JP2004320476A - Image processing apparatus and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processing apparatus and method for small memory capacity since a price of an image memory which stores raster data which should be printed has a big influence on the cost of a page printer, namely, it is desirable that the capacity of the image memory is small when considering the cost of the page printer. <P>SOLUTION: A compression part 21 compresses image data to be inputted and stores it in the image memory 2. A prediction/judgment part 11 predicts use quantity Y of the image memory 2 based on data quantity after compression and the number of compressed pixels to be successively supplied from the compression part 21 during execution of the compression and outputs a comparison result between the predicted use quantity Y and a preset threshold S. A CPU 501 cancels the image data stored in the image memory 2, instructs lowering of resolution of the inputted image data and makes the compression part 21 perform the compression of the image data after lowering of the resolution when the comparison result shows Y≥S. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image processing apparatus and a method thereof, and for example, relates to image processing for storing image data in a memory from which image data is read in a predetermined unit for image formation.
[0002]
[Prior art]
The engine of the page printer (hereinafter simply referred to as “engine”) operates at a constant speed. Therefore, it is necessary to supply raster data to the engine without delaying the operation of the engine. If the supply of raster data cannot keep up with the operation of the engine, the engine runs idle and printing becomes impossible.
[0003]
There are various methods to prevent the engine from running idle. One method starts printing after holding one page of raster data in an image memory. When this method is used, for example, when printing four-color full-color images at a recording density of 600 dpi on A4 recording paper, an image memory of 135 MB or more is required. Further, when the printing speed of the page printer increases, it is not enough to start the creation of raster data of the next page after printing is completed, and it is necessary to start the creation of raster data of the next page during printing. In this case, an additional image memory is required.
[0004]
Of course, if a large capacity image memory can be used, the above problem is solved. However, the price of an image memory for storing raster data to be printed has a great influence on the cost of a page printer. That is, considering the cost of the page printer, it is desirable that the capacity of the image memory be small.
[0005]
Therefore, a method of compressing raster data and storing it in an image memory is widely used. By compressing the raster data, the required capacity of the image memory is reduced. However, depending on the characteristics of the page, the data amount of the compressed raster data may be larger than the capacity of the image memory, and may not be stored in the image memory. This problem can be solved by lowering the resolution of the raster data and recompressing it.
[0006]
The simplest method of recompressing the raster data is a method of detecting that the image memory has run out, and then lowering the resolution and starting recompression. This approach adds little hardware and has little effect on printer cost. However, since recompression is started after the image memory becomes full, there is much waste, and improvement in processing speed cannot be expected.
[0007]
As another method, as disclosed in JP-A-4-323060, JP-A-6-233141, and JP-A-11-88189, there is a method of appropriately switching a plurality of compression circuits and compression methods. According to these methods, the processing speed is improved. However, this is not possible with a small amount of hardware, and has a great effect on the cost of the printer.
[0008]
[Patent Document]
JP-A-4-323060, JP-A-6-233141, JP-A-11-88189
[Problems to be solved by the invention]
An object of the present invention is to solve the above-mentioned problems individually or collectively, and it is an object of the present invention to prevent a memory from reading out image data in a predetermined unit for image formation with a simple configuration.
[0010]
Another object of the present invention is to predict the fullness of the memory and suppress an increase in image processing time.
[0011]
[Means for Solving the Problems]
The present invention has the following configuration as one means for achieving the above object.
[0012]
According to the present invention, when image data is stored in a memory from which image data is read out in a predetermined unit for image formation, input image data is compressed, stored in the memory, and sequentially supplied during execution of the compression. Based on the data amount after compression and the number of compressed pixels to be used, the usage amount of the memory is predicted, and a comparison result between the predicted usage amount and a preset threshold is output. When the usage amount ≧ the threshold value, the image data stored in the memory is discarded, the resolution of the input image data is reduced, and the compression of the image data after the resolution is reduced is performed.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, image processing according to an embodiment of the present invention will be described in detail with reference to the drawings.
[0014]
[Constitution]
FIG. 1 is a block diagram illustrating a configuration example of a data compression device 1 according to the embodiment.
[0015]
The data compression device 1 includes an image memory usage prediction / determination unit 11 and a compression unit 21.
[0016]
The prediction / judgment unit 11 predicts the use amount of the image memory 2 from time to time from the compressed raster data amount 103, and when the predicted use amount of the image memory 2 becomes larger than a preset threshold value, activates the image memory overflow signal 110. To The image memory overflow signal 110 is supplied to a CPU or a sequencer 500 that controls the entire printer system including the data compression device 1.
[0017]
The compression unit 21 compresses the raster data 101 by a method described later, and stores the compressed raster data 102 in the image memory 2. Further, the raster data amount 103 after compression and the number P of processed pixels are output to the prediction / determination unit 11.
[0018]
The prediction / determination unit 11 includes a memory counter 12, a differentiation circuit 13, a setting register 14, a prediction unit 15, and a determination unit 16.
[0019]
The memory counter 12 is a counter for accumulating the compressed raster data amount 103. The memory counter 12 is initialized when the compression operation starts.
[0020]
The differentiating circuit 13 calculates a differential coefficient a = dc / dP by differentiating the count value c of the memory counter 12 with the number P of pixels subjected to the compression processing. Since the count value c of the memory counter 12 indicates the usage amount of the image memory 2, the differential coefficient a indicates the rate of increase of the memory usage amount.
[0021]
The setting register 14 holds the number D of preceding pixels and the threshold S of the memory usage used by the determination unit 16. The number D of preceding pixels indicates how much the use amount of the image memory 2 is predicted at the pixel position preceding the current pixel position.
[0022]
The prediction unit 15 calculates a predicted usage amount Y from the differential coefficient a obtained by the differentiating circuit 13, the number of preceding pixels D held in the setting register 14, and the current count value c of the memory counter 12.
[0023]
The determination unit 16 compares the predicted usage amount Y obtained by the prediction unit 15 with the threshold value S held in the setting register 14, and predicts that the image memory 2 will be full if Y ≧ S, and overflows the image memory. Enable signal 110.
[0024]
The CPU 500 controls the entire printer system including the data compression device 1.
[0025]
FIG. 2 is a block diagram illustrating a configuration example of the compression unit 21. The compression unit 21 includes a buffer memory 201, a dither processing unit 202, a FIFO 203, an exclusive OR operation unit 204, a Huffman encoding unit 205, and a control unit 206. The operation of the compression unit 21 is controlled by the control unit 206.
[0026]
The input raster data 101 is stored in the buffer memory 201. The capacity of the buffer memory 201 may be a capacity that can hold raster data necessary for the processing of the dither processing unit 202. The dither processing unit 202 performs dither processing on the raster data buffered in the buffer memory 201. The dither processing result is delayed by FIFO 203 by the width of the dither matrix.
[0027]
The exclusive OR operator 204 performs an exclusive OR (XOR) operation on the dither processing result and the output of the FIFO 203. The Huffman encoding unit 205 encodes the result of the XOR operation and generates the compressed raster data 102.
[0028]
Since the data after the dither processing is delayed by the width of the dither matrix by the FIFO 203, the output of the FIFO 203 becomes the data of the pixel preceding the current pixel by the width of the dither matrix. Since the dither processing has periodicity, the data after the dither processing is likely to be similar data for each width of the dither matrix. Therefore, in the XOR operation performed by the exclusive OR operation unit 204, the probability of XORing the same value increases, and as a result, the output of the exclusive OR operation unit 204 is continuously “0” and the run length is long. Become.
[0029]
The control unit 206 controls the operation of the compression unit 21, accumulates and outputs the number of processed pixels P, and outputs the raster data amount 103 after compression.
[0030]
[Processing flow]
FIG. 3 is a flowchart illustrating the operation of the data compression device 1. The data compression device 1 is controlled by a CPU (or sequencer) 501.
[0031]
When raster data compression is required, such as when printing is instructed, the CPU 501 activates the data compression device 1, initializes the memory counter 12, and sets the preceding pixel number D and the threshold value S in the setting register 14 (S1). .
[0032]
After the initialization is completed, the data compression device 1 reads the raster data (S2), performs the compression process, and at the same time, predicts the predicted usage amount Y of the image memory 2 (S3). Then, every time the estimated usage amount Y is updated, the estimated usage amount Y is compared with the threshold value S (S4). If the comparison result is Y <S, there is space in the image memory 2 and the compression operation can be continued, but the end of the page is determined before the compression operation is continued (S5). When the compression processing for one page is completed, the CPU 501 is notified that the compression processing for one page is completed, and the compression processing is terminated. If the entire page has not been compressed, the process returns to step S2 to repeat the operation of reading and compressing the raster data.
[0033]
On the other hand, when Y ≧ S, the image memory 2 becomes full if the compression operation is continued as it is, so that the data compression device 1 enables the image memory overflow signal 110 and causes the CPU 501 to continue the compression operation. Signal that 2 is full. When the image memory overflow signal 110 becomes valid, the CPU 501 discards the compressed image data by, for example, initializing the image memory 2 and changes the resolution of the raster data (S6). Is returned to step S1.
[0034]
The resolution change of the raster data is realized by the CPU 501 notifying the drawing unit and the image processing unit that supply the raster data to the data compression device 1 of the change in the resolution and instructing the restart of the output of the raster data. .
[0035]
FIG. 4 is a flowchart illustrating a processing example of the prediction / determination unit 11.
[0036]
The data compression apparatus 1 is started, the memory counter 12 is initialized, and the number D of preceding pixels and the threshold value S are set in the setting register 14 (S11).
[0037]
The prediction / determination unit 11 accumulates the data amount after compression output from the compression unit 21 by the memory counter 12 (S12). The count value c of the memory counter 12 corresponds to the used amount of the image memory 2. The count value c is sent to the differentiating circuit 13 to be differentiated by the number of processed pixels P supplied from the compression unit 21 to calculate a differential coefficient a = dc / dP.
[0038]
Next, the prediction / judgment unit 11 supplies the differential coefficient a, the number of preceding pixels D held in the setting register 14 and the current count value c to the prediction unit 15, and causes the prediction unit 15 to calculate the predicted usage amount Y (S13). Then, the estimated use amount Y and the threshold value S held in the setting register 14 are supplied to the determination unit 16 to determine whether the image memory 2 is full (S14). If the determination result is Y ≧ S, the image memory overflow signal 110 is enabled (S15). If the determination result is Y <S, the process returns to step S12.
[0039]
FIG. 5 is a flowchart showing the use amount prediction processing of the image memory 2 by the differentiating circuit 13 and the prediction unit 15.
[0040]
The count value c is differentiated by the processed pixel number P to calculate a differential coefficient a = dc / dP (S21). Based on the differential coefficient a, the preceding pixel number D and the current count value c, according to the prediction formula (1), The predicted usage amount Y is calculated (S22), and the predicted usage amount Y is output to the determination unit 16 (S024). The above processing is repeated.
Y = a × D + c (1)
[0041]
When performing run-length compression after pre-processing raster data so as to make the run length as long as possible, the cumulative total of the compressed data increases almost linearly as the compression process proceeds. Since the compression unit 11 of the present embodiment performs the above-described pre-processing to perform the run-length compression, it is possible to predict the usage amount of the image memory 2 by a linear expression as shown in the prediction expression (1). Since the amount of use of the image memory 2 is predicted by a linear expression, the required hardware is small.
[0042]
Since it is possible to determine whether or not the image memory 2 becomes full before the image memory 2 becomes full, the compression operation is stopped before the image memory 2 becomes full, and the raster data It is possible to take measures such as lowering the resolution, and it is possible to eliminate waste of processing time without advancing the compression operation unnecessarily. In particular, since the amount of compressed data ahead of the number of preceding pixels D can be predicted, it can be determined whether or not the image memory 2 becomes full, and raster data with reduced resolution is compressed. In this case, it is possible to reduce the time from the start of compression to the restart of compression.
[0043]
Since the threshold value for determining whether or not the image memory 2 becomes full can be changed, the same hardware can cope with printers having different capacities of the image memory 2.
[0044]
In particular, in a page printer equipped with a small-capacity page memory, it is possible to prevent the page memory from being full and increase the image processing time by adding a small amount of hardware.
[0045]
[Other embodiments]
The present invention can be applied to a system including a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.), but may be a device including one device (for example, a copying machine, a facsimile machine, etc.). May be applied.
[0046]
Further, an object of the present invention is to supply a storage medium (or a recording medium) in which a program code of software for realizing the functions of the above-described embodiments is recorded to a system or an apparatus, and a computer (or a CPU or a CPU) of the system or the apparatus. Needless to say, the present invention can also be achieved by an MPU) reading and executing a program code stored in a storage medium. In this case, the program code itself read from the storage medium realizes the function of the above-described embodiment, and the storage medium storing the program code constitutes the present invention. When the computer executes the readout program code, not only the functions of the above-described embodiments are realized, but also an operating system (OS) running on the computer based on the instruction of the program code. It goes without saying that a part or all of the actual processing is performed and the functions of the above-described embodiments are realized by the processing.
[0047]
Further, after the program code read from the storage medium is written into a memory provided in a function expansion card inserted into the computer or a function expansion unit connected to the computer, the function of the program is performed based on the instruction of the program code. It goes without saying that the CPU included in the expansion card or the function expansion unit performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.
[0048]
When the present invention is applied to the storage medium, the storage medium stores program codes corresponding to the flowcharts described above.
[0049]
【The invention's effect】
As described above, according to the present invention, it is possible to prevent the memory from being read out from the image data in a predetermined unit for image formation with a simple configuration.
[0050]
Further, it is possible to predict the fullness of the memory and suppress an increase in the image processing time.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration example of a data compression device;
FIG. 2 is a block diagram illustrating a configuration example of a compression unit.
FIG. 3 is a flowchart for explaining the operation of the data compression device;
FIG. 4 is a flowchart illustrating a processing example of a prediction / determination unit;
FIG. 5 is a flowchart illustrating a process of estimating a usage amount of an image memory by a differentiating circuit and a prediction unit;

Claims (4)

An image processing apparatus for storing image data in a memory from which image data is read in a predetermined unit for image formation,
Compression means for compressing input image data and storing it in the memory;
Prediction means for predicting the amount of use of the memory, based on the data amount after compression and the number of compressed pixels sequentially supplied from the compression means performing compression;
A comparison unit that outputs a comparison result between the predicted usage amount and a preset threshold value,
If the comparison result indicates the usage amount ≧ the threshold value, the image data stored in the memory is discarded, the resolution of the input image data is reduced, and the compression of the image data after the resolution is reduced is performed by the compression unit. Control means to be executed,
A compression unit configured to perform dither processing by comparing the input image data with a threshold value in a dither matrix, and to exclude a processing result of the dither processing unit from a result of preceding dither processing by a width of the dither matrix; A logical operation unit for taking a logical sum, and a compressor for run-length compression of the result of the exclusive logical sum,
The prediction means is an accumulator that accumulates the compressed data amount sequentially supplied from the compression means, a differentiator that differentiates the accumulation result by the number of compressed pixels, and the differentiation result and the An image processing apparatus, comprising: a predictor for predicting the memory usage based on a cumulative result. An image processing method for storing image data in a memory from which image data is read in a predetermined unit for image formation,
Compress the input image data and store it in the memory,
Based on the data amount after compression and the number of compressed pixels that are sequentially supplied during the execution of the compression, predict the amount of memory used,
Outputting a comparison result between the predicted usage amount and a preset threshold value,
When the comparison result indicates the usage amount ≧ the threshold value, discarding the image data stored in the memory, instructing a reduction in the resolution of the input image data, and executing compression of the image data after the resolution reduction. Characteristic image processing method. A program for causing an image processing apparatus to execute the image processing according to claim 2. A recording medium on which the program according to claim 3 is recorded.

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