JP3368125B2 - Image data encoding apparatus and encoding method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image data coding apparatus and a coding method for compressing and storing image data by block coding.

[0002]

2. Description of the Related Art A digital copying machine that handles image data as a digital signal is known as one of image processing apparatuses. The structure of the digital copying machine of this means is briefly shown in FIG. That is, the scanner 31 reads the image data, the A / D conversion unit 32 converts it into a digital signal, the image processing unit 33 performs image processing such as gamma conversion and image quality correction, and the image output unit 34 outputs the image data on paper. The image is output by printing for each pixel.

In a copying machine that handles an image as a digital signal, the image can be stored in a memory. If the image data can be stored in the memory, the image once captured can be used many times, and the input and output addresses can be changed to perform processing and editing such as image rotation. However, the amount of information of an image is large, and if it is stored in the memory as it is, a large memory capacity is required (for example, an A4 size original document is read with 256 gradations per pixel and a resolution of 4).
Read at 00 dpi, it will be about 16 megabytes. ), Because the unit price of the memory is high, the overall cost becomes expensive. Therefore, a method is generally adopted in which the image data is not stored as it is, but is encoded once and the data amount is compressed and stored in a memory. That is, the data can be compressed and stored in the memory, and the required memory amount is reduced to reduce the cost.

In a block coding method which is a compression method of image data, an image is decomposed into blocks as shown in FIG. 4, and a density value Lij of 1 byte in the block is averaged by La (1 Byte), gradation range index Ld
(1 byte), data is compressed into a code φij (2 bits × 16 pixels) for each pixel. By this encoding method, as shown in FIG. 6, the data amount of 16 bytes of a 4 × 4 pixel block of 1 byte of pixels becomes 6 bytes, and 3 /
It is possible to compress to the data amount of 8. Qj in FIG. 5 is a quantized representative value at the time of decoding and is a gradation value to which each code is assigned at the time of decoding as shown in FIG.

By the way, there is a recent digital copying machine which, when the image data includes a specific color such as red, discriminates the pixel of the specific color and outputs the specific color. For example, as shown in FIG. 8, when a copy is made of a document in which the area 41 is red and the other areas 42 are black and white,
The original in red is output as a copy. In such a copy, if the data of the red image is treated as multi-valued data similarly to the black-and-white image, the amount of information increases, so that it is possible to output by handling a specific color (often red or blue). For the sake of convenience, the copying machine configured as described above is referred to as a spot color copying machine in order to distinguish it from a full-color copying machine. The construction of such a spot color copying machine is shown in FIG. In this configuration, first, the scanner 51 uses R, G, B
Image sensor reads the R, G, B signals for each pixel, the A / D converter 52 converts the image data into an 8-bit digital signal, and the specific color signal determiner 53 converts the R, G, B for each pixel.
The color of the pixel is determined from the difference between the G and B signals, and if it is determined to be the specific color, the specific color flag signal 54 is turned on. If not determined, the specific color flag signal 54
Turn off. In response to the specific color flag signal 54, the image data switching unit 55 outputs the specific color gradation data converted from the R, G, B signals when the specific color flag signal 54 is on, and the R, G when it is off. , B signals converted from the black-and-white gradation data are switched pixel by pixel and sent to the image processing unit 56 together with the specific color flag signal data. After the image processing unit 56 performs image processing such as γ conversion, the image output unit 5
In step 7, an image consisting of a specific color and a black and white image is output from these data.

Next, a case will be described in which the image data is encoded and stored in the image data storage unit 58, the encoded data is decoded, and the image data is output.

The operations up to the scanner 51, the A / D conversion section 52, the specific color signal determination section 53, and the image data switching section 55 are the same as in the above case. The multi-gradation black-and-white / specific color mixed image sent from the image data switching unit 55 is coded by the block coding method described above, and the image data storage unit 5
8 and the specific color flag signal for each pixel is directly stored in the image data storage unit 58 as binary data. As a result, the data for one block to be stored is the block code 6 bytes plus the specific color flag signal 2 bytes (1 bit × 16 pixels) as shown in FIG. When reading from the image data storage unit 58, the accumulated code is decoded and returned to multi-tone black and white / specific color mixed data, and a specific color flag signal for each pixel is added to this, and the image processing unit 56 is added. The image output unit 57 outputs an image composed of a specific color and a monochrome image from these data.

[0008]

However, if such a system is adopted, it is necessary to accumulate not only the original image data but also the specific color flag signal for each pixel as binary data in the image data storage unit 58. Therefore, the required memory amount is increased and the cost for realizing the image memory unit is increased. Note that the amount of memory increase is A4 size and resolution is 400 dpi.
In case of the image, it becomes 2 megabytes. As described above, it is necessary to increase the memory amount for the red image signal, and if the memory amount is increased, the cost naturally rises.

The present invention has been made in view of the above points, and an object thereof is an image data encoding apparatus capable of realizing a spot color copying machine capable of copying a specific color with the same memory capacity as a monochromatic copying machine. And to provide a method.

[0010]

[0011]

A first means is to preset multi-tone black and white and specific color mixed image data in an image data encoding device which encodes multi-tone black and white and specific color mixed image data. A means for dividing into blocks composed of the number of pixels and a pixel value for which a flag signal indicating a multi-tone specific color pixel is set in the block-divided multi-tone monochrome / specific color mixed image data is set in advance. And a means for changing the pixel value of the white image when the pixel value is higher than the threshold value, and changing the specific color pixel for lowering the flag signal of the pixel when the pixel value is lower than the threshold value. , Multi-tone black and white processed by the changing means
The means for obtaining the average gradation value in one block of the specific color mixed image data and the flag signal processed by the changing means are checked, and each pixel in one block of the multi-tone monochrome / specific color mixed image data is examined. Means for obtaining a gradation dispersion index value indicating how much the gradation value of the above is varied, and the flag signal processed by the changing means,
Means for determining whether or not a specific color exists in one block of multi-tone black-and-white / specific color mixed image data, and the average gradation value and the gradation dispersion index when the specific color exists in the block. The value is used to quantize the multi-tone black-and-white / specific color mixed image data in the block into two levels, and when the specific color does not exist in the block, it is quantized into four levels And a means for embedding the result at the preset position of the gradation dispersion index value, and the result judged by the means for judging the multi-tone black and white / specific color mixed image data as the average gradation value. The gradation dispersion index value having is encoded in block units,
In the block in which the specific color exists, the 2-level quantized value and the flag signal obtained by the quantizing means, and in the block in which the specific color does not exist, the 4-level quantized value obtained by the quantizing means. It is characterized by encoding in block units.

[0012]

The second means is an image data encoding method for encoding multi-tone black and white, specific color mixed image data,
Multi-tone black-and-white and specific color mixed image data is divided into blocks of a preset number of pixels, and the multi-tone black and white and specific color mixed image data is divided into multi-tone specific color pixels. The pixel value for which the flag signal is set is compared with a preset threshold value, if the pixel value is higher than the threshold value, it is changed to the pixel value of the white image, and if the pixel value is lower than the threshold value, the pixel The flag signal is lowered, the average gradation value in one block of the multi-gradation black-and-white / specific color mixed image data processed in this way is obtained, and the flag signal processed by the changing means is examined,
Multi-tone black-and-white / specific color A gray-scale dispersion index value indicating how much the gray-scale value of each pixel varies in one block of mixed image data, and the flag signal is checked to check the multi-tone black-and-white / specific color. It is determined whether or not a specific color exists in one block of the mixed image data, and if the specific color exists in the block, the average gradation value and the gradation dispersion index value are used to determine the multi-level in the block. Quantize mixed tone black and white / specific color image data into 2 levels, and 4 if no specific color exists in the block.
Quantize to a level, embed the judgment result in a preset position of the gradation dispersion index value, and have the multi-gradation black-and-white / specific color mixed image data with an average gradation value within a block and the judgment result. The gradation dispersion index value within the block is coded in block units, and the block having a specific color has the 2-level quantized value and the flag signal, and the block having no specific color has the 4-level quantized value. It is characterized by encoding in units.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

[First Embodiment] Since the configuration of this embodiment is the same as that shown in FIG. 9, the same reference numerals are allotted to the same parts as in the above-described conventional example in the following description. The overlapping description will be appropriately omitted.

The feature of the present invention resides in the internal structure of the image data storage unit 58 in FIG. 9, the details of which are shown in FIG.
In FIG. 1, of the multi-tone black and white / specific color mixed image data and the multi-tone black / white / specific color mixed image data of the pixel-specific color flag signals, four lines of data are stored once by the 4-line FIFO 1. To the data separation unit 2 in the form of a 4 × 4 pixel block. At this time, at the same time, the specific color flag signal 54 is sent to the data separation section 2 and the color mixture determination section 4 through the 4-line FIFO memory 3. The data separation unit 2 uses the specific color flag signal 54 to perform multi-tone black and white
The specific color mixed image data is divided into black and white data and specific color data and sent to the black and white data encoding unit 5 and the specific color data encoding unit 6, respectively. These are separately coded by the block coding method described above, and the code data of La, Ld, and φij are sent to the code data conversion unit 7. At the same time, the color mixture determination unit 4 checks whether all the specific color flag signals 54 in one block are on, all are off, or whether on-off is mixed. This can be realized by taking the logical product and the logical sum of all the specific color flag signals 54 of each pixel in the block. When all the specific color flag signals 54 in one block are turned on, both the logical product and the logical sum are turned on. When all the specific color flag signals 54 in one block are off, both the logical product and the logical sum are off. When the specific color flag signals 54 in one block are mixed on and off, the logical product is off but the logical sum is on. In this way, the 2-bit determination result of the logical product and the logical sum is sent to the code data conversion unit 7. In the code data conversion unit 7, the specific color flag signal 5 in one block is based on the determination result of the color mixture determination unit 4.
If all 4 are turned on or all are turned off, the coded data sent from the black-and-white data coding unit 5 or the specific color data coding unit 6 is selected according to the value, and Ld The least significant bit is replaced with the logical sum result of the color mixture determination unit 4. When the specific color flag signals 54 in one block are mixed on and off, that is, when the values of the logical product and the logical sum of the determination results of the color mixing determination unit 4 are different, they are sent from the monochrome data encoding unit 5. The upper 4 bits of the code data La and the upper 4 bits of the code data La sent from the specific color data encoding unit 6 are connected,
It is stored in the code memory 7 as a new La. Similarly, the code data L sent from the monochrome data coding unit 5
The upper 4 bits of d and the upper 4 bits of the code data Ld sent from the specific color data encoding unit 6 are concatenated to make a new Ld, and the least significant bit of Ld is the logic of the color mixture determination unit 4. The sum result is replaced and stored in the code memory 7.

For φ data, the upper 1 bit of the code data φij sent from the monochrome data coding unit 5 and the upper 1 bit of the code data φij sent from the specific color data coding unit 6 are combined. As a result, new φij data is stored in the code memory 7.

In the code data stored by such processing, when the specific color flag signals 54 in one block are all on or all are off, the least significant bit of Ld is simply judged as a color mixture. Since only one bit of the logical sum result of the unit 4 is replaced, the code amount is the same as in the case of performing normal block coding. Even when the specific color flag signals in one block are mixed on and off, as described above, La and Ld are 4 bits (the least significant bit of a part of Ld is the logical sum result of the color mixture determination unit 904). Since it is replaced by bits, it is reduced to 3 bits.) The reduced one is concatenated and accumulated, and φij is also concatenated by reducing 1 bit at a time. And the code amount is the same.

Second Embodiment Since the configuration of this embodiment is the same as the configuration shown in FIG. 9, the same reference numerals will be given to the same parts as in the above-mentioned conventional example in the following description. The overlapping description will be appropriately omitted.

The feature of the present invention resides in the internal configuration of the image data storage unit 705 in FIG. 9, the details of which are shown in FIG. In FIG. 2, among the multi-tone black and white / specific color mixed image data and the specific color flag signal for each pixel,
The specific color mixed image data is stored in the 4-line FIFO 21 once for 4 lines and then sent to the specific color pixel changing unit 22 in the form of a 4 × 4 pixel block. At this time, the specific color flag signal 54 is simultaneously sent to the 4-line FIFO memory 23.
Through the specific color pixel changing unit 22.

The specific color pixel changing section 22 uses the specific color flag signal 54 to compare the multi-tone monochrome / specific color mixed image data with the preset value of the threshold value register 24 for only the specific color data. If the pixel value is higher than the threshold value, the specific color data is changed to the pixel value of the white image, and if the pixel value is lower than the threshold value, the specific color flag signal 54 of the pixel is turned off.

Next, the image data passing through the specific color pixel changing unit 22 is sent to the encoding unit 25 and encoded by the block encoding method described above, and the encoded data of La, Ld and φij are converted into the encoded data converting unit. Sent to 26. At the same time, the specific color flag signal is sent to the color mixing determination unit 27, and it is determined whether all the specific color flag signals 54 in one block are off or not off. This can be realized by taking the logical sum of all the specific color flag signals 54 of each pixel in the block. When the specific color flag signals 54 in one block are all off, the logical sum is also off. When all the specific color flag signals 54 in one block are on, and when both on and off are mixed, the logical sum is on. In this way, the 1-bit result of the logical sum is sent to the code data conversion unit 26.

In the code data conversion unit 26, when all the specific color flag signals 54 in one block are turned off based on the judgment result of the color mixture judgment unit 27, it is sent from the coding unit 25. The least significant bit of Ld is replaced with the logical sum result of the color mixture determination unit 27. If all of the specific color flags in one block are on or there is a mixture of on and off, the least significant bit of Ld is the color mixture determination unit 27.
At the same time, the lower 1 bit of each pixel in the code data of φij is replaced with the specific color flag signal 54. The code data thus converted is stored in the code memory 28.

[0024]

As described above, according to the present invention, the following effects can be obtained.

[0025]

According to the first and second aspects of the present invention, when the specific color exists in each block of the image data to be encoded, the processing content of the block encoding is switched to the normal encoding method. By encoding and including the specific color flag signal in the encoded block code, it is not necessary to store the block code data separately from the block code data, thereby reducing the memory for the specific color flag signal. Can be implemented with the same amount of memory as a monochromatic copying machine. At that time, if the gradation of the specific color is not important, the specific color can be binarized and stored in the memory, and the influence on the encoding of the monochrome image can be reduced. Further, this makes it possible to switch the processing contents as appropriate according to the importance of gradation.

[Brief description of drawings]

FIG. 1 is a diagram showing an internal configuration of an image data storage unit and a processing procedure according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an internal configuration of an image data storage unit and a procedure of processing according to a second embodiment of the present invention.

FIG. 3 is a block diagram showing a schematic configuration of a digital copying machine according to an embodiment and a conventional example.

FIG. 4 is an explanatory diagram showing an image data compression method of a block coding method.

FIG. 5 is an explanatory diagram showing an algorithm of an image data compression method of a block coding method.

FIG. 6 is an explanatory diagram showing a state when image data is compressed by a block coding method.

FIG. 7 is an explanatory diagram showing density values at the time of decoding.

FIG. 8 is a diagram showing a document having red and black images.

FIG. 9 is a block diagram showing a schematic configuration of a copying machine capable of two-color output having a function of compressing and storing an image in a memory.

FIG. 10 is an explanatory diagram showing a storage state of image data for one block.

[Explanation of symbols]

1,3,21,23 4-line FIFO 2 Data separation unit 4 color mixture determination section 5 Black and white data encoder 6 Specific color data encoder 7,26 Code data converter 8,28 Code memory 22 Specific color pixel change unit 24 threshold register 25 Encoder 27-color mixture determination section 51 scanner 52 A / D converter 53 Specific color determination unit 54 Specific color flag signal 55 Image data switching unit 56 Image processing unit 57 Image output section 58 Image data storage

Continuation of the front page (56) Reference JP-A-9-163150 (JP, A) JP-A-9-163149 (JP, A) JP-A-8-307691 (JP, A) JP-A-8-51547 (JP , A) JP-A-6-334870 (JP, A) JP-A-5-110869 (JP, A) JP-A-5-308529 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB) Name) H04N 1/41-1/419

Claims (2)

(57) [Claims] 1. An image data encoding device for encoding multi-tone black-and-white and specific color mixed image data, and means for dividing the multi-tone black-and-white and specific color mixed image data into blocks each having a preset number of pixels. Multi-tone black and white / specific color mixed image data divided into blocks
Flag signal indicating that the pixel is a multi-gradation specific color pixel
Compare the pixel value for which is set with a preset threshold value
However, if the pixel value is higher than the threshold, the pixel value of the white image
If the pixel value is lower than the threshold value,
The means for changing the specific color pixel for lowering the flag signal, and the multi-tone black / white / specification processed by the changing means
Obtaining the average gradation value in one block of color mixed image data
Means and the flag signal processed by the changing means
1 block of multi-tone black and white / specific color mixed image data
Shows how much the gradation value of each pixel varies within
Means for obtaining a gradation dispersion index value and the flag signal processed by the changing means.
1 block of multi-tone black and white / specific color mixed image data
Means for determining whether or not a specific color exists in the block, and the average gradation value when the specific color exists in the block.
Using the gradation distribution index value, multi-gradation black and white in a block
The specific color mixed image data is quantized into two levels, and the specific color is
If it does not exist in the block, it can be quantized into 4 levels.
Wherein the stage, and means for embedding the result determined by said determining means to a preset position of the gradation distribution indicator value comprises, the multi-tone black-and-white-specific color mixed image data
The result determined by the determining means as the average gradation value
With the gradation distribution index value having
In the block in which the specific color exists, the quantization means
The two-level quantized value obtained by
And a 4-level quantized value obtained by the quantizing means in a block in which a specific color does not exist are coded in block units. 2. An image data encoding method for encoding multi-tone black-and-white and specific color mixed image data, wherein the multi-tone black-and-white and specific color mixed image data is divided into blocks each having a preset number of pixels. Of the divided multi-tone black-and-white / specific color mixed image data, the pixel value for which a flag signal indicating a multi-tone specific color pixel is set is compared with a preset threshold value, and a pixel higher than the threshold value is compared. change the pixel value of the white image in the case of the value, to the case of low pixel values than the threshold Kudaro the flag signal of the pixel, thus treated multi tone monochrome-specific color mixed image data Me seek average gradation value in one block, the examined changes the flag signal processed by means of the gradation value of each pixel within a block of multi-tone black-and-white-specific color mixed image data is how If For it has either a tone distribution indicator value determined Me a showing, before Symbol examine a flag signal, determines whether a specific color exists in the multi-tone black-and-white-specific color within one block of the mixed image data
And, if a particular color are present in the block blocks in the multi-tone black and white using said gradation distribution indicator value and the average gradation value
Quantizes the specific color mixed image data to the two levels, if a particular color is not present in the block is quantized into four levels, embed the-size Teiyui result a preset position of the gradation distribution indicator value look, the front SL multi-tone black-and-white-specific color mixed image data, encodes the block <br/> average gradation value, the said block gradation distribution indicator value with the determination result in block units, the specific before Symbol 2 level quantized value and the flag signal is a block of color present, the image data encoding method characterized in that encoded in block units to 4 level quantized value before Symbol is a block that does not exist specific color .