JP2882285B2 - Color image compression / expansion method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for compressing and expanding a color image, and in particular, guarantees the correspondence between pixels on the compression side and the expansion side, such as image transmission between different models, or the correspondence on a frame on the time axis. The present invention relates to a color image compression / expansion method capable of performing high-efficiency color image expansion in a system that is not performed.

[0002]

2. Description of the Related Art Various methods for compressing image information have been proposed. For example, when the signal level is equally divided for each sample value of the image signal converted into a digital signal, and a linear quantization (equal quantization) unit that replaces a value included in each range with one representative value is employed. In general, when it is assumed that the difference between the representative point and the original value is not known, 6 bits (64 gradations) to 8 bits (256 gradations) are required for a natural image.
In order to record a signal obtained by digitizing an image signal by equal quantization as described above, it is necessary to handle a large amount of information as described above for each sample value.

[0003] In order to encode a signal with a smaller amount of information, human visual and other sensory features, for example,
The part where the signal changes little is sensitive to the change,
If there is a certain amount of error in the part where the signal changes drastically, it is difficult to detect it. For example, after the image is decomposed into pixels, a small number of approximate values of the original information is transmitted using the height of the adjacent correlation of the luminance value of each pixel, or the difference between pixels or the frame is used. To transmit the difference between
Alternatively, the amount of data is reduced by applying various high-efficiency coding schemes that reduce the amount of information per sample by reducing the frequency element by utilizing the fact that the high frequency component is small. The compressed digital data is recorded, transmitted, and transmitted, and after the digital data compressed as described above is reproduced and received, the data is expanded. It is well known that image restoration has been conventionally performed.

[0004]

In the above-mentioned conventional compression method of general image information, it is important to properly restore the decomposed pixels. In many cases, it is assumed that the number of pixels in the expanded image (expanded image) is the same. Therefore, when a compression / expansion operation is performed between images having different numbers of pixels, the pixels after expansion are separately provided. It is necessary to perform interpolation, thinning, and the like. That is, in the conventional image information compression method, only true valid information is extracted and not restored, and in the conventional image information compression method, to some extent, physical information Means that the original image and the restored image (decompressed image) have the same number of pixels. The problem is that the compression ratio cannot be increased by the image information compression method.

[0005] In order to solve the above-mentioned problem, the applicant of the present invention disclosed in Japanese Patent Application No. 5-39492, irrespective of the level of pixel density in an image to be subjected to image information processing. Then, only the feature points of the image are extracted to obtain compressed image data of the image information, and when decompression, pixel restoration is not performed from the above-mentioned image data, but a new pixel density plane is obtained. In order to render an image, the brightness of the above-mentioned image information is obtained for two-dimensionally distributed luminance information or three-dimensionally distributed image information including a time axis in the two-dimensionally distributed luminance information. A feature point is a positive / negative maximum point of curvature of a function isoluminance line, or a positive / negative maximum point of curvature of an isoluminance surface, or a straight line obtained by linearly approximating the luminance function isoluminance line and the luminance function described above. Error from line or brightness The difference between the plane obtained by approximating the number of isoluminance planes and the luminance function isoluminance plane described above is determined as a feature point of the image at a point exceeding a predetermined threshold. When the values are transmitted and recorded, and the positions of the characteristic points and the luminance values are used for image restoration, the pixels other than the characteristic points are determined by an interpolation plane or an interpolation solid determined by a plurality of neighboring characteristic points during expansion. The luminance information is determined, and from the image information of the three-dimensional distribution including the time axis in the image information of the luminance information distributed two-dimensionally,
A plurality of sets of the two-dimensionally distributed luminance information are targeted, and the positive and negative maxima of the curvature of the equiluminance line of the luminance function of each of the sets, or the equiluminance lines of the luminance function of each of the sets are straight lines. The error between the approximated straight line and the isoluminance line of the luminance function,
A point exceeding a predetermined threshold is defined as a feature point of the image.
The position and the brightness value of the feature point of the image are transmitted, recorded,
When used for image restoration, a multidimensional image compression / expansion method has been provided in which luminance information of pixels other than characteristic points is determined by an interpolation solid determined by a plurality of nearby characteristic points upon expansion.

[0006] When the image is a color image,
For example, a color image can be divided into three primary color image components,
Alternatively, recording, reproduction, transmission, signal processing, and the like are separately performed for a luminance component and a color difference component, and a color image is compressed and decompressed, for example, into three primary colors. It is also common practice to separately encode and decode the plurality of signal components separately into image components or into a luminance component and a chrominance component, as described above. When the luminance component and the chrominance component are individually encoded and decoded during the compression and decompression of the, the separate code is assigned to each of the luminance component and the chrominance component. I can't control it. The above-mentioned problem is solved by the applicant of the present invention in the Japanese Patent Application No. 5-39 when compressing and expanding a color image.
It is difficult to solve the above-described image compression / expansion method proposed by the U.S. Pat. No. 492 simply by simply applying the method. In the case where each feature point is determined by extracting the feature points, there is a problem that the number of feature points increases and a color shift occurs between image components due to polygon approximation performed for information compression. A solution was sought.

[0007]

According to the present invention, an equal luminance line set for each predetermined specific luminance value in a luminance component of a luminance component and a color difference component constituting a color image is specified. The position and the brightness value of the feature point meeting the conditions are used for transmission, recording, and image restoration, and the position of the feature point of the color difference component in the color image is set to be the same as the position of the feature point of the brightness component. A compression / expansion method of a color image in which the color difference component value at the position is used for transmission, recording, and image restoration, and a predetermined specification of a luminance component among a luminance component and a color difference component constituting the color image The positions of characteristic points and luminance values that meet specific conditions for isoluminance lines set for each luminance value are used for transmission, recording, and image restoration, and the positions of characteristic points of color difference components in the color image described above. Also, in the same as the position of the feature point of the luminance component, transmitting the color difference component value of its position, recording,
In the color image compression / expansion method used for image restoration, an allowable value is set for each color difference component value at each feature point of the equi-luminance line, and when the color difference component value at the feature point does not exceed the allowable value, The color difference component value of the feature point is
As the same value as the color difference component value of the feature point before that feature point,
Provided is a method for compressing and expanding a color image, which reduces the frequency of occurrence of color difference component values.

[0008]

The position and the luminance value of a characteristic point that meets a specific condition with respect to an isoluminance line set for each predetermined specific luminance value in a luminance component of a luminance component and a color difference component constituting a color image. And the color difference component value at the position of the feature point of the luminance component are used for transmission, recording, and image restoration. Also,
An allowable value is set for each chrominance component value at each feature point of the equi-luminance line. If the chrominance component value at the feature point does not exceed the allowable value, the chrominance component value of the feature point is changed to the value before the feature point. , The occurrence frequency of the color difference component value is reduced.

[0009]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a color image compression / expansion method according to the present invention. 1 to 3 are block diagrams showing an example of the configuration of a compression-side device in a color image compression / expansion apparatus configured by applying the color image compression / expansion method of the present invention, and FIG. 4 is a color image compression / expansion of the present invention. FIG. 5 is a block diagram illustrating a configuration example of a decompression-side device in a color image compression / decompression device configured by applying the method. FIGS. 5 to 12 are used to explain the configuration principle and operation principle of the color image compression / decompression method of the present invention. FIG.

In FIGS. 1 to 3, which show a configuration example of a compression side device in a color image compression / expansion apparatus to which the color image compression / expansion method of the present invention is applied, an image source 1 is a color image signal source. The image source 1 outputs a luminance component (luminance signal) and a color difference component (color difference signal) constituting a color image to be compressed. The luminance component and the color difference component sent from the image source 1 are converted into digital signals of a predetermined number of bits by the analog-to-digital converter 2. The luminance component Y converted to a digital signal by the analog-to-digital converter 2 is supplied to an extraction unit 3 for specific luminance level information, and the color difference component C converted to a digital signal by the analog-to-digital converter 2 is Are supplied to the color memory 7.

According to the method for compressing and expanding a color image of the present invention, the position of a characteristic point satisfying a specific condition with respect to an isoluminance line set for each specific luminance value in a luminance component and a color difference component constituting a color image. The luminance value and the color difference component value at the position of the characteristic point of the luminance component are transmitted, recorded, and used for image restoration, and an allowable value is set for each color difference component value at each characteristic point of the isoluminance line. If the color difference component value at the feature point does not exceed the allowable value, the color difference component value of the feature point is set to the same value as the color difference component value of the feature point before the feature point, and the generation of the color difference component value is performed. Since the frequency can be reduced, firstly, for each predetermined specific luminance value in the luminance component among the luminance component and the color difference component constituting the color image, About luminance line Or obtain the image data compressed by the position and the luminance value of the feature points consistent with the condition, means will be described or decompresses the image data of the.

Now, taking as an example a case where the isoluminance plane indicating a specific luminance value in the luminance component of the original color image to be compressed is represented by FIG. The following is an example of the case where the operation is performed. In FIG. 13, pixels surrounded by a dotted line are white pixels having a luminance value higher than the luminance value of the equi-luminance plane, and pixels surrounded by a solid line and shaded are pixels of the equi-luminance plane. The pixel group is assumed to be a black pixel having a lower luminance value than the luminance value, and the pixel group shown in FIG. 13 described above has a contour of a binary image as disclosed in JP-A-5-35872. When the tracking method is applied and the boundary between the white pixel and the black pixel is tracked, the outline of the image as shown in FIG. 14 is obtained.

In the above-described tracing of the boundary line, first, the scanning is started from the upper left corner of the screen in accordance with the raster scanning order, and the scanning is performed. As a result, the first boundary designated as the first boundary in FIG. A boundary is discovered. When the tracking is started with the above-mentioned point as the starting point, if the high-luminance surface is on the left side of the tracking direction, if the tracking start direction matches the horizontal scanning direction (CW: clockwise), the tracking starts. The direction coincides with the vertical scanning direction (CCW: counterclockwise). In FIG. 14, tracking direction type flags (CW, CCW) are provided for each tracking equal luminance line. Then, as illustrated in FIG. 14 described above, after the contour of the pixel is traced and obtained for each predetermined specific luminance value in the luminance component of the image, the tracking start direction coincides with the vertical scanning direction ( The isoluminance line (CCW: counterclockwise) is shifted to the pixel center position to the left in the tracking direction, and the tracking start direction matches the horizontal scanning direction (CW: clockwise).
Is shifted rightward in the tracking direction to the pixel center position, and the specific isoluminance line passing point coordinate is moved to the center position of each pixel constituting the specific luminance boundary as illustrated in FIG. Let it. As a result, when a reproduced image is obtained based on a specific luminance boundary obtained by tracking the contour of a pixel, one pixel of black pixels is generated on a specific side in the tracking direction, thereby deteriorating the image quality. Problems can be improved satisfactorily.

Next, the starting point is fixed, and the pixels on the isoluminance line are successively connected by a virtual straight line from the starting point, and the distance between the virtual straight line and the real pixels existing therebetween is predetermined. An actual pixel exceeding the error allowable range is registered as a feature point pixel. Then, when a feature point pixel is found as described above, the feature point pixel is set as a new starting point, and pixels on the isoluminance line are sequentially connected from the new starting point by a virtual straight line, and the virtual straight line is connected. And, the distance between the real pixels existing between the real pixels and the real pixels that exceed a predetermined error allowable range is registered as a feature point pixel. Hereinafter, successive feature point pixels are sequentially set as successive start points. When the user finds and registers, the new isoluminance line obtained by connecting the feature points sequentially obtained as described above is as shown in FIG.

By performing the above operation for each of the equal luminance planes having different luminance values, the luminance component of the original color image is reduced to the data of the characteristic points of the equal luminance line. Is performed. The positions and luminance values of the characteristic points on the isoluminance line in the color image are used for transmission, recording, image restoration, and the like as information in which luminance information in the original color image is compressed at high efficiency. Based on the position of the characteristic point and the luminance value, an equal luminance line can be easily drawn and restored on the extension side. Since the isoluminance line restored on the decompression side is drawn by the end point (feature point) designation vector, the pixel density of the image memory provided on the decompression side is reduced by the image memory provided on the compression side. Even if the pixel density is different, the shape of the isoluminance line restored on the expansion side is
It hardly depends on the above physical conditions.

As described above, the information obtained by expanding the highly efficient information into the information of the position and the luminance value of the characteristic point of the luminance component of the image meeting the specific condition obtained for each specific isoluminance line is expanded and reproduced. Is obtained, for each threshold value for obtaining an isoluminance line for each specific luminance value, a bright region having the above-described isoluminance line as a boundary is filled with a bright symbol, and a dark region having the above-mentioned isoluminance line as a boundary. A region is filled with a dark symbol to create a mask using a light and dark binary symbol. FIG. 17 shows a mask created by filling pixels on the decompression side through which an equal luminance line at a specific luminance value has passed, and an area on the right side (low luminance side) in the tracking direction.

As described above, the brightness 2
By creating a mask with a value symbol, the isoluminance line (or isoluminance surface) is approximated by a polygon (or polygon),
Equiluminance line (or equiluminance surface) approximated by a polygon (or polygonal approximation) by a straight line connecting feature points during expansion
In the case where the luminance information of pixels other than the characteristic points is determined by the interpolation plane (or the interpolation solid) determined by the plurality of nearby characteristic points, the equiluminance line (or the luminance plane) is used.
No inversion of the brightness order between
It does not cause an abnormal state in the luminance distribution in the image to cause deterioration of the image quality.

FIG. 18 shows a case where the gradation of the luminance of an image is 256 (000 to 255) by an 8-bit digital luminance signal, as shown in FIG. An example is shown in which nine types of masks for converting the above-mentioned 256 levels of luminance into nine types of luminance levels are formed by the first to eighth threshold values having the appropriate luminance values as threshold values. FIG. 19 shows an example in which a mask having a mask number corresponding to the mask number shown in FIG. 18B is created for an original color image having a luminance gradation of 256. I have. In FIG. 19, mask 1
18 is white in its entirety, but as shown in FIG. 18B, the mask 1 has a threshold value set to a luminance value corresponding to 30 out of 256 gradations. Since a portion where the luminance value of the image is higher than the threshold value is painted white, and a portion where the luminance value of the image is lower than the threshold value is painted black, the mask shown in FIG. The fact that the entire screen displayed as the mask 1 in the middle is shown in white means that the image to be compressed has a portion lower than the luminance value corresponding to 30 out of 256 gradations. Means not.

Although the screen shown as mask 8 in FIG. 19 is entirely black, the mask 8 has a threshold of 25 as shown in FIG.
It is set to a luminance value corresponding to 240 out of 6 gradations,
Since a portion where the brightness value of the image is higher than the threshold value is painted white, and a portion where the brightness value of the image is lower than the threshold value is created as a black-filled mask,
The fact that the entire screen displayed as the mask 8 in FIG. 19 is shown in black means that a part of the image to be compressed that has a higher luminance value than 240 corresponding to 240 out of 256 gradations Does not exist. Further, FIG.
9 is black in a part of the screen in which the masks 2 to 7 are displayed.
This means that luminance values higher and lower than each threshold value used to create are mixed in the image to be compressed.

When a plurality of masks indicated by each mask number shown in FIG. 18B and FIG. 19 are superimposed, an image having nine levels of luminance is reproduced. Now, in each mask indicated by each mask number shown in FIG. 18B and FIG. 19, the luminance value of a portion painted white is expressed by a numerical value of each mask number. That is, FIG.
FIG. 20 shows the luminance distribution of an image obtained by superimposing a plurality of masks indicated by mask numbers 1 to 8 on the basis of numerical values.

In FIG. 18B, the luminance of 256 gradations represented by an 8-bit digital luminance signal is compressed into luminance values corresponding to the respective thresholds defined by mask numbers 0 to 8. It is in a state of being left. Generally, assuming that the mask group is n masks, a mask number 0 → a pixel having a luminance value 0 to a first equal luminance value A mask number 1 → a first equal luminance value to a second equal luminance value Pixel of mask number 2 → second equal luminance value to third equal luminance value Pixel of mask number 3 → third equal luminance value to fourth equal luminance value Pixel:::::: Mask number i → second Pixels with i-equal luminance value to (i + 1) -th equal luminance value:::::: mask number n → n-th equal luminance value to 255th pixel That is, if n masks are created as described above, the luminance values of each pixel distributed from luminance 0 to luminance 255 are classified into n + 1 categories. The example shown in FIG. 18B is an example where n = 8.

When the luminance of the pixels included in each of the above categories is represented by an intermediate representative value of the luminance range, nine levels of equiluminance lines are reproduced in the examples of FIG. 18B and FIG. Will be done. Next, among the plurality of isoluminance lines described above, the neighboring 3 isoluminance lines from the neighboring
When a pixel is selected and the luminance between the two equal luminance lines is interpolated on the interpolation plane formed by the three pixels, a one-dimensional display as shown in FIG. can get. By the way, although the original image has 256 gradations, for example, in the above example, the image expansion is performed by interpolation in a state where the luminance gradation is reduced to 9 luminance levels. The quality of the reproduced image is not sufficient.

Therefore, in order to improve the quality of the reproduced image, the luminance value of the interpolation end point is not set to the intermediate value of the simple category as described above in the interpolation reproduction of the luminance value. After arranging the masks in the order of the magnitudes of the luminance values according to the thresholds, and filling the area between the adjacent masks with an intermediate value of the luminance values according to the thresholds of the two adjacent masks, the luminance value of each pixel is (1) When the luminance value of the surrounding pixels is equal to the luminance value of the central pixel, the luminance value of the central pixel is undecided. , (2) when the luminance value of the surrounding pixels is not higher than the luminance value of the central pixel,
The luminance value of the center pixel is defined as “an intermediate value of luminance values based on threshold values of both adjacent masks−a” (where a is a positive value).
(3) When the luminance value of the surrounding pixels is not lower than the luminance value of the central pixel, the luminance value of the central pixel is set to “the intermediate value of luminance values by the threshold values of both adjacent masks + a”. When the relationship between the luminance value of the pixel and the luminance value of the center pixel is other than the above-described relationships (1) to (3), the luminance value is set to an intermediate value between the luminance values based on the threshold values of both adjacent masks. The determination is made according to which of the conditions shown in (1) to (4) is satisfied, so that the quality of the reproduced image can be improved.

A specific example in which the relationship between the central pixel and the luminance values of the eight surrounding pixels is (1) to (4) is surrounded by four dotted frames shown in FIG. Each of the four dotted line frames shown in FIG. 20 is taken out for easy understanding and is shown in FIG. 21. By the way, with the central pixel,
When the relationship with the luminance values of the eight surrounding pixels is the above (1), that is, when the luminance value of the peripheral pixels is equal to the luminance value of the central pixel, the luminance value of the central pixel is undecided.
An example of the case is indicated by nine pixels in a dotted frame illustrated at the leftmost end in FIG. 21, and the luminance value of the nine pixels is the same numerical value 4. In this case, the luminance value of the center pixel is "undefined", and in FIG. 22 and subsequent figures, "undefined" means "."
It is indicated by using the symbol.

When the relationship between the central pixel and the luminance values of the eight surrounding pixels is the above (2), that is, when the luminance value of the peripheral pixels is not higher than the luminance value of the central pixel, An example of a case where the luminance value is “an intermediate value of luminance values based on threshold values of both adjacent masks−a” (where a is a positive value) is shown by a dotted frame shown second from the left in FIG. As shown by the nine pixels inside,
In such a case, the luminance value of the center pixel is set to “low”, and in FIG. 22 and subsequent figures, the state where the luminance of the center pixel is “low” is represented by a “−” symbol for simplification of the drawing. I will show you.

Further, when the relationship between the center pixel and the luminance values of the eight surrounding pixels is the above (3), that is, when the luminance value of the surrounding pixels is not lower than the luminance value of the center pixel, FIG. 2 shows an example in which the luminance value of a pixel is set to “an intermediate value of luminance values by threshold values of both adjacent masks + a”.
1, the luminance value of the center pixel in such a case is set to “high”, and is shown in FIG. 22 and subsequent figures. For simplicity of illustration, the state where the luminance of the center pixel is “high” is indicated by using a “+” symbol.

Further, the relationship between the central pixel and the luminance values of the eight surrounding pixels is the above-mentioned case (4), that is, the relationship between the peripheral pixel luminance value and the central pixel luminance value is as described above. In cases other than the relationships (1) to (3) above, the luminance value is set to an intermediate value between the luminance values based on the threshold values of both adjacent masks. An example of the case is that 9 in the dotted frame shown at the right end in FIG.
In this case, the luminance value of the central pixel is “intermediate”, and in FIGS. 22 and subsequent figures, the luminance of the central pixel is “intermediate” for simplicity of illustration. Is indicated by using a symbol “=”. FIG. 22 illustrates the relationship between the luminance values of the respective pixels shown in FIG. 20 using the symbols “•”, “−”, “+”, and “=”. a)-(l)
FIG. 7 is an explanatory diagram showing the luminance value in a three-dimensional manner in the height direction so that the relationship between the central pixel and the luminance values of the eight surrounding pixels and how to use the above-mentioned symbols can be clearly understood.

Next, with respect to the indeterminate brightness area, a center line (skeleton) of the area, that is, a group of points equidistant from the end of the area is extracted, and the brightness values of the pixels on the center line of the area are compared with the adjacent masks. Is an intermediate value of the luminance values based on the threshold value.
FIG. 25 to FIG. 28 are diagrams illustrating the above process. FIG. 25 shows the luminance values before correction only of the undefined area indicated by the symbol “•” in FIG.
Indicates the skeleton extracted from the undefined area with an asterisk “*” and the pixels other than the skeleton with “•”
FIG. 27 is a diagram showing a state in which an intermediate mark = and an intermediate luminance value are added to pixels on the center line of the indefinite area, and FIG. 28 shows all the marks attached in accordance with the above-described rules. FIG. 6 is a diagram showing the luminance value of each pixel when used.

FIG. 18A shows the relationship between the luminance values when the luminance value of the pixel is "intermediate level", "intermediate luminance-", and "intermediate luminance +". In FIG. 18A, the difference between the threshold values of the adjacent masks described above, that is, the difference between the i-th threshold value and the (i + 1) -th threshold value is indicated as d. The intermediate level shown in FIG. 18A is an intermediate luminance value between the luminance values determined by the threshold values of the adjacent masks described above. The luminance level of the low level “intermediate luminance−” shown in FIG. 18 is lower than the above-mentioned intermediate level by d / 3, and the high level shown in FIG. The luminance level of the level “intermediate luminance +” is a luminance level higher by d / 3 than the above-mentioned intermediate level. And FIG.
8 (b), for each mask number,
Intermediate level, low level, high level values, display symbols and the like are shown.

FIG. 29 shows the luminance value of each pixel using the intermediate level, low level, and high level values for each mask number shown in FIG. 18B. In FIG. 29, the luminance value of the pixel is still “undefined”, and there is a pixel indicated by the undefined mark “•”. As described above, after the luminance value of the pixel on the region center line is set to an intermediate value between the luminance values based on the threshold values of the two adjacent masks, the luminance values of the remaining luminance value indefinite pixels are shown in FIG. As described above, the luminance value and the distance (L1, L2, or L3, L3, L3) of the pixel (p1, p2, or p3, p4) of the known luminance at both ends of the extension line in the fixed direction of the pixel px having the undefined luminance value.
L4) to determine the luminance value by the primary interpolation method, or to calculate the luminance value of the pixel whose luminance value is undetermined by using both extended line ends of straight lines in different directions of the pixel whose luminance value is not determined in different directions. Determined by the average value of the luminance values obtained by the primary interpolation method using the luminance value and the distance of the pixel of the known luminance in the above, or the luminance value of the remaining luminance value undetermined pixel is determined by the luminance value undetermined pixel. Are determined by surface interpolation values performed using three known pixels. As a result, a reproduced image as illustrated in FIG. 30 in which the luminance values of all the pixels are determined is obtained.

The compression operation of the luminance component in the compression / expansion operation of the luminance component described so far with reference to FIGS. 13 to 31 applies the color image compression / expansion method of the present invention. 1 to 3 showing an example of a configuration on the compression side in the color image compression / expansion apparatus described above, such as a specific luminance level information extraction unit 3, a luminance memory 4, an equiluminance line tracer 5, a polygon approximate address list 6, and the like. The expansion operation of the compressed luminance component is performed in each component,
Each of the polygon approximate address list 22, the luminance component reproducer 23, the luminance memory 24, and the like in FIG. 4 showing a configuration example on the expansion side in the color image compression / expansion apparatus to which the color image compression / expansion method of the present invention is applied. This is done in the component part.

In FIGS. 1 to 3 described above, an image source 1 (image signal source 1) for generating a color image signal, for example, a luminance signal (luminance component) output from an imaging device (color TV camera) or a VTR, The color difference signal (color difference component) is supplied to the analog-to-digital converter 2, and the analog-to-digital converter 2 outputs a predetermined number of pixels (luminance signal for each image) in each of the horizontal and vertical directions of the image. For example, 512 pixels in the horizontal direction of the image and 4 pixels in the vertical direction of the image.
80 pixels), a digital luminance component Y of a predetermined number of bits (for example, 8 bits) is provided for each pixel in a decomposed state.
And supplies it to the specific luminance level information extraction unit 3, and a digital signal based on color difference components (BY represented as a color difference component U and RY represented as a color difference component V) is
It is supplied to the color memory 7.

As is well known, the resolution of the human eye differs depending on the wavelength of light, and attention is paid to the fact that the resolution for chromatic colors is smaller than the resolution for achromatic colors. It has been widely practiced to narrow the frequency band of the chrominance component compared to the frequency band of the luminance component of the color image, and the luminance component and the chrominance component generated by the image source 1 described above are Usually, the number of pixels due to the component is larger than the number of pixels due to the color difference component. But,
In the color image compression / expansion method of the present invention, since the chrominance component value of the feature point in the luminance component is adopted, the number of pixels by the luminance component and the number of pixels by the chrominance component are the same, or It is necessary that the number of pixels due to the component and the number of pixels due to the color difference component be equivalent to the same state. Therefore, for the chrominance component having a smaller number of pixels than the luminance component, the coordinate values of x and y are each reduced to 1/2 by sub-sampling so that the chrominance component can be extracted, or interpolation calculation as illustrated in FIG. To obtain a color difference component value.

The luminance component Y from the analog-to-digital converter 2
The specific luminance level information extraction unit 3 to which the image information is supplied is binarized and output at a predetermined luminance threshold, and also outputs a pixel address. That is, the luminance component Y supplied to the specific luminance level information extraction unit 3 is compared with a specific luminance threshold supplied from the luminance threshold setting unit, for example, in a comparator (magnitude comparator), and A binary output of the luminance signal Y generated corresponding to the threshold value is transmitted. The brightness threshold setting unit sets a predetermined brightness threshold in a binary number using a ROM, a DIP switch, a fuse array, or the like. The binarized output of the luminance component output from the specific luminance level information extraction unit 3 is stored (stored) in the luminance memory 4, and the binarized output of the luminance component stored in the binarized memory 4 is described. Are read out at the address specified by the binary memory address output from the address counter provided in the equal luminance line tracer 5 and supplied to the equal luminance line tracer 5.

In the equi-luminance line tracer 5, FIG.
For the binarized pixel group as shown in
Start scanning from the upper left corner of the screen according to the raster scanning order, scan, and when the first boundary is found, start tracking the outline of the pixel with a specific luminance value starting from that point, and follow the tracking direction When the tracking start direction matches the horizontal scanning direction when the high-luminance surface is set to the left of
Either W (clockwise) or the case where the tracking start direction coincides with the vertical scanning direction (CCW: counterclockwise), traces the contour of the pixel and generates an output signal (address strobe) of contour information. And output the information of the step history (change in the position in the horizontal scanning direction, change in the position in the vertical scanning direction) in the tracking of the contour of the pixel having the specific luminance value to the address counter. The tracking address sequence is sequentially transmitted as a contour line address output based on the above-described step history.

An output signal (address strobe) of contour line information (contour line information) output from the contour line tracer 5 and a contour line address (contour line address) output are exemplified in FIG. 15 described above. Then, the coordinates of the specific luminance line passing point have been moved to the center position of each pixel constituting the specific luminance boundary, and the coordinates are supplied to the approximate polygon address list 6. In FIG. 32 showing a specific configuration example of the polygon approximate address list 6, an input terminal 6a has an address of the center position of each pixel constituting a specific luminance boundary output from the isoluminance line tracer 5. Information is entered. Then, the address information of the center position of each pixel constituting the specific luminance boundary supplied to the input terminal 6a of the polygon approximate address list 6 is supplied to the end point address register 62 and the shift register 64. The output of the end point address register 62 is supplied to the interpolation address calculator 63. The interpolation address calculator 63 is also supplied with the address information of the first storage section in the shift register 64.

In the interpolation address calculator 63, in order to compare the distance between each of the above-mentioned feature points and the interpolation straight line with a simplified value, and to compare the horizontal scanning direction of the image and the vertical scanning direction, When the Yv axis is set, each of the feature points and the Xh axis in the horizontal scanning direction (or the Yv axis in the vertical scanning direction)
The address for comparing the address value of the Yv axis in the vertical scanning direction (or the address value of the Xh axis in the horizontal scanning direction) on the interpolation straight line at the above address is calculated. The switching of the corresponding axis is performed at the intersection angle between the interpolation straight line and the horizontal scanning direction Xh axis, and the threshold value is set to 45 degrees on the assumption that one pixel is a square.

That is, when the absolute value of the intersection angle between the interpolation straight line and the horizontal scanning direction Xh axis is 45 degrees or less (or other than 45 degrees), the first accumulation section in the shift register 64 is The contour line address information which is sequentially input to the shift register 64 and sequentially held for the successive storage sections in the shift register 64, and the interpolation of the position corresponding to the horizontal scanning direction Xh axis (or vertical scanning direction Yv axis) address An address group (address value calculated based on the end point address and the sequential address information in the first accumulation section in the shift register 64) is supplied to the register 65 as an interpolation address.

The sequential contour pixel addresses sequentially stored in the shift register 64 and the register 65
The interpolation addresses sequentially stored in the comparison extractors C2, C2,
C3... Cn. Each comparison extractor C described above
2, C3... Cn, when the absolute value of the difference obtained as a result of comparing the contour pixel address supplied thereto and the register interpolation address exceeds a predetermined value, the output is set to the feature point address. The data is supplied to a register 66, and the address value of the feature point is stored in the feature point address register 66. At the same time, the address value of the feature point is provided to the endpoint address register 62 as a new endpoint address value.

At the input terminal 6a in the polygon approximate address list 6 illustrated in FIG. 32, the address information of the center position of each pixel constituting the specific luminance boundary supplied from the equiluminance line tracer 5 is used as the tracking start point. Assuming that the operation in the polygon approximate address list 6 is started, the above-described tracking start point address information is stored in the end point address register 62 and at the same time is stored in the first storage section 1 of the shift register 64. Is also stored. Since the above-described polygon approximate address list 6 is supplied with the sequential contour address group output from the above-described contour luminance line tracer 5, the storage sections 1, 2, 3,... The memory contents in are shifted one after another.

However, the above-mentioned end point address register 6
Since the storage contents of No. 2 have not yet changed, the storage of the first storage section 1 in the shift register 64 supplied from the first storage section 1 in the shift register 64 to the interpolation address calculator 63 has been described. A linear interpolation value address group in which only the contents are updated is output. As described above, each time a group of linear interpolation value addresses is output, each of the storage sections 1, 2,... N in the shift register 64 and the horizontal (or vertical) An interpolated value address group corresponding to the direction address is output to the accumulation sections 2, 3, 4,... N of the register 65.

Each of the storage sections 2, 3, 4... N in the above-described shift register 64 and the storage section 2,
, C3,... Cn, respectively, from the comparison extractors C2, C2, C3.
2, C3... Cn, two pieces of input information individually supplied from the respective storage sections 2, 3, 4,... N of the shift register 64 and the storage sections 2, 3, 4,. The absolute value of the difference (corresponding to the distance between the contour line and the interpolation straight line on the screen) exceeds the predetermined threshold value, and the point of the contour line address is set as a feature point. Store.

A number of the above-mentioned comparative extractors C2, C2, C3
When the information of the feature points is simultaneously output from a plurality of comparison and extraction units in Cn, the contour line address closer to the address value stored in the endpoint address register 62 is adopted as a new endpoint address. Then, the address value is stored in the feature point address register 66, and the new endpoint address is stored in the endpoint address register 62. In the above case, even if a plurality of feature point addresses disappear, it is not necessary to restore them as feature point addresses. The feature point address group output from the polygon approximate address list 6 is provided to the encoder 14 via the multiplexer 13.
A chrominance component is also supplied from a chrominance component signal processing system, which will be described later, via a multiplexer 13. The encoder 14 converts the supplied signal into a known signal such as Huffman coding. Perform efficiency coding,
The data is transmitted (or recorded) to the receiving side (or reproducing side) via the transmission line (or recording medium) 14.

Heretofore, the detection of the feature point address group for each different brightness threshold value has been performed according to the contour line {the contour plane in the case of three-dimensional brightness information} from the detected feature point pixel.
With respect to a virtual straight line between a pixel traced in a certain direction and a pixel between the two pixels, a pixel indicating a distance exceeding a certain threshold distance is determined to be a feature point. Although the description has been given of the case where the detection of the feature point address group for each different luminance threshold is different from the above, in the case of the luminance function equiluminance line (contour line) ｛three-dimensional luminance information, Pixels at the maximum and negative maximum points of the curvature of the isoluminance plane ま た は, or pixels in the case where the contour line ｛the curvature of the contour line 場合 in the case of three-dimensional luminance information exceeds a predetermined threshold angle May be determined as a feature point, and the feature point may be determined.

Signal processing for the luminance component indicated by the specific luminance level information extraction unit 3 → luminance memory 4 → equal luminance line tracer 5 → polygonal approximate address list 6 shown in FIGS. The components of the system are configured so that a feature point address group can be detected for each of a plurality of equal luminance lines having different predetermined luminance thresholds. This point is the same for a component of a signal processing system for a color difference component described later, which is configured between the color memory 7 and the multiplexer 13.

In the description so far, the original image information output from the image source 1 (image signal source 1) for generating a color image signal has a luminance signal (luminance component) Y as illustrated in FIG.
And the color difference signals (color difference components) U and V in FIG.
As shown in the example, a contour point of a specific luminance level in a luminance component Y (an isoluminance line obtained for a specific threshold) is obtained, a feature point is obtained, polygon approximation is performed, and the luminance component is compressed. A sequence of coordinate points (x1, y1), (x2, y2),
(X3, y3), (x4, y4) and (x5, y5).

When the original image information output from the image source 1 (image signal source 1) for generating a color image signal is of three types, a luminance component Y and color difference components U and V as described above. In the compression of the image information for the two color difference components U and V, the same method as that for the compression of the image information as described above performed for the luminance component Y is applied. A feature point group may be obtained for each of a plurality of contour lines, and a sequence of coordinate points may be obtained.In such a case, the number of feature points increases, and color shift occurs due to polygon approximation. As described above, the compression and decompression of the color image according to the present invention requires the luminance component Y when compressing the image information on the two color difference components U and V. Features in the feature points obtained for The position of the point, used as it is, transmitting the color difference component value at that position, recording, as used in image restoration, it was solved the above problems.

As described above, in the color image compression / expansion method of the present invention, when compressing the image information on the two color difference components U and V, the position of each feature point in the feature point group obtained for the luminance component Y is calculated as follows. Regarding the point that it is used as it is, or the luminance value in a color image,
Since color should generally be irrelevant, it is conceivable that the above method is not appropriate, but according to the results of experiments on various color images, natural images have It has been clarified that good results can be obtained even when the compression / expansion method of the present invention is applied to perform compression / expansion.

FIG. 7 shows two color difference components U and V in a color image in the method for compressing and expanding a color image according to the present invention.
, U5, v5 in FIG.
1, v2... V5), the coordinate point sequence (x1, y1) → (x2, y2) → (x3, y2) of the feature point group shown in FIG. 6 obtained for the luminance component Y of the color image. y3) → (x
4, y4) → (x5, y5) at each coordinate point (x
1, y1), (x2, y2), (x3, y3), (x4, y4),
FIG. 7 is a diagram illustrating that (x5, y5) is used. FIG. 7 shows the chrominance component values u1, u2... U5 of each feature point in the chrominance component U and the chrominance of the feature point in the chrominance component V. The component values v1, v2... V5 are illustrated as examples.

Therefore, in the color image compression / expansion method of the present invention, the color image is obtained by polygon approximation on an isoluminance line (loop) for each specific luminance value determined by a preset threshold value. Each coordinate value (x1, y1), (x2, y2),
(X3, y3), (x4, y4), (x5, y5) and the coordinate values (x1, y1), (x2, y2), (x3, y3),
A quaternary data sequence composed of the color difference component values u1, u2,... U5 of the color difference component U of the pixel corresponding to (x4, y4), (x5, y5) and the color difference component values v1, v2,. (X1, y
1, u1, v1), (x2, y2, u2, v2), (x3, y
3, u3, v3), (x4, y4, u4, v4), (x5, y5,
u5, v5), that is, compression encoding is performed with the chrominance component value added to the feature point of the loop for each luminance value.

As described above, the coordinate point sequence (x1, y1) of the feature point group obtained for the luminance component Y of the color image → (x2,
y2)-> (x3, y3)-> (x4, y4)-> (x5, y5) coordinate points (x1, y1), (x2, y2),
When (x3, y3), (x4, y4), (x5, y5) are also used as feature points for two color difference components U and V in a color image, the number of pixels of the color difference component is represented by luminance. It is necessary to set the same state as the number of pixels of the component. For this reason, as described above, for example, the coordinate values of x and y are set to 1/2.
The color difference component value is extracted using the address obtained as an address, or an interpolation calculation as illustrated in FIG. 8 is performed, and the value obtained when the color difference component is expanded to the same number of pixels as the luminance component is obtained. Component value.

The quaternary data string (x1, y) obtained by the compression encoding by the color image compression / expansion method of the present invention.
It is said that the information amount of the data of the color difference component values in (1, u1, v1), (x2, y2, u2, v2)... Is desirably as small as possible within a range that does not adversely affect the quality of the restored image. Not even. Therefore, in the color image compression / expansion method of the present invention, an allowable value (allowable value) of an error is set for each color difference component value at each feature point of the equi-luminance line, and the color difference component value at the feature point is set to an allowable value of the error. If the value does not exceed the value, the color difference component value of the feature point is set to the same value as the color difference component value of the feature point before the feature point, and the frequency of occurrence of the color difference component value is reduced.

As described above, the allowable value of the error to be set for each color difference component value at each feature point of the isoluminance line depends on the amount of information to be transmitted and the image quality required for the restored image. Is given. First, the starting point (x1, y) of each loop among the characteristic points on the isoluminance line
The color difference component values u1 and v1 of the color difference components u and v in 1) are set as initial values. Next, the characteristic point of the above-mentioned starting point (x1, y1)
The second feature point (x2, y) following the (first feature point)
The difference between the chrominance component values u2, v2 of the chrominance components u, v in 2) and the chrominance component values u1, v1 of the chrominance components u, v at the first feature point described above is calculated. If the value of the difference does not exceed the set allowable value, the color difference component values of the color difference components u and v at the second feature point (x2, y2) are set as the first color difference component values. The values of the color difference component values u1, v1 of the color difference components u, v at the feature point (x1, y1) are used as they are as the representative values of the color difference component values. If the value of the difference from the color difference component value at the second feature point exceeds the set allowable value, the color difference component u, v at the second feature point (x2, y2) The color difference component values u2 and v2 are determined as representative values of new color difference component values.

After the representative value of the color difference component values at the second feature point is determined as described above, the color difference component values u3 and v3 of the color difference components u and v at the third feature point are calculated.
The difference between the color difference component value determined for the second feature point (x2, y2) and the representative value is determined. If the difference value of the color difference component values does not exceed the set allowable value, the color difference component values of the color difference components u and v at the third feature point (x3, y3) are set as follows: The second mentioned above
The representative value of the chrominance component values of the chrominance components u and v determined for the second feature point (x2, y2) is used as it is. If the value of the difference from the color difference component value at the third feature point exceeds the set tolerance, the color difference between the color difference components u and v at the third feature point (x3, y3) is set. The component values u3 and v3 are determined as new representative values.

The determination of the representative value of the color difference component values of the color difference components u and v at the respective feature points from the fourth to the end points of the loop is also performed by determining the representative values of the color difference components u and v at the first to third feature points. The representative values of the color difference component values of the color difference components u and v at the successive feature points are determined in the same manner as the method of determining the representative value of the color difference component values. FIG. 12 is a diagram illustrating a state in which the above-described allowable value is set to 5 and the representative values of the color difference component values of the 12 feature points on the equi-luminance line are sequentially set. In the example of FIG. The value of the color difference component u is
6, 7, 10, and 12, and the value of the color difference component v changes at the feature points 1, 6, 7, and 10. As in the above example, an allowable value is set for each color difference component value at each feature point of the isoluminance line, and when the color difference component value at the feature point does not exceed the allowable value, the color difference component value of that feature point is set. ,
As the same value as the color difference component value of the feature point before that feature point,
Since the frequency of occurrence of color difference component values can be reduced,
Thus, the transmission amount can be reduced.

The description so far made with reference to FIGS. 6 to 8 and FIG. 12 shows that the compression encoding by the color image compression / decompression method of the present invention is determined by a preset threshold value. Isoluminance line (loop) for each specific luminance value
Each coordinate value (x1, y1), (x2, x1, y2) in the coordinate point sequence of the feature points as illustrated in FIG.
y2), (x3, y3), (x4, y4), (x5, y5),
The coordinate values (x1, y1), (x2, y2), (x3,
.., u5 of the color difference component U of the pixel corresponding to (y3), (x4, y4), (x5, y5) and the color difference component values v1, v2... v5 of the color difference component V. (X1, y1, u1, v1), (x2, y2, u2, v2),
(X3, y3, u3, v3), (x4, y4, u4, v4), (x
5, y5, u5, v5), that is, in the case where the color difference component value is added to the characteristic point of the loop for each luminance value, the embodiment is carried out. May be performed using a color difference component value group obtained by collecting the color difference component values added to the feature points in a certain unit.

As described above, when the present invention is implemented using the color difference component value group obtained by collecting the color difference component values to be added to the feature points in a certain unit, the color difference component value group includes, for example, a specific luminance. An appropriate loop may be adopted from a single loop in an equal luminance line (loop) for each value, a plurality of loops grouped for the same luminance value, or all loops in one frame. In order to express the color difference component values included in the above color difference component value group, in addition to the above-described method of using the color difference component values as they are, for example, using the correlation between feature points, It is also possible to obtain a difference value from the immediately preceding color difference component value, and set the difference value list of the color difference component value as an encoding target. As described above, when the difference value of the color difference component values is adopted, there is an advantage that the bit distribution is statistically smaller than that of the original information.

Even in the case of using the above-mentioned difference value list of the color difference component values, the tolerance value of the error as described above is set, and the difference value of the newly obtained color difference component value is compared with the color difference component value of the immediately preceding color difference component. If the difference between the value and the difference value does not exceed the set error tolerance, the difference value of the immediately preceding color difference component value is calculated as
The difference between the newly obtained color difference component value and the difference value of the immediately preceding color difference component value is adopted as the representative value of the difference value of the color difference component values, and the difference between the difference value of the immediately preceding color difference component value and the set error tolerance is set. If the difference is exceeded, the difference value of the new color difference component value can be adopted as a representative value of the difference value of the color difference component value. In this case as well, the number of transmissions of the difference value of the color difference component value can be reduced. Can be. It is also possible to apply a logarithmic difference method in which the steps of the above-described difference expression of the color difference component values are logarithmically performed, and the steps are finely performed for a small difference, and the steps are coarsely performed for a large difference.

Next, when the above color difference component values are vector-quantized, the color difference component values (u, v) are regarded as two-dimensional vectors, and the color difference component value groups distributed in the vector space are densely packed. The representative vectors are determined by focusing on some of the groups, and numbers are assigned to the representative vectors, and a correspondence table (codebook) of the numbers and the component values of each representative vector is transmitted and recorded. Also, when performing vector quantization, the effect of vector quantization can be reduced by combining the change of the chrominance component value by setting the allowable value of error as described above as preprocessing when determining the representative vector. Can be raised.

In the configuration example on the compression side of the color image compression / expansion apparatus constructed by applying the color image compression / expansion method of the present invention shown in FIGS. , Color difference component value reading interpolator 8
Is supplied with the data of each feature point coordinate. The chrominance component value reading interpolator 8 is adapted to handle the case where the chrominance component value data is sub-sampled.
And performs an interpolation calculation on the color difference component values read from the color memory 7. Then, the color difference component values read out from the color memory 7 and the color difference component values in the state where the interpolation calculation is performed by the color difference component value reading interpolator 8 are given to the color difference component value list 9.

In the configuration example on the compression side in the color image compression / expansion apparatus shown in FIG. 1, the color difference component values in the color difference
Tolerance (allowable value) of the error set in the determination unit 10
Are compared. As described above with reference to FIG. 12 for the sequential feature points, the determination unit 10 determines the allowable value of the error (allowable value) set in the error allowable value setting unit 11 and the value on the isoluminance line. The representative value of the chrominance component values at the successive feature points is determined by the relative magnitude relationship between the chrominance component values of the successive feature points and the difference smaller than the above-described error allowable value is ignored. The color difference component values in a state where the values are smoothed are output, and the color difference component values are supplied to the multiplexer 13 via the color difference component value list 12.

In the configuration example on the compression side in the color image compression / expansion apparatus shown in FIG. 2, when the color difference component values of the color difference component value list 9 are supplied to the difference converter 16, the difference The converter 16 uses the correlation between the feature points to obtain a difference value from the immediately preceding chrominance component value, which is provided to the chrominance component value list 17. The value is compared with the permissible error value (permissible value) set in the permissible error value setting unit 11 by the determiner 10. As described above with reference to FIG. 12 for the sequential feature points, the determination unit 10 determines the allowable value of the error (allowable value) set in the error allowable value setting unit 11 and the value on the isoluminance line. The representative value of the chrominance component values at the successive feature points is determined by the relative magnitude relationship between the chrominance component values of the successive feature points and the difference smaller than the above-described error allowable value is ignored. The color difference component values in a state where the values are smoothed are output, and the color difference component values are supplied to the multiplexer 13 via the color difference component value list 12. It goes without saying that the step of expressing the difference of the color difference component values may be performed as a logarithmic one.

Further, in the configuration example on the compression side in the color image compression / decompression device shown in FIG. 3, the case of the compression side configuration in the color image compression / decompression device shown in FIG. Similarly to the above, the chrominance component value of the chrominance component value list 9 is compared with the allowable value of the error (allowable value) set in the error allowable value setting unit 11 by the determiner 10. As described above with reference to FIG. 12 for the sequential feature points, the determination unit 10 determines the allowable value of the error (allowable value) set in the error allowable value setting unit 11 and the value on the isoluminance line. The representative value of the chrominance component values at the successive feature points is determined by the relative magnitude relationship between the chrominance component values of the successive feature points and the difference smaller than the above-described error allowable value is ignored. The color difference component values in the state where the values are smoothed are output and supplied to the color difference component value list 12, and the color difference component values supplied to the color difference component value list 12 are supplied to the vector quantizer 18.

The vector quantizer 18 considers (u, v) of the chrominance component values as a two-dimensional vector based on the distribution of the chrominance component values included in the chrominance component value list in the vector space. The representative vectors are determined by focusing on some of the dense groups of the color difference component values distributed in the space, and the representative vectors are numbered, and the number is given to the multiplexer 13 via the vector code list 19.
And a correspondence table (code book) between the numbers and the component values of the representative vectors is stored in the vector code book 2.
0 is supplied to the multiplexer 13.

A multiplexer 1 in a configuration example on the compression side in a color image compression / expansion apparatus configured by applying the color image compression / expansion method of the present invention shown in FIGS.
3, the feature point address group supplied from the polygon approximate address list 6 and the color difference component value information supplied from the above-described color difference component signal processing system are coded by the encoder 14.
In the encoder 14, the transmission line (or recording medium) 14 is coded as coded data obtained by subjecting the supplied signal to known high-efficiency coding such as Huffman coding. (Or recording) to the receiving side (or reproducing side) via The encoder 14 described above may be configured to have a transmission function, or may be configured such that a transmission unit follows the encoder 14. 1 to 4, reference numeral 15 denotes a transmission path or a recording medium.

Next, a description will be given of a configuration example on the expansion side in a color image compression / expansion apparatus configured by applying the color image compression / expansion method of the present invention shown in FIG. As the decoder 21 in FIG. 4, a decoder configured to have a receiving function may be used, or a configuration in which the decoder 21 is provided with a transmitting unit in front may be used. Is also good. After the encoded data supplied from the transmission path 15 (or the recording medium 15) is decoded by the decoder 21, the luminance component is supplied to the polygon approximate address list 22, and the chrominance component is supplied to the chrominance component value list 25. Supplied to

In the components between the end point address register 23 and the luminance memory 72 described on the left side in FIG. 4, the image signal binarized using different specific luminance thresholds is compressed. The signal processing is performed on the high-efficiency coded signal of the binarized image signal by using a specific luminance threshold among the high-efficiency coded signals.
3 and the end point address register 24, the end point address register 23 and the end point address register 2
4 and the characteristic point addresses are given to the polygon interpolation mask generator 68 as both end point addresses. The polygon interpolation mask generator 68 calculates the address of the linearly interpolated pixel at the two end points given thereto and writes the address value in the multi-port local image memory 67 with the designated luminance.

Next, a new feature point address is supplied from the polygon approximate address list 22, and the new feature point address is stored in the endpoint address register 23, and the endpoint stored in the endpoint address register 23 so far. When the address is moved to the end point address register 24 and stored therein, the polygon interpolation mask generator 68 calculates the address of the linear interpolation pixel of the two end points given thereto, and stores the address value in the multiport address. In the local image memory 67 at the designated luminance. In the polygon interpolation mask generator 68, the polygon approximate address list 22
Each time a new feature point address is supplied from, the above operation is performed, successive new interpolation lines are calculated, and successive addresses are written in the local image memory 67 with the designated luminance.

When the closed curve is completed by the interpolation line, the polygon interpolation mask generator 68 fills the inside of the closed curve in the local image memory 67 with light and dark to generate a mask of a specific luminance level. . In this manner, for each threshold value for obtaining an isoluminance line for each specific luminance value, a bright region having the above-described isoluminance line as a boundary is filled with a bright symbol, and a dark region having the above-mentioned isoluminance line as a boundary. A region can be filled with a dark sign to create a mask with a light and dark binary sign. In the above-described components, the image signal binarized using the specific luminance threshold among the high-efficiency coded signals compressed with respect to the image signal binarized using the different specific luminance threshold is used. Since a plurality of sets of signal processing units for performing signal processing on the high-efficiency coded signal are provided, the signal processing operation performed by each of the above-described signal processing units causes an equal luminance for each specific luminance value different from each other. A plurality of masks as illustrated in FIG. 19 can be generated in which a bright region having a line as a boundary is filled with a bright symbol, and a dark region having a boundary with the isoluminance line is filled with a dark symbol.

After the above operation in the polygon interpolation mask generator 68 is completed, the multi-value determination operator 69 and the skeleton luminance determiner 70 are connected to the local image memory 6 described above.
7 is operated to change the luminance plane to multi-value luminance. That is, as described above, in order to improve the quality of the reproduced image, the luminance value of the interpolation end point is not used as the intermediate value of the simple category as described above in the interpolation reproduction of the luminance value. , The masks are arranged in the order of the magnitude of the luminance value according to the threshold, and the area between adjacent masks is
After filling with an intermediate value of the luminance values based on the threshold values of the two adjacent masks described above, the relationship between the luminance value of each pixel and the luminance values of eight surrounding pixels each having the pixel as a central pixel is as follows: When the brightness value of the surrounding pixels is equal to the brightness value of the center pixel, the brightness value of the center pixel is undecided. (2) When the luminance value of the surrounding pixels is not higher than the luminance value of the central pixel, the luminance value of the central pixel is set to (the intermediate value of luminance values by the threshold values of both adjacent masks-a) (where a is a positive value). Value). (3) When the luminance value of the surrounding pixels is not lower than the luminance value of the central pixel, the luminance value of the central pixel is set to (the intermediate value of luminance values by threshold values of both adjacent masks + a). (4) When the relationship between the luminance value of the surrounding pixels and the luminance value of the center pixel is other than the above-mentioned relationships (1) to (3), the intermediate value between the luminance values by the threshold values of both adjacent masks I do. This is determined according to which of the conditions (1) to (4) is satisfied, so that the quality of the reproduced image can be improved.

In the case of an undefined brightness value area, a center line (skeleton) of the area, that is, a group of points equidistant from the end of the area is extracted, and the brightness value of a pixel on the above-mentioned center line of the area is compared between adjacent masks. The skeleton brightness determiner 70 is set so that the brightness value is set to an intermediate value between the brightness values (see FIGS. 25 to 28).
Operates to write the determined brightness value in the local image memory 67 described above. When the above-described brightness determination operation by the multi-value determination operator 69 and the skeleton brightness determiner 70 is completed, the brightness interpolation plane calculator 71 calculates the brightness value of the undetermined brightness pixel, for example, as shown in FIG. Intermediate level ",
A luminance value having a luminance value relationship such as “intermediate luminance−” or “intermediate luminance +” is determined, or a luminance value of a pixel on the area center line is determined by a threshold value of both adjacent masks. As shown in FIG. 31, the luminance value of the remaining pixel with an undefined luminance value after the intermediate value is set to the known luminance value at both ends of the extension line in the fixed direction of the pixel px with the undefined luminance value. Pixels (p1, p2, or p3,
The luminance value is determined by the primary interpolation method using the luminance value of p4) and the distance (L1, L2 or L3, L4), or the luminance value of the luminance value undetermined pixel is replaced with the luminance value undetermined pixel. Using the luminance value and the distance of the pixel of the known luminance at both ends of the extension line of the straight line in each fixed direction in each of the different directions.
The surface determined by the average value of the luminance values obtained by the following interpolation method, or the luminance value of the remaining luminance value undetermined pixels is determined using three pixels whose luminance values near the luminance value undetermined pixels are known. Determined by interpolation values. The luminance signal expanded by performing the signal processing as described above is stored in the luminance memory 7.
2 is stored. The above-mentioned luminance memory 72 operates so that the two memories alternately repeat the writing operation and the reading operation one after another. The luminance signal read from the luminance memory 72 is supplied to the video signal generator 30.

On the other hand, a chrominance component value list 2 to which chrominance component value data decoded by the decoder 21 is supplied.
5, and a polygon approximate address list 22 as described above.
From the feature point address and chrominance component list 26 to which the coordinate data of the coordinate point sequence of the feature points on the equal luminance line are supplied from
Line generator 27, interpolation calculator 28, color memory 29
In the signal processing unit configured as described above, a line drawing is performed by connecting a series of coordinate points of feature points on an isoluminance line as illustrated in FIG. 9, or as illustrated in FIG. 10. The color difference component value of the pixel at the end point is taken as the color difference component value of each feature point, and the color difference component value of the intermediate pixel between the end points is determined by linear interpolation from both end points, After line drawing and color difference component value setting,
As illustrated in FIG. 11, for a pixel whose color difference component value is unknown, a value of a peripheral pixel obtained by searching for a pixel having a known color difference component value in the horizontal, vertical, and oblique directions is given by:
The color difference component value is determined by performing linear interpolation based on the distance.

That is, the aforementioned color difference component value list 2
5. In the signal processing unit including the feature point address and color difference component list 26, the line generator 27, the interpolation calculator 28, the color memory 29, and the like, the feature point address and the color difference component After the color difference component values on the equi-luminance lines are developed in the color memory 29 by combining the list with the line generator 27, the remaining unknown color difference component values are obtained by interpolation by the interpolation calculator 28. Then, the color difference component is restored in the color memory 29. The above operation is performed for both the color difference components U and V, and the color difference signal expanded by the signal processing is stored in the color memory 29. The above-mentioned color memory 29 operates so that the two memories alternately repeat the write operation and the read operation one after another, and the luminance signal read from the color memory 29 is transmitted to the video signal generator 30. Supplied.

Then, in the video signal generator 30,
Based on the luminance signal supplied from the luminance memory 72 and the color difference signal supplied from the color memory 29, a video signal according to a specific scanning standard television system is generated and supplied to the monitor receiver 31. And a reproduced image is displayed on the display surface of the monitor receiver.

[0075]

As is apparent from the above description, the method for compressing and expanding a color image of the present invention extracts only the characteristic points of the image irrespective of the pixel density of the color image. Obtain compressed image data of image information, and use a method using isoluminance lines that can draw an image on another pixel density surface when decompressing, using the method of using luminance and chrominance components that constitute a color image. The position and luminance value of a feature point that meets a specific condition for an isoluminance line set for each predetermined specific luminance value in a luminance component of
The chrominance component value at the position of the feature point of the luminance component described above is used for transmission, recording, and image restoration, and an allowable value is set for each chrominance component value at each feature point of the isoluminance line. If the chrominance component value at does not exceed the allowable value, the chrominance component value of the feature point is set to the same value as the chrominance component value of the feature point before the feature point, and the occurrence frequency of the chrominance component value is reduced. Therefore, in the color image compression / expansion method of the present invention, the feature points of the luminance component and the color difference component are shared, so that the amount of transmitted information can be reduced, and the image quality due to color shift and the like can be reduced. By replacing the color difference that does not affect the quality of the restored image with the representative value, it is possible to further reduce the color information, so that the color image information can be further reduced. Can be easily .

[Brief description of the drawings]

FIG. 1 is a block diagram on the compression side in a color image compression / expansion apparatus to which the color image compression / expansion method of the present invention is applied.

FIG. 2 is a block diagram on the compression side in a color image compression / expansion apparatus to which the color image compression / expansion method of the present invention is applied.

FIG. 3 is a block diagram on the compression side in a color image compression / expansion apparatus to which the color image compression / expansion method of the present invention is applied.

FIG. 4 is a block diagram of a decompression side in a color image compression / decompression apparatus to which the color image compression / decompression method of the present invention is applied.

FIG. 5 is an explanatory diagram of a luminance component and a color difference component constituting a color image.

FIG. 6 is an explanatory diagram of a feature point on an isoluminance line in a luminance component.

FIG. 7 is an explanatory diagram of a feature point based on a color difference component on an equiluminance line.

FIG. 8 is a diagram for explaining a pixel relationship between a luminance component and a color difference component.

FIG. 9 is an explanatory diagram of line drawing using feature points on the extension side.

FIG. 10 is a diagram used to explain an example of determining a color difference component value of an unknown pixel.

FIG. 11 is a diagram used to explain an example of determining a color difference component value of an unknown pixel.

FIG. 12 is a diagram used to explain a representative value based on a color difference component.

FIG. 13 is a plan view illustrating a binary image to be compressed;

FIG. 14 is a plan view showing an outline of a binary image to be compressed.

FIG. 15 is a plan view showing a state in which the outline of the binary image to be compressed has been moved so as to pass through the pixel center.

FIG. 16 is a plan view for explaining polygon approximation of a binary image to be compressed.

FIG. 17 is a plan view illustrating a pixel distribution of an expanded reproduced binary image.

FIG. 18 is a diagram for explaining masks of luminance values having different threshold values and intermediate levels, high levels, and low levels.

FIG. 19 is a plan view for explaining a mask of luminance values having different threshold values.

FIG. 20 is a distribution diagram of luminance values of each pixel of an image.

FIG. 21 is a plan view used to explain four states defined by the relationship between the luminance value of one pixel in an image and the luminance values of eight pixels surrounding the one pixel.

FIG. 22 is a distribution diagram of luminance values of respective pixels of an image.

FIG. 23 is a diagram used to explain image expansion.

FIG. 24 is a three-dimensional diagram used to explain a specific state determined by the relationship between the luminance value of one pixel in an image and the luminance values of eight pixels surrounding the one pixel.

FIG. 25 is a diagram illustrating a distribution example of luminance values of respective pixels under specific conditions in an image.

FIG. 26 is a diagram illustrating a distribution example of a skeleton in an image.

FIG. 27 is a diagram illustrating a distribution example of luminance values of respective pixels under specific conditions in an image.

FIG. 28 is a diagram illustrating a distribution example of luminance values of respective pixels of a reproduced image in a decompression process.

FIG. 29 is a diagram illustrating a distribution example of luminance values of respective pixels of a reproduced image in a decompression process.

FIG. 30 is a diagram illustrating a distribution example of luminance values of each pixel of an expanded reproduced image.

FIG. 31 is a diagram used to explain an example of determining a luminance value of an unknown pixel.

FIG. 32 is a block diagram of a polygon approximate address list in a signal processing unit on the compression side.

[Explanation of symbols]

1. Image source (signal source of image signal targeted for compression / expansion of color image) 2. Analog-to-digital converter (AD
C) 3, extraction unit for specific luminance level information, 4, 72 luminance memory, 5 equiluminance line tracer, 6 approximate polygon address list, 7, 29 color memory, 8 color difference component value reading interpolator , 10 ... determiner, 9, 12, 17, 25 ... color difference component value list, 11 ... error allowable value setting unit, 13 ... multiplexer, 14 ... encoder, 15 ... transmission path (or recording medium), 16 ... difference Transformer, 18: Vector quantizer, 19: Vector code list, 20: Vector codebook, 21: Decoder, 22: Polygon approximate address list, 23, 24: Endpoint address register, 26: Feature point address and Color difference component list, 27 ... line generator, 2
8 ... Interpolation calculator, 30 ... Video signal generator, 31 ... Monitor receiver, 67 ... Local image memory, 68 ... Polygon interpolation mask generator, 69 ... Multi-value decision operator, 20 ... Skeleton luminance decider, 71 ... Luminance interpolation plane calculator,

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04N 11/00-11/24 G06T 9/00-6/40 H04N 1/41-1/419 H04N 7 / 24-7/68

Claims (5)

(57) [Claims] 1. The method according to claim 1, wherein a position of a feature point that meets a specific condition is set for an equal luminance line set for each predetermined specific luminance value in a luminance component of a luminance component and a color difference component forming a color image. The luminance value is used for transmission, recording, and image restoration. The position of the characteristic point of the color difference component in the color image is set to be the same as the position of the characteristic point of the luminance component, and the color difference component value at that position is transmitted. Compression / expansion method of color image used for recording, image restoration. 2. The method according to claim 1, wherein a position of a feature point that meets a specific condition is set for an isoluminance line set for each predetermined specific luminance value in a luminance component of a luminance component and a color difference component forming a color image. The luminance value is used for transmission, recording, and image restoration. The position of the characteristic point of the color difference component in the color image is set to be the same as the position of the characteristic point of the luminance component, and the color difference component value at that position is transmitted. In the compression / expansion method of a color image used for recording, recording, and image restoration, when an allowable value is set for each color difference component value at each characteristic point of an equiluminance line, and the color difference component value at the characteristic point does not exceed the allowable value. A method for compressing and expanding a color image in which the color difference component value of the feature point is set to the same value as the color difference component value of the feature point before the feature point to reduce the frequency of occurrence of the color difference component value. 3. The method for compressing and expanding a color image according to claim 1, wherein a group of color difference component values obtained by applying a difference method is used. 4. A method for compressing and expanding a color image according to claim 1, wherein a group of color difference component values obtained by applying a logarithmic difference method is used. 5. The method for compressing and expanding a color image according to claim 1, wherein a color difference component value group obtained by applying a vector quantization method is used.