CN101594545B - Color gamut expanding system and method - Google Patents

Abstract

The invention provides a color gamut expanding system comprising a signal input unit, a forward conversion unit, a color gamut expanding unit, an inverse conversion unit and a signal output unit; wherein, the signal input unit is used for inputting pixel color information; the forward conversion unit is used for converting the pixel color information into values of L, a and b in liner Lab color space; the color gamut expanding unit is used for receiving color gamut expanding coefficients, and expands the values of L, a and b provided by the forward conversion unit into new values of L, a and b in the linear Lab color space according to the color gamut expanding coefficients; the inverse conversion unit is used for converting expanded values of L, a and b into the pixel color information of a large color gamut; the signal output unit is used for outputting the color information of the large color gamut. The invention also provides a corresponding color gamut expanding method. The invention can realize continuous adjustment, has high calculation efficiency, can better avoid the phenomenon of hue deviation, and has higher precision and accuracy.

Description

A kind of color domain expanding system and method

Technical field

The present invention relates to the demonstration field, especially show the gamut extension technology in field.

Background technology

Large colour gamut display device can show than the more color content of original display device, as darker redness.Yet the colour gamut of the video content of existing colors of image standard and these color standard of employing is less, so reproduce described video content with large colour gamut display device, the abundant color displays ability of large colour gamut display device can not demonstrated fully.

A kind of feasible solution is to adopt the gamut extension technology, is about to the Color Gamut Mapping of original color standard regulation to the colour gamut of large colour gamut display device.The common method that realizes this gamut extension in prior art is the technology that adopts three dimensional lookup table and interpolation to combine, and this is also step important in the color management normal process.According to this method, the color displays effect depends primarily on data in the specification of three dimensional lookup table and table, and the interpolation method that adopts; Color management system can have a plurality of three dimensional lookup table, the corresponding gamut extension scheme of each look-up table, and the user therefrom selects a color displays effect according to the needs of oneself.Although the method for color gamut mapping of color based on three dimensional lookup table and interpolation has open and certain flexibility, but also there is simultaneously following deficiency: 1) because the kind of color displays effect is consistent with the number of three dimensional lookup table, because the number of three dimensional lookup table is limited, and consider cost, can not arrange too much yet, so the user is defined in limited several effects to the selection of color displays effect, can't reach the purpose of continuous adjusting; 2) versatility is not high, and the described look-up table data that namely a kind of display device is corresponding can not be applicable to another kind of display device well; 3) will take a large amount of being used for deposits the memory resource of described look-up table data, thereby has improved hardware cost; 4) and, with regard to gamut extension, the check colors impression of enlargement of color photos exhibition effect of user depends primarily on the user to the preference of hobby look, this preference varies with each individual, limited several described look-up table is difficult to satisfy all kinds of crowds' this preference.In a word, adopt the method for color gamut mapping of color based on three dimensional lookup table and interpolation not solved well on the degree of freedom, versatility, hardware cost problem.

In addition, although much existing display device is provided with saturation adjusting device and method, but the saturation of its definition mainly is based on the color difference signal of matrixing, as the YCbCr signal, the RGB color signal is decomposed into a brightness signal Y and two color difference signal Cb, Cr, saturation is regulated main by regulating this two color difference signals realizations.And above-mentioned color difference signal is not defined on homogeneous color space, so this class saturation adjusting device and method adjustment precision are low, if be used for gamut extension, obvious hue shift can occur.So-called homogeneous color space refers in this space the identical color space of color-aware difference of human eye in district of all kinds.

Summary of the invention

The object of the invention is to overcome above-mentioned technological deficiency, a kind of color domain expanding system and method that can realize adjusting continuously is provided.

For achieving the above object, color domain expanding system provided by the invention comprises: signal input unit, positive-going transition unit, gamut extension unit, reverse transformation unit and signal output unit;

Described signal input unit is used for the input pixel color information;

Described positive-going transition unit is used for described pixel color information is converted to L, a, the b value of linear Lab color space;

Described gamut extension unit is used for according to the gamut extension coefficient, L, a, the b value that described positive-going transition unit provides being expanded to new L, a, b value at linear Lab color space;

L, a after described reverse transformation unit is used for expanding, the pixel color information that the b value is converted to large colour gamut;

Described signal output unit is used for exporting the pixel color information of described large colour gamut.

In technique scheme, described color domain expanding system also comprises gamut extension coefficient input unit, (form of input is not limit here to be used for inputting the gamut extension coefficient for the user, such as: can freely be inputted by the user, also can preset a series of numerical value, be selected by the user).

In technique scheme, described color domain expanding system also comprises the colour temperature selected cell, is used for selecting color temperature value for the user, and this color temperature value is as the input parameter of described positive-going transition unit and reverse transformation unit.

In technique scheme, described pixel color information is rgb signal.

In technique scheme, described positive-going transition unit comprises XYZ colorimeter system positive-going transition unit and linear Lab color space positive-going transition unit; Described XYZ colorimeter system positive-going transition unit is used for R, the G of RGB system, X, Y, the Z tristimulus specifications that the B tristimulus specifications is transformed into XYZ system; Described linear Lab color space positive-going transition unit is used for X, Y, Z tristimulus specifications are transformed to L, a, the b value of linear Lab color space;

Described reverse transformation unit comprises linear Lab color space inverse transformation block and large colour gamut XYZ inverse transformation block; It is large colour gamut X, Y, the Z excitation value of XYZ system with the L after gamut extension, a, b value transform that described linear Lab color space inverse transformation block is used for; Described large colour gamut XYZ inverse transformation block is used for described large colour gamut X, Y, Z excitation value are transformed to R, G, the B excitation value of large colour gamut RGB system.

For achieving the above object, color domain expanding method provided by the invention comprises the steps:

1) input pixel color information;

2) described pixel color information is converted to L, a, b value in linear Lab color space;

3) in linear Lab color space, according to the gamut extension coefficient, with described step 2) L, a, the b value that provide expand to new L, a, b value;

4) L, a after expanding, the pixel color information that the b value is converted to large colour gamut;

5) pixel color information of the described large colour gamut of output.

In technique scheme, described step 3) in, described gamut extension coefficient is inputted by the user.

In technique scheme, described step 2) in, also comprise by the user and select color temperature value, according to this color temperature value, pixel color information is converted to L, a, b value in linear Lab color space; Described step 4) in, according to described color temperature value, with L, a after expansion, the pixel color information that the b value is converted to large colour gamut.

In technique scheme, described pixel color information is rgb signal.

In technique scheme, described step 2) comprise following substep:

21) with R, the G of RGB system, X, Y, the Z tristimulus specifications that the B tristimulus specifications is transformed into XYZ system;

22) X, Y, Z tristimulus specifications are transformed to L, a, b value in linear Lab color space;

Described step 4) comprise following substep:

41) with the L after gamut extension, a, b value transform be large colour gamut X, Y, the Z excitation value of XYZ system;

42) described large colour gamut X, Y, Z excitation value are transformed to R, G, the B excitation value of large colour gamut RGB system.

The useful technique effect that the present invention has comprises:

1, color domain expanding system of the present invention and method can realize the continuous adjusting of gamut extension coefficient;

2, the algorithm computational efficiency of color domain expanding method of the present invention is high, and is low to the system resource requirement, satisfies better the vision signal requirement of processing in real time of high data volume;

3, the present invention carries out the gamut extension processing at linear Lab color space, and it is the fine approximate of standard Lab color space, and standard Lab color space is the homogeneous color space of the CIE of Commission Internationale De L'Eclairage definition, is the standard operation space in the color management flow process.So-called homogeneous color space refers to a kind of like this color space, and in district of all kinds, the color-aware difference of human eye is identical in this space.But the algorithm that the color signal of video is transformed into standard Lab color space is very complicated, be unfavorable for real-time processing, so just greatly simplify transfer algorithm on linear Lab color space so color domain expanding method of the present invention is defined in working space, reduced amount of calculation; And because the present invention carries out the gamut extension computing at the linear Lab color space that is similar to homogeneous color space, so relative method of adjustment based on color difference signal, the present invention can avoid the generation of form and aspect bias phenomenon preferably, has higher precision and accuracy.

Description of drawings

Below, describe by reference to the accompanying drawings embodiments of the invention in detail, wherein:

Fig. 1 is the device schematic diagram of continuously adjustable gamut extension of the present invention.

Embodiment

Embodiment 1

Below in conjunction with Figure of description, describe the present invention in detail.Fig. 1 has represented the device schematic diagram of continuously adjustable gamut extension of the present invention.What this device was total is comprised of user selection unit 2 and control system 1, and this control system 1 receives the signal of user selection unit 2 transmissions and completes gamut extension.Wherein, user selection unit 2 comprise can for the user select color temperature value colour temperature selected cell 21 and can be by the gamut extension coefficient input unit 22 of user's free setting gamut extension coefficient, wherein colour temperature selected cell 21 provides several color temperature values to select to the user, such as 5400K, 6500K, 9300K etc.; Control system 1 comprises rgb signal input unit 11, the positive-going transition of XYZ colorimeter system unit 12, linear Lab color space positive-going transition unit 13, gamut extension unit 14, linear Lab color space inverse transformation block 15, large colour gamut XYZ inverse transformation block 16 and rgb signal output unit 17.Described rgb signal refers to represent the digital signal of video data pixel color information.Rgb signal input unit 11 receives the vision signal that meets certain color-code standard (as Rec.ITU-R BT.709 standard), each picture element in this signal comprises the excitation value information of red-green-blue, be made as R, G and B, XYZ colorimeter system positive-going transition unit 12 is transformed into R, G, B tristimulus specifications the tristimulus specifications of XYZ colorimeter system, wherein conversion process Yin Sewen is different and different, and color temperature value is selected by colour temperature selected cell 21 by the user.Linear Lab color space positive-going transition unit 13 transforms to L, a and b in linear Lab color space with the XYZ tristimulus specifications, this conversion process also determines by color temperature value, the definition of above-mentioned linear Lab color space and transform to transfer process in linear Lab color space by the XYZ tristimulus specifications and be disclosed in the scientific and technical literature of " Evaluation of smoothness tonal change reproductionon multi-primary display:Comparison of color conversion algorithm " by name in the SPIE magazine of publishing in 2004.Gamut extension unit 14 receives the value that users utilize gamut extension coefficient input unit 22 free settings, a and b is carried out the gamut extension computing obtain a _newAnd b _newThen linear Lab color space inverse transformation block 15 is with a after gamut extension _newAnd b _newAnd the excitation value X of XYZ system is returned in the L conversion _new, Y _newAnd Z _newLarge colour gamut XYZ inverse transformation block 16 is with X _new, Y _newAnd Z _newTransform to the R of large colour gamut RGB system _new, G _newAnd B _new, and through rgb signal output unit 17 output R _new, G _newAnd B _newSignal.

Embodiment 2

Realize the method for continuously adjustable gamut extension below in conjunction with specific embodiment explanation the present invention, the method comprises:

The vision signal of step 201:RGB signal input unit 11 input pre-color coding standards, wherein each picture element in vision signal comprises the information of red-green-blue excitation value, is R, G and B;

Step 202: the user selects one of them by the colour temperature selected cell 21 on user selection unit 2 from several color temperature values;

Step 203:XYZ colorimeter system positive-going transition unit 12 becomes X, Y and Z with B according to corresponding color-code canonical transformation with R, G according to the color temperature value that the user selects;

Wherein the concrete steps of above-mentioned steps 203 are:

Step 2031: three one dimension look-up tables by corresponding redgreenblue are transformed into linear color data Rs, Gs and Bs with R, G and B, and transformation relation depends on the color coding standard that adopts, and for example to the BT.709 standard, adopt formula (1)

Formula (1)

Wherein, M is the normalization signal strength signal intensity, and V is the linearisation data result.Represent with the n bit binary data as the RGB color signal, M=R/2 ⁿ(or G/2 ⁿ, or B/2 ⁿ) (span of R, G, B is 0～2 ⁿ-1), corresponding V=Rs (or Gs, or Bs), and all V value calculated in advance are complete is stored in the mode of look-up table in the memory of XYZ colorimeter system positive-going transition unit 12.

There is the positive-going transition matrix corresponding with all color temperature values that can select by colour temperature selected cell 21 in step 2032:XYZ colorimeter system positive-going transition unit 12, by the color temperature value that the user selects, XYZ colorimeter system positive-going transition unit 12 can find the positive-going transition matrix corresponding with this color temperature value $\left[\begin{array}{ccc}C11& C12& C13\\ C21& C22& C23\\ C31& C32& 33\end{array}\right],$ Obtain X, Y and Z by formula (2).

$\left[\begin{array}{c}X\\ Y\\ Z\end{array}\right]=\left[\begin{array}{ccc}C11& C12& C13\\ C21& C22& C23\\ C31& C32& C33\end{array}\right]\·\left[\begin{array}{c}\mathrm{Rs}\\ \mathrm{Gs}\\ \mathrm{Bs}\end{array}\right]$ Formula (2)

For example, if the colour temperature that the user arranges is 6500K, its positive-going transition is closed and is:

$\left[\begin{array}{c}X\\ Y\\ Z\end{array}\right]=\left[\begin{array}{ccc}0.4124& 0.3576& 0.1805\\ 0.2126& 0.7152& 0.0722\\ 0.0193& 0.1192& 0.9505\end{array}\right]*\left[\begin{array}{c}\mathrm{Rs}\\ \mathrm{Gs}\\ \mathrm{Bs}\end{array}\right]$ Formula (2-1)

Step 204: linear Lab color space positive-going transition unit 13 according to formula (3) with L, a and b in X, Y and the linear Lab color space of Z-transformation.

$\left[\begin{array}{c}L\\ a\\ b\end{array}\right]=T_{\mathrm{Lab}}*\left[\begin{array}{c}X\\ Y\\ Z\end{array}\right]=\left[\begin{array}{ccc}0& 100/Y_n& 0\\ 500/X_n& -500/Y_n& 0\\ 0& 200/Y_n& -200/Z_n\end{array}\right]*\left[\begin{array}{c}X\\ Y\\ Z\end{array}\right]$ Formula (3)

Wherein, T corresponding to different colour temperatures _Lab, the user selects each corresponding T of all color temperature values of setting by colour temperature selected cell 21 _Lab, all T _LabAll be stored in linear Lab color space positive-going transition unit 13, linear Lab color space positive-going transition unit 13 can find the T corresponding with it easily by reading the color temperature value that the user sets _LabT _LabIn X _n, Y _nAnd Z _nBe to determine like this, the user sets each color temperature value and has corresponding chromaticity coordinate, for example the user to set color temperature value be T _A, T _ACorresponding chromaticity coordinate is (x _A, y _A, z _A), X _n, Y _nAnd Z _nCalculate with formula (4).

$\left\{\begin{array}{c}{X}_n=\frac{x_A}{y_A}*100\\ Y_n=100\\ Z_n=\frac{z_A}{y_A}*100\end{array}\right.$ Formula (4)

For example, be 6500K if the user sets colour temperature, its chromaticity coordinate is (0.3127,0.3290,0.3583), can get (X by formula (4) _n, Y _n, Z _n)=(95.04,100,108.89); Thereby by formula (3) can be under this colour temperature the XYZ colorimeter system to the transformation for mula of linear Lab color space:

$\left[\begin{array}{c}L\\ a\\ b\end{array}\right]=\left[\begin{array}{ccc}0& 1.0& 0\\ 5.2609& -5.0& 0\\ 0& 2.0& -1.8367\end{array}\right]*\left[\begin{array}{c}X\\ Y\\ Z\end{array}\right]$ Formula (4-1)

The present invention carries out gamut extension at linear Lab color space and processes, and it is the fine approximate of standard Lab color space, and standard Lab color space is the homogeneous color space of the CIE of Commission Internationale De L'Eclairage definition, is the standard operation space in the color management flow process.So-called homogeneous color space refers to a kind of like this color space, and in district of all kinds, the color-aware difference of human eye is identical in this space.But the algorithm that the color signal of video is transformed into the Lab color space is very complicated, be unfavorable for real-time processing, so color domain expanding method of the present invention is defined in working space on linear Lab color space, has so just greatly simplified transfer algorithm, has reduced amount of calculation; And because the present invention carries out the gamut extension computing at the linear Lab color space that is similar to homogeneous color space, so relative method of adjustment based on color difference signal, the present invention can avoid the generation of form and aspect bias phenomenon preferably, has higher precision and accuracy.

Step 205: gamut extension unit 14 reception users pass through the gamut extension coefficient VGE of gamut extension coefficient input unit 22 free settings, and in linear Lab color space, a and b are carried out extension process, obtain a _newAnd b _new, computational methods adopt formula (5):

$\left\{\begin{array}{c}{a}_{\mathrm{new}}=a*\mathrm{VGE};\\ b_{\mathrm{new}}=b*\mathrm{VGE};\end{array}\right.$ Formula (5)

Step 206: linear Lab color space inverse transformation block 15 is with L, a _newAnd b _newConversion is returned in XYZ space, obtains X _new, Y _newAnd Z _new, the formula (6) below conversion process adopts:

$\left[\begin{array}{c}{X}_{\mathrm{new}}\\ Y_{\mathrm{new}}\\ Z_{\mathrm{new}}\end{array}\right]=T_{\mathrm{Lab}}^{-1}\left[\begin{array}{c}L\\ a_{\mathrm{new}}\\ b_{\mathrm{new}}\end{array}\right]$ Formula (6)

Wherein, T _Lab ^-1Be the T in step 204 _LabInverse matrix, therefore also corresponding different T of different color temperature values _Lab ^-1, all T _Lab ^-1Be stored in the memory of linear Lab color space inverse transformation block 15, linear Lab color space inverse transformation block 15 reads out corresponding T according to the color temperature value that the user sets _Lab ^-1, utilize formula (6) to obtain setting X under colour temperature _new, Y _newAnd Z _new

Step 207: large colour gamut XYZ inverse transformation block 16 is with X _new, Y _newAnd Z _newThe excitation value R in the RGB system is returned in conversion _new, G _newAnd B _new

The detailed process of above-mentioned steps 207 is as follows:

Step 2071: utilize large colour gamut display device XYZ colorimeter system reverse transformation matrix $\left[\begin{array}{ccc}T11& T12& T13\\ T21& T22& T23\\ T31& T32& T33\end{array}\right],$ This matrix determines by the colour temperature of the brilliant white of the three primary colors chromaticity coordinate of large colour gamut display device and this display device field correspondence, and its computational methods can be gained knowledge from relevant colourity and be obtained.With X _new, Y _newAnd Z _newBe transformed into linear color data R _Snew, G _SnewAnd B _SnewConversion process adopts formula (7):

$\left[\begin{array}{c}{R}_{\mathrm{snew}}\\ G_{\mathrm{snew}}\\ B_{\mathrm{snew}}\end{array}\right]=\left[\begin{array}{ccc}T11& T12& T13\\ T21& T22& T23\\ T31& T32& T33\end{array}\right]\left[\begin{array}{c}{X}_{\mathrm{new}}\\ Y_{\mathrm{new}}\\ Z_{\mathrm{new}}\end{array}\right]$ Formula (7)

Step 2072: by the look-up table from linear color data to RGB system incentive value of setting up in advance, with R _Snew, G _SnewAnd B _SnewTransform to the excitation value R in the RGB system _new, G _newAnd B _new

In above-mentioned conversion process, also step 206 and the synthetic step of step 207 can be completed.

Step 208:RGB signal output unit 17 is with R _new, G _newAnd B _newOutput.

Because the matrix that all conversion processes in the color domain expanding system of the present embodiment and method need can be precalculated, and be deposited in memory, therefore relate to the multiplication of matrices computing and only need carry out several linear calculating, and there is no nonlinear calculating in the algorithm that the present invention adopts, therefore computational efficiency is very high, satisfies the requirement of the real-time processing of big data quantity video.

In the present embodiment, the pixel color information of input is rgb signal, but the present invention also can adopt other signal as pixel color information, and as the YCbCr signal, this is that those skilled in the art can understand.

Above-described specific embodiment has been described in detail purpose of the present invention, technical scheme and beneficial effect.Institute's foregoing that it should be understood that is not limited to the present invention only for specific embodiments of the invention.All within spirit of the present invention and principle, any modification of making, be equal to and replace and improvement etc., within all should being included in protection scope of the present invention.

Claims (10)

1. color domain expanding system comprises: signal input unit, positive-going transition unit, gamut extension unit, reverse transformation unit and signal output unit;

Described signal input unit is used for the input pixel color information;

Described positive-going transition unit is used for described pixel color information is converted to L, a, the b value of linear Lab color space;

Described gamut extension unit is used for according to the gamut extension coefficient, L, a, the b value that described positive-going transition unit provides being expanded to new L, a at linear Lab color space _new, b _newValue; Computational methods adopt formula: $\left[\begin{array}{c}{a}_{\mathrm{new}}=a*\mathrm{VGE};\\ b_{\mathrm{new}}=b*\mathrm{VGE};\end{array}\right]$ Wherein, VGE is the gamut extension coefficient of user's free setting;

L, a after described reverse transformation unit is used for expanding, the pixel color information that the b value is converted to large colour gamut;

Described signal output unit is used for exporting the pixel color information of described large colour gamut.

2. color domain expanding system according to claim 1, is characterized in that, described color domain expanding system also comprises gamut extension coefficient input unit, is used for inputting the gamut extension coefficient for the user.

3. color domain expanding system according to claim 1, is characterized in that, described color domain expanding system also comprises the colour temperature selected cell, is used for selecting color temperature value for the user, and this color temperature value is as the input parameter of described positive-going transition unit and reverse transformation unit.

4. color domain expanding system according to claim 1, is characterized in that, described pixel color information is rgb signal.

5. color domain expanding system according to claim 4, is characterized in that, described positive-going transition unit comprises XYZ colorimeter system positive-going transition unit and linear Lab color space positive-going transition unit; Described XYZ colorimeter system positive-going transition unit is used for R, the G of RGB system, X, Y, the Z tristimulus specifications that the B tristimulus specifications is transformed into XYZ system; Described linear Lab color space positive-going transition unit is used for X, Y, Z tristimulus specifications are transformed to L, a, the b value of linear Lab color space;

Described reverse transformation unit comprises linear Lab color space inverse transformation block and large colour gamut XYZ inverse transformation block; It is large colour gamut X, Y, the Z excitation value of XYZ system with the L after gamut extension, a, b value transform that described linear Lab color space inverse transformation block is used for; Described large colour gamut XYZ inverse transformation block is used for described large colour gamut X, Y, Z excitation value are transformed to R, G, the B excitation value of large colour gamut RGB system.

6. a color domain expanding method, comprise the steps:

1) input pixel color information;

2) described pixel color information is converted to L, a, b value in linear Lab color space;

3) in linear Lab color space, according to the gamut extension coefficient, with described step 2) L, a, the b value that provide expand to new L, a _new, b _newValue; Computational methods adopt formula:

Wherein, VGE is the gamut extension coefficient of user's free setting;

4) L, a after expanding, the pixel color information that the b value is converted to large colour gamut;

5) pixel color information of the described large colour gamut of output.

7. color domain expanding method according to claim 6, is characterized in that, in described step 3), described gamut extension coefficient is inputted by the user.

8. color domain expanding method according to claim 6, is characterized in that, described step 2) in, also comprise by the user and select color temperature value, according to this color temperature value, pixel color information is converted to L, a, b value in linear Lab color space; In described step 4), according to described color temperature value, with L, a after expansion, the pixel color information that the b value is converted to large colour gamut.

9. color domain expanding method according to claim 6, is characterized in that, described pixel color information is rgb signal.

10. color domain expanding method according to claim 6, is characterized in that, described step 2) comprise following substep:

21) with R, the G of RGB system, X, Y, the Z tristimulus specifications that the B tristimulus specifications is transformed into XYZ system;

22) X, Y, Z tristimulus specifications are transformed to L, a, b value in linear Lab color space;

Described step 4) comprises following substep:

41) with the L after gamut extension, a, b value transform be large colour gamut X, Y, the Z excitation value of XYZ system;

42) described large colour gamut X, Y, Z excitation value are transformed to R, G, the B excitation value of large colour gamut RGB system.

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