JPH09166971A - Color signal conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten the processing time for color space transformation operation by storing a YrCrCb signal obtained by performing color space transformation operation processing for RGB signals corresponding to addresses specified by pixel data. SOLUTION: Pixel data D1 outputted from a graphic memory 1 one pixel by one pixel is converted into video data of a YrCrCb signal type. A color space transforming unit 2 receives the pixel data D1 and provided with a transformation table 3 for transforming it into the YrCrCb signal. And, this pixel data D1 is overlapped by a YrCrCb signal D2 outputted from other video deck and the like and a weight control section 5 and outputted. Therefore, a YrCrCb signal D3 outputted from the weight control section 5 and a picture outputted from the video deck and the like and displayed on a display are overlapped by a picture generated by a computer and the like.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to RGB (red green blue).
The graphic data in the signal format is converted to YCrCb (luminance,
The present invention relates to a color signal conversion device for converting video data in a (color difference) signal format.

[0002]

2. Description of the Related Art In a general personal computer, in order to display a color image on a display, an RG is used.
Graphic data in the B signal format is used. on the other hand,
2. Description of the Related Art In a personal computer, a screen output from a video deck, a television or the like is superimposed and displayed on graphic data generated by the computer itself. In this case, for example, RGB
A method is adopted in which graphic data in the signal format is converted into video data in the YCrCb signal format and then screen synthesis is performed. For example, 256 kinds of colors are selected for pixel data composed of 8 bits per screen pixel, and 8-bit R (red) signal, G (green) signal and B (blue) signal are obtained respectively. If these signal intensities are Er, Eg, and Eb, respectively, and the luminance signal intensity is Ey, the following (1) to (3)
The YCrCb signal is obtained by the equation. Y: Ey = 0.3Er + 0.59Eg + 0.11Eb ... (1) Cr: Er-Ey = -0.59Eg + 0.7Er-0.11Eb ... (2) Cb: Eb-Ey = -0.59Eg-0.3Er + 0. 89Eb (3) Er: 8bit red signal intensity Eg: 8bit green signal intensity Eb: 8bit blue signal intensity Ey: 8bit luminance signal intensity This arithmetic processing is executed by a predetermined high-speed arithmetic processing circuit.

[0003]

The conventional color signal conversion device as described above has the following problems to be solved. When video data in the YCrCb signal format is obtained as described above, the RGB signals of a total of 24 bits are calculated according to a predetermined mathematical expression in the color space conversion calculation processing, and the 8-bit luminance signal Y and 8-bit luminance signal Y are calculated. Color difference signal C
b or Cr is output. Note that the total output is 16 bits, the luminance signal Y is always output, and the color difference signal Cb
Only one of Cr and Cr is output alternately. Therefore, the arithmetic processing unit is composed of a relatively large-scale circuit such as a multiplier and an adder for alternately executing such arithmetic processing. This hinders the miniaturization of the circuit and causes a cost increase.

[0004]

The present invention employs the following structure to solve the above problems. <Structure 1> Graphic data in RGB (red, green, blue) signal format is converted into video data in YCrCb (luminance, color difference) signal format, and pixel data for specifying the content of RGB signal pixel by pixel is predetermined. In accordance with the control clock, and at the address designated by the pixel data, the conversion table storing the YCrCb signal obtained by performing the color space conversion arithmetic processing on the corresponding RGB signal, and in synchronization with the control clock, A selector for outputting the Y signal output from the conversion table and alternately selecting and outputting either the Cr signal or the Cb signal output from the conversion table is provided.

<Explanation> RGB (red-green-blue) signal format graphic data is data that expresses colors by the three primary colors of light. The R signal represents red, the G signal represents green, and the B signal represents blue signal levels. It is a digital signal. The pixel data specifies the contents of the RGB signal pixel by pixel. RGB
The content of the signal means each signal level of the R signal, the G signal, and the B signal.

A YCrCb (luminance, color difference) signal can be calculated based on the signal levels of the R signal, G signal, and B signal. This calculation process is a color space conversion calculation process. The conversion table is a memory that stores the results of calculation of YCrCb (luminance, color difference) signals based on R signals, G signals, and B signals corresponding to pixel data in advance. Y when the pixel data is input to the address
A CrCb (luminance, color difference) signal is output. Therefore, the processing time for the color space conversion calculation is sufficiently shortened as compared with the case where the calculation is performed each time. Further, the Y signal is output in synchronization with the control clock, while the Cr signal and the Cb signal are alternately selected and output. This makes it possible to obtain video data that alternately outputs a combination of Y signals and Cr signals and a combination of Y signals and Cb signals.

<Structure 2> The selector is provided with an averaging circuit for averaging a plurality of Cr signals and Cb signals which are continuously output from the conversion table in synchronization with the control clock and before being supplied to the selector. . <Explanation> Since the Cr signal and the Cb signal which are output every time in synchronization with the control clock are alternately selected and output,
The Cr signal and the Cb signal are thinned out every time. Therefore, the continuity of the image is compensated by averaging the Cr and Cb signals that are continuously output.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to specific examples. <Specific Example> FIG. 1 is a block diagram showing a specific example of the color signal conversion apparatus of the present invention. This device includes a graphic memory 1, a color space converter 2, and a superposition control unit 5. The color space converter 2 is provided with a conversion table 3 and a selector 4. With this configuration, the pixel data D output from the graphic memory 1 for each pixel
1 is converted into YCrCb signal format video data. The YCrCb signal D2 output from another video deck (not shown) or the like is superimposed and output by the superimposition control unit 5. Therefore, the YCrCb signal D3 output from the superposition control unit 5 superimposes and displays the image generated by the computer and the image output from the VCR on the display.

The color space converter 2 has pixel data D1
Is provided and a conversion table 3 for converting this into a YCrCb signal is provided. FIG. 2 shows a data structure explanatory diagram of each part of the circuit shown in FIG. First, from the color space converter 2, as shown in FIG.
1 combining r signal or Y signal and Cb signal
A 6-bit signal is output. In this case, Cr signal and C
The b signal is alternately output once each. For this,
In the color space converter 2, the pixel data D1 having an 8-bit structure as shown in FIG.
To enter. This 8-bit pixel data is 2
56 types of colors are selected and the levels of R, G and B signals are designated respectively as shown in FIG. The red signal strength Er, the green signal strength Eg, and the blue signal strength Eb thus obtained
And the luminance signal intensity Ey obtained by adding these, Y
The CrCb signal is obtained as a result of the arithmetic processing.

FIG. 3 shows an explanatory diagram of the structure of such a conversion table 3. In the conversion table 3, the color space conversion calculation processing results of the corresponding YCrCb signals are stored in 256 addresses specified by the pixel data. Therefore, as soon as the pixel data D1 is input to the conversion table 3, the corresponding 8-bit Y after color space conversion is applied.
The signal, the Cr signal, and the Cb signal are output at the same time.

FIG. 4 shows a block diagram of a configuration example of the selector. Flip-flops R1 and R2 for temporarily storing and delaying the Y signal output from the conversion table 3 shown in FIG. 1 are connected in series to this circuit. Further, flip-flops R3 and R4 for temporarily storing and delaying the Cr signal and flip-flops R5 and R6 for temporarily storing and delaying the Cb signal are provided in series. . Flip-flop R2
Is an 8-bit Y signal output, and the outputs of the flip-flops R3 and R4 are low-pass filters (L
It is configured to be input to the PF) 11. The outputs of the flip-flops R5 and R6 are input to the low pass filter 13. This low pass filter 1
Reference numerals 1 and 13 have a function of removing the high frequency components from the signals continuously output from the conversion table 3 and stored in the respective flip-flops in the selector, and outputting the signals. That is, here, at least two consecutive Cr signals and Cb signals output from the conversion table 3 are averaged and then output to the selection circuit (SEL) 15.

The data storage and output timing of the shift registers R1 to R6 are controlled in synchronization with the pixel clock CLK. The pixel clock CLK is the same as the control clock when supplying the pixel data D1 to the color space converter 2 shown in FIG. Further, as shown in FIG. 4, the selection circuit 15 includes a low-pass filter 11
It is a circuit that accepts the Cr signal input from the input terminal and the Cb signal input from the low-pass filter 13 and selects either of them to be output alternately. For this selection control, a control clock obtained by dividing the pixel clock CLK by half is supplied to the selection circuit 15. Frequency divider 14
Is a circuit that divides such a clock signal.

FIG. 5 shows an operation timing chart of the above apparatus. (A), (b) and (c) in the figure
Represents the Y signal, the Cb signal, and the Cr signal output from the conversion table 3. The clock signal is t in the figure.
Shall have a cycle of. Here, as shown in the circuit of FIG. 4, since a flip-flop for temporarily storing and delaying a signal is provided in the selector, it is shown in (a), (b), and (c) of FIG. As described above, the Y signal, the Cr signal, and the Cb signal are delayed by the number of flip-flops and output. As shown in (d), the Y signal is output after being delayed by two clocks due to the two flip-flops in the case of FIG. 4, for example. On the other hand, Cr signal and Cb
A signal is a clock as shown in FIG.
The signals are alternately output from the selection circuit 15 shown in FIG. However, the Cr signal and the Cb signal are both (b) and (c).
Conversion table 3 in synchronization with the basic clock (i)
Output from Therefore, for example, in the case of a Cr signal, FIG.
The continuous signals temporarily stored in the flip-flops R3 and R4 shown in FIG.
The averaged signal is output to the selection circuit 15. Cb
The same applies to signals. The relationship between such averaging and selected output is shown in FIGS. 4 (e), (f), and (g). Like the Y signal, both the Cr signal and the Cb signal are delayed by the number of flip-flops shown in the figure, that is, the delay number τ, and output from the selector 4 shown in FIG.

The low-pass filters 11 and 13 described above are used.
Is to prevent deterioration of image quality when continuously output Cr signals and Cb signals are thinned out alternately. Even if consecutive 2 bits or 3 to 4 bits are added, these are added. The same purpose can be achieved by a circuit that averages. This is similar to FIG.
As shown in FIG. 3, since the calculation processing result is immediately output using the conversion table 3, the Cr signal and the Cb signal, which should be alternately output, are output all at once, so that the device for adjusting that portion is used. is there. Therefore, a simple averaging filter, an FIR (non-recursive digital) filter, or the like can be used for the averaging circuit.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a specific example of a color signal conversion device of the present invention.

FIG. 2 is an explanatory diagram of a data configuration.

FIG. 3 is an explanatory diagram of a configuration of a conversion table.

FIG. 4 is a block diagram of a specific example of a selector.

FIG. 5 is an operation timing chart of the device of the present invention.

[Explanation of symbols]

 1 Graphic Memory 2 Color Space Converter 3 Conversion Table 4 Selector 5 Superposition Control Unit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H04N 1/46 H04N 9/74 Z 9/67 1/40 D 9/74 1/46 Z

Claims (2)

[Claims] 1. A method for converting graphic data in an RGB (red, green, blue) signal format into video data in a YCrCb (luminance, color difference) signal format, wherein pixel data designating contents of an RGB signal pixel by pixel is provided. YCrCb obtained by receiving a predetermined control clock and performing color space conversion calculation processing on the corresponding RGB signal at the address specified by this pixel data.
A conversion table storing signals and a Y signal output from the conversion table are output in synchronization with the control clock, and one of the Cr signal and the Cb signal output from the conversion table is alternately selected. A color signal conversion device comprising a selector for outputting. 2. In the selector, a plurality of Cr signals and C are continuously output from the conversion table in synchronization with the control clock and before being supplied to the selector.
2. The color signal conversion device according to claim 1, further comprising an averaging circuit for averaging the b signal.