KR20050111806A - Color conversion apparatus and method of using the same - Google Patents

Abstract

 Disclosed are a color conversion device and a method for performing color gamut mapping using a look up table generated by performing post-processing on a color band correction and a look-up table, respectively, before and after color band mapping. The present invention provides an input signal line processing unit for correcting a region located outside the color band of the target device in which the input color signal is reproduced among the color bands of the input color signal, and corresponding to the input color signal so that the color band of the corrected input color signal matches the color band of the target device. A color band mapping unit for outputting the output color signal, a lookup table for the input color signal and an output color signal corresponding to the input color signal, a lookup table post-processing unit for smoothing the lookup table, and a smoothed lookup table And an output unit for outputting an output color signal by mapping the color band to the color band of the target device. Therefore, when mapping the color signal of the source device to the target device, preprocess the color band of the source device and then map the color band, and post-process the output lookup table generated after the color band mapping to construct a lookup table. This improves color matching.

Description

Color conversion apparatus and method of using the same}

The present invention relates to a color conversion device and a method thereof, and more particularly, when the color band of the input standard color signal and the target device that reproduces the input color signal are different, the color signal of the source device is converted into the color signal of the target device. A color converting apparatus for converting an input color signal using a lookup table so as to be mapped, and a method thereof.

As a method of mapping a color signal of a source device to a color band of a target device, a method of implementing an algorithm using a lookup table and a method of directly implementing hardware are used.

In general, a lookup table uses color signals of color spaces such as RGB and CMYK as linear color spaces such as XYZ and WYV, or general color spaces such as CIE L * a * b, CIE L * u * v, IPT, and DIN99. By performing the conversion, color band detection and color band mapping algorithm were performed. In the direct hardware implementation, the algorithm itself is composed of hardware using a linear color space.

The hardware implementation method is relatively easy to set according to the characteristics of the device because the algorithm itself is composed of hardware. However, there is a problem that the lookup table must also be used in the area such as color band detection, and various algorithms are difficult to apply. There is this.

In addition, in the conventional method using the lookup table, since the lookup table is sampled when mapping from the narrow source color band to the wide target color band, the output image is not continuous or the boundary effect occurs. In addition, in the conventional method using the lookup table, although the source color band is narrower than the target device's color band as a whole, the source color band is wider than the target color band, so that the color band is expanded when the color band is mapped. There is a problem that a phenomenon in which the halftone colors of the color fades or the luminance is lowered.

Accordingly, an object of the present invention is to use color gamut mapping by using a lookup table generated by color gamut correction and post-processing for a color gamut mapping and a look-up table, respectively, when color gamut mapping of two systems having different color gamuts is performed. An object of the present invention is to provide a color converting apparatus and a method thereof.

The color conversion apparatus according to the present invention for achieving the above object is an input signal line processing unit for correcting the region located outside the color band of the target device to reproduce the input color signal of the color band of the input color signal, the color band and the target of the corrected input color signal A color band mapping unit for outputting an output color signal corresponding to the input color signal so that the color bands of the apparatus are matched, a lookup table post-processing unit for forming the lookup table for the input color signal and the output color signal corresponding to the input color signal, and smoothing the lookup table; And an output unit which outputs an output color signal by mapping the color band of the input color signal to the color band of the target device using the smoothed lookup table.

Here, the input color signal is an RGB color signal, and the output color signal is a color signal convertible to an LCH color signal.

Preferably, the input signal processing unit comprises: a color detector for detecting a hue of the input color signal, a minimum value detector for determining whether a color band of the input color signal falls outside the color band of the target device, and a color detector; And a color band corrector for correcting the color band of the input color signal using the result of the minimum value detector.

Here, the color band correction unit corrects the color band of the input color signal by the following equation. , , Using the equation The RGB values after color gamut correction are respectively Is the gain for the color, Is the gain for the minimum value of R, G, and B, Are gains for R, G, and B values, respectively.

The color gamut mapping unit preferably converts an input color signal into a device independent color space and outputs a first color signal, and converts the first color signal into an LCH color space to output a second color signal. And a second color space converter for mapping a second color signal to a color band of the target device, and a third color space converter for converting the mapped second color signal to a device independent color space.

The lookup table post-processing unit includes a lookup table forming unit for forming an input color signal and an output color signal mapped to the input input color signal as a lookup table, a smoothing unit for smoothing the output color signal, and a color tone enhancement unit for improving the color of the smoothed output color signal. do.

Here, the smoothing part may be a low pass filter.

On the other hand, the color conversion method of the present invention comprises the steps of (a) correcting an area outside the color band of the target device to reproduce the input color signal of the color band of the input color signal, (b) the color band and the target device of the corrected input color signal (C) forming a lookup table for the input color signal and the output color signal corresponding to the input color signal, smoothing the lookup table, and (d) using the smoothed lookup table. And outputting an output color signal by mapping the color band of the target device to the color band of the target device.

Preferably, the step (a) includes detecting a color of the input color signal, determining whether the color of the input color signal corresponds to an area located outside the color band of the target device, and the result of the color detector and the minimum value detector. And correcting the color band of the input color signal using.

Step (b) includes converting an input color signal into a device independent color space, converting an input color signal converted into a device independent color space into an LCH, and reproducing an input color signal and an input color signal converted into an LCH. Matching the color bands of the target device, and converting the matched output color signal back into the device independent color space.

Step (c) includes forming an input color signal and an output color signal mapped to the input input color signal as a lookup table, smoothing the output color signal, and improving the color of the smoothed output color signal.

Hereinafter, with reference to the drawings will be described the present invention in more detail.

1 is a diagram showing a color band of a source device and a color band of a target device according to an embodiment of the present invention, respectively.

Referring to FIG. 1, S denotes a color band of a source device and T denotes a color band of a target device. Here, the source device is a three-channel sRGB system and the target device is a five-channel RYGCB system. Area I shows a case in which the color band of the target device is wider than that of the source device, and the color in the sRGB is expanded when the source color band is mapped to the target color band. On the other hand, the II and III regions show a case in which the color band of the source device is reduced in color from the source color band to the target color band. Lines B1 and B2 refer to the case where the minimum values of the color signals R, G, and B are zero. Line B1 is when the G value and B value are 0, and line B2 is when the R value is 0.

Hereinafter, the input device as the source device and the target device as the output system will be described as an example of a wide color gamut display of a 3-channel sRGB system and a 5-channel RYGCB. However, the present invention can also be applied to the case of an axis color gamut display, such as when the color gamut of the source device is wide.

2 is a block diagram illustrating a color conversion apparatus according to an embodiment of the present invention.

As shown in FIG. 2, the color conversion apparatus according to the present invention includes an input LUT generation unit 201, a look-up table (LUT), an RGB line processing unit 203, and a color space conversion unit 205. , A color band mapping unit 207, an output LUT generation unit 209, and an LUT post-processing unit 211.

The input LUT generation unit 201 forms an input color signal as a lookup table (LUT) having three dimensions.

The RGB line processor 203 preprocesses the RGB signal for correcting a predetermined color band of the source device in order to correct the geometric difference between the two color bands in the process of mapping from the color band of the source device to the color band of the target device. -process).

The RGB line processing unit 203 will be described with reference to FIG. 1. In a predetermined region such as regions II and III, although the color band of the source apparatus is narrower than that of the target apparatus, the source color band is larger than the target color band. When the color band is wide, the color band may be expanded. In this case, in order to reduce the phenomenon that the halftones of the primary colors are discolored or the luminance is lowered by preprocessing the RGB signal in order to correct the color bands of the II and III areas to the target color band range before the color band mapping. do.

The color space conversion unit 205 converts the RGB value of the color band corrected by the RGB line processor 203 into a device independent color space for mapping from the color band of the source device to the color band of the target device. Convert the color space.

The color gamut mapping unit 207 maps an input color signal converted from the color space conversion unit 205 into a device independent color space from the color band of the source device to the color band of the target device through a color band mapping algorithm.

The output LUT generation unit 209 forms an output signal mapped to the color band of the target device by the color band mapping unit 207 into a lookup table. That is, the output LUT generation unit 209 forms an output lookup table corresponding to the input lookup table mapped to the color band of the target device.

The LUT post-processing unit 211 smoothes the generated lookup table (LUT) so that the color signal of the source device can be mapped to the color signal of the target device, and improves the color tone of the output color signal.

3 is a block diagram specifically illustrating an RGB line processor of FIG. 2.

As shown in FIG. 3, the RGB line processor 203 of the present invention includes a color detector 301, a minimum detector 303, and a gamut boundary enhancemnet 305. .

First, the color detector 301 detects a hue of the input RGB. This is because the degree of correction of the color band in the color band compensator 305 varies depending on the color.

The minimum value detector 303 determines whether the minimum values min (R, G, B) of R, G, and B are zero in the source color band. That is, it is determined whether the source color band corresponds to lines B1 and B2 of FIG. 1. As the minimum value of the R, G, and B values approaches 0, the color signals are located near the B1 and B2 lines of FIG. This is because the case where the source color band, which is required to correct the source color band, is wider than the target color band, occurs mainly in the region where the minimum values of R, G, and B, such as B1 and B2 lines, are zero.

The color band corrector 305 properly corrects the color band using an arbitrary function of the input lookup table RGB values according to the results of the minimum value detector 303 and the color detector 301. At this time, the correction of the color band uses the following equation.

here, Denotes input R, G, and B signals corrected by the RGB line processing unit 203, respectively. H denotes a color, and since the correction degree of the color band varies depending on the color, the color of the input color signal is detected. min (R, G, B) is the minimum value of the G, R, B color signals, and the closer to 0, the closer the line B1 or B2 of FIG.

When Equation 1 is again shown in detail, each of the following Equations is shown.

here, Denotes input R, G, and B signals corrected by the RGB line processing unit 203, respectively. Are the increments of R, G, and B, respectively. And Uses the result detected by the color detector 301 as a gain for the color. Since the corrected value of the input color signal varies depending on the color of the input color signal. A value is required. Is used as a function of the minimum value of the current R, G, and B values, i.e., the gain detected by the minimum value detector 303 as a gain of how closely the line B1 and B2 of FIG. This is because the degree of correction varies depending on how close the line is to the B1 or B2 line. And, Are the gains for the R, G, and B values, respectively. Each gain and increase amount can be calculated by any function.

As described above with reference to FIG. 1, when the source device is a three-channel sRGB and the target device is a five-channel RYGCB, the color of the target device is wide so that the color in the sRGB of the source device is generally expanded when the color band is mapped. In some cases, the color band may be reduced during mapping, such as the B1 region and the B2 region of FIG. 2. In this case, the color band correction unit 305 properly corrects the source color band using the results of the color detector 301 and the minimum value detector 303 and the above-described equation.

On the other hand, the color space conversion unit 205 converts the RGB signal value of which the color band is increased in the RGB line processing unit 203 into a device-independent space in order to map the color band. Here, the RGB color signal of the color band corrected by the RGB line processor 203 is converted into a WYV signal.

In general, as a color space, coordinate systems such as XYZ, which is a standard color coordinate system, and LAB, LUV, DIN99, and IPT, which have non-linearly converted the XYZ coordinate system in accordance with human visual characteristics, are used. However, since color band mapping is generally performed for chroma and lightness without changing the characteristics of hue, a color coordinate system convertible to LCH (Lightness, Chroma, Hue) is required. Since the color and saturation cannot be calculated in the XYZ coordinate system, the case where color band mapping is performed using the WYV coordinate system in which the XYZ coordinate system with Y as the gray axis is linearly transformed will be described. WYV can be calculated by linear transformation of 3 × 3 matrix of XYZ. The transformation matrix for sRGB is as follows.

Here, each coefficient will vary depending on the color device.

4 is a block diagram illustrating in detail the color band mapping unit of FIG. 2.

As shown in FIG. 4, the color gamut mapping unit 207 includes a first color space conversion unit 401, a color gamut mapping algorithm 403, and a second color space conversion unit 405. do.

The color gamut mapping unit 207 converts an input signal converted from the color space conversion unit 205 into a WYV coordinate system into an LCH coordinate system and maps the color band from the source color band to the target color band, and then the first color space converter 401. Outputs the signal input to WYV again.

First, the first color space converter 401 converts an input signal whose color space is converted into WYV by the color space converter 205 to LCH. The conversion from WYV to LCH uses the following equation.

The color band mapping operator 403 maps the color signal values output from the first color space converter 401 to the target device. After the WYV is converted into the LCH by the first color space converter 401, the color gamut mapping operator 403 is mapped using the source color band and the target color band to which the LCH belongs.

The second color space converter 405 converts the LCH output from the color band mapping unit 403 back to WYV and outputs the converted WCH.

On the other hand, the output LUT generation unit 209 generates the output corresponding to the input lookup table value mapped to the color band of the target device after the color band is mapped by the color band mapping unit 207 as a lookup table.

FIG. 5 is a block diagram illustrating in detail the LUT post-processing unit of FIG. 2.

Referring to FIG. 5, the LUT post-processing unit 211 includes a low pass filter 501 and a color tone enhancement unit 503.

First, the low pass filter 501 smoothes the lookup table generated by the output LUT generation unit 209. Since the lookup table is sampled, interpolation in the final system may result in non-consecutive results, resulting in a boundary effect on the final image output, and increase in random noise contained in the input. Because this phenomenon occurs, smoothing is required.

The color tone enhancer 503 changes the color tone of a specific portion of the output image by editing the value of the lookup table. By editing the values of the lookup table, you can directly apply the effects of brightness, saturation, hue control, and selective color control using the lookup table instead of hardware. Can improve the color.

6 is a flowchart illustrating a color conversion method according to an embodiment of the present invention.

Referring to FIG. 6, when the primary color of the source color band is reduced even when the source color band is narrower than the target color band during color band mapping, the input RGB color signal is preprocessed to correct the source color band before the color band mapping ( S601). The input color signal line processing is performed by the RGB line processing unit 203 including the color detection unit 301, the minimum value detection unit 303, and the color band compensator 305. The color detection unit 301 detects the color of the RGB color signal input to the source device, and the minimum value detection unit 303 determines whether the minimum value of the input color signal R, G, B values is zero. The color band compensator 305 calculates the above-described equation (2) according to the degree of color detected by the color detector 301 and whether the input color signal color band detected by the minimum value detector 303 corresponds to a region requiring correction. By correcting the R, G, B value of the input color signal, the color band is corrected.

Subsequently, the RGB value having the color band corrected by the RGB line processing unit 203 is converted into a WYV which is a device independent color space in the XYZ coordinate system by the color space conversion unit 205 (S603). This converts the color signals of the source device into device independent color spaces for color band mapping from source devices having different color bands to target devices.

The color signal converted into the device independent color space is mapped to the target color band by the color band mapping unit 207 (S605). The input color signal converted into WYV is converted into LCH by the first color space converter 401, mapped to the target color band by the color band mapping operator 403, and then again by the second color space converter 405. Is converted to output.

The color signal mapped by the color band mapping unit 207 is generated as a lookup table by the output LUT generation unit 209. That is, the output corresponding to the input lookup table value mapped to the target color band is generated as the lookup table.

The lookup table for the output generated by the output LUT generation unit 209 is subjected to the smoothing and color tone enhancement process by the LUT post-processing unit 211 (S609). Smoothing of the lookup table is performed by the low pass filter 501, and color tone enhancement for the output image is made by editing the lookup table generated by the output LUT generation unit 209 by the color tone enhancement unit 503.

As described above, according to the present invention, when the color band of the source device and the target device are different, the color band is mapped after preprocessing to increase the color band of the source device when the color signal of the source device is mapped to the target device. The color matching is improved by performing post-processing on the output lookup table generated after the color band mapping to configure the lookup table.

In addition, color gamut mapping using a lookup table may reduce the burden on hardware.

In addition, although the preferred embodiment of the present invention has been shown and described above, the present invention is not limited to the specific embodiments described above, but the technical field to which the invention belongs without departing from the spirit of the invention claimed in the claims. Of course, various modifications can be made by those skilled in the art, and these modifications should not be individually understood from the technical spirit or the prospect of the present invention.

1 is a view showing a color band of a source device and a color band of a target device according to an embodiment of the present invention, respectively;

2 is a block diagram showing a color conversion apparatus according to an embodiment of the present invention;

3 is a block diagram specifically illustrating an RGB line processor of FIG. 2;

4 is a block diagram specifically illustrating a color band mapping unit of FIG. 2;

5 is a block diagram showing in detail the LUT post-processing unit of FIG.

6 is a flowchart illustrating a color conversion method according to an embodiment of the present invention.

* Description of the symbols for the main parts of the drawings *

201: input LUT generation unit 203: RGB line processing unit

205: color space conversion unit 207: color band mapping unit

209: output LUT generation unit 211: LUT post-processing unit

301: color detection unit 303: minimum value detection unit

305: color band correction unit 401: first color space conversion unit

403: color band calculation unit 405: second color space conversion unit

501: low pass filter 503: color tone enhancing unit

Claims (11)

An input signal line processor for correcting an area outside the color band of the target device in which the input color signal is reproduced among the color bands of the input color signal; A color band mapping unit configured to output an output color signal corresponding to the input color signal so that the color band of the corrected input color signal matches the color band of the target device; A look-up table post processor configured to form a look-up table for the input color signal and an output color signal corresponding to the input color signal, and smooth the look-up table; And And an output unit which outputs an output color signal by mapping a color band of the input color signal to a color band of the target device using the smoothed lookup table. The method of claim 1, The input color signal is an RGB color signal, and the output color signal is a color signal convertible to an LCH color signal. The method of claim 1, The input signal processor, A color detector detecting a hue of the input color signal; A minimum value detector which determines whether the color band of the input color signal corresponds to a region located outside the color band of the target device; And And a color band compensator for correcting a color band of the input color signal by using the results of the color detector and the minimum value detector. The method of claim 3, And the color band correcting unit corrects a color band of the input color signal by the following equation: , , , here The RGB values after color gamut correction are respectively Is the gain for the color, Is the gain for the minimum value of R, G, and B, Are gains for R, G, and B values, respectively. The method of claim 1, The color band mapping unit, A first color space conversion unit converting the input color signal into a device independent color space and outputting a first color signal; A second color space conversion unit converting the first color signal into an LCH color space and outputting a second color signal; A color band calculator configured to map the second color signal to a color band of the target device; And And a third color space converting unit converting the mapped second color signals back into the device independent color space. The method of claim 1, The lookup table post-processing unit, A lookup table forming unit configured to form a lookup table with the input color signal and an output color signal mapped to the input input color signal; A smoothing unit to smooth the output color signal; And And a color tone enhancer for improving a color of the smoothed output color signal. The method of claim 6, And the smoothing part is a low pass filter. (a) correcting an area outside the color band of the target device in which the input color signal is reproduced among the color bands of the input color signal; (b) matching a color band of the corrected input color signal with a color band of the target device; (c) forming a lookup table for the input color signal and an output color signal corresponding to the input color signal, and smoothing the lookup table; And (d) mapping the color gamut of the input color signal to the color gamut of the target device using the smoothed lookup table and outputting an output color signal; a color conversion method comprising a The method of claim 8, In step (a), Detecting a color of the input color signal; Determining whether a color band of the input color signal corresponds to a region located outside a color band of the target device; And And correcting the color band of the input color signal by using the results of the color detector and the minimum value detector. The method of claim 8, In step (b), Converting the input color signal into a device independent color space; Converting an input color signal converted into the device independent color space into an LCH; Matching a color band of an input color signal converted into the LCH with a target device in which the input color signal is reproduced; And Converting the matched output color signal back into the device independent color space. The method of claim 8, Step (c) is, Forming a lookup table with the input color signal and an output color signal mapped to the input input color signal; Smoothing the output color signal; And And improving the color of the smoothed output color signal.