CN107133009B - Method for calculating color gamut boundary of display device - Google Patents
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- CN107133009B CN107133009B CN201710265715.3A CN201710265715A CN107133009B CN 107133009 B CN107133009 B CN 107133009B CN 201710265715 A CN201710265715 A CN 201710265715A CN 107133009 B CN107133009 B CN 107133009B
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Abstract
The invention provides a method for calculating the color gamut boundary of a display device, which is characterized by comprising the following steps: step 1, determining an initial maximum value r of a sphere radius r in an LCH color spacemaxAnd an initial minimum value rminStep 2, reading the hue angle α value, its initial value α ═0°，α∈[0°,360°](ii) a And 3, reading the elevation angle theta, wherein the initial value theta is-90 degrees, theta is epsilon-90 degrees and 90 degrees]Step 4, iterative calculation of r value according to preset formula, step 5, using spherical coordinates (α, theta, r) of color pointk) Calculating CIE XYZ values of the color points; step 6, judging whether one of the three values of X, Y and Z is less than 0 or not and respectively comparing X, Y, Z and Xw，Yw，ZwThe method comprises the steps of 7, substituting X, Y and Z values into a reverse characterization model to calculate, 8, judging whether a color point is a color gamut boundary point by using a device driving value RGB, 9, recording a chromatic value of the color point, 10, enabling an elevation angle theta value to be theta + delta theta until theta is 90 degrees, 11, enabling a color phase angle α value to be α + delta α until α is 360 degrees, and 12, recording all the color gamut boundary points.
Description
Technical Field
The invention relates to the field of color display replication and color management, in particular to a method for calculating a color gamut boundary of display equipment.
Background
With the continuous progress of science and technology, color image display equipment is developed greatly, the color reproduction capability of various intelligent mobile terminals is improved continuously, and users watch information such as videos and pictures on mobile terminals such as smart phones and tablet computers more and more. The same color information may be displayed on different display media, and therefore, it is important to ensure that the colors are accurately transferred between different carrier media. The device color gamut is an important index for measuring the color reproduction capability of the device, the color gamut ranges of different display media are different, and the accurate description of the device color gamut is a premise of reproducing colors as accurately as possible, and has important significance.
The gamut boundary of a device refers to the outermost periphery of the range of colors that the device is capable of reproducing. In the device-dependent color space, the device gamut appears as a regular polyhedron whose boundaries are the outer surfaces of the regular polyhedron. For any color point on the outer surface, one or more device actuation values should be maximized or minimized. Therefore, in the device-dependent color space, it can be determined whether a color point is a color gamut boundary point according to specific data of a certain color, such as an RGB value.
However, in the device-independent color space, the shape of the device color gamut is an irregular polyhedron, and it cannot be determined whether the device color gamut is a boundary point directly according to specific data representing the color, such as the CIE XYZ value or the CIE La × b value. Therefore, describing the gamut boundary of a device in a device-independent color space is complicated.
However, to ensure accurate transfer and reproduction of colors between different devices, gamut boundary descriptions must be made in a device independent color space. In general, a gamut boundary description of a device refers to a gamut boundary description performed in a device-independent color space. The existing methods for describing the gamut boundary of a display device can be divided into two categories: one is a physical model method, which is suitable for professional displays or traditional CRT displays, these displays have better color constancy and channel additivity, or at least have better channel additivity, and the forward characterization model can also be used to realize reverse characterization, such as models of GOG, PLCC, etc., and the characterization model can be used to calculate the device color gamut boundary; the other type is a general description method, the color gamut boundary is determined based on a certain sample point set, at present, a convex hull method, an alpha method and a partition maximum boundary method are mainly used, the method mainly utilizes an interpolation method to calculate the required color gamut boundary point, and compared with a model method, the method has larger error and needs to store a large amount of data.
Song dynasty super, Deng Itachio, Wang Rui light and the like propose a method for iteratively calculating a device color gamut boundary point value of an LED display, whether a calculated value range of a device primary color scalar belongs to [0,1] is used for judging whether a color point is in a device color gamut or outside the device color gamut, and the color point approaches to the color gamut boundary point through specified times of iterative calculation.
For most commercial LCD displays and displays of various intelligent mobile terminals, the color quality constancy and the channel additivity are relatively poor, the device color gamut boundary description is usually realized by adopting a universal description method, the method has large error and long calculation time, a large number of data points need to be stored, and the method is not favorable for accurate reproduction of colors.
Disclosure of Invention
The present invention is made to solve the above-mentioned problems, and an object of the present invention is to provide a method for calculating a color gamut boundary of a display device, which has a small calculation error and a short calculation time.
The invention provides a method for calculating the color gamut boundary of a display device, which is characterized by comprising the following steps:
Step 2, reading a hue angle α value, wherein an initial value α is 0 degrees, and α belongs to [0 degrees and 360 degrees ];
step 3, reading an elevation angle theta value, wherein an initial value theta is-90 degrees, theta is belonged to [ -90 degrees, and the angle theta is 90 degrees ];
step 4, iteratively calculating the r value according to a preset formula;
step 5, the spherical coordinates (α, theta, r) of the color points are calculatedk) Calculating CIE XYZ values of the color points;
step 6, judging whether one of the three values of X, Y and Z is less than 0 or not and respectively comparing X, Y, Z and Xw，Yw，Zw；
Step 7, substituting the X, Y and Z values into a reverse characterization model for calculation;
step 8, judging whether the color point is a color gamut boundary point or not by using the device driving value RGB;
step 9, recording the chromatic value of the color point;
step 10, making the elevation angle θ equal to θ + Δ θ until θ is equal to 90 °;
step 11, let the hue angle α be α + Δ α until α be 360 °, and
step 12, recording all gamut boundary points.
The invention provides a method for calculating the color gamut boundary of a display device, which is also characterized in that: wherein the initial minimum value rminIs an iterative initial value in the gamut, L is commonly used*The midpoint of the axis, point E (50, 0, 0) as the center of the color space, then has r min0, initial maximum value rmaxIs the initial value of the iteration outside the gamut.
The invention provides a method for calculating the color gamut boundary of a display device, which is also characterized in that: wherein the predetermined formula is
rk＝(ri_k-1+ro_k-1)/2，
The subscript k denotes the kth iteration, rkSphere radius value, r, representing the k-th iteratively calculated approximated gamut boundary pointi_k-1Represents the initial value of the iteration in the gamut, ro_k-1Indicating the initial value of the iteration outside the gamut.
The invention provides a method for calculating the color gamut boundary of a display device, which is also characterized in that: wherein, Xw，Yw，ZwIs the CIE XYZ normalized value of the white point.
The invention provides a method for calculating the color gamut boundary of a display device, which is also characterized in that: in step 6, if any one of the three values of X, Y and Z is less than 0 or X is not less than>XwOr Y>YwOr Z>Zw(ii) a And (4) judging that the color point is out of the color gamut, and returning to the step 4.
The invention provides a method for calculating the color gamut boundary of a display device, which is also characterized in that: step 7, if the corresponding device driving value RGB can be calculated, entering step 8; otherwise, the color point is judged to be out of the color gamut, and the step 4 is returned.
The invention provides a method for calculating the color gamut boundary of a display device, which is also characterized in that: and 8, if the color gamut boundary point is the color gamut boundary point, the step 9 is carried out, and if the color gamut boundary point is not the color gamut boundary point, the step 4 is returned.
The method for calculating the color gamut boundary of the display device is further characterized in that delta theta is a step value of increasing elevation angle theta value, and delta α is a step value of increasing hue angle α value.
The invention provides a method for calculating the color gamut boundary of a display device, which is also characterized in that: wherein, step 8, have the following steps:
step 8-1, judging the R value, and entering step 8-2 if the R belongs to (0, 255); if R is 0, R is 255, entering step 8-4; otherwise, entering step 8-7;
step 8-2: judging the value G, and if the value G meets the G e (0, 255), entering the step 8-3; if the condition that G is 0 and G is 255, entering the step 8-5; otherwise, entering step 8-7;
step 8-3: judging the value B, and if the value B meets the B epsilon (0, 255), entering the step 8-6; if B is 0, B is 255, entering the step 8-8; otherwise, entering step 8-7;
step 8-4: judging the value G, and entering the step 8-5 if the value G belongs to [0, 255 ]; otherwise, entering step 8-7;
and 8-5: judging the value B, and entering the step 8-8 if B belongs to [0, 255 ]; otherwise, entering step 8-7;
and 8-6: returning to the step 4 when the color point is in the color gamut;
and 8-7: returning to the step 4 when the color point is outside the color gamut; and
and 8-8: the color points are gamut boundary points and the iteration is terminated and step 9 is entered.
Action and Effect of the invention
According to the method for calculating the color gamut boundary of the display equipment, aiming at the non-professional liquid crystal display and the mobile terminal display equipment, the calculation precision of the color gamut boundary point of the display equipment is high; the method comprises the steps of calculating a device driving value by utilizing a reverse characterization model of the display device, wherein the reverse characterization model has no special requirement, and can be used in the color gamut boundary calculation of the display device provided by the invention as long as the display device is suitable for the reverse characterization model; the method has the advantages of simple principle, quick calculation and convenience for application and popularization of actual industrial production.
Drawings
FIG. 1 is a flow chart of a method of computing a gamut boundary for a display device in an embodiment of the invention; and
fig. 2 is a flowchart of determining whether a color point is a color gamut boundary point using RGB values in an embodiment of the present invention.
Detailed Description
The following describes a method for calculating a color gamut boundary of a display device according to the present invention in detail with reference to the accompanying drawings and embodiments.
Examples
In the embodiment, the IPAD2 is used as a display device, the color displayed by the IPAD2 is measured under the normal use environment, and the illumination intensity perpendicular to the surface of the IPAD2 is 320 LX. The following examples are illustrative only and not intended to be limiting, and therefore should not be construed as limiting the scope of the invention.
Fig. 1 is a flowchart of a method for calculating a color gamut boundary of a display device according to an embodiment of the present invention.
As shown in fig. 1, a method for calculating a color gamut boundary of a display device has the following steps:
step 1: determining an initial maximum value r of a sphere radius r in an LCH color spacemaxAnd an initial minimum value rminProceed to step 2.
Initial minimum value rminIs an iterative initial value in the gamut, L is commonly used*The midpoint of the axis, point E (50, 0, 0) as the center of the color space, then has r min0, the initial maximum value rmaxIs the initial value of the iteration outside the gamut.
And 2, reading the hue angle α value, wherein the initial value α is 0 degrees, α belongs to [0 degrees and 360 degrees ], and entering the step 3.
And step 3: the value of the elevation angle θ is read with an initial value θ ═ 90 °, θ ∈ [ -90 °,90 ° ], and the procedure proceeds to step 4.
And 4, step 4: and (5) iteratively calculating the r value according to a preset formula, and entering the step 5.
The predetermined formula is
rk＝(ri_k-1+ro_k-1)/2，
The subscript k denotes the kth iteration, said rkA value of a sphere radius, r, approximating the gamut boundary point representing a k-th iterative computationi_k-1Represents an initial value of the iteration in the gamut, said ro_k-1Indicating the initial value of the iteration outside the gamut.
Step 5. from the spherical coordinates (α, theta, r) of the color pointsk) And calculating CIE XYZ values of the color points, and entering the step 6.
Step 5 has the following steps:
step 5-1 first, from (α, θ, r) as knownk) Value calculation L*，a*，b*The value, as stated in the formula:
and entering the step 5-2.
Step 5-2: according to formula 3 from L*a*b*The X, Y and Z values are calculated according to the following formula
Wherein the content of the first and second substances,
Xw，Yw，Zwis the CIE XYZ normalized value of the white point.
Step 6: judging whether the value of X, Y and Z is less than 0 and comparing X, Y, Z and X respectivelyw，Yw，ZwIf X is satisfied<0||Y<0||Z<0||X>Xw||Y>Yw||Z>ZwThen the color point is out of the color gamut, let ri_k＝ri_k-1，ro_k＝rkAnd returning to the step 4, otherwise, entering the step 7.
And 7: substituting the X, Y, Z values into a reverse characterization modelCalculating, and if the corresponding equipment driving value RGB can be obtained through calculation, entering step 8; otherwise, the color point is outside the color gamut, let ri_k＝ri_k-1，ro_k＝rkAnd returning to the step 4.
And 8: judging whether the color point is a color gamut boundary point or not by using the device driving value RGB, and entering step 9 if the color point is the color gamut boundary point; if not, returning to the step 4.
Fig. 2 is a flowchart for determining whether a color point is a color gamut boundary point using RGB values in an embodiment of the present invention.
As shown in fig. 2, step 8 has the following steps:
step 8-1, judging the R value, and entering step 8-2 if the R belongs to (0, 255); if R is 0, R is 255, entering step 8-4; otherwise, go to step 8-7.
The step 8-2: judging the value G, and if the value G meets the G e (0, 255), entering the step 8-3; if the condition that G is 0 and G is 255, entering the step 8-5; otherwise, the step 8-7 is entered.
The step 8-3: judging the value B, and if the value B meets the B epsilon (0, 255), entering the step 8-6; if B is 0, B is 255, entering the step 8-8; otherwise, the step 8-7 is entered.
The step 8-4: judging the value G, and entering the step 8-5 if the value G belongs to [0, 255 ]; otherwise, the step 8-7 is entered.
The step 8-5: judging the value B, and entering the step 8-8 if B belongs to [0, 255 ]; otherwise, the step 8-7 is entered.
The steps 8 to 6 are as follows: the color point is in the color gamut, let ri_k＝rk，ro_k＝ro_k-1And returning to the step 4.
The steps 8 to 7 are as follows: the color point is outside the color gamut, let ri_k＝ri_k-1，ro_k＝rkAnd returning to the step 4.
The step 8-8: the color point is the gamut boundary point, the iteration is terminated, and the step 9 is performed.
And step 9: recording the chromatic value of the color point, and entering step 10.
Step 10: let the elevation angle θ be θ + Δ θ, and Δ θ be a step value in which the elevation angle θ is incremented until θ becomes 90 °, and proceed to step 11.
And 11, enabling the hue angle α to be α + delta α, enabling the delta α to be a step value of increasing the hue angle α until α is 360 degrees, and entering the step 12.
Step 12: and recording all the color gamut boundary points, and ending.
The invention aims to provide a device color gamut boundary calculation method suitable for common commercial LCD displays or mobile terminal display screens under the condition of a conventional illumination environment, wherein the chromaticity value data of all colors are measured under the conventional use environment instead of the conventional standard darkroom.
Effects and effects of the embodiments
According to the method for calculating the color gamut boundary of the display device, aiming at the non-professional liquid crystal display and the mobile terminal display device, the calculation precision of the color gamut boundary point of the device is high; the method comprises the steps of calculating a device driving value by utilizing a reverse characterization model of the display device, wherein the reverse characterization model has no special requirement, and can be used in the color gamut boundary calculation of the display device provided by the invention as long as the display device is suitable for the reverse characterization model; the method has the advantages of simple principle, quick calculation and convenience for application and popularization of actual industrial production.
The above embodiments are preferred examples of the present invention, and are not intended to limit the scope of the present invention.
Claims (6)
1. A method for calculating a gamut boundary of a display device, comprising the steps of:
step 1, determining an initial maximum value r of a sphere radius r in an LCH color spacemaxAnd an initial minimum value rmin；
Step 2, reading a hue angle α value, wherein an initial value α is 0 degrees, and α belongs to [0 degrees and 360 degrees ];
step 3, reading an elevation angle theta value, wherein an initial value theta is-90 degrees, theta is belonged to [ -90 degrees, and the angle theta is 90 degrees ];
step 4, iteratively calculating the r value according to a predetermined formula, wherein the predetermined formula is
rk＝(ri_k-1+ro_k-1)/2，
The subscript k denotes the kth iteration, said rkA value of a sphere radius, r, approximating the gamut boundary point representing a k-th iterative computationi_k-1Represents an initial value of the iteration in the gamut, said ro_k-1Indicating the initial value of the iteration outside the gamut,
step 5, the spherical coordinates (α, theta, r) of the color points are calculatedk) Calculating CIE XYZ values of the color points;
step 6, judging whether one of the three values of X, Y and Z is less than 0, and respectively comparing X, Y, Z and Xw，Yw，ZwWherein, X iswSaid Y iswZ is the same aswIs the CIE XYZ normalized value of the white point,
step 7, substituting the X, the Y and the Z values into a reverse characterization model for calculation;
step 8, judging whether the color point is a color gamut boundary point or not by using the device driving value RGB;
step 9, recording the chromatic value of the color point;
step 10, making the elevation angle θ equal to θ + Δ θ until θ becomes 90 °;
step 11, making the hue angle α equal to α + delta α until α equal to 360 DEG, and
step 12, recording all the color gamut boundary points,
wherein the delta theta is a step value by which the elevation theta value is incremented,
the Δ α is a stepped value by which the hue angle α value is incremented.
2. The method of claim 1, wherein the method comprises:
wherein the initial minimum value rminIs an iterative initial value in the gamut, L is commonly used*The midpoint of the axis, point E (50, 0, 0) as the center of the color space, then has rmin＝0，
The initial maximum value rmaxIs the initial value of the iteration outside the gamut.
3. The method of claim 1, wherein the method comprises:
wherein, in the step 6, if any one of the three values of X, Y and Z is less than 0 or X is not included>Said XwOr said Y>Said Y iswOr said Z is>Z iswAnd judging that the color point is out of the color gamut, and returning to the step 4.
4. The method of claim 1, wherein the method comprises:
in step 7, if the corresponding device driving value RGB can be calculated, the process proceeds to step 8; otherwise, judging that the color point is out of the color gamut, and returning to the step 4.
5. The method of claim 1, wherein the method comprises:
and in the step 8, if the color gamut boundary point is the color gamut boundary point, the step 9 is performed, and if the color gamut boundary point is not the color gamut boundary point, the step 4 is performed.
6. The method of claim 1, wherein the method comprises:
wherein, the step 8 comprises the following steps:
step 8-1, judging the R value, and entering step 8-2 if the R belongs to (0, 255); if R is 0, R is 255, entering step 8-4; otherwise, entering step 8-7;
the step 8-2: judging the value G, and if the value G meets the G e (0, 255), entering the step 8-3; if the condition that G is 0 and G is 255, entering the step 8-5; otherwise, entering the step 8-7;
the step 8-3: judging the value B, and if the value B meets the B epsilon (0, 255), entering the step 8-6; if B is 0, B is 255, entering the step 8-8; otherwise, entering the step 8-7;
the step 8-4: judging the value G, and entering the step 8-5 if the value G belongs to [0, 255 ]; otherwise, entering the step 8-7;
the step 8-5: judging the value B, and entering the step 8-8 if B belongs to [0, 255 ]; otherwise, entering the step 8-7;
the steps 8 to 6 are as follows: the color point is in the color gamut, and the step 4 is returned;
the steps 8 to 7 are as follows: the color point is outside the color gamut, and the step 4 is returned; and
the step 8-8: the color point is the gamut boundary point, the iteration is terminated, and the step 9 is performed.
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