JPS6354093A - Color picture processing system - Google Patents

Abstract

PURPOSE:To reproduced a high-definition color picture efficiently by applying adaptive correction processing in response to a luminance signal to a chrominance signal whose spatial frequency is reduced. CONSTITUTION:Picture data resolved to an RGB signal 102 by a picture input device 101 is converted into a luminance and color difference I, Q signals 104 by a conversion table 103. The I, Q signals are subjected to spatial frequency reduction by smoothing circuits 105, 106 respectively, inputted to a transmitter 107 and sent through a transmission line 108. A receiver 109 receiving its signal outputs signals Y, I', Q'. Then an image decision circuit 100 applies image decision and when it is decided as a edge part, correction processing sections 111, 112 receive a decision signal 206. Both the correction processing sections apply correction in response to the signal Y to output signals I'', Q''. The signals I'', Q'', Y are converted into R', G', B' 115 by a conversion table 114 and reproduced (116). The edge of the picture is not fogged.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a color image processing method for reproducing a color image signal that has been converted into a luminance signal and a chromaticity signal with reduced spatial frequency.

[Prior Art] Conventionally, when transmitting and recording a color image, the image is decomposed into three primary color image signals RGB, and these are divided into luminance Y1 and color difference signals 1. There is a method of converting the chromaticity signal into a chromaticity signal such as Q, saturation C9, hue H, etc., and transmitting and recording the converted signal. A typical example is transmission using Y (luminance), I, and Q (color difference) of the NTSC system, which is known as the transmission system for color television, and uses R, G, B, and Y.

The relationship between 1 and Q can be expressed as follows.

Y=0.30R+0.59G+0.11B
1=0.74(RY)-0,27(B-Y)Q=0.
48 (RY) - 0, 41 (B-Y) This NTSC system utilizes the viewing angle characteristic that when transmitting a luminance 1 color difference signal in analog, it is difficult to see colors in small areas on the screen.
Color difference signal 1. The Q frequency band is limited.

That is, while the luminance signal Y is transmitted in a wide band of 3 to 4 MHz, the color difference signal I is transmitted in a wide band of 0 to 1.5 MHz,
, Q is O~0.5M)12.

Incidentally, in recent years, in addition to analog systems, digital systems have been actively researched and developed for image transmission and recording. Under these circumstances, even in digital systems, R, G,
Once B is luminance, color difference (Y.

1.Q) Methods of converting, transmitting, and recording signals are being considered. According to it, similar to analog methods, transmission,
In order to improve recording efficiency, we are considering limiting the color difference (I, Q) signals, and one of them is reducing the spatial frequency (bandwidth compression) by block smoothing, as shown in FIG.

In the reduction as shown in Fig. 2, the color difference before reduction is I,
Q, if the color difference after reduction is I', Q', there is almost no problem in areas where the hue changes slowly, but blurring occurs in areas where the hue changes rapidly, such as the edges of letters etc. occurs. This will be explained using FIG. 3. In the example in Figure 3, the character "E" has a "white" background and a "white" character section.
shown as "red". RGB-4YIQ shown earlier
From the conversion formula, for the background part that is "white", Y=
1.0, I = O, Q = O, and for the character part that is "red", Y = 0.30, I = 0.599
, Q = 0°213. The color difference signals of such an image are smoothed. For example, when smoothing is performed while cutting out a block, if the block is a 4×4 block as shown in FIG. Since the areas of "red" and "white" are equal, there is no difference before and after the edge in the color difference signal after smoothing, and background: Y = 1.0, I' = 0.30, Q'
=0.106 characters: Y=0.30, I' =0.30
, Q' =0.108. That is, at this point, already
There is no difference between the background part and the text part except for the brightness. Therefore, when inversely converting this (when playing) Background: R' = 1.35, G' = 0.85, B' = 0.9
5 characters: R' = 0.65, G' = 0.15, B' =
0.25, and it can be seen that blurring occurs at the edges.

[Problems to be Solved by the Invention] The present invention has been proposed to solve the problems of the prior art described above, and its purpose is to provide a color image processing method that enables efficient and high-quality recording. The point is to propose.

[Means for Solving the Problems] The configuration of the present invention for achieving the above-mentioned problems is to convert a color image into one luminance signal and one chromaticity signal, reduce the spatial frequency of the chromaticity signal, and then convert the luminance and In a color image processing method for reproducing a reduced chromaticity signal, there is provided a cutting means for cutting out an image area of the luminance and chromaticity signals, a recognition means for recognizing the image tone of the image area from the luminance signal, and a recognized image tone. and a correction means for correcting the chromaticity signal according to the luminance.

[Operation] In the present invention having the above configuration, the deterioration in the quality of the reproduced image due to the reduction of the spatial frequency is compensated for by correcting the chromaticity signal according to the recognized image tone and luminance, and the high Obtain high-quality color reproduction images.

[Examples] Examples according to the present invention will be described in detail below with reference to the accompanying drawings. In this embodiment, an example will be described in which a color difference signal is used as a chromaticity signal representing a color. The outline of this example is as follows:
When obtaining a color image signal from a color image, the color difference signal I
, Q are compressed by smoothing etc., and these Y,
When reproducing I, Q or reproducing after transmission, Y, I,
When inversely converting the Q color image signal to the R, G, B color image signal, the band-compressed color difference 1. The Q signal is corrected according to the image tone of the color image signal and the luminance Y signal. Here, the image tone refers to the characteristics of an image signal. In the following example, for simplicity, "white" shown in the conventional example is used.
The processing at the edges of an example image of "red" text on the background will be described.

FIG. 1 is a block diagram of an embodiment to which the present invention is applied. 101 is an image input device such as a color camera or a color document reader. 102 is the output of the three primary colors R, G
, B signal, 103 is R2O, B is Y, 1. 104 is a conversion table for converting the Y, I, and Q signals output from the conversion table 103; 105 and 106 are smoothing circuits for reducing the spatial frequencies of the I and Q signals, respectively; 107 is a transmission 108 is a transmission path.

109 and 107 are receiving equipment, and 111 and 112 are correction processing units that respectively perform correction processing characteristic of the embodiment and output signals I" and Q". 113 is the processed color difference signal I"
4Q'', 114 is an inverse conversion table from signals Y, I, Q to R, G, B, and 115 is its output R'G' B
'Signal 116 is an image display or forming device such as a cathode ray tube monitor or a color printer. Reference numeral 110 denotes an image area determination circuit for detecting edge portions.

FIG. 4 shows the simplest image area determination method in the image area determination circuit 110. This method cuts out a block of a certain size from an image signal, and among the pixels in that block, the maximum level of luminance Y□8 and the minimum level of luminance Yll
If the difference between the block and the block exceeds a certain -quantitative value, it is determined that the image tone of the block has a significant change in hue or gradation, that is, it is determined to be an edge portion. In this example, the brightness Y is "0" for the white background and "1" for the red text area, which is the maximum.
It is.

FIG. 6 is a detailed diagram of the image area determination circuit 110.

As mentioned above, since image area determination is performed from image tone determination within a block, the line memory 200 is used to extract the block.
~203 is used. A 4×4 block as shown in FIG. 4 is cut out from these line memories, and a discrimination circuit 20
4 outputs the determination signal 206 and the luminance Y of the approximately middle pixel in the block. The logical value of the judgment signal 206 is Y□
If the difference between 8 and Y win is less than the threshold value of 205, it is “1”.
”, and when it is small, it is “0”.

FIG. 7 shows the judgment circuit 110 and the correction processing circuit 111.1.
12. FIG. Each correction processing circuit receives the luminance Y1 determination signal 206 from the determination circuit 110, and receives the Y1 determination signal 206 from the determination circuit 110.
A predetermined correction is performed by inputting I' and Q' corresponding to the . That is, the correction processing content of the processing units 111 and 112 is that when the determination signal 206 is "1", the manually input I', Q
' according to Y, that is, for pixels where Y is "1", I'
, Q' are each doubled, and for pixels where Y is "0", ■゛.

Let Q be "0". When the determination signal 206 is "0", no correction is performed. Through such correction, edges are emphasized and edges are faithfully reproduced.

The above operation will be explained in its entirety with reference to FIG. The image data decomposed into RGB signals 102 by the image input device 101 is converted into luminance 71 by the conversion table 103.
The 1.Q signal is converted into color difference I and Q signals 104"', after its spatial frequency is reduced by smoothing circuits 105 and 106, respectively, and then input to the transmitter 107 and transmitted through the transmission line 108. transmitted.

Then, the receiving device 109 that received the signal is Y, I.
',Q' are output. Therefore, the image area determination circuit 110 performs image area determination using the method shown in FIGS. 4 and 6, and when it is determined that it is an edge portion, it issues a determination signal 206 to the correction processing units 111 and 112.

As shown in FIG. 5, both correction processing units perform correction according to the value of Y and output I", Q". ■”.

As shown in FIG. 5, the edge part of Q'' has been restored.
The signals are converted into R', G', B' 115 and reproduced by the display device 116.

The image reproduced on the display device 116 no longer has blurred edges as in the past.

Note that the above-mentioned embodiment is the simplest image area determination and color difference processing (
Although an embodiment of the correction) has been shown, the effects of the present invention remain the same even if image area determination or the like is performed using a more advanced method.

That is, it is also possible to calculate the density difference between each adjacent pixel and determine the image area based on the magnitude of the average density difference for the block and a predetermined threshold value.

Further, although the same correction processing is shown for the I and Q signals, it would be even better if the correction processing could be adaptively changed for each.

In addition, in this embodiment, although the NTSC system is explained, PAL
, SECAM, and other methods. In addition, in addition to the YIQ color system, there are also XYZY color system, L*a*b
*, L*u*v* color system, HVC system, etc. are similar as long as they consist of luminance (brightness, density) and color difference (color information). In short, it is sufficient to have a color signal component (for example, luminance Y, etc.) that preserves edge portions well.

[Effects of the Invention] As explained above, according to the present invention, efficient and high-quality color can be achieved by adaptively performing correction processing on a chromaticity signal whose spatial frequency has been reduced according to a luminance signal. Images can now be played back.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment according to the present invention, FIG. 2 is a diagram illustrating image changes due to smoothing as an example of frequency reduction, and FIG. 3 is a diagram illustrating blurring at edges in a conventional example. FIG. 4 is a diagram explaining the image area determination method in this embodiment. FIG. 5 is a diagram explaining the concept of correction processing in the embodiment. FIG. 6 is an image area determination circuit in the embodiment. FIG. 7 is a diagram illustrating the relationship between the image area determination circuit and the correction processing circuit in the embodiment. In the figure, 101... Image human power device, 103, 114... Conversion table, 105, 106... Smoothing circuit, 107...
... Transmitting device, 109... Receiving device, 110... Image area determination circuit, 111, 112... Correction processing circuit, 11
6...Display device, 200-203...Line memory, 204...Discrimination circuit, 205...Threshold value, 206...
...This is a judgment signal. Patent applicant Canon Corporation I-Q r, O' Figure 2 Figure 5 Figure 1 Figure 4 Start of Figure 7

Claims (1)

[Claims] In a color image processing method that converts a color image into luminance and chromaticity signals, reduces the spatial frequency of the chromaticity signals, and then reproduces the chromaticity signals after the luminance and spatial frequency reduction, the luminance and chromaticity signals are The image forming apparatus includes a cutting means for cutting out an image area, a recognition means for recognizing the image tone of the image area from the luminance signal, and a correction means for correcting the chromaticity signal according to the recognized image tone and luminance. Color image processing method.