JPS63196173A - Method and device for processing color image - Google Patents

Abstract

PURPOSE:To efficiently perform the encoding and decoding of a picture data, by deciding whether a remarked image area is the graphic image area or the dot image area of a character, etc., by an image decision means, and deciding whether a picture element block includes a color edge or not based on a bit of chromaticity information by a color edge decision means. CONSTITUTION:Original chrominance signal data L*, a*, and b* are stored in a buffer memory 3, and are processed with the picture element block unit of a picture element of (nXm) (for example, 4X4) sequentially. An image area decision apparatus 5 decides whether the said picture element block is a part belonging to a character area or not by checking the property, etc., (for example, the property of two color forming tendency or pattern forming tendency, etc., of a character image) of the chrominance signal data L*, a*, and b*. If it is the part constituting the character area, the decision apparatus 5 sets a decision output signal MFLG at a logic (1), and if it is not the part constituting the character area, sets the decision output signal MFLG at a logic (0). An AND gate 21 discriminates a condition that the said one picture element block includes the color edge and constitutes the character image area, and when the decision of the said condition is satisfied, 1 dicision output signal FLG is set at the logic (1).

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a color image processing method and apparatus, and particularly to a color image processing method that efficiently encodes and decodes color image data associated with transmission and recording of color images. The present invention relates to an image processing method and apparatus.

[Prior Art] Generally, a color image having halftones has a huge amount of information. For example, if an A4 size (297 x 210 mm) color image is decomposed into three primary color signals RGB with a resolution of 16 pels and quantized with 8 bits per pixel, the total amount of data will be 297 x 210 x 16" x 8 x 34383.2 Mbits, which is a huge amount of data. Therefore, recording and transmitting such color image data requires a large capacity memory and a high-speed transmission device, which poses problems in terms of cost and technology.

Therefore, in order to enable efficient data compression of color image data taking visual characteristics into consideration, the applicant has
For each block of n pixels, it is determined whether the block contains a color edge or not, and for a block determined to contain a color edge, multiple sets of chromaticity data are provided within a range less than the number of m×n pixels. Select and encode the block, and at the time of decoding, allocate multiple sets of chromaticity data decoded for all pixels in the block to the block area, while,
For a block determined not to contain a color edge, one set of chromaticity data is selected and the block is encoded;
An image information processing apparatus has already been proposed that provides a set of decoded chromaticity data for all pixels in a block during decoding. When such image encoding/decoding processing is performed on input color image data such as color text, color photographs, or color halftone printed images, the color and color edges of the color text and color photographs are removed. Good reproduction with little visual deterioration; however, for color halftone printed images, there may be isolated areas with poor color reproducibility,
Alternatively, areas with poor color reproducibility periodically occurred, resulting in noticeable visual deterioration.

[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 efficiently encode and decode even color halftone printed images. It is an object of the present invention to provide a color image processing method and apparatus that can reproduce color images visually and visually.

[Means for Solving the Problems] In order to achieve the above object, the color image processing method of the present invention includes a dividing step of dividing color image data into pixel blocks of m×n pixels, and a dividing step of dividing color image data into pixel blocks of m×n pixels; A conversion step of converting the image into brightness data, density data, or brightness data representing the brightness and chromaticity information representing the hue data and color of the saturation data, and the image area of interest is a line drawing image area such as text, or an image area determination step of determining whether the pixel block is a halftone image area; a color edge determination step of determining whether the pixel block includes a color edge based on the chromaticity information; and a color edge determination step of determining whether the pixel block includes a color edge based on the chromaticity information. a first color determining step of determining a set of chromaticity information whose number is smaller than the number of m×n pixels for a pixel block that includes the image area and is determined to be a diagram image area in the image area determining step; a first encoding step of encoding a set of chromaticity information determined in the first color determining step; and a pixel block determined not to contain a color edge in the color edge determining step or the image area determining step. A second color determination step of determining one set of chromaticity information for a pixel block determined to be a halftone image area, and encoding one set of chromaticity information determined in the second color determination step. The outline thereof is to include a second encoding step.

Preferably, the method further includes a first decoding step of decoding the chromaticity information encoded in the first encoding step;
One aspect thereof is to include a first color allocation step in which a plurality of sets of chromaticity information decoded in the decoding step are allocated to each pixel in a pixel block.

Preferably, the method further includes a second decoding step of decoding the chromaticity information encoded in the second encoding step;
One aspect thereof is to include a second color allocation step of allocating the set of chromaticity information decoded in the decoding step to all pixels in the pixel block.

Preferably, in the second color determination step, for the pixel block determined not to include a color edge in the color edge determination step or the pixel block determined to be a halftone image area in the image area determination step, One aspect of this is to determine a set of chromaticity information based on each average value of chromaticity information of all pixels of the pixel block.

Further, in order to achieve the above object, the color image processing device of the present invention includes a dividing means for dividing color image data into pixel blocks of m×n pixels; or converting means for converting luminance data into brightness information representing the brightness and hue data and chroma data representing the color, and determining whether the image area of interest is a line drawing image area such as characters or a halftone image area. image area determining means for determining whether or not the pixel block includes a color edge based on the chromaticity information; a first color determining means for determining a set of chromaticity information smaller than the number of m×n pixels for a pixel block determined to be a diagram image area by the means; and the first color determining means a first encoding means for encoding the set of chromaticity information determined by the pixel block determined as not containing a color edge by the color edge determination means or determined to be a halftone image area by the image area determination means; a second color determining means that determines a set of chromaticity information for the pixel block that has been determined, and a second encoding that encodes the set of chromaticity information determined by the second color determining means. The outline is to provide the means.

Preferably, the first decoding means further includes a first decoding means for decoding the chromaticity information encoded by the first encoding means;
One aspect thereof is to include a first color allocation means for allocating a plurality of sets of chromaticity information decoded by the decoding means to each pixel in a pixel block.

Preferably, the second decoding means further includes a second decoding means for decoding the chromaticity information encoded by the second encoding means;
One aspect thereof is to include a second color allocation means for allocating a set of chromaticity information decoded by the decoding means to all pixels in a pixel block.

[Operation] In this configuration, the dividing means divides the color image data into m
Divide into pixel blocks of ×n pixels. The conversion means converts the color image data into brightness data, density data, or brightness data representing brightness, and chromaticity information representing color, hue data and saturation data. Furthermore, the image area determination means determines whether the image area of interest is a line image area such as characters or a halftone image area. The color edge determining means determines whether the pixel block includes a color edge based on the chromaticity information. If the color edge determining means includes a color edge and the image area determining means determines that the area is a diagram image area, the first color determining means determines that the pixel block has a color edge, and the image area determining means determines that the pixel block contains a color edge. The first encoding means encodes the set of chromaticity information determined by the first color determination means. Further, for a pixel block determined by the color edge determination means to not contain a color edge or for a pixel block determined to be a halftone image area by the image area determination means, the second color determination means Chromaticity information is determined, and the second encoding means encodes the set of chromaticity information determined by the second color determining means.

Preferably, the first decoding means further decodes the chromaticity information encoded by the first encoding means, and the first color allocation means further decodes the chromaticity information encoded by the first encoding means. A plurality of sets of chromaticity information are assigned to each pixel within the pixel block.

Preferably, the second decoding means further decodes the chromaticity information encoded by the second encoding means, and the second color allocation means further decodes the chromaticity information encoded by the second encoding means. A set of chromaticity information is assigned to all pixels within the pixel block.

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

The figure is a block diagram of a color image processing device according to an embodiment of the present invention. This embodiment shows the encoding process when writing read color image data into the image data memory 12 and the decoding process when reading and recording color code data from the image data memory 12.

First, the following configuration forms the reader portion of the color image processing apparatus of this embodiment. In the figure, 1 reads the color image of the original, and the three primary color image data R,
A color image input device 2 outputs three primary color image data R, G, and B from the color image input device 1 in a perceptually uniform color space, for example, CIE1976 (
L”.

a", b") three-dimensional color signal data L based on the color space
3 is a buffer memory that temporarily stores each color signal data L"IJ+a"IJ, b"IJ for a plurality of pixels (for example, one pixel block of m×n). , 4 indicates the visual color edge of the pixel block (color edge including hue difference, brightness difference, and saturation difference)
5 is an image area determiner that determines whether a character area or a halftone dot area is included; 6 is a color edge block determiner that determines whether or not a pixel block contains a color edge block; 7 is an encoder that performs degenerate coding including average brightness information of one pixel block; 7 is a block smoother that smoothes the chromaticity data a"IJ, b"IJ in the one pixel block; 8
is each chromaticity data a″th, b″i in the corresponding one pixel block
Based on J, two sets of chromaticity data (a ``In b ''l) and (
a′2+b ”2); 9 is the smoothed chromaticity data i” output from the block smoother 7; an encoder degenerately encodes the τ′; a″b degenerately encodes the chromaticity data (a″1.b″1) and (aゝ2.b″2), respectively;

The encoder 11 is an AND gate 12 that satisfies a predetermined condition.
Code data Cabl from encoder 9 and code data Cab2 from encoder 10 according to the logic 110 level from
A selector 13 selects the brightness code data C5 from the encoder 6, the chromaticity code data Cabl or C5b2 from the encoder 9 or 10, and the condition judgment from the AND gate 12. A buffer memory 14 temporarily stores the output signal FLG, and an image data memory 14 stores the encoded image data C of the entire color image.

The image area judger 5 is based on the brightness data L"lJ and the chromaticity data a4□j, b"IJ, and its judgment is based on frequency analysis of the image area, autocorrelation function, pixel continuity, and pixel block continuity. , based on color distribution, etc.

Further, the following configuration forms the printer portion of the color image processing apparatus of this embodiment. That is, 15 is a buffer memory for reading the encoded image data C from the image data memory 14 and temporarily storing it, and 16 is the brightness data L"1j representing one pixel block from the brightness code data CL and the block average brightness data L. L′ decoder, 17
is the brightness data L "IJ" is the block average brightness data L8
18 is a decoder that decodes the chromaticity code data Cab into chromaticity data a'' and b'; 19 is a decoder that decodes the chromaticity code data Cab into two sets of chromaticity data (a IIl .

A decoder 20 decodes the two sets of decoded chromaticity data (am□, bl.

) and (a ``2+ b ``t) to determine which of the chromaticity data a''IJ and b1 of one pixel block is selected, and 21 outputs the decoded chromaticity data as a condition determination output signal. A color determiner selects according to the logic 110 level of FLG, and 22 is brightness data L for one pixel block.
IJ and chromaticity data a ``IJ and b'' Buffer memory provided to take the timing when IJ comes out, 23 is three-dimensional color signal data L''IJ ha ``IJsb'' IJ
The three primary color image data R, G.

A color converter 24 performs inverse conversion to B, and a color image output device 24 forms a reproduced color image.

In the above description, the configurations of the color converter 2, 23 and the buffer memory 3, 220 largely depend on the type of the image input device 10 and the type of the image output device 24, and thus their configurations are not uniform.

In this configuration, the color image data of three primary colors 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, then C
Image data Xo, Yo, Z based on IE's XYZ display system
o can be found as follows.

Furthermore, if R, G, and B are image data from the image input device 1, then image data X, which conforms to CIH's 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, CIH three-dimensional color signal data L", a"
,b" is L'"-118(Y/Yo)""-16a"-50
0[(X/XO)"'-(Y/YO)"' ]b ”
= 200 [(Y/Yo)”3- (Z/Zo)””
] However, Y/Yo> 0.008856 L゛: Image representing brightness, data a'', b'' Image data representing dichromaticity.

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 [H] is a matrix for converting into image data conforming to CIE's X72 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
OK LIP TABLE, so the above conversion relationship is The relationship can be easily established by the relationship between the address input of the ROM table and the data.

In this way, the three-dimensional color signal data L II , am , bm that has been sequentially converted pixel by pixel is stored in the buffer memory 3, and is then sequentially processed in units of pixel blocks of nxm (for example, 4x4) pixels. Ru. Note that the buffer memory 3 has, for example, a two-stage configuration in order to simultaneously perform the writing operation of new image data and the reading operation of already stored image data.

Lightness data L″, (i, j 21, 2, 3.4
) is degenerately encoded by the encoder 6, and is converted into code data CL that is a code representative of the brightness data of one pixel block and also includes the average brightness information of one pixel block. It is stored in the memory 13. Note that the internal configuration of the encoder 6 is not the main focus of the present invention, so a description thereof will be omitted.

The chromaticity data a″lJ and b″IJ are encoded using different paths depending on whether the 1-pixel block contains a visual color edge and whether the image area to which the 1-pixel block belongs is a character area. It is done. That is, the color edge block determiner 4 determines the presence or absence of a color edge in the one pixel block using the method described later, and if a color edge is included, the determiner 4 sets the determination output signal EFLG to logic "1". set, and if the color edge is not included, the judgment output signal EFL
Reset G to logic "0". Further, the image area determiner 5
Properties of color signal data L II, am, bg, etc. (
For example, it is determined whether or not the one pixel block belongs to the character image area by examining the properties of the character image, such as its tendency to become two-color and its tendency to form a pattern. If the part constitutes a character image area, the determiner 5 sets the determination output signal MFLG to logic "1", and if it does not constitute the character image area, the determiner 5 sets the determination output signal MFLG to logic "1".
0".The AND gate 12 determines the condition that the one pixel block contains a color edge and is part of a character image area, and when the condition is satisfied, outputs a determination output signal FLG. This determination output signal FLG is stored in the buffer memory 13 and is also input to the selector 11 as a control signal.

Regarding the input chromaticity data a″lJ+1)″iJ, the following color edge processing and color edge processing are simultaneously processed in parallel. In the color edge processing, the block smoother 7 smoothes the chromaticity data a ``1, 1. b '' IJ according to the following.

Then, the encoder 9 encodes the smoothed chromaticity data a'', b8 into Cab+ according to Cab+ = fw (a'', b''). This encoder 9 also encodes one or It can be composed of two or more LOOK UP TABLEs.

On the other hand, in color edge processing, the color selector 8 selects two sets of chromaticity data (a'', ,b''I
) and (a"2. b"2) are selected in the following manner.

(STEP 1) Use the brightness data and calculate the average brightness L of one pixel block starting from the 8th pixel.

(STEP 2) Group pixels according to the average brightness. In other words, group I L "pixel gro with IJ≧τ1"
up 2 L"lJ <L".

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

(STEP 3) Chromaticity data a ” for each group
I.J.

Find the average value of b″ij. That is, (a″,, b″+): group 1 (7) Average value (a ″2. b ″2): group 2 c
7) Average value (STEP 4) Set of each average value obtained (a
"H,b"2).

(a"2.b"2) is output to the color edge pixel block determiner 4 and encoder 9. In encoder 10, Cab2=f6
(a”+, bZ+ a”2+ b”□). This encoder 10 also encodes according to the set of average values (a”+, b
"+, a"2. b”2) To mark + Cabz To (D
UP to one or more t, 00 that gives a relationship
It can be configured with TABLE.

The color edge block determiner 4 receives the input average chromaticity data of each group (a"l+b"1) and (a"2.
b'2), the color edge judgment amount ΔEab is calculated as A E ab” 1/2 ・(IΔa′l+lΔb
"l) However, ΔaII = a II , -a II2Δ
b" = b"l - b'"2, and compare the obtained value of ΔEab with a preset threshold value, and if ΔEab≧, the pixel block is designated as a color edge. It is determined that it is a pixel block and the color edge flag EFLG is set, and if ΔEab<k, it is determined that it is not a color edge pixel block and the color edge flag EFLG is reset.

However, if the color flatness flag HFLG from the color selector 8 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 output to the AND gate 12. In this way, the buffer image data 13 temporarily stores the brightness code data Ct, the chromaticity code data Cab, and the discrimination flag FLG, synchronizes these data, and outputs them as a single encoded image data C. The image is stored in the image memory 14.

By repeating the above operations for each pixel block, all image data is degenerately encoded and stored in the image memory 14.

Although two sets of chromaticity data are selected, the present invention is not limited to this. As long as the number of bits, compression rate, image quality, etc. are considered, any number of sets can be selected.

Next, the operation of reading encoded image data C from the image memory 14, decoding it, and outputting a reproduced image will be described. The code data C read from the image memory 14 is temporarily stored in the buffer memory 15. The decoder 16 decodes the brightness code data CL out of the code data C in the buffer memory 15 to form the brightness data LIJ and the brightness average value L', of which the brightness data L''lj is stored in the buffer memory 22. , and the brightness data L″
IJ and the average brightness value L' are input to the comparator 17.

Furthermore, as for the chromaticity code data Cab of the code data C in the buffer memory 15, the decoder 18 performs a ”H = f sa (Cab) b ”M= f sb (Cab) The selector 21 decodes the chromaticity data a″□, b□.
Enter. This decoder 18 also has fHa and f between code data Cl1b and chromaticity data a ``Ml b ''o.
It can be configured with UP TABLE to one or more Loos that give the ib relationship.

In addition, as a color edge decoding process, the decoder 19 performs a
zy (C-b) a ”2= f !a2 (Cab) b “2= f
tba (C-b) and outputs the chromaticity data a It1 to b''2 to the color determiner 20. This decoder 19 also decodes the coded data C
fE! between ab and chromaticity data am, ~bm2! I~
f One or more L that gives the relationship of Eb2
It can be configured with OOK UP TABLE.

The color determiner 20 determines the brightness of each pixel by the comparator 17.
Based on the comparison result between 1j and the average brightness L of the pixel block, the chromaticity data (a ``It b ''+) or (a''2+
b" Select either one of 2).

Here, (a ``l+ 1) ``l): L'IJ≧L
″(a″z, b″2): L″+ <L″, but it is also possible to set it in reverse.The chromaticity determined in this way Data (a8°, b
“@) is output to the selector 21.

The selector 21 selects the chromaticity data ("Ml b "- from the decoder 18 and the chromaticity data (a "*, b ') from the color determiner 18 based on the content of the determination flag FLG read from the buffer memory 15 e), select one set of decoded chromaticity data of each pixel (a″IJ,
bll, , ) to the buffer memory 22.

If the judgment flag FLG is set, (a ”@, b
Select "*), and if FLG is in reset state, a"n
, b”o).

The thus determined chromaticity data (a"sJ* b'■) is output to and stored in the buffer memory 22. The buffer memory 22 receives the brightness data L"IJ from the decoder 18,
By storing the chromaticity data am, . . . bm from the selector 21 in units of one pixel block, synchronization timing is obtained and output to the color converter 23.

Color converter 23 is an LO that performs the inverse relationship of color converter 2.
It consists of O and UP TABLE, and their relationship is shown below.

R-Fl (L", ", b") G-f, (L", ", b") B=f, (L", ", b") In this way, the color-converted color signals R, G, B is output to the image output device 24. Then, a color image is formed by performing the above decoding process on the entire image area.

Incidentally, in the above embodiment, recording to the image data memory 14 and
Although we have dealt with the case of reading, it can easily be applied to transmitting color images by connecting to a communication device or transmission line instead of the image data memory 4.

In addition, although a 4×4 pixel block was targeted as the image area of interest, this is not limited to this. However, the scale of the circuit,
Considering the number of bits of image data or code data, etc.
It seems best to use 4×4 pixel blocks.

Furthermore, the color data L" based on the uniform color space of 1976 CIE L"a'b" is not limited to "l", 1)", but the color data L" based on the uniform color space of 1976 CIE L"u"v" , u'', v''.Furthermore, it is also possible to use the color television transmission system (
YIQ signals in the NTSC system may also be used. In that case, Y can be used instead of Ll, and I and Q can be used instead of a'' and b''.

In addition, the image area determiner 5 judges character areas and halftone dot areas, but in addition, a judger that takes into account the determination of flat areas, for example, is used, and the color edge block judger 4 is used in the image area judger 5.
It can also be constructed in such a way that it includes the gate 12.

[Effects of the Invention] As described above, according to the present invention, since the character area and the halftone dot area are separated by image area determination, good encoding/decoding can be performed without impairing the properties of the image.

That is, it is possible to reproduce a color image with good quality in terms of color reproduction in halftone dot areas and edge preservation of characters.

Further, since the encoding process in the halftone dot area is performed after block smoothing, it is effective to suppress the occurrence of moire when digitally processing the halftone dot image.

[Brief explanation of the drawing]

The figure is a block diagram of a color image processing device according to an embodiment of the present invention. In the figure, 1... Image input device, 2... Color converter, 3.22... Buffer memory, 4... Color edge block judger, 5... Image area judger, 6...・Encoder, 7...
・Block smoother, 8... Color selector, 9... Encoder, 10... Encoder, 11... Selector, 12...-A
ND circuit, 13.15... buffer memory, 14
-...Image memory, 16...Decoder, 17...Comparator, 18...Decoder, 19...Decoder, 20...
Color determiner, 21... selector, 23... color converter,
24... Image output device.

Claims (7)

[Claims] (1) A dividing step of dividing color image data into pixel blocks of m×n pixels, and dividing the color image data into brightness data, density data, or brightness information representing the brightness of luminance data, and color of hue data and saturation data. a conversion step for converting into chromaticity information representing the pixel block, an image area determination step for determining whether the image area of interest is a line drawing image area such as characters or a halftone image area, and includes a color edge, and m× a first color determining step of determining a set of chromaticity information whose number is less than n pixels; and a first encoding step of encoding the set of chromaticity information determined in the first color determining step. and a step of determining a set of chromaticity information for a pixel block determined not to include a color edge in the color edge determination step or a pixel block determined to be a halftone image area in the image area determination step. 1. A color image processing method, comprising: a second color determining step; and a second encoding step of encoding a set of chromaticity information determined in the second color determining step. (2) Furthermore, a first decoding step of decoding the chromaticity information encoded in the first encoding step, and a plurality of sets of chromaticity information decoded in the first decoding step. 2. The color image processing method according to claim 1, further comprising a first color allocation step of allocating a color to each pixel in a pixel block. (3) Furthermore, a second decoding step of decoding the chromaticity information encoded in the second encoding step, and a set of chromaticity information decoded in the second decoding step. 3. The color image processing method according to claim 1, further comprising a second color allocation step of allocating colors to all pixels in a pixel block. (4) The second color determination step is performed for a pixel block determined to not include a color edge in the color edge determination step or for a pixel block determined to be a halftone image area in the image area determination step. 2. The color image processing method according to claim 1, wherein one set of chromaticity information is determined by each average value of chromaticity information of all pixels of a pixel block. (5) dividing means for dividing color image data into pixel blocks of m×n pixels, and dividing the color image data into brightness data, density data, or brightness information representing brightness of luminance data, and color of hue data and saturation data. conversion means for converting into chromaticity information representing the chromaticity information; image area determination means for determining whether the image area of interest is a line drawing image area such as characters or a halftone image area; m× a first color determining means for determining a set of chromaticity information whose number is less than n pixels; and a first encoding means for encoding the set of chromaticity information determined by the first color determining means. and a step of determining a set of chromaticity information for a pixel block determined by the color edge determination means to not include a color edge or for a pixel block determined to be a halftone image area by the image area determination means. 1. A color image processing device comprising: two color determining means; and a second encoding means for encoding a set of chromaticity information determined by the second color determining means. (6) Furthermore, a first decoding means for decoding the chromaticity information encoded by the first encoding means, and a plurality of sets of chromaticity information decoded by the first decoding means. 6. The color image processing device according to claim 5, further comprising first color allocation means for allocating a color to each pixel in a pixel block. (7) Furthermore, a second decoding means decodes the chromaticity information encoded by the second encoding means, and a set of chromaticity information decoded by the second decoding means. 7. The color image processing device according to claim 5, further comprising second color allocation means for allocating all pixels in a pixel block.