将每一组RGB的输入值转化成输出值，对输入的采样数据的RGB值进行转换，对采样数据中的非线性属性，比如：颜色串扰、色相、饱和度和亮度等进行修正，以使得转换后的采样数据在经过三维映射表转换，对其进行显示校准后，能实现对其更为精准的控制。
结合图3所示，基于三维映射表中如含有全部要传输的像素数据，则数据量较大，因此在进行图像数据传输时，一般采取输入有限采样点的数据，根据采样点的是多少，有17×17×17，24×24×24等形式，因此在所述三维映射表中含有多个采样点，在具体的色域映射步骤中，仅仅采取将多个有限采样点对应的色坐标映射到显示色域，实现图像数据的传输。
步骤S2、基于每一所述采样点的亮度值分别对传输端的三维色域模型和显示端的三维色域模型进行等亮度切割，形成对应的等亮度二维面。
传输端的三维色域模型，反映了信号端所要传输的色彩；显示端的三维色域模型，反映了显示器所能够呈现的色彩能力。
为了实现基于三维映射表，提取出所述图像数据中各个采样点的亮度值，
所述获取传输色域的图像数据的步骤之前，还包括：
分别建立传输端的三维色域模型和显示端的三维色域模型。
在色彩空间内，分别建立传输色域的三维色域模型和显示色域的三维色域模型，如图4所示，为三维色域模型的示意图，所述三维色域模型反映了各个采样点在的三维色坐标所组成的立体结构，其反映是三个色域维度上的坐标值，为了获相同亮度值的二维色域平面，需要提取各个采样点的亮度值，而提取各个采样点的亮度值，需要首先建立传输色域的三维色域模型和显示色域的三维色域模型。
具体的，如图5所示，所述建立传输端的三维色域模型的步骤包括：
步骤S211、对获取到的所述图像数据进行线性化处理，得到线性化处理后所述图像数据中各个像素点的线性RGB坐标。
由于接收到的传输图像数据均为非线性的，首先需要对其进行线性化处理，使得线性化处理的图像数据在预设范围内，便于对其传输控制。以BT709信号源的图像数据为例，其取值范围为0-(2 n-1)(n为数据比特数)，因此对其进行线性化或归一化处理后，将其图像数据取值范围设置在0-1以内，得到线性RGB坐标。
步骤S212、利用预设矩阵参数和各个像素点的线性RGB坐标确定所述线性RGB坐标转换到XYZ颜色空间的三维色坐标。
预设矩阵参数为预设的常数，该常数与传输端信号源的色坐标相关，例如：BT709信号源的R、G、B顶点(x，y)色坐标分别为(0.640,0.330)、(0.300,0.600)、(0.150,0.060)，白点(x，y)坐标为(0.3127,0.3290)，根据上述已知信号源的顶点和白点所在坐标值，求得所述预设矩阵参数。具体的矩阵参数的求取步骤，可参考俞斯乐等《电视原理》第 四版1.4.2章节相关内容。
根据预设矩阵参数和各个像素的线性RGB坐标通过坐标转换，将所述线性RGB坐标转换到XYZ颜色空间的三维色坐标。
步骤S213、根据转换到所述XYZ颜色空间的三维色域坐标确定所述线性RGB坐标转换到Yxy颜色空间的三维色域坐标。
将上述步骤中获取到的线性RGB坐标转换到XYZ颜色空间的三维色域坐标，再次坐标变换将其转换到Yxy颜色空间，得到Yxy颜色空间内所述线性RGB坐标的三维色域坐标。
步骤S214、根据转换到所述Yxy颜色空间上的三维色域坐标构建传输色域的三维色域模型。
根据所述线性RGB坐标转换到Yxy颜色空间的三维色域坐标，构建传输色域的三维色域模型，也即是将线性RGB值对应到Yxy颜色空间的三维色域坐标依次填充到Yxy颜色空间内，得到传输色域的三维色域模型，也即其色坐标组成的立体三维立体模型。
如图6所示，所述建立显示端的三维色域模型的步骤包括：
步骤S221、获取显示器上的与显示设置参数相对应的显示图像数据，并对所述显示图像数据进行归一化处理，得到线性化处理后所述显示图像数据中各个像素点的线性RGB坐标。
由于获取显示器上的与显示设置参数相对应的显示图像数据均为非线性的，首先需要对其进行线性化处理，使得线性化处理的图像数据在预设范围内，便于对其传输控制，因此对其进行线性化或归一化处理后，将其图像数据取值范围设置在0-1以内，得到线性RGB坐标。
步骤S222、根据预存储的显示参数矩阵和各个显示像素的线性RGB坐标确定所述线性RGB坐标转换到XYZ颜色空间的三维色域坐标。
本步骤与上述步骤S212中不同的，预设显示参数矩阵是基于显示端的显示器的RGB顶点色坐标和白点坐标来决定的，通过显示器的RGB顶点色坐标和白点坐标计算得到预设显示参数矩阵，再基于求取到的预设显示参数矩阵和线性RGB坐标，计算出转换到XYZ颜色空间的三维色域坐标。
步骤S223、根据转换到所述XYZ颜色空间的三维色域坐标确定各个显示像素的线性RGB坐标转换到Yxy颜色空间的三维色域坐标。
步骤S224、根据转换到Yxy颜色空间上的三维色域坐标构建出显示端的三维色域 模型。
基于上述步骤中建立出的传输端的三维色域模型和显示端的三维色域模型进行亮度值提取以及根据提取出的亮度值对三维色域模型中的等亮度区域进行分割。由于三维色域模型中各个采样点的坐标值分别对应亮度值、色度和色相，因此亮度值相同的采样点处于一个二维色域平面内，因此基于同一个亮度值，可以划分出三维色域模型中等亮度的区域。
具体的，所述基于所述亮度值对传输端的三维色域模型和显示端的三维色域模型进行等亮度区域分割的步骤包括：
基于所述每一所述采样点的像素值，计算出所述每一所述采样点处于所述传输端的三维色域模型中的传输三维色域坐标；
根据所述传输三维色域坐标中所含的亮度值分别对所述传输端的三维色域模型和显示端的三维色域模型进行等亮度切割，得到一系列等亮度的二维面。
具体的，所述步骤中基于所述每一所述采样点的像素值，计算出所述每一所述采样点处于所述传输端的三维色域模型中的传输三维色域坐标的步骤包括：
步骤S231、对所述每一所述采样点进行线性化处理，得到线性化处理后的每一所述采样点的线性RGB坐标；
由于仅仅需要根据采样点对应的亮度值进行三维色域模型的等亮度区域分割，因此本步骤中仅仅需要提取三维映射表中各个采样点所对应的线性RGB坐标。
步骤S232、根据所述预设矩阵参数和每一所述采样点所对应的线性RGB坐标确定每一所述采样点的所述线性RGB坐标转换到XYZ颜色模型的三维色域坐标；
步骤S233、根据转换到XYZ颜色模型的三维色域坐标确定所述每一所述采样点的线性RGB坐标转换到Yxy颜色模型的传输三维色域坐标。
上述步骤S232至步骤S233，逐步将线性RGB坐标转换到XYZ颜色空间，再将其从XYZ颜色空间转换到Yxy颜色空间，将获取到的转到Yxy颜色空间上的每一个所述采样点的所对应的三维色域坐标。
具体的，所述根据每个采样点的线性RGB坐标转换到所述Yxy颜色空间上的三维色域坐标中的亮度值进行传输色域的三维色域模型的等亮度区域分割的步骤包括：
根据所述传输三维色域坐标中所含的亮度值分别对所述传输端的三维色域模型和显示端的三维色域模型进行等亮度切割，得到一系列等亮度的二维面。
步骤S3、基于所形成的等亮度二维面进行色彩映射，输出映射数据。
本步骤中通过等亮度值建立传输端的等亮度二维面上的每个采样点的RGB坐标与显示端的等亮度二维面上的每个采样点的RGB坐标之间的映射关系，根据所述映射关系，将传输端的每个采样点的RGB坐标值映射到显示端的等亮度二维面上。所述映射数据为将传输端的每个采样点的RGB坐标值映射到显示端的等亮度二维面上的图像数据。
本步骤具体包括以下内容：
步骤S31、分别获取等亮度的所述传输色域的二维色域平面和所述显示色域的二维平面；
步骤S32、根据预存储的传输端所对应白点的RGB坐标、显示端所对应白点的RGB坐标、等亮度二维面内每一所述采样点的线性RGB坐标，所述白点与每一所述采样点之间的连接线分别与所述传输端的等亮度二维面和所述显示端的等亮度二维面的交点坐标，计算出所述传输端的等亮度二维面上每个所述采样点的线性RGB坐标映射到所述显示端的等亮度二维面上的线性RGB坐标；
结合图7所示，以信号源BT709举例。其中，横轴为色度坐标x,纵轴为色度坐标y。图中的面积稍小的三角形为二维传输色域平面，其中所对应的亮度值为3D LUT输入的17×17×17数据中某一像素的亮度Y，在信源BT709三维色域中，所切割出的等亮度二维色域面；面积稍大三角形，是用同一亮度Y，在显示端三维色域中，所切割出的等亮度二维色域面。
W(x w,y w)为BT709及显示器的白点。A i(x Ai,y Ai)即为17×17×17数据之一的某一已知像素。连接W和A i，并延长，分别交两个三角形于E(x E,y E)点和F(x F,y F)点。WF上的点因x,y比例一致，因此均为等色调。A o为目标点。
A o点的坐标(x AO,y AO)计算如下：
WA i/WE＝WA O/WF
x AO＝(x Ai-x w)*(x F-x w)/(x E-x w)
y AO＝(y Ai-y w)*(y F-y w)/(y E-y w)
这里，W(x w,y w)，A i(x Ai,y Ai)为已知。E(x E,y E)，F(x F,y F)点可由三维色域中求得，因此，x AO，y AO可求。
经过图6中所示的计算步骤流程及图7的计算，对于一个给定的3D LUT输入值RGB，会有一个对应Yxy值与其对应。
步骤S33、将每个所述采样点在所述显示端的等亮度二维面上的线性RGB坐标与 亮度值相结合，转换成映射数据，并输出显示。
由于各个采样点由于上述步骤S3中传输端的等亮度二维面上的线性RGB坐标映射到显示端的等亮度二维面上，其中不含有亮度值，因此本步骤中需要为该二维坐标添加上其相对应的亮度值。又由于添加上亮度值的三维色域坐标为Yxy颜色空间内的色坐标，因此为了正常显示，需要将其转换到得到显示器所在的显示色域空间内，从而得到三维映射表的输出数据。
结合图8所述，将每个所述采样点在所述显示端的等亮度二维面上的线性RGB坐标与亮度值相结合，转换成映射数据，并输出显示的步骤包括：
根据目标色域的二维像素值与其亮度值相结合，得到目标色域的三维RGB值；
根据XYZ颜色模型的RGB值与Yxy颜色模型的RGB值之间的转换公式，将所述目标色域的三维RGB值由Yxy颜色模型的三维色域坐标转换到XYZ颜色模型的三维色域坐标；
根据转换到XYZ颜色模型的目标色域的三维色域坐标、预设显示器的显示参数矩阵，计算出输出图像数据。
由于三维映射表输出数据中仅仅含有有限个采样点数据，因此，所述根据三维映射表输出数据得到显示图像数据的步骤包括：
利用线性内插法对所述三维映射表输出数据进行填充，得到显示图像数据。
利用线性内插法对所述三维映射表输出数据进行扩充，使得显示图像数据像素值满足高清显示条件或者满足其他更高或者更低显示像素的要求，从而得到显示图像数据。
下面以本实施例的一个具体应用实例，对本公开上述方法进行更为详细的说明。下面的应用实例中色彩空间Yxy，以BT709为信号源，17×17×17的3D LUT为例。信号源可以是其他类型，例如：BT601，三维映射表也可以是：24×24×24等形式。
图5是传输端三维色域建立流程图，其处理流程如下：
(1)、BT709图像数据输入，是非线性的R，G，B图像数据。取值范围为0-(2 n-1)(n为数据比特数)。
(2)、归一化/线性化模块，是对非线性的R，G，B图像数据的最大值进行归一化。归一化后的图像数据取值范围为0-1。
R 1＝R/(2 n-1)
G 1＝G/(2 n-1)
B 1＝B/(2 n-1)
线性化模块，是将非线性的数据进行线性化处理。得到线性的R ′，G ′，B ′数据。
(3)、线性的R′G′B′到XYZ的转换。
BT709信源的R、G、B顶点(x，y)色坐标分别为(0.640,0.330)、(0.300,0.600)、(0.150,0.060)，白点(x，y)坐标为(0.3127,0.3290)。则R′G′B′到XYZ的转换由下式：
Figure PCTCN2020113021-appb-000001
(4)、XYZ到Yxy的转换。按下列方程进行转换：
Y＝Y
x＝X/(X+Y+Z)
y＝Y/(X+Y+Z)
(5)、基于Yxy数据，构建三维色域。
假设BT709图像输入(R，G，B)数据为8bit,则有256×256×256组(R，G，B)数据，每组数据，经转换对应一组Yxy数据，于是有256×256×256组Yxy数据，构成了BT709的三维色域。由于计算量较大，这些计算是预先计算好的。
图6是显示端三维色域建立流程。
与传输端三维色域建立流程不同的是，在进行R′G′B′到XYZ的转换时，所使用的矩阵由显示器的R、G、B顶点色坐标及白点坐标来决定。即：
Figure PCTCN2020113021-appb-000002
其中矩阵系数b10,b11….b32，由显示器的物理参数，即R、G、B顶点色坐标及白点坐标决定。
按上述图5和图6的流程图所示，根据BT709及显示器的R、G、B顶点色坐标及白点坐标，基于Yxy的三维色域模型就建立起来了。
在图5中256×256×256组R、G、B的BT709输入数据，经归一/化线性化后，得到256×256×256组线性R′、G′、B′数据,其中的17×17×17组R′、G′、B′作为3D LUT采样数据，即为3D LUT的输入数据R i′、G i′、B i′。
3D LUT的输入数据R i′、G i′、B i′，按公式1的矩阵系数转换为转XYZ，再将XYZ转换成Yxy。得到的与R i′、G i′、B i′相对应的Y值。这里的Y即是接下来的等亮度二维面的亮度值。
按照亮度Y的大小对三维色域进行等亮度相切，得到17×17×17个等亮度二维面。图7的基于等亮度、等色调的彩色映射，就是在传输端与显示端的17×17×17×2个等亮度二维面中进行的。
图8为3D LUT输出计算流程。
经过图6的流程及图7的计算，对于一个给定的3D LUT输入值R′G′B′，会有一个对应Yxy值与其对应。图8的3D LUT输出计算流程，是将这个对应的Yxy值转换成R o′G o′B o′值的过程，也即3D LUT的输出数据计算过程。
首先，将映射输出的Yxy数据，转换成XYZ：
X＝xY/y
Y＝Y
Z＝(1-x-y)Y/y
然后，将XYZ转换成Ro′Go′Bo′输出。
Figure PCTCN2020113021-appb-000003
其中矩阵系数c10,c11….c32，由显示器的物理参数，即R、G、B顶点色坐标及白点坐标决定。
Ro′Go′Bo′就是3D LUT的输出数据。
经过图6、7、8的流程及计算，使得3D LUT中17×17×17的每一组R i′G i′B i′值，按照等亮度，等色调的彩色映射，都有一组Ro′Go′Bo′值与其对应。即，完成了基于3D LUT的等亮度，等色调的彩色映射。图9为3D LUT等效图。
在实际运用中，因计算量较大，上述图5-9的流程，是在离线中进行的。经过上述过程，最终计算得到17×17×17组数值，并将这17×17×17组数据写入3D LUT中。
实施例2
本实施例还提供了一种色域映射系统，如图10所示，包括：
亮度值获取模块110，用于基于三维映射表获取传输端的图像数据对应的每一采样点的亮度值；
等亮度切割模块120，用于用于基于每一所述采样点的亮度值分别对传输端的三维色域模型和显示端的三维色域模型进行等亮度切割，形成对应的等亮度二维面；
输出数据转换模块130，用于基于所形成的等亮度二维面进行色彩映射，输出映射 数据。
本公开实施例所述提供的系统，根据输入图像数据计算出三维映射表中每个采样点的亮度值；基于所述每个采样点的亮度值分别对预先建立的传输端的三维色域模型和显示端的三维色域模型进行等亮度区域分割，得到传输端中等亮度的二维面和显示端的等亮度的二维面；对传输端的二维面和显示端的二维面进行等亮度和等色调的彩色映射，计算出目标色域的二维像素值；将所述目标色域的二维像素值与亮度值相结合，转换成输出图像数据。可见，本公开所述方法在进行色域映射时，保持亮度和色调不变，实现传输色域到显示色域的三维色域映射的精确匹配，避免了因为传输色域到显示色域之间映射不匹配，而导致的图像失真或显示错误等问题。
以上所述仅为本公开的较佳实施例，并不用以限制本公开，凡在本公开的精神和原则之内，所作的任何修改、等同替换、改进等，均应包含在本公开的保护范围之内。

Claims (15)

  1. 一种色域映射方法，其中，包括：
    基于三维映射表获取传输端的图像数据对应的每一采样点的亮度值；
    基于每一所述采样点的亮度值分别对传输端的三维色域模型和显示端的三维色域模型进行等亮度切割，形成对应的等亮度二维面；
    基于所形成的等亮度二维面进行色彩映射，输出映射数据。
  2. 根据权利要求1所述的色域映射方法，其中，所述基于三维映射表获取传输端的图像数据对应的每一采样点的亮度值的步骤之前，还包括步骤：
    分别建立传输端的三维色域模型和显示端的三维色域模型。
  3. 根据权利要求2所述的色域映射方法，其中，所述建立传输端的三维色域模型的步骤包括：
    对获取到的所述图像数据进行线性化处理，得到线性化处理后所述图像数据中各个像素点的线性RGB坐标；
    利用预设矩阵参数和各个像素点的线性RGB坐标确定所述线性RGB坐标转换到XYZ颜色模型的三维色域坐标；
    根据转换到所述XYZ颜色模型的三维色域坐标确定所述线性RGB坐标转换到Yxy颜色模型的三维色域坐标；
    根据转换到所述Yxy颜色模型上的三维色域坐标构建传输端的三维色域模型。
  4. 根据权利要求3所述的色域映射方法，其中，所述对获取到的所述图像数据进行线性化处理的步骤包括：
    将获取到的所述图像数据的取值范围由0-(2 n-1)转换成取值范围为0-1以内。
  5. 根据权利要求2所述的色域映射方法，其中，所述建立显示器端的三维色域模型的步骤包括：
    获取显示器上的与显示设置参数相对应的显示图像数据，并对所述显示图像数据进行归一化处理，得到线性化处理后所述显示图像数据中各个像素点的线性RGB坐标；
    根据预存储的显示参数矩阵和各个显示图像数据中各个像素点的线性RGB坐标确定所述显示图像数据中各个像素点的所述线性RGB坐标转换到XYZ颜色模型的三维色域坐标；
    根据转换到所述XYZ颜色模型的三维色域坐标确定所述显示图像数据中各个像素点的线性RGB坐标转换到Yxy颜色模型的三维色域坐标；
    根据转换到Yxy颜色模型上的三维色域坐标构建显示端显示色域的三维色域模型。
  6. 根据权利要求1或2所述的色域映射方法，其中，所述基于每一所述采样点的亮度值分别对传输端的三维色域模型和显示端的三维色域模型进行等亮度切割，形成对应的等亮度二维面的步骤包括：
    基于所述每一所述采样点的像素值，计算出所述每一所述采样点处于所述传输端的三维色域模型中的传输三维色域坐标；
    根据所述传输三维色域坐标中所含的亮度值分别对所述传输端的三维色域模型和显示端的三维色域模型进行等亮度切割，得到一系列等亮度的二维面。
  7. 根据权利要求6所述的色域映射方法，其中，所述基于所述每一所述采样点的像素值，计算出所述每一所述采样点处于所述传输端的三维色域模型中的传输三维色域坐标的步骤包括：
    对所述每一所述采样点进行线性化处理，得到线性化处理后的每一所述采样点的线性RGB坐标；
    根据所述预设矩阵参数和每一所述采样点所对应的线性RGB坐标确定每一所述采样点的所述线性RGB坐标转换到XYZ颜色模型的三维色域坐标；
    根据转换到XYZ颜色模型的三维色域坐标确定所述每一所述采样点的线性RGB坐标转换到Yxy颜色模型的传输三维色域坐标。
  8. 根据权利要求2所述的色域映射方法，其中，所述基于所形成的等亮度二维面进行色彩映射，输出映射数据的步骤包括：
    基于等亮度值建立传输端的等亮度二维面上的每个采样点的RGB坐标与显示端的等亮度二维面上的每个采样点的RGB坐标之间的映射关系；
    根据所述映射关系，将传输端的每个采样点的RGB坐标值映射到显示端的等亮度二维面上。
  9. 根据权利要求8所述的色域映射方法，其中，所述基于等亮度值建立传输端的等亮度二维面上的每个采样点的RGB坐标与显示端的等亮度二维面上的每个采样点的RGB坐标之间的映射关系的步骤包括：
    分别获取等亮度的所述传输色域的二维色域平面和所述显示色域的二维平面；
    根据预存储的传输端所对应白点的RGB坐标、显示端所对应白点的RGB坐标、等亮度二维面内每一所述采样点的线性RGB坐标，所述白点与每一所述采样点之间的连接线分别与所述传输端的等亮度二维面和所述显示端的等亮度二维面的交点坐标，建立传输端的等亮度二维面上的每个采样点的RGB坐标与显示端的等亮度二维面上的每个 采样点的RGB坐标之间的映射关系。
  10. 根据权利要求9所述的色域映射方法，其中，所述传输端的等亮度二维面上的每个采样点的RGB坐标与显示端的等亮度二维面上的每个采样点的RGB坐标之间的映射关系的关系式为：
    WA i/WE＝WA O/WF
    x AO＝(x Ai-x w)*(x F-x w)/(x E-x w)
    y AO＝(y Ai-y w)*(y F-y w)/(y E-y w)
    其中，W(x w,y w)为预存储的传输端所对应白点的RGB坐标，A i(x Ai,y Ai)为已知采样点的线性RGB坐标，E(x E,y E)，F(x F,y F)点分别为W(x w,y w)和A i(x Ai,y Ai)的连接线分别与所述传输端的等亮度二维面和所述显示端的等亮度二维面的交点坐标，WA i为W(x w,y w)与A i(x Ai,y Ai)两点组成的直线，WE为W(x w,y w)与E(x E,y E)两点组成的直线，WA O为W(x w,y w)与A o(x AO,y AO)两点组成的直线，WF为W(x w,y w)与F(x F,y F)两点组成的直线。
  11. 根据权利要求10所述的色域映射方法，其中，所述根据所述映射关系，将传输端的每个采样点的RGB坐标值映射到显示端的等亮度二维面上的步骤包括：
    根据预存储的传输端所对应白点的RGB坐标、显示端所对应白点的RGB坐标、等亮度二维面内每一所述采样点的线性RGB坐标，所述白点与每一所述采样点之间的连接线分别与所述传输端的等亮度二维面和所述显示端的等亮度二维面的交点坐标，以及所述映射关系的关系式，计算出所述传输端的等亮度二维面上每个所述采样点的线性RGB坐标映射到所述显示端的等亮度二维面上的线性RGB坐标；
    将每个所述采样点在所述显示端的等亮度二维面上的线性RGB坐标与亮度值相结合，转换成映射数据，并输出显示。
  12. 根据权利要求11所述的色域映射方法，其中，所述将每个所述采样点在所述显示端的等亮度二维面上的线性RGB坐标与亮度值相结合，转换成映射数据，并输出显示的步骤包括：
    根据目标色域的二维像素值与其亮度值相结合，得到目标色域的三维RGB值；
    根据XYZ颜色模型的RGB值与Yxy颜色模型的RGB值之间的转换公式，将所述目标色域的三维RGB值由Yxy颜色模型的三维色域坐标转换到XYZ颜色模型的三维色域坐标；
    根据转换到XYZ颜色模型的目标色域的三维色域坐标、预设显示器的显示参数矩 阵，计算出输出图像数据。
  13. 根据权利要求11所述的色域映射方法，其中，所述将每个所述采样点在所述显示端的等亮度二维面上的线性RGB坐标与亮度值相结合，转换成映射数据，并输出显示的步骤包括：
    利用线性内插法对所述映射数据进行填充，并将填充后的所述映射数据进行输出显示。
  14. 根据权利要求1所述的色域映射方法，其中，所述获基于三维映射表获取传输端的图像数据对应的每一采样点的亮度值的步骤之前，还包括步骤：
    根据信号源端RGB顶点色坐标和白点坐标的二维坐标值，计算得到所述预矩阵参数；
    根据显示端RGB顶点色坐标及白点坐标的二维坐标值，计算得到预设显示参数矩阵。
  15. 一种色域映射系统，其中，包括：
    亮度值获取模块，用于基于三维映射表获取传输端的图像数据对应的每一采样点的亮度值；
    等亮度切割模块，用于基于每一所述采样点的亮度值分别对传输端的三维色域模型和显示端的三维色域模型进行等亮度切割，形成对应的等亮度二维面；
    输出数据转换模块，用于基于所形成的等亮度二维面进行色彩映射，输出映射数据。
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