JP2009017222A - Color adjustment apparatus, color adjustment method, and integrated circuit of color adjustment apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color adjustment apparatus, a color adjustment method, and an integrated circuit of the color adjustment apparatus which reduces noise generated in a saturation signal S, and performs more delicate color adjustment when an image signal has a low luminance like monochrome. <P>SOLUTION: The color adjustment apparatus is provided with: a color space conversion unit 1 which converts a color signal into three signals of a hue signal, a saturation signal, and a lightness signal; a saturation correction unit 2 which corrects the saturation signal output from the color space conversion unit 1. The saturation correction unit 2 includes a detection unit 3 which detects the maximum value and the minimum value of the color signal, a discrimination unit 4 which discriminates an operation method based on a difference of the maximum value and the minimum value of the color signal detected by the detection unit 3, and an operation unit 5 which corrects the saturation signal based on the operation method discriminated by the discrimination unit 4. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a color adjustment device that performs color adjustment on a color image signal after RGB-HSV conversion, a color adjustment method, and an integrated circuit of the color adjustment device.

  When displaying an input color signal in a display device such as a monitor, color adjustment processing is performed in order to obtain an image output having a desired color reproducibility in accordance with usage conditions and the like. When performing color adjustment processing, the HSV color space represented by the three attributes of hue, saturation, and brightness is similar to the method of human perception of color, so that color adjustment is easy and widely used. . This is because the RGB color space of the color signal that is the input data is converted into an HSV color space represented by hue, saturation, and lightness, color adjustment processing is performed on the HSV color space, and then the original RGB color space is restored. This is realized by inverse transformation.

  There are a cylindrical model and a cone model as a representation method of the HSV color space. The cone model has a smaller color space than the cylindrical model, and is not suitable for finer color adjustment. The color adjustment device described in Patent Document 1 converts a color signal serving as input data into hue, saturation, and brightness using an RGB-HSV color space conversion formula of a cylindrical model, and the hue, saturation, and brightness respectively. Other output is adjusted.

JP 2003-250058 A

  The color adjustment apparatus described in Patent Document 1 performs color space conversion using an RGB-HSV color space conversion formula that is a well-known technique. When the maximum value of the color signals R, G, and B as input data is MAX and the minimum value is MIN, the saturation signal S is obtained by the following equation.

  The signal levels of the color signals R, G, and B each take a value of 0 to 255, and the signal level of the saturation signal S takes a value of 0 to 1. For example, the saturation signal S changes as shown in Table 1 from Equation (1).

  As described above, in the cylindrical model, a phenomenon in which the saturation signal S repeats 1 and 0 occurs in the case of an image signal close to monochrome with low luminance. Low luminance means a case where all signal levels of the color signals R, G, and B are small. Due to this phenomenon, the saturation signal S has a problem that noise is emphasized in a portion close to low luminance monochrome.

  The present invention solves the above-described problems, and can reduce noise generated in the saturation signal S in the case of a low-brightness monochrome image signal, thereby enabling finer color adjustment. The purpose is to provide.

  The color adjustment device according to the present invention includes a color space conversion unit that converts a color signal into three signals of a hue signal, a saturation signal, and a brightness signal, and a saturation that corrects the saturation signal output from the color space conversion unit. A saturation correction unit, a saturation correction unit that detects a maximum value and a minimum value of the color signal, and a calculation method based on a difference between the maximum value and the minimum value of the color signal detected by the detection unit. A determination unit for determining, and a calculation unit for correcting and calculating the saturation signal based on the calculation method determined by the determination unit.

  When the determination unit determines that the difference between the maximum value and the minimum value of the color signal is equal to or greater than the first predetermined value, the calculation unit outputs the saturation signal output from the color space conversion unit as it is, and the determination unit However, when it is determined that the difference between the maximum value and the minimum value of the color signal is less than the first predetermined value, the calculation unit calculates a correction coefficient based on the difference between the maximum value and the minimum value of the color signal, The saturation signal output from the space conversion unit may be multiplied by a correction coefficient, and the multiplication result may be output.

  When the determination unit determines that the difference between the maximum value and the minimum value of the color signal is greater than or equal to the second predetermined value and less than the first predetermined value, the calculation unit is based on the difference between the maximum value and the minimum value of the color signal. The correction coefficient is calculated, the saturation signal output from the color space conversion unit is multiplied by the correction coefficient, the multiplication result is output, and the determination unit determines that the difference between the maximum value and the minimum value of the color signal is the second value. When it is determined that the value is less than the predetermined value, the calculation unit may output 0.

  The color adjustment method according to the present invention includes a color space conversion step for converting a color signal into three signals of a hue signal, a saturation signal, and a brightness signal, a detection step for detecting the maximum value and the minimum value of the color signal, A determination step for determining a calculation method based on the difference between the maximum value and the minimum value of the color signal detected by the detection step, and the saturation converted by the color space conversion step based on the calculation method determined by the determination step And a calculation step for correcting the signal.

  In the determination step, when it is determined that the difference between the maximum value and the minimum value of the color signal is equal to or greater than the first predetermined value, the saturation signal converted by the color space conversion step is output as it is in the calculation step, and the determination is performed. In the step, when it is determined that the difference between the maximum value and the minimum value of the color signal is less than the first predetermined value, the correction coefficient is calculated based on the difference between the maximum value and the minimum value of the color signal in the calculation step. The saturation signal converted by the color space conversion step may be multiplied by a correction coefficient, and the multiplication result may be output.

  In the determination step, when it is determined that the difference between the maximum value and the minimum value of the color signal is greater than or equal to the second predetermined value and less than the first predetermined value, the difference between the maximum value and the minimum value of the color signal is calculated in the calculation step. A correction coefficient is calculated based on the saturation signal, and the saturation signal converted by the color space conversion step is multiplied by the correction coefficient, and the multiplication result is output. In the determination step, the difference between the maximum value and the minimum value of the color signal is the second value. If it is determined that the value is less than the predetermined value, 0 may be output in the calculation step.

  An integrated circuit according to the present invention includes the color adjusting device.

  According to the color adjustment apparatus of the present invention, noise generated in the saturation signal S can be reduced and finer color adjustment can be performed in the case of an image signal close to monochrome with low luminance.

  Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1
The color adjustment apparatus according to the present invention uses a cylindrical cone model newly created by correcting a cylindrical model in the HSV color space. First, the cylindrical model will be described, and then the cylindrical cone model will be described.
[Cylinder model]
Since the color adjustment apparatus according to the present embodiment adopts a partial cylindrical model, the cylindrical model will be described below. FIG. 1A is a perspective view of a cylindrical model in the HSV color space, and FIG. 1B is a longitudinal sectional view of FIG. The hue Ho changes along the outer circumference of the circle, the saturation So changes with the distance from the center of the circle, and the lightness Vo changes from the bottom to the top. The cylindrical model has a feature that the image reproducibility is good because the image is bright and the image can be clearly seen in the image signal of medium brightness.
[Configuration of Color Adjustment Device]
FIG. 2 is a block diagram showing the configuration of the color adjustment apparatus according to Embodiment 1 of the present invention. The color adjustment apparatus according to the present embodiment includes a color space conversion unit 1 that converts color signals R, G, and B, which are input data, into a hue signal Ho, a saturation signal So, and a lightness signal Vo of a cylindrical model. In the color space conversion unit 1, when the maximum value of the color signals R, G, and B is MAX and the minimum value is MIN, the hue signal Ho, the saturation signal So, and the lightness signal Vo are obtained by the following equations, respectively.

  The color adjustment apparatus according to the present embodiment further includes a saturation correction unit 2 that corrects the saturation signal So output from the color space conversion unit 1. The saturation correction unit 2 includes a detection unit 3 that detects the maximum value MAX and the minimum value MIN of the color signals R, G, and B serving as input data, and the maximum of the color signals R, G, and B detected by the detection unit 3. A determination unit 4 that determines a calculation pattern based on a difference D between the value MAX and the minimum value MIN; a saturation signal So that is corrected based on the calculation pattern determined by the determination unit 4; and a calculation result that is a corrected saturation signal And an arithmetic unit 5 that outputs as Sc. A difference D between the maximum value MAX and the minimum value MIN of the color signals R, G, B represents the degree of monochrome.

[Cylindrical cone model]
FIG. 3 is a conceptual diagram of saturation correction processing by the color adjusting apparatus according to the first embodiment of the present invention. FIG. 3A is a perspective view of the cylindrical cone model of the present embodiment, and FIG. 3B is a longitudinal sectional view of FIG. The hue changes along the outer circumference of the circle, the saturation changes with the distance from the center of the circle, and the lightness changes from the bottom to the top in FIG. The color adjustment apparatus according to the present embodiment employs a cylindrical model in the region A where the accuracy of the saturation signal can be ensured in the cylindrical model, and adopts the concept of the cone model in the region B where the accuracy of the saturation signal is suspicious. In the region C where the signal is indefinite, the saturation signal is set to zero. Specifically, in a non-monochrome area (area A), that is, an area where the difference D between the maximum value MAX and the minimum value MIN of the color signals R, G, B is equal to or greater than the first predetermined value, the corrected saturation signal Sc The saturation signal So calculated using the cylindrical model is set, and the corrected saturation signal Sc is set in an area close to monochrome (area B), that is, in an area where the difference D is greater than or equal to the second predetermined value and less than the first predetermined value. Is set to a value obtained by attenuating the saturation signal So using the concept of a conical model, and in the monochrome region (region C), that is, the region where the difference D is less than the second predetermined value, the corrected saturation signal Sc is minimal. A value, for example, 0 is set. The first predetermined value is greater than the second predetermined value.

[Description of operation]
FIG. 4 is a flowchart showing processing (main routine) by the color adjusting apparatus according to the first embodiment of the present invention. In the present embodiment, the signal levels of the color signals R, G, and B each take a value of 0 to 255. Color signals R, G, and B, which are input data, are input (S1). The color space conversion unit 1 converts the color signals R, G, and B into a hue signal Ho, a saturation signal So, and a lightness signal Vo using a cylindrical model conversion formula (S2). The detection unit 3 detects the maximum value MAX and the minimum value MIN of the color signals R, G, B (S3). The determination unit 4 calculates the difference D between the maximum value MAX and the minimum value MIN of the color signals R, G, B detected by the detection unit 3 (S4). It is determined whether or not the difference D between the maximum value MAX and the minimum value MIN is greater than or equal to a first predetermined value (S5). For example, the first predetermined value is 2 ⁶ (= 64). When the difference D between the maximum value MAX and the minimum value MIN is equal to or larger than the first predetermined value (Yes in S5), that is, in the area A, the calculation unit 5 outputs the corrected saturation signal Sc from the color space conversion unit 1. The saturation signal So is set as it is (S6), and the corrected saturation signal Sc is output (S7).

When the difference D between the maximum value MAX and the minimum value MIN is less than the first predetermined value (No in S5), noise is generated in the saturation signal So output from the color space conversion unit 1, so this saturation signal So Correct. It is determined whether or not the difference D between the maximum value MAX and the minimum value MIN is greater than or equal to a second predetermined value (S8). The second predetermined value is smaller than the first predetermined value, for example, 2 ³ (= 8). When the difference D between the maximum value MAX and the minimum value MIN is greater than or equal to the second predetermined value (Yes in S8), that is, in the region B, the calculation unit 5 corrects the saturation signal So according to the difference D, and the correction result Is set to the corrected saturation signal Sc (S9). When the difference D between the maximum value MAX and the minimum value MIN is less than the second predetermined value (No in S8), that is, in the region C, 0 is set to the corrected saturation signal Sc (S10). Finally, the calculation unit 5 outputs the corrected saturation signal Sc (S7).

  FIG. 5 is a flowchart showing the saturation correction process (subroutine) in step S9 of FIG. The calculation unit 5 normalizes the difference D between the maximum value MAX and the minimum value MIN (S11), and sets the normalized result as the correction coefficient C (S12). FIG. 6A shows the relationship between the correction coefficient C, the maximum value MAX, and the difference D between the minimum values MIN of the color adjustment apparatus according to Embodiment 1 of the present invention. As shown in FIG. 6A, normalization means that the difference D decreases as the correction coefficient C becomes 1 when the difference D is 64 and the correction coefficient C becomes 0 when the difference D is 8. The correction coefficient C is also reduced. Specifically, the correction coefficient C is expressed by the following equation.

  The saturation signal So output from the color space conversion unit 1 is multiplied by the correction coefficient C (S13), and the multiplication result is set in the corrected saturation signal Sc (S14).

  Hereinafter, an example of the saturation correction process in the color adjustment apparatus of the present embodiment will be described with reference to FIG. FIG. 6B is a diagram illustrating the relationship between the saturation signal So and the corrected saturation signal Sc, and the difference D between the maximum value MAX and the minimum value MIN when the minimum value MIN is zero. For example, when the difference D is 0, the maximum value MAX is also 0 and the minimum value MIN is 0, and when the difference D is 64, the maximum value MAX is 64 and the minimum value MIN is 0. FIG. 6C is a diagram illustrating the relationship between the saturation signal So and the corrected saturation signal Sc, and the difference D between the maximum value MAX and the minimum value MIN when the minimum value MIN is 1. For example, when the difference D is 0, the maximum value MAX is 1 and the minimum value MIN is 1, and when the difference D is 64, the maximum value MAX is 65 and the minimum value MIN is 1. The corrected saturation signal Sc is a multiplication result obtained by multiplying the saturation signal So by the correction coefficient C of FIG.

  In the region A in which the accuracy of the saturation signal can be ensured in the cylinder model and the difference D is 64 or more, the color adjustment apparatus of the present embodiment corrects the saturation signal So calculated from the conversion equation of the cylinder model as it is. Output as signal Sc. In the case of a non-monochrome image signal, finer color adjustment can be performed by using a cylindrical model having a wide color space.

  Further, in the region B where the accuracy of the saturation signal is suspicious in the cylinder model and the difference D is 8 or more and less than 64, the color adjustment apparatus of the present embodiment applies the saturation signal So calculated from the conversion equation of the cylinder model to the cone. Correction is performed using the concept of the model, and the correction result is output as a corrected saturation signal Sc. In the case of an image signal close to monochrome, as shown in FIGS. 6B and 6C, the saturation signal So is attenuated by correction, so that noise is hardly superimposed.

  In the region C in which the saturation signal is indefinite in the cylindrical model and the difference D is less than 8, the color adjustment apparatus according to the present embodiment outputs 0 as the corrected saturation signal Sc. Thereby, no noise is generated in the case of a monochrome image signal.

  As described above, in the case of an image signal close to monochrome, the color adjustment apparatus according to the present embodiment attenuates the saturation signal So and finally converges to 0, thereby generating noise in the saturation signal S. Can be reduced, and finer color adjustments can be made.

Embodiment 2
The color adjustment apparatus according to the first embodiment classifies input signals into three regions and corrects the saturation signal using a correction method for each region. In contrast, the color adjustment apparatus according to the present embodiment classifies the input signal into two regions and corrects the saturation signal using a correction method for each region.

  Since the configuration of the color adjustment apparatus according to the present embodiment is the same as the configuration of the color adjustment apparatus according to the first embodiment, description thereof is omitted.

[Description of operation]
FIG. 7 is a flowchart showing processing (main routine) by the color adjusting apparatus according to the second embodiment of the present invention. Steps S1 to S7 are the same as those in the first embodiment, and thus the description thereof is omitted. In step S5, when the difference D between the maximum value MAX and the minimum value MIN is less than the first predetermined value 64 (No in S5), noise is generated in the saturation signal So output from the color space conversion unit 1. Therefore, the calculation unit 5 corrects the saturation signal So, sets the correction result to the corrected saturation signal Sc (S15), and outputs the corrected saturation signal Sc (S7).

FIG. 8 is a flowchart showing the saturation correction process (subroutine) in step S15 of FIG. The calculation unit 5 normalizes the difference D between the maximum value MAX and the minimum value MIN in 2 ⁴ (= 16) stages (S16), and sets the normalized result as the correction coefficient C (S12). The following table shows the relationship between the difference D between the maximum value MAX and the minimum value MIN and the correction coefficient C.

  That is, assuming that the quotient when the difference D between the maximum value MAX and the minimum value MIN is divided by 4, the correction coefficient C is expressed by the following equation.

  Steps S13 and S14 are the same processes as those in the first embodiment, and thus description thereof is omitted. From the table (2), when the difference D between the maximum value MAX and the minimum value MIN is less than 4, the correction coefficient C is 0, and as a result, the correction saturation signal Sc is also 0.

The above process will be described more specifically. The difference D between the maximum value MAX and the minimum value MIN calculated in step S4 is represented by 10 bits. The upper 4 bits are the integer part and the lower 6 bits are the decimal part. The integer part is read, and it is determined whether or not there is 1 in the integer part (S5). When there is even 1 in the integer part, that is, when the difference D is 2 ⁶ (= 64) or more (Yes in S5), the process proceeds to steps S6 and S7 without reading out the decimal part. On the other hand, when there is no 1 in the integer part, that is, when the difference D is less than 2 ⁶ (= 64) (No in S5), the lower 2 bits of the decimal part are rounded down, and the remaining higher 4 bits are read out. The value (A) of the upper 4 bits is normalized (decimated) to 2 ⁴ (= 16) stages (S16). The normalized result, that is, the decimal value is set as the correction coefficient C (S12), and the process proceeds to steps 13 and 14.

  As described above, in the region A in which the accuracy of the saturation signal can be ensured in the cylindrical model and the difference D is 64 or more, the color adjustment device of the present embodiment is similar to the first embodiment in the conversion formula of the cylindrical model. The saturation signal So calculated from the above is output as the corrected saturation signal Sc as it is. By using a cylindrical model with a wide color space, finer color adjustment can be performed.

  Further, in the regions B and C in which the accuracy of the saturation signal in the cylinder model is suspicious or the saturation signal is indefinite and the difference D is less than 64, the color adjustment apparatus of the present embodiment is calculated from the conversion equation of the cylinder model. The saturation signal So is corrected step by step using the concept of a cone model, and the correction result is output as a corrected saturation signal Sc. Specifically, the saturation signal So is attenuated to 16 levels, finally converged to 0, and output as the corrected saturation signal Sc. This makes it difficult for noise to be superimposed as in the first embodiment.

  The color adjustment device according to the present invention has an effect that noise generated in the saturation signal S can be reduced in the case of an image signal close to monochrome with low luminance, and is useful as a color adjustment device for an image display device.

Conceptual diagram of cylindrical model in HSV color space 1 is a block diagram showing a configuration of a color adjustment apparatus according to Embodiment 1 of the present invention. Conceptual diagram of saturation correction processing by the color adjustment apparatus according to the first embodiment of the present invention. The flowchart which shows the process (main routine) by the color adjustment apparatus of Embodiment 1 of this invention. Flowchart showing the saturation correction process (subroutine) in step S9 of FIG. The figure which shows an example of the saturation correction process in the color adjustment apparatus of Embodiment 1 of this invention. The flowchart which shows the process (main routine) by the color adjustment apparatus of Embodiment 2 of this invention. Flowchart showing the saturation correction process (subroutine) in step S15 of FIG.

Explanation of symbols

1 Color space conversion unit 2 Saturation correction unit 3 Detection unit 4 Determination unit 5 Calculation unit

Claims (7)

A color space conversion unit that converts a color signal into three signals of a hue signal, a saturation signal, and a brightness signal;
A saturation correction unit for correcting a saturation signal output from the color space conversion unit,
The saturation correction unit
A detection unit for detecting the maximum value and the minimum value of the color signal;
A determination unit that determines a calculation method based on a difference between the maximum value and the minimum value of the color signal detected by the detection unit;
A color adjustment apparatus comprising: a calculation unit that corrects and calculates a saturation signal based on the calculation method determined by the determination unit. When the determination unit determines that the difference between the maximum value and the minimum value of the color signal is equal to or greater than the first predetermined value, the calculation unit outputs the saturation signal output from the color space conversion unit as it is. ,
When the determination unit determines that the difference between the maximum value and the minimum value of the color signal is less than the first predetermined value, the calculation unit calculates a correction coefficient based on the difference between the maximum value and the minimum value of the color signal. 2. The color adjustment apparatus according to claim 1, wherein the color adjustment device calculates, multiplies the saturation signal output from the color space conversion unit by the correction coefficient, and outputs the multiplication result. When the determination unit determines that the difference between the maximum value and the minimum value of the color signal is greater than or equal to the second predetermined value and less than the first predetermined value, the calculation unit determines the difference between the maximum value and the minimum value of the color signal. A correction coefficient is calculated based on the color signal, the saturation signal output from the color space conversion unit is multiplied by the correction coefficient, and the multiplication result is output,
3. The color adjustment according to claim 2, wherein when the determination unit determines that the difference between the maximum value and the minimum value of the color signal is less than a second predetermined value, the calculation unit outputs 0. 4. apparatus. A color space conversion step for converting the color signal into three signals of a hue signal, a saturation signal, and a brightness signal;
A detection step for detecting a maximum value and a minimum value of the color signal;
A determination step of determining a calculation method based on a difference between the maximum value and the minimum value of the color signal detected by the detection step;
A color adjustment method comprising: a calculation step of correcting the saturation signal converted by the color space conversion step based on the calculation method determined by the determination step. In the determination step, when it is determined that the difference between the maximum value and the minimum value of the color signal is equal to or greater than the first predetermined value, the saturation signal converted by the color space conversion step is output as it is in the calculation step. And
In the determination step, when it is determined that the difference between the maximum value and the minimum value of the color signal is less than the first predetermined value, the correction coefficient is calculated based on the difference between the maximum value and the minimum value of the color signal in the calculation step. 5. The color adjustment method according to claim 4, further comprising: multiplying the saturation signal converted by the color space conversion step by the correction coefficient and outputting the multiplication result. In the determination step, when it is determined that the difference between the maximum value and the minimum value of the color signal is greater than or equal to a second predetermined value and less than the first predetermined value, the maximum value and minimum value of the color signal are determined in the calculation step. A correction coefficient is calculated based on the difference, the saturation signal converted by the color space conversion step is multiplied by the correction coefficient, and the multiplication result is output.
6. The color according to claim 5, wherein in the determination step, when it is determined that the difference between the maximum value and the minimum value of the color signal is less than a second predetermined value, 0 is output in the calculation step. Adjustment method.   An integrated circuit comprising the color adjusting device according to claim 1.

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