JPH09214753A - Method for encoding image data and image forming device using the method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To adopt both kinds of data, multi-level black and white image data and specified color image data, to be a compression code without increasing a memory quantity. SOLUTION: Multi-level black and white and specified color coexisting picture data is divided into the blocks with a prescribed picture element number, an encoding part 202 calculates an average gradation index and a gradation distributing index in the divided blocks, a color coexisting judging part 204 judges whether or not the picture element inside the block is a coexisting picture based on a specified color flag signal, an encoding data converting part 205 replaces a judgement result with designation data of average gradation index data and gradation distributing index data, encoding is executed to replaced average gradation index data and gradation distributing index data and multi- level picture data which is quantized in four levels unless the picture element is the coexisting picture and encoding is executed to the replaced average gradation index data and gradation distributing index data, multi-level picture data which is quantized in the two levels and a specified color flag signal when the picture element is the coexisting picture.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image data encoding method and an image forming apparatus using the method, and more particularly, in an image forming apparatus such as a spot color copying machine, a multi-level image forming method without increasing memory capacity. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image data encoding method for accumulating mixed black and white / specific color image data and an image forming apparatus using the method.

[0002]

2. Description of the Related Art FIG. 6 is a block diagram showing the outline of an image forming apparatus according to the prior art. In the figure, 601
Is a scanner for optically reading image data, 602 is an A / D conversion unit for converting the image data optically read by the scanner 601 into a digital signal, and 603 is an A / D converter. Reference numeral 604 denotes an image processing unit for performing image processing such as gamma conversion and image quality correction on the image data converted into digital signals by the D conversion unit 602. Reference numeral 604 denotes a digital image processed by the image processing unit 603. An image output unit for outputting an image by printing signalized image data on a transfer paper in pixel units.

In such an image forming apparatus, when the image data is handled as a digital signal, the image data can be stored in a storage medium such as a memory. By storing the data in the storage medium in this way, the image data can be rotated by reading and outputting the once stored image data many times without changing the original from the scanner and changing the reading order. Then, it can be output.

Storing image data as a digital signal in a storage medium has the above-mentioned effects.
It also includes the following problems.

That is, since the image data generally has an enormous amount (for example, when an A4 size document has 256 gradations per pixel and is read at a resolution of 400 dpi, it becomes about 16 megabytes), the memory is kept as it is. A large-capacity memory is required to store in a storage medium such as.

Therefore, in order to use the large-capacity memory in an image forming apparatus such as a digital copying machine, the cost of a storage medium such as a memory mounted in the image forming apparatus becomes a problem.

Therefore, there is a method in which the image data is not stored as it is, but is encoded once to reduce the amount of data and then stored in a storage medium such as a memory.

FIG. 7 is an explanatory diagram showing a block encoding system which is one of the encoding systems for compressing and reducing image data, and FIG. 8 is an explanatory diagram showing an algorithm for block encoding. In FIG. 7, FIG. 7A shows the manuscript 1
7B is a model of the original image for one sheet. FIG. 7B shows that the image data of the original image shown in FIG. 7A is divided into blocks and the image data for one block is enlarged. It is shown. The gradation value Lij for each pixel in one block shown in FIG. 7B is calculated by using the algorithm shown in FIG. 8 with an average gradation index code La (1 byte), a gradation dispersion index code Ld (1 byte), Grayscale quantization code φij for each pixel
Encode to (2 bits × 16 pixels).

FIG. 9 is an explanatory diagram showing a comparison of the data amount before and after encoding one block of image data. As shown in FIG. 9, when the block coding method based on the algorithm shown in FIG.
The data amount of one block composed of × 4 pixels was 16 bytes, but it becomes 6 bytes after encoding, and the data amount can be compressed and reduced to 3/8 of that before encoding.

FIG. 10 is an explanatory diagram showing an algorithm for decoding image data encoded by the algorithm shown in FIG. By the algorithm shown in FIG. 10, the gradation value L * ij of each pixel is calculated from the data of the above-mentioned average gradation index code La, gradation dispersion index code Ld, and gradation quantization code φij for each pixel. As a result, the encoded image data can be decoded.

By the way, in an image forming apparatus such as a digital copying machine which has been recently developed, an image forming apparatus which distinguishes a pixel of a specific color when a specific color exists in an original image and outputs it as the specific color (hereinafter, "Spot color image forming apparatus").

FIG. 11 is an explanatory diagram showing an example of original data, in which the original 1101 is "confidential".
The area 1102 indicated by is a red image, and the other area 1103 is a monochrome image. This manuscript 1
When 101 is copied by the spot color image forming apparatus, the area 1102 shown as "Confidential" is output as red, and the other area 1103 is output as a monochrome image.

As described above, the spot color image forming apparatus can output a specific color such as red or blue like the area 1102, in addition to the black and white image like the area 1103. Note that this spot color image forming apparatus is distinguished from a full color image forming apparatus that handles all image data as color originals.

FIG. 12 is an explanatory diagram showing an outline of switching of image data in the spot color image forming apparatus. In the figure, a scanner 601 reads an original image as an RGB full-color signal with a line sensor for RGB (the three primary colors of light), and a digital signal converted by an A / D conversion unit 602 is read by a specific color determination unit 1201 for each pixel. The color of the pixel is judged from the difference between the RGB signals, and if the result of the judgment is that it is a specific color, the specific color flag signal is turned on, and if it is judged that it is not a specific color, the specific color The flag signal is turned off.

In response to the specific color flag signal, the specific color flag signal is "on" in the image data switching section 1202.
In that case, the specific color gradation data converted from the RGB signal is switched in pixel units.

On the other hand, if "OFF", the black and white gradation data converted from the RGB signal is switched in pixel units, and after switching, it is sent to the image processing unit 603 together with the specific color flag signal data, and image processing is performed. After the image processing such as gamma conversion is performed by the unit 606, the image output unit 604 outputs an image including a specific color and a monochrome image from these data.

When image data is encoded and stored in the image data storage unit 1203 and the accumulated code data is decoded and the image data is output, the multi-gradation levels sent from the image data switching unit 1202. Of the monochrome / specific color mixed image data and the specific color flag signal for each pixel, the multi-gradation monochrome / specific color mixed image data is encoded by the block encoding method described above.

The encoded multi-tone black and white / specific color mixed image data is stored in the image data storage unit 1203. Further, the specific color flag signal for each pixel is directly stored in the image data storage unit 1203 as digital data.
With such a configuration and operation, a spot color image forming apparatus is realized.

[0019]

However, the conventional image forming apparatus described above has the following problems.

FIG. 13 is an explanatory diagram showing the data structure of code data for one block to be accumulated. In FIG.
301 is an average gradation index code La (1 byte), and 1
302 is a gradation distribution index code Ld (1 byte), and 1
Reference numeral 303 denotes a gradation quantization code φij (2 bits × 1) for each pixel.
6 pixels). 1304 is a pixel specific color flag signal 1304 (2 bytes). The data amount of the pixel specific color flag signal 1304 is 1 bit per pixel,
Since there are 16 pixels per block, 1 bit x 16 =
16 bits, that is, 2 bytes.

The block code is, as described above with reference to FIG. 9, the average gradation index code La1301,
The gradation dispersion index code Ld1302 and the gradation quantization code φij1303 for each pixel are 6 bytes in total.
Therefore, the data for one block to be accumulated has a block code of 6 bytes, and a specific color flag signal and 2 bytes, which is a data amount of 8 bytes.

When reading out from the image data storage unit 1208, the accumulated code is decoded and returned to multi-tone monochrome / specific color mixed image data, to which a pixel specific color flag signal for each pixel is added. Sent to the image processing unit 1206 in the form of
The image output unit 1207 outputs an image composed of a specific color and a monochrome image from these data.

Since the image data storage unit 1208 needs to store not only the original image data but also the specific color flur signal for each pixel as digital data, the required memory amount increases. For example, when an A4 size document is read at a resolution of 400 dpi, the data amount increases by about 2 megabytes. Therefore, a large amount of memory is required correspondingly, and there is a problem that it must be stored separately from the normal block code.

The present invention has been made in view of the above, and realizes encoding for accumulating multi-tone black and white / specific color mixed image data and a specific color flag signal for each pixel without increasing the memory amount. It is an object of the present invention to provide an image data encoding method and an image forming apparatus using the method.

[0025]

In order to achieve the above object, an image data encoding method according to a first aspect of the present invention is a block of multi-gradation black-and-white / specific color mixed image data having a predetermined number of pixels. The average gradation index and the gradation dispersion index in each of the divided blocks are calculated, and all the pixels in the block are black and white based on the specific color flag signal indicating the specific color in each pixel. , All of them are specific color images, or whether a black-and-white image and a specific color image are mixed, and the data related to the determined result is the average gradation index data and / or the gradation dispersion index data. If all the pixels in the block are black-and-white images or all specific-color images based on the result of the above determination, the data is replaced with the data specified in advance. , Multi-tone image data is quantized into four levels, and when a black-and-white image and a specific color image are mixed in the block, the multi-tone image data is quantized into two levels, and all of the blocks in the block are quantized. If the pixels of are only black and white images or all are specific color images,
In the case where the replaced average gradation index data, gradation dispersion index data, and multi-gradation image data quantized into four levels are encoded, and a black-and-white image and a specific color image are mixed in the block. Further, the average gradation index data and the gradation dispersion index data that have been replaced, the multi-gradation image data quantized into two levels, and the specific color flag signal are encoded.

That is, the multi-tone black-and-white / specific color mixed image data is divided into blocks having a predetermined number of pixels, and the average tone index and tone variance index in each divided block are calculated, Based on a specific color flag signal indicating a specific color for each pixel, it is determined whether all the pixels in the block are black and white images, all are specific color images, or whether black and white images and specific color images are mixed. Then, the data related to the judged result is replaced with the data specified in advance among the average gradation index data and / or the gradation dispersion index data, and based on the judged result, all data in the block is replaced. If the pixels of are black-and-white images or all specific color images,
When multi-tone image data is quantized into four levels and a black and white image and a specific color image are mixed in the block,
The multi-tone image data is quantized into two levels, and when all the pixels in the block are black-and-white images only or all are specific color images, the replaced average tone index data and tone dispersion index When the data and the multi-gradation image data quantized into four levels are encoded, and a black and white image and a specific color image are mixed in the block,
The average gradation index data and the gradation dispersion index data that have been replaced, the multi-gradation image data quantized into two levels, and the specific color flag signal are encoded.

In the image forming apparatus according to the second aspect of the present invention, the multi-gradation monochrome / specific color mixed image data is divided into blocks having a predetermined number of pixels, and the block dividing means divides the image data. An average gradation index calculating means for calculating an average gradation index in each block, a gradation dispersion index calculating means for calculating a gradation dispersion index in each block divided by the block dividing means, and a pixel On the basis of a specific color flag signal indicating a specific color for each pixel, all pixels in the block divided by the block dividing means are monochrome images, all are specific color images, The color mixture determination means for determining whether or not there is a mixture and the data relating to the result determined by the color mixture determination means are calculated by the average gradation index calculation. Index value changing means that replaces the prespecified data of the average gradation index data calculated by the means and / or the gradation dispersion index data calculated by the gradation dispersion index calculating means, and the color mixture determination On the basis of the result determined by the means, when all the pixels in the block are black-and-white images or all specific-color images, the multi-tone image data is quantized into four levels, and the black-and-white image and the specific image are specified in the block. When color images are mixed, an image data quantizing means for quantizing the multi-tone image data into two levels, and all pixels in the block are black and white images or all are specific color images. In this case, the average gradation index data and the gradation dispersion index data replaced by the index changing means, and four levels by the image data quantizing means Average gradation index data and gradation dispersion index encoded by the quantized multi-tone image data and replaced by the index changing means when a black-and-white image and a specific color image are mixed in the block. Data, multi-tone image data quantized to two levels by the image data quantization means, and image data encoding means for encoding the specific color flag signal are provided.

That is, the block dividing means divides the multi-tone black-and-white / specific color mixed image data into blocks having a predetermined number of pixels, and the average tone index calculating means divides by the block dividing means. The average gradation index in each block is calculated, the gradation distribution index calculating unit calculates the gradation distribution index in each block divided by the block dividing unit, and the color mixture determining unit determines each pixel. On the basis of a specific color flag signal indicating a specific color, all pixels in the blocks divided by the block dividing means are monochrome images, all are specific color images, or a monochrome image and a specific color image are mixed. The index value changing means determines whether the data about the result determined by the color mixture determining means is in the average gradation index calculating means. Of the average gradation index data calculated and / or the gradation dispersion index data calculated by the gradation dispersion index calculating means is replaced with the data specified in advance, and the image data quantizing means makes the color mixture determination. On the basis of the result determined by the means, when all the pixels in the block are black-and-white images or all specific-color images, multi-tone image data is quantized into four levels, and a black-and-white image When color images are mixed, the multi-gradation image data is quantized into two levels, and the image data encoding means sets all pixels in the block to black and white images only or all to specific color images. In this case, the average gradation index data and the gradation dispersion index data replaced by the index changing means, and the image data quantizing means to obtain four levels. Average gradation index data and gradation dispersion index encoded by the sub-gradation multi-gradation image data and replaced by the index changing means when a black-and-white image and a specific color image are mixed in the block. The data, the multi-tone image data quantized into two levels by the image data quantization means, and the specific color flag signal are encoded.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of an image data encoding method according to the present invention and an image forming apparatus using the method will be described in detail below with reference to the drawings.

(Structure of Image Forming Apparatus According to this Embodiment) FIG. 1 is a block diagram showing an outline of the image forming apparatus according to this embodiment. In the figure, 101 is a scanner, 102 is an A / D conversion unit, 103 is a specific color determination unit, 104 is a specific color flag signal, 105 is an image data switching unit, and 106 is image processing. Part,
107 is an image output unit, and 108 is an image data storage unit.

The scanner 101 has RGB (the three primary colors of light)
The line sensor reads the original image as an RGB full color signal.

The A / D converter 102 is for converting the data of the original image read by the scanner 101 into a digital signal.

The specific color determination unit 103 is for determining the color of the pixel based on the difference between the RGB signals of each pixel. As a result of the determination, the specific color flag signal 104 is turned "on" when it is determined that the color is the specific color, and the "off" is determined when the color is not the specific color.

The image data switching unit 105 receives the specific color flag signal 104, and switches the specific color gradation data converted from the RGB signal in pixel units if the specific color flag signal 104 is "ON". On the other hand, specific color flag signal 1
If 04 is “OFF”, the black-and-white gradation data converted from the RGB signal is switched in pixel units, and after switching, it is transmitted to the image processing unit 106 together with the data of the specific color flag signal 104.

The image processing unit 106 includes the image data switching unit 1
This is for performing image processing such as gamma conversion on the image data transmitted from 05.

The image output unit 107 outputs an image composed of a monochrome image and a specific color image on the recording paper based on the data subjected to the image processing by the image processing unit 106.

The image data storage unit 108 is composed of an encoding unit for encoding and storing image data, a memory, etc., as will be described later.

(Structure of Image Data Storage Unit) FIG. 2 is a block diagram showing the internal structure of the image data storage unit 108. In FIG. 2, 201 is a unit for storing multi-tone black and white / specific color mixed image data. A 4-line FIFO memory for storing multi-gradation black-and-white / specific color mixed image data, 202 is an encoding unit, and 203 is a 4-line FIFO for storing a specific color flag signal for storing a specific color flag signal for each pixel.
Reference numeral 204 is a memory, 204 is a color mixture determination unit, 205 is a code data conversion unit, and 206 is a code memory.

The 4-line FIFO memory 201 for storing multi-tone black and white / specific color mixed image data includes an image data switching unit 1.
Of the multi-tone black and white / specific color mixed image data and the specific color flag signal for each pixel transmitted from
This is for storing the specific color mixed image data for four lines.

The encoding unit 202 stores 4 lines of multi-tone black and white / specific color mixed image data stored by the 4-line FIFO memory 201 for storing multi-tone black / white / specific color mixed image data in a 4 × 4 pixel block. Each block is captured and coded using the block coding method to obtain code data of the average gradation index code La in the block, the gradation dispersion index code Ld in the block, and the gradation quantization code φij for each pixel. Then, the code data is sent to the data conversion unit 205.

4-line FIFO for storing specific color flag signal
The memory 203 stores the multi-gradation monochrome / specific color mixed image data transmitted from the image data switching unit 105 and the specific color flag signal for each pixel among the specific color flag signals for each pixel.
It is for storing lines.

The color mixing determination unit 204 determines whether all the specific color flag signals in one block are "on", all "off", or "on" and "off" are mixed. This is for judging any of the three ways.

The code data conversion unit 205 is for converting the code data based on the determination result of the color mixture determination unit 204.

The code memory 206 includes a code data conversion unit 2
In 05, it is for storing the changed code data.

(Procedure of Color Mixing Judgment Unit) Next, the procedure of color mixing judgment in the color mixing judgment unit 204 will be described. The color mixture determination is performed by taking the logical product and the logical sum of all the specific color flag signals of each pixel in the block. That is, when all the specific color flag signals in one block are "on", both the logical product and the logical sum are "on".

When all the specific color flag signals in one block are "off", both the logical product and the logical sum are "off". Further, when the specific color flag signals in one block include both "on" and "off", the logical product is "off" but the logical sum is "on". The summary is as follows.

1. Logical product = "ON", logical sum = "ON" → Specific color flag signal = all "ON" Logical product = "OFF", logical sum = "OFF" → Specific color flag signal = all "OFF" Logical product = "off", logical sum = "on" → Specific color flag signal = "on" / "off" mixed

In this way, the logical product bit of the color mixture determination result is 1 bit and the logical sum bit of the color mixture determination result is 1 bit, and 2 bits are transmitted to the code data conversion unit 205 as the determination result.

(Conversion Procedure of Code Data Converter) Next, the conversion procedure of code data in the code data converter 205 will be described. When all the specific color flag signals in one block are "on" or when all are "off", that is, the color mixture determination unit 204
When both the logical product and the logical sum of the color mixture determination result of are “ON” or “OFF” and the logical product and the logical sum match, the maximum gradation index code La of the encoded data of the block is the highest. The logical product bit of the color mixture determination result is held in the lower bit, and the logical sum bit is held in the least significant bit of the gradation distribution index code Ld.

Since the logical product bit of the color mixture determination result and the logical sum bit of the color mixture determination result are held, the least significant bits originally having the average gradation index code La and the gradation dispersion index code Ld are stored. The data disappears.

Further, in this case, the coded data of the gradation quantization code φij for each pixel is not converted and remains as it is.

FIG. 3 shows that when all the specific color flag signals in one block are "on" or all "off", that is, the logical product bit and the logical sum of the color mixture determination results. It is explanatory drawing which shows the data structure of the code data for 1 block when both bits are "on" or "off." In FIG. 3, (a) shows the same configuration as the encoded code data before conversion, and (b) shows the configuration of the code data converted by the code data conversion unit 205. It is a thing.

In FIG. 3A, 301 is an average gradation index code La (1 byte), 302 is a gradation dispersion index code Ld (1 byte), and 303 is a gradation for each pixel. The quantization code is φij (2 bits × 16 pixels = 4 bytes), and the total amount of data is 6 bytes.

In FIG. 3B, 304 is an average gradation index code La, 305 is a logical product bit of the color mixture determination result, and 306 is a gradation distribution index code L.
d, 307 is a logical sum bit of the color mixture determination result, and 308 is a gradation quantization code φij for each pixel.

As described above, the average gradation index code L
Since the least significant bit of a304 is converted to the logical product bit 305 of the color mixture determination result, the average gradation index code La
The data amount of 304 is 1 byte (8 bits) -1 bit =
It is 7 bits. In addition, since the logical product bit 305 of the color mixture determination result is 1 bit, the total is 8 bits (that is, 1 byte), and the average gradation index code La301
It becomes the same as the data amount of.

Similarly, the gradation distribution index code Ld306 is also
7 bits + logical sum 307 of color mixture determination result is 1 bit =
It has 8 bits, which is the same as the data amount of the gradation distribution index code Ld302. Further, in this case, since the gradation quantization code φij308 for each pixel is not converted, it becomes the same data as the gradation quantization code φij303 for each pixel. Therefore, the amount of data does not change.

On the other hand, when the specific color flag signals in one block are mixed "on" and "off", that is, the logical product of the color mixture determination results of the color mixture determination unit 204 is "on", and the logical sum is obtained. Even if the value of is “off” and the logical product and the logical sum do not match, the logical product bit of the color mixture determination result is gradation distributed to the least significant bit of the average gradation index code La of the encoded data of the block. The logical sum bit is held in the least significant bit of the index code Ld. As the logical product bit of the color mixture determination result and the logical sum bit of the color mixture determination result are held, the data of the least significant bits originally having the average gradation index code La and the gradation dispersion index code Ld disappear.

In this case, the lower 1 bit of each pixel of the coded data of the gradation quantization code φij for each pixel is replaced with the specific color flag signal. That is,
In the gradation quantization code φij for each pixel before conversion, each pixel having 16 pixels in one block is composed of 2 bits. Of these 2 bits, only the upper 1 bit is left and the lower 1 bit is left. For, extinguish. By this processing, 16 bits, that is, 2 bytes are applied to the specific color flag. As a result, the code data quantized into 4 levels is converted into the code data of 2 levels.

In FIG. 4, when the specific color flag signals in one block are mixed "on" and "off", that is, the logical product of the color mixture determination results of the color mixture determination unit 204 is "on".
Is a diagram illustrating the data structure of the code data for one block when the logical product and the logical sum do not match because the value of the logical sum is “OFF”. In FIG. 4, (a) shows the same configuration as the encoded code data before conversion, and (b) shows the configuration of the code data converted by the code data conversion unit 205. It is a thing. Note that the basic configuration is the same as that in FIG. 3, and the same reference numerals indicate common configurations, so only different portions will be described here.

In FIG. 4B, 401 is a gradation quantization code φij for each pixel, and 104 is a specific color flag signal as shown in FIG.

As described above, the average gradation index code L
Since the least significant bit of a304 is converted to the logical product bit 305 of the color mixture determination result, the average gradation index code La
The data amount of 304 is 1 byte (8 bits) -1 bit =
It is 7 bits. In addition, since the logical product bit 305 of the color mixture determination result is 1 bit, the total is 8 bits, that is, 1 byte, which is the same as the data amount of the average gradation index code La301.

Similarly, the gradation distribution index code Ld306 is 7
The logical sum bit 307 of the bit + color mixture determination result is 1 bit = 8 bits, which is the same as the data amount of the gradation distribution index code Ld302.

Further, the gradation quantization code φij40 for each pixel
1 means that each pixel consists of 2 bits, and 1 in 1 block
Since there are 6 pixels, the data amount is 2 bits x 16
= 32 bits (4 bytes). By leaving only the upper 1 bit of the 2 bits for each pixel, the data amount of the gradation quantization code φij for each pixel becomes 2 bytes which is 1/2 of 4 bytes. The data amount of the specific color flag signal 104 is 1 bit per pixel, and 1 block per block.
Since there are 6 pixels, 1 bit × 16 = 16 bits, that is, 2 bytes. Therefore, the amount of encoded data after conversion does not change.

(Operation of Image Data Storage Unit) The operation of the image data storage unit 108 of the image data encoding apparatus according to the present embodiment having the above configuration will be described.

FIG. 5 is a flow chart for explaining the processing flow of the image data storage unit 108. In the flowchart of FIG. 5, first, the 4-line FIFO memory 201 for storing multi-tone black / white / specific color mixed image data stores multi-tone black / white / specific color mixed image data and multi-level of the specific color flag signal for each pixel. Image data of mixed tonal black and white / specific color for four lines is stored (S501).

The multi-tone black-and-white / specific color mixed image data stored in step S501 is taken into the coding unit 202 for each 4 × 4 pixel block, and the coding unit 20
2 encodes the above-mentioned data into code data of an intra-block average gradation index code La, an intra-block gradation distribution index code Ld, and a gradation quantization code φij for each pixel (S502). ). The data encoded in step S502 is the encoded data conversion unit 205.
Sent to.

On the other hand, the specific color flag signal 104 is fetched by the color mixing determining unit 204 through the specific color flag signal storing 4-line FIFO memory 203, and the color mixing determining unit 20
No. 4 shows that the fetched specific color flag signals 104 are all "on" or all "off" for the specific color flag signals in one block, or "on" and "off" are mixed. It is determined. The determination result is transmitted to the code data conversion unit 205 as a logical product and a logical sum signal.

The code data conversion unit 205 replaces the average gradation index code La301 with the average gradation index code L of the code data.
a304 and the color mixture determination result transmitted from the color mixture determination unit 204 are converted into the logical product bit 305 (S503), and the tone distribution index code Ld302 is converted to the tone distribution index code Ld30.
6 and the logical sum bit 307 of the color mixture determination result (S504).

Next, it is determined whether or not the logical product bit 305 and the logical sum bit 307 of the color mixture determination result match (S505). In this step, if they do not match, the gradation quantization code φij303 for each pixel
The lower 1 bit for each pixel of the specific color flag signal 104
The process of replacing with is performed (S506). Thereafter, the code memory 206 stores the converted code data (S5
07), the process ends.

(Effect of this Embodiment) As described above, according to the image data encoding method and the image forming apparatus using the method according to this embodiment, a separate memory for accumulating the specific color flag signal 104 is provided. Without allocating an area, with the same memory amount as the conventional code block data,
It is possible to store multi-tone monochrome / specific color mixed image data and a specific color flag signal for each pixel.

[0071]

As described above, according to the image data encoding method (claim 1) of the present invention, when all the pixels in the block are only black and white images or all are specific color images. , The replaced average gradation index data, gradation dispersion index data, and multi-gradation image data quantized into four levels are encoded, and a black-and-white image and a specific color image are mixed in the block. In this case, the replaced average gradation index data and gradation distribution index data,
Since the multi-gradation image data quantized into two levels and the specific color flag signal are encoded, it is possible to reduce the memory for the specific color flag signal, which has conventionally needed to be stored separately from the block code data. it can.

An image forming apparatus of the present invention (claim 2)
In this case, when all the pixels in the block are black-and-white images only or all are specific color images, the replaced average gradation index data and gradation dispersion index data are quantized into four levels. When the block contains a black-and-white image and a specific color image, the replaced average gradation index data and gradation dispersion index data and the two-level quantum data are encoded. Since the encoded multi-gradation image data and the specific color flag signal are encoded, it is possible to reduce the memory for the specific color flag signal, which has conventionally been required to be stored separately from the block code data. Color image formation can be realized with the same memory capacity as a monochromatic image forming apparatus.

[Brief description of the drawings]

FIG. 1 is a block configuration diagram showing an outline of an image forming apparatus according to an embodiment.

FIG. 2 is a block diagram illustrating an internal configuration of an image data storage unit of the image forming apparatus according to the present exemplary embodiment.

FIG. 3 is an explanatory diagram showing a data configuration of code data for one block.

FIG. 4 is an explanatory diagram showing another data structure of code data for one block.

FIG. 5 is a flowchart illustrating a processing flow of an image data storage unit of the image forming apparatus according to the present exemplary embodiment.

FIG. 6 is a block diagram showing an outline of an image forming apparatus according to a conventional technique.

FIG. 7 is an explanatory diagram showing a block coding method which is one of the coding methods for compressing and reducing image data.

FIG. 8 is an explanatory diagram showing an algorithm for block coding.

FIG. 9 is an explanatory diagram showing a comparison of the data amount before and after encoding one block of image data.

FIG. 10 is an explanatory diagram showing an algorithm for decoding encoded image data.

FIG. 11 is an explanatory diagram showing an example of document data.

FIG. 12 is an explanatory diagram showing an outline of switching of image data in a spot color image forming apparatus according to a conventional technique.

FIG. 13 is an explanatory diagram showing a data configuration of accumulated code data of one block in a spot color image forming apparatus according to a conventional technique.

[Explanation of symbols]

Reference Signs List 101 scanner 102 A / D converter 103 specific color determination unit 104 specific color flag signal 105 image data switching unit 106 image processing unit 107 image output unit 108 image data storage unit image input unit 201 multi-tone monochrome / specific color mixed image data 4-line FIFO memory for storage 202 Encoding unit 203 4-line FIFO memory for storing specific color flag signal 204 Color mixture determination unit 205 Code data conversion unit 206 Code memory 301 Average gradation index code La (before conversion) 302 Grayscale dispersion index Code Ld (before conversion) 303 Grayscale quantization code for each pixel φij (before conversion) 304 Average grayscale index code La (after conversion) 305 Logical product bit of color mixture determination result 306 Grayscale distribution index code Ld (after conversion) 307 OR bit of the color mixture determination result 308 Gradation quantization code φij (variable for each pixel Tone quantization code φij not performed) 401 for each pixel (after conversion)

Claims (2)

[Claims] 1. Multi-gradation black-and-white / specific color mixed image data is divided into blocks each having a predetermined number of pixels,
An average gradation index and a gradation dispersion index in each of the divided blocks are calculated, and based on a specific color flag signal indicating a specific color in each pixel, whether all the pixels in the block are black and white images, It is determined whether all the images are specific color images, or a mixture of black-and-white images and specific color images, and the data related to the determined result is the average gradation index data and / or the gradation dispersion index data,
Substituting data designated in advance, and based on the result of the determination, when all the pixels in the block are black and white images or all images of a specific color, multi-tone image data is quantized into four levels, When a black-and-white image and a specific color image are mixed in the block, the multi-tone image data is quantized into two levels, and all pixels in the block are only the black-and-white image or all are the specific color image. In this case, the replaced average gradation index data, gradation dispersion index data, and multi-gradation image data quantized into four levels are coded, and a black-and-white image and a specific color image are mixed in the block. , The replaced average gradation index data and gradation dispersion index data, multi-gradation image data quantized into two levels, and the specific color flag signal Image data encoding method characterized in that encoded into. 2. A block dividing means for dividing multi-tone black-and-white / specific color mixed image data into blocks having a predetermined number of pixels, and an average gradation index in each block divided by the block dividing means. Average gradation index calculating means, a gradation distribution index calculating means for calculating a gradation distribution index in each block divided by the block dividing means, and a specific color flag signal indicating a specific color for each pixel On the basis of the above, a color mixture determination for determining whether all the pixels in the block divided by the block dividing means are monochrome images, all are specific color images, or whether monochrome images and specific color images are mixed Means and data relating to the result judged by the color mixture judging means, and the mean gradation index data calculated by the mean gradation index calculating means. Data and / or the gradation dispersion index data calculated by the gradation dispersion index calculation means,
If all the pixels in the block are black-and-white images or all specific-color images, based on the result of the index value changing device that replaces the data specified in advance and the color mixture determining device, Image data quantizing means for quantizing tonal image data into four levels, and quantizing the multi-tone image data into two levels when a black-and-white image and a specific color image are mixed in the block; If all the pixels in the pixel are black-and-white images only or all are specific color images, the average gradation index data and gradation dispersion index data replaced by the index changing means, and the image data quantizing means When the block is encoded with multi-tone image data quantized into levels and a black-and-white image and a specific color image are mixed, the index is changed. An image to be encoded into average gradation index data and gradation dispersion index data replaced by steps, multi-gradation image data quantized to two levels by the image data quantization means, and the specific color flag signal. An image forming apparatus comprising: a data encoding unit.