JPS63184475A - Method and apparatus for processing color picture - Google Patents

Abstract

PURPOSE:To improve the color picture reproduction by dividing a picture area depending on lightness, brightness or density data, deciding and coding one color based on a color data so as to select a representative proper color. CONSTITUTION:Color picture data R, G, B from a picture input device 1 are converted by a color converter 2, stored in a buffer memory 3 and processed in the unit of picture blocks. Any one of a mean lightness data, mean brightness data or mean density data of a picture area and any one corresponding to each lightness data, each brightness data or each density data is compared by a color selector 7 to divide the picture area into two groups. The group color is decided by using the mean value of the color data in the group.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a color image processing method and apparatus, and in particular to a method and apparatus for processing a color image, and in particular, a method for processing a color image by encoding an image area including a color edge faithfully and efficiently to the color edge. 2. Description of the Related Art Relating to a color image processing method and apparatus capable of reproducing beautiful color images with a small amount of information [Prior Art] Generally, a color image having halftones has a huge amount of information. For example, an A4 size (297x210mm) color image with a resolution of 16'pe1. When decomposing into three primary color signals RGB and quantizing each pixel with 8 bits, the total amount of data is 297 x 210 x 162 x 8 x 34383.2M.
It becomes a bit, which becomes a huge amount of data. Therefore, recording and transmitting such color image data requires a large capacity image memory or a high-speed transmission device, which poses problems in terms of cost and technology.

Therefore, the present applicant treats an image in units of pixel blocks of mxn pixels, determines whether or not each pixel block includes a color edge, and, for example, for a pixel block that includes a color edge, selects a plurality of The spatial frequency of the color data is reduced by extracting the color data and degenerately encoding it using code data, and smoothing the pixel blocks that do not include color edges, while also significantly degenerating them. A device capable of encoding has already been proposed. In this way, color edge information is not lost, and a beautiful color image can be reproduced.

In such processing, especially when the image area of interest includes a color edge, it is necessary to select chromaticity data of two colors representative of the color edge from the image area using an appropriate method. Also, in a broader sense, selecting a plurality of characteristic colors from an image region of interest is necessary when performing image processing such as image determination and feature extraction.

Several such techniques have already been proposed for black and white image data. For example, there is a method that uses the maximum density value and minimum density value of the image area of interest. However, general color image data is formed based on tristimulus codes R, G, B, which include signals Y, I, Q, etc. used in the color television transmission system. Therefore, unlike conventional black and white image data, which is expressed by one type of signal such as density, brightness, brightness, etc., in color image data, color is simply expressed from the maximum value and minimum value of one type of signal. It is not possible to identify changes in

That is, for example, three signals R and G from a certain image area.

Maximum value of each of B RMAX + GMAX + B M
AX and minimum value RMIN + G MIN + BM
Even if IN is extracted, in reality, the color of that combination (R
MAX + GMAX + BMAX) or (RMIN
, GMIN, BMIN) exist, and it is even less certain that these two colors are the two colors that constitute the color edge of the image area. Therefore, conventional techniques for black and white image data cannot simply be applied to color image data.

[Problems to be Solved by the Invention] The present invention has been made in view of the problems of the prior art described above, and its purpose is to create a color that is representative of the image area of interest. Therefore, it is possible to select two colors that are particularly representative of color edges, and by degenerating these two colors, effective compression of color image data is possible, and color image data can be reproduced with good quality. An object of the present invention is to provide a processing method and an apparatus for the same.

[Means for Solving the Problems] In order to achieve the above object, the color image encoding method of the present invention divides the image region of interest into a plurality of groups based on brightness data, luminance data, or density data. a color determining step of determining one color for each group divided by the dividing step based on color data; and a color determining step of determining one color for each group divided by the dividing step, and determining a plurality of colors determined in the color determining step as a representative of the image area of interest. The outline thereof is to include an encoding step of encoding as a color.

Further, in order to achieve the above object, the color image encoding device of the present invention includes a dividing means for dividing an image area of interest into a plurality of groups based on brightness data, luminance data, or density data, and color determining means for determining one color for each divided group based on color data; and encoding means for encoding the plurality of colors determined by the color determining means as representative colors of the image area of interest. The outline is to prepare.

Preferably, the dividing means divides any one of average brightness data, average brightness data, or average density data of the image area of interest into a corresponding one of each brightness data, each brightness data, or each density data of the image area of interest. One aspect of this is to divide the image area of interest into two groups by comparing either of them.

Preferably, one aspect of the color determining means is to determine the color of the group based on the average value of color data within the group.

[Operation] In this configuration, the dividing means divides the image area of interest into a plurality of groups based on brightness data, brightness data, or density data. And preferably, the dividing means is
By comparing any one of the average brightness data, average brightness data, or average density data of the image area of interest with the corresponding one of each brightness data, each brightness data, or each density data of the image area of interest, The image area of interest is divided into two groups. The color determining means determines one color for each group divided by the dividing means based on the color data. Preferably, the color determining means determines the color of the group based on the average value of color data within the group. Then, the encoding means encodes the plurality of colors determined by the color determining means as representative colors of the image area of interest.

[Description of Embodiments] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram of a color image processing apparatus according to an embodiment of the present invention. This embodiment shows the encoding process until the color image data read from the image data system is written to the image data memory, and the decoding process when the color code data is read from the image data memory and reproduced and recorded. .

The following configuration forms the reader section of the color image processing apparatus of the embodiment. In Figure 1, 1 is an image-powered device that reads a color image of a document and outputs color image data R, G, and B in three primary colors, and 2 is a human-powered image device that outputs image data R, G, and B in a perceptually uniform color space. For example, CIE197
6(L”.

am, b*) three-dimensional color signal data L based on the color space
3 is a buffer memory that temporarily stores color signal data L''J+a''lj+b''IJ for a plurality of pixels (for example, one pixel block of mxn pixels); 4 is a color edge block determination device that determines whether a pixel block includes a visual color edge (for example, a color edge including hue difference, brightness difference, and saturation difference);
Reference numeral 5 denotes an encoder that performs degeneracy encoding in a form that includes brightness (brightness index) data L"IJ representative of the brightness of one pixel block, as well as average brightness information of the one pixel block, and 6 denotes a one pixel block. Chromaticity data a″IJ, b″1 in
A block smoother 7 smoothes two sets of chromaticity data (a) suitable to represent the color edges of one pixel block based on each chromaticity data a ``lJ, b'' IJ in one pixel block. “l+ b ”+) and (”2+b′
2), an encoder 8 degenerately encodes the smoothed chromaticity data i", τ' output from the block smoother 6;
9 is the chromaticity data from the color selector 7 (a "1. b"
t) and (a"2. b""2), respectively, and an encoder 10 degenerates code data Cabl from the encoder 8 according to the logic 110 level of the color edge flag EFLG from the color edge block determiner 4. A selector 11 selects either the code data Cab2 from the encoder 9, the lightness code data CL' from the encoder 5, or one of the chromaticity code data Cab'l or Cab2 from the encoder 8 or 9. 12' is an image memory that stores the encoded image data C of the entire color image; be.

The following configuration forms the printer section of the color image processing apparatus of the embodiment. In other words, 13 is a buffer memory that reads the encoded image data C from the image memory 14 and temporarily stores it, and 14 is the brightness data L''+ representing one pixel block from the brightness code data CL, and the average brightness data of one pixel block. A decoder 15 decodes the decoded brightness data L''I・ into L3 as average brightness data L of one pixel block.
3 is a comparator for binarization, 16 is chromaticity code data Cab
A decoder 17 decodes the chromaticity code data Cab into two sets of chromaticity data (a''1.b''l) and ('a ''21 b
2) A decoder 18 decodes which of the two decoded sets of chromaticity data of one pixel block a''th, b''lJ
19 is a selector that selects the decoded chromaticity data according to the logic 110 level of the color edge judgment output signal EFLG; 20 is the brightness data for one pixel block, the first eye and the chromaticity; Data a'1. and b'1. 21 is a color converter for inversely converting color image data into R, G, B, and 22 is a color image output device for forming a reproduced color image.

Note that in the above description, the configurations of the color converter 2.21 and the buffer memory 3.20 largely depend on the type of the image input device 1 and the type of the image output device 22, so the configurations are not uniform.

In this configuration, the three primary color image data R, G, B read by the image input device 1 is converted by the color converter 2 into three-dimensional color signal data L″, a′, b″.

The conversion method is as follows.

If Ro, Go, and Bo are reference white image data, image data X conforming to the CIE XYZ display system is
o, Yo, and Zo are obtained as follows.

Furthermore, if R, G, and B are image data from the image human-powered device 1, image data x conforming to the CIE XYZ display system,
y and z are calculated as follows. However, in the above, [H] is a conversion matrix to the XYZ display system.

Also, from this, CIE three-dimensional color signal data L", a"
, b" is L"-116(y/yo)l/3 1Ba"-500
((X/Xo)"3(Y/Yo)"3]b" -20
0[(Y/Ya) '' (Z/Zo) ''3 However, Y/YO>0.008851+L" : Image data representing brightness a", b" 1 It is determined by image data representing chromaticity.

Generally, the three primary color image data R, G, and B from the image input device 1 often have a meaning specific to the device. Therefore, the above conversion matrix [8] is a matrix for converting into image data conforming to the CIE XYZ color system, taking into account such device-specific characteristics. In particular, if the three primary color image data R, G, and B are data based on the CIE r, g, b color system, it is easy to determine the transformation matrix [H]. However, in any case, the color converter 2 of the apparatus of this embodiment has, for example, one or more LO
Since it can be configured with OK UP TABLE, the above conversion relationship, that is, L" = f+ (R, G, B) a" = f2 (R, G, B) b", = f3 (R, G, B) can be easily related to the ROM table address manual and data relationship.

In this way, the tertiary light color signal data L'', *, bg sequentially converted pixel by pixel is stored in the buffer memory 3, and is then sequentially processed in pixel blocks of nXm (for example, 4 x 4) pixels. Incidentally, the buffer memory 3 has, for example, a two-stage structure in order to perform the writing operation of new image data and the reading operation of already stored image data at the same time.

Brightness data L'th (i, j = 1.2, 3.4)
is degenerately encoded by the encoder 5 and converted into code data CL, which is a code representative of the brightness data of one pixel block and also includes the average brightness information of one pixel block, and is stored in the buffer memory. 11.

Note that the internal configuration of the encoder 5 is not the main focus of the present invention, so a description thereof will be omitted.

Regarding the chromaticity data a''j, 1.b''IJ, the following color flattening processing and color edge processing are performed simultaneously. In the color flattening process, the block smoother 6 converts the chromaticity data "lJ+b"1. smooth.

Then, the encoder 8 encodes the smoothed chromaticity data i'', ■'' into C, b, according to Cabl °f, (a'', b''). This encoder 9 can also be configured with one or more LOGs and UP TABLEs that give the above relationship.

On the other hand, in color edge processing, the color selector 7 selects two sets of chromaticity data (a ``l + b
"+) and (a"2. b"2) in the following method l
Select with

(STEP 1) Find the average brightness τ' of one pixel block from the first brightness datum.

(STEP 2) Pixels are divided into groups based on the average brightness τ". In other words, the pixels are grouped according to the average brightness τ".
p 2 L is a pixel called "eye-catching stone".

In addition, if such grouping is not possible, for example,
When all pixel data satisfy L"IJ"L", the color flatness flag HFLG is set to logic "°1°".

(STEP 3) Chromaticity data a″i for each group
J+b'6. Find the average value. That is, (a"1. b"+): group 1 (7) average value (i"2. b"2): mean value of group 2 (STEP 4) Each set of average values obtained (i"1. τ″
2).

(M ” 2 + τ52) by the color edge block judger 4
is output to the encoder 9. In the encoder 9, Cabl = f E (a“l+ b“l+ 8・
2+b・, ). This encoder 9 also
Average value am (a”+, 1)”l+ 8”2+ b
2) It can be composed of one or more LOOK UPTABLEs that provide a relationship with the target code Cab2.

The color edge block judger 4 calculates the average chromaticity data (a+18.b''1) and (M''2) of each group manually.
*τ"2), the color edge judgment amount ΔE'ab is calculated as ΔE ab='1/2 ・(l Δa"l+l
ΔB"l) However, the value of ΔEab calculated according to ΔB" - a"l a"2 Δb" = b'"l b"2 is compared with the threshold value set in advance. If ΔEab≧, the pixel block is determined to be a color edge block and the color edge flag EFLG is set; if ΔEab<k, it is determined not to be a color edge block and the color edge flag EFL is set.
Reset G.

However, if the color flatness flag HFLG from the color selector 7 is set, the color edge flag EFLG is reset regardless of the above determination. Reverse color flat flag HFLG
When is in the reset state, the above judgment is followed. thus,
The color edge flag EFLG output from the color edge block determiner 4 is manually input to the selector 10 and the buffer memory 11.

When the color edge flag EFLG is set, the selector 10 selects the chromaticity code Cab2 created by the color edge processing and outputs it to the buffer memory 11 as chromaticity code data Cab of one pixel block. Conversely, when the color edge flag EFLG is in a reset state, the chromaticity data code Cabl created by the color flattening process is selected and stored in the buffer memory 11 as the chromaticity code data Cab of one pixel block.
Output to. Buffer memory 11 contains brightness coat data C
L, chromaticity code data Cab, and color edge flag EF
Temporarily memorize LG and synchronize these data,
As a single encoded image data C, the image memory 1
2 is stored. By repeating the above operations for each pixel block, all image data is degenerately encoded and stored in the image memory 12.

Next, the operation of reading encoded image data C from the image memory 12, decoding it, and outputting a reproduced image will be described. The coat data C read out from the image memory 12 is temporarily stored in the buffer memory 13. The decoder 14 decodes the brightness code data C1 of the coat data C in the buffer memory 13 to form the brightness data LIJ and the brightness average value L1, of which the brightness data L"iJ is stored in the buffer memory 20, In addition, the brightness data L″
1. and the brightness average value L'' are manually input to the comparator 15.

Furthermore, color edge decoding processing and color flatness decoding processing are performed in parallel on the chromaticity code data Cab of the code data C in the buffer memory 13. As color flat decoding processing, the decoder 16 performs 11'H: f 8+1 (Cab
) b'H= f ob (Cab) and inputs the chromaticity data am, , bmll to the selector 19. This decoder 16 also uses code data Cab.
One or more LOOK UPs that give the relationship f□ and fHb between and the chromaticity data a″0.b″□
It can be configured with TABLE.

In addition, as a color edge decoding process, the decoder 17 performs a ``+= f Eat (Cab) b''+= f
Eb+ (Cab) a “2= f E112 (Cab) b”2= f
cb2(Cab) and outputs the chromaticity data alt, ~bM2 to the color determiner 18. This decoder 17 also uses code data Ca.
fEal~f between b and chromaticity data am,~bm2
One or more LOs that give the relationship Eb2
It can be configured with OK UP TABLE.

The color determiner 18 determines the brightness L″ of each pixel by the comparator 15.
Based on the comparison result between IJ and the average brightness L'' of the pixel block, the chromaticity data of one pixel block (a''2. b
"Choose one of 2).

Here, (a”l+ b”+): L”lJ ≧L
4(a"2.b"2): L"+ <L" is set in advance, but the reverse setting is also possible. Chromaticity data determined in this way (a”a+b
”.) is output to the selector 19.

The selector 19 selects the chromaticity data (a''□, b''H) from the decoder 16 and the chromaticity data (a''11. b Select one set of ``a'' and calculate the decoded chromaticity data of each pixel (a''+, +
, b''+j) to the buffer memory 20.

If the color edge flag EFLG is set (a”ll+
Select b”a), and if EFLG is in the reset state, select (a).
″□, b″□).

The chromaticity data thus determined (a″lJ+b″IJ) is
The signal is output to the buffer memory 20 and stored therein. The buffer memory 20 receives the brightness data L1° from the decoder 14,
The chromaticity data from the selector 19 is set to 1
By storing the data in units of pixel blocks, synchronization timing is determined and output to the color converter 21.

Color converter 21 is an LO that performs the inverse relationship of color converter 2.
It consists of OK IIP TABLE, and their relationship is shown below.

R=f+ (L", a", b") G=f2 (
L", a", b") B=f3 (L', a"
, b”) In this way, the color signals R, G, B
is output to the image output device 22. A color image is then formed by performing the above decoding process on the entire image area.

FIG. 2 is a block diagram showing details of the color selector 7. As shown in FIG. In the figure, 30 is the average brightness τ″ within one pixel block
31 is a comparator that compares the average brightness stone with the brightness L'' of each pixel; 32.33 is a selector that controls the flow of chromaticity data a'' and b''1 degrees; 34
is a counter that counts the output pulse signal PLS of the comparator 31, 35 to 38 are accumulators, and 39 to 42 are accumulators 35
The cumulative output of ~38 is the output of counter 34 CNT 1 or C
Dividers 43 to 49 for dividing by NT2 are latch circuits.

As described above, the brightness data L"1j of each pixel of the one-pixel pro-ref is read out from the buffer memory 3, and the average brightness data τ" is obtained by the block smoother 30. The comparator 31 holds the average brightness data τ'', and again sequentially reads out the brightness data L''IJ of each pixel from the buffer memory 3, and the comparator 31 compares the average brightness data τ' with the brightness data L''1. , if L'IJ≧τ1, group 1
The output signal PLS (one-shot pulse signal) is output to the counter 34, selectors 32 and 33.
Output to. Furthermore, if j<L", a non-active (LOW) state is output. The counter 34 uses the signal PL
The number of S is counted and its coefficient value is output as CNT1, and the value obtained by subtracting CNT1 from the number of pixels in one pixel block, 16, is outputted as CNT2. Here, if CN
If T1=16, the color flatness flag HFLG is set, indicating that the pixel block cannot be grouped by the above method.

On the other hand, the chromaticity data a″l of each pixel is transferred from the buffer memory 3.
j, t)i, are sequentially read out and held in the latches 43 and 44, and the selectors 32 and 33 are driven by the output signal P L S from the comparator 31 in synchronization with the processing of the L''th brightness data. and chromaticity data a″iJ+ b
″Control the flow of the eyes.

Here, if there is a one-shot pulse as the output signal PLS (that is, if it is determined to be group 1), the selectors 32 and 33 are connected to the S1 side, and the chromaticity data a++, .
b"I, 1 is output to the accumulator 35.37. Conversely, if the output signal PLS is LOW (that is, group 2
), the selectors 32 and 33 are connected to the S2 side, and the chromaticity data a'' is selected.

b″II is output to the accumulator 36.38.

The accumulators 35 to 38 receive the output chromaticity data a"lJ
, the sum of each group in one pixel block of b″Ij s″a, s″a2 + S ″Thl + S″
Find b2.

FIG. 3 shows details of the accumulator, which consists of an adder 50, a counter 51, and a latch circuit 52. Sum output S″al + S″82°8″bl +
S''b2 is output to the dividers 39 to 42, of which S''
'3□, S''b1 is divided by CNTl, and the quotient is the chromaticity data a''1. b “1” is held in the latch circuits 46 and 48. Also, S ′a2 = S ”b2 is CN
It is divided by T2, and the quotient is held in the latch circuits 47 and 49 as a″2.b′2.

Incidentally, the dividers 39 to 42 are composed of ROMs that use the sum and count values as addresses.

FIG. 4 shows an encoder 8 for chromaticity data (a'', b'') including a selector 10, and an encoder 8 for chromaticity data (''l+
b'+), ('', 2+ a'2) is a block configuration diagram showing details of the encoder 9. In the figure, 60 to 6
3 is a code conversion ROM, 64 and 65 are latch circuits, and 66 is an inverter circuit. Here, we will consider handling chromaticity data as 8 bits each, a total of 16 bits, and encoding it into a 10-bit chromaticity code Cab. Therefore, ROMs 60 to 63 are configured to output 8-bit data using a 16-bit address manually, and the ROMs 60 to 63 are configured to output 8-bit data using a 16-bit address.
2 bit (64 byte) ROM can be used. Also, commercially available TTL 8-bit latch circuits can be used as the latch circuits 64 and 65.

Next, the operation will be explained. Color edge block judger 4
If the output flag EFLG from is in the active state (determined to be a color edge block), ROM 62.63 is enabled and ROM 60.61 is disabled. At this time, when the read signal READ/ (/ indicates negative logic) becomes active, the chromaticity code data Cab2 for the color edge is read out from the ROM 62.63, and is held in the latch circuit 64.65 by the latch clock signal CLK2. Ru. Conversely, the output flag E from the color edge block determiner 4
If FLG is in a non-active state (determined to be a color plain pixel block), ROM60.61 is enabled and the ROM
62.63 is disabled. At this time, the read signal R
When EAD/ becomes active, the chromaticity code data Cabl for color flatness is read out from the ROM 60.61 and held in the latch circuits 64 and 65 by the latch clock I8 CLK2.

In the above embodiment, each image area of interest is 4×4.
Although the target pixel block is not limited to this.

However, considering the circuit scale, the number of bits of image data or code data, etc., it seems better to use 4) 24 pixel blocks.

Furthermore, the color data is not limited to L'', a'', b'' based on the uniform color space of 1976 CIE'L''a''b'', but also color data based on the uniform color space of 1976 CIE L'''u''v''. It is also possible to use LL", u", v". Furthermore, a YIQ signal in the color television transmission system (NTSC system) may be used.

In that case, Y can be used instead of L10, and I and Q can be used instead of a'' and b''.

Furthermore, although only the chromaticity data (a'', b'') was treated as the average value of the color data of each group, it is also possible to use the lightness data L1.

[Effects] As explained above, according to the present invention, it is possible to select an accurate representative color for each image area of interest, and by encoding this representative color, effective compression of color image data is possible. This makes it possible to reproduce color images with good image quality.

[Brief explanation of the drawing]

FIG. 1 is a block configuration diagram of a color image processing device according to an embodiment of the present invention, FIG. 2 is a block configuration diagram showing details of a color selector 7, FIG. 3 is a block configuration diagram showing details of an accumulator, FIG. 4 shows the data including the selector 10 and the degree data (i",
τ″) encoder 8 and the chromaticity data (a ″In b ″)
+), (a ``2.a ''2) is a block configuration diagram showing details of the encoder 9. In the figure, 1... Image input device, 2... Color converter, 3.20... Buffer memory, 4... Color edge block determiner, 5... Encoder, 6... Block smoother, 7
...Color selector, 8...Encoder, 9...Encoder, 1
0...Selector, 11.13...Buffer memory,
12... Image-mori, 14... Decoder, 15...
Comparator, 16... Decoder, 17... Decoder, 18.
. . . color determiner, 19 . . . selector, 21 . . . color converter, 22 . . . image output device+.

Claims (4)

[Claims] (1) In a color image processing method that processes a color image based on three primary color signals, a dividing step of dividing an image area of interest into a plurality of groups based on brightness data, luminance data, or density data, and A color determining step of determining one color for each divided group based on color data, and an encoding step of encoding the plurality of colors determined in the color determining step as representative colors of the image area of interest. A color image processing method comprising: (2) In a color image processing device that processes a color image based on three primary color signals, a dividing means divides an image area of interest into a plurality of groups based on brightness data, luminance data, or density data; color determining means for determining one color for each divided group based on color data; and encoding means for encoding the plurality of colors determined by the color determining means as representative colors of the image area of interest. A color image processing device comprising: (3) The dividing means uses any one of average brightness data, average brightness data, or average density data of the image area of interest;
Claim 1, characterized in that the image area of interest is divided into two groups by comparing corresponding one of each brightness data, each luminance data, or each density data of the image area of interest. 2. The color image processing device according to item 2. (4) The color image processing device according to claim 2, wherein the color determining means determines the color of the group based on an average value of color data within the group.