JP2023048313A - Image processing apparatus and image forming apparatus - Google Patents

Abstract

To provide an image processing apparatus and an image forming apparatus that make output dots into a cluster at a high speed in a relatively small storage area.SOLUTION: In an image processing apparatus, a quantizer 2 quantizes pixel values after filter processing by a filter processing part 1, to generate output pixel values. A buffer 5 stores, for each of the pixels, a difference between the output pixel value and a sum of the pixel value after the filter processing by the filter processing part 1, and an input pixel value. The filter processing part 1 comprises a plurality of processing elements 11. The plurality of processing elements 11 sequentially selects target pixels in a plurality of blocks obtained by dividing an object image in a main scanning direction, and on the basis of, the difference stored in the buffer 5, executes band-pass filter processing in parallel on the target pixels. A size in the main scanning direction of the blocks is equal to or more than a value obtained by adding 1 to a value obtained by making half a size in the main scanning direction of a filter window of the filter processing into an integer.SELECTED DRAWING: Figure 1

Description

The present invention relates to an image processing apparatus and an image forming apparatus.

An image processing device applies a spatial band-pass filter to output pixel values from values obtained by applying a spatial low-pass filter to input pixel values when binarizing input pixel values. The value obtained by subtracting the value obtained by the application is quantized (binarized) while performing error diffusion. By doing so, the binarized output dots are clustered according to the cluster size (the degree of aggregation of the output dots) according to the filter characteristics of the bandpass filter.

When output dots are clustered, depending on the image to be output, the graininess of the image may become large during color output. , performs band-pass filtering on the difference between the output pixel value and the input pixel value of pixels surrounding the pixel of interest, performs error diffusion processing of the quantization error on the output of the filtering processing, and performs The obtained value is quantized to specify the output pixel value of the pixel of interest. In the filtering process, the bandpass filter has different characteristics in the main scanning direction and the sub-scanning direction, and also for each constituent color of the image. Filter processing is executed, and the filter coefficients of the band-pass filter processing are corrected for each component color of the image with a correction coefficient corresponding to the angle from the main scanning direction in order to reduce banding (see, for example, Patent Document 1). .

In another image processing device, a buffer stores, for each pixel, the difference between the sum of the pixel value after filtering by the filtering unit 1 and the input pixel value and the output pixel value, and the filtering unit stores: Based on the difference stored in the buffer 5, bandpass filtering is performed, and the quantizer quantizes the pixel values filtered by the filtering unit to generate output pixel values. (see, for example, Patent Document 2). As a result, only one buffer holds the value of the past pixel of interest, so the required storage area is relatively small. , the amount of data calculation can be reduced, and the circuit scale can be reduced.

JP 2017-046275 A JP 2021-019257 A

However, the filtering process described above is executed sequentially for each pixel along the scanning direction, resulting in a long processing time.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and provides an image processing apparatus and an image forming apparatus that cluster output dots at high speed with a relatively small storage area.

An image processing apparatus according to the present invention is an image processing apparatus that generates and outputs binarized output pixel values from input pixel values of a target image, and includes a filter processing unit, and a quantizer for quantizing a pixel value to generate the output pixel value; and a buffer for storing. The filter processing unit includes a plurality of processing elements, and the plurality of processing elements sequentially select pixels of interest in each of a plurality of blocks obtained by dividing the target image in the main scanning direction. A band-pass filtering process is performed in parallel on the pixel of interest based on the difference stored in the buffer. The size of the block in the main scanning direction is equal to or greater than a value obtained by adding 1 to a value obtained by converting half the size of the filter window in the filtering process in the main scanning direction into an integer.

An image forming apparatus according to the present invention includes the image processing apparatus described above and a printing apparatus that prints an image based on the output pixel values.

According to the present invention, it is possible to obtain an image processing apparatus and an image forming apparatus that cluster output dots at high speed with a relatively small storage area.

The above and other objects, features and advantages of the present invention will become further apparent from the following detailed description together with the accompanying drawings.

FIG. 1 is a block diagram showing the configuration of an image processing apparatus according to an embodiment of the invention. 2A and 2B are diagrams for explaining pixels referred to in order to perform a filter operation on a pixel of interest in the parallel processing of the filter processing unit 1 in FIG.

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a block diagram showing the configuration of an image processing apparatus according to an embodiment of the invention. The image processing apparatus shown in FIG. 1 generates and outputs binarized output pixel values from input pixel values of a target image. there is This image processing apparatus is implemented by, for example, a microcomputer, an ASIC (Application Specific Integrated Circuit), or the like. The input pixel value is, for example, an 8-bit multi-gradation value and takes any value from 0 to 1. The output pixel value is either 0 or 1.

The image processing device shown in FIG. Input pixel values of target pixels are sequentially input to the image processing apparatus in accordance with a predetermined scanning order.

The filtering unit 1 performs bandpass filtering based on the difference stored in the buffer 5 and described later. Specifically, the filter processing unit 1 performs a sum-of-products operation between the above-described differences and filter coefficients for peripheral pixels of the pixel of interest.

The quantizer 2 quantizes the pixel values after filtering by the filtering unit 1 to generate output pixel values. Here, the threshold value is set to 0, and the output pixel value is set to 1 if the output of the filter processing unit 1 is 0 or more, and set to 0 otherwise. When the input pixel value of the pixel of interest is 0 or 1, the quantizer 2 directly sets the output pixel value of the pixel of interest to 0 or 1. FIG.

The adder 3 calculates the sum of the input pixel value and the pixel value after processing by the filter processing unit 1 for the pixel of interest.

The subtractor 4 calculates the difference between the value of the calculation result of the adder 3 and the output pixel value for the pixel of interest. When calculating the difference, the difference is calculated after converting the binarized output pixel value (0 or 1) into a multi-tone value (0 or 1).

The buffer 5 has a storage area such as a memory (SRAM (Static Random Access Memory), DRAM (Dynamic Random Access Memory), etc.), which is not shown, and sequentially stores the values of the calculation results of the subtractor 4 for the pixel of interest. Store in the memory area. That is, the buffer 5 stores, for each pixel, the difference between the sum of the pixel value after filtering by the filtering unit 1 and the input pixel value and the output pixel value.

The size of the buffer 5 is set to a size capable of storing difference data for NX×((int)M/2+1) pixels or more. Here, NX is the number of pixels in the main scanning direction of the target image, int is the integer operation (that is, truncation below the small end point), and M is the size of the filter window in the sub-scanning direction for filtering. (filter size in the sub-scanning direction).

Specifically, the buffer 5 stores the difference between the output pixel values that have already been generated in the above-described scanning order, and the filter processing unit 1 stores the difference in the output pixel values that have already been generated in the above-described scanning order. Based on the difference stored in 5, band-pass filtering is performed on the pixel of interest.

2A and 2B are diagrams for explaining pixels referred to in order to perform a filter operation on a pixel of interest in the parallel processing of the filter processing unit 1 in FIG.

The filter processing unit 1 includes a plurality of processing elements 11, and uses the plurality of processing elements 11 to execute the filtering process described above in parallel. Specifically, the plurality of processing elements 11 sequentially select target pixels in a plurality of blocks obtained by dividing the target image in the main scanning direction (with the same size). Bandpass filtering is performed in parallel based on the differences stored in . Here, the size of the block in the main scanning direction (block size B) is obtained by converting a half of the size N of the filter window in the main scanning direction in the filtering process described above into an integer (that is, truncating the small end point and below). It is equal to or greater than the value obtained by adding 1 to the value. That is, a pixel of interest is set for each block, and filtering of the pixel of interest is executed in parallel. The processing elements 11 are respectively processors, and for example, processor cores of GPUs (Graphics Processing Units) may be used as the processing elements 11 . Also, the buffer 5 is shared by a plurality of processing elements 11, and the processing elements 11 are capable of reading the difference for pixels within each block and its adjacent blocks.

At this time, since the target pixel is moved along the main scanning direction and the sub-scanning direction (or meandering scanning) for each block, the output pixel values are calculated for the pixels subsequent to the current target pixel. not been Therefore, as shown in FIG. 2, the filter processing unit 1 performs a product-sum operation of the above-described difference already derived from among the pixels surrounding the pixel of interest and the filter coefficients. That is, the sum-of-products operation of the above-described difference and filter coefficient is executed with the difference for subsequent pixels set to zero. Here, when pixels of an adjacent block are included in the filter window centered on the position of the target pixel, if the difference of the pixels of the adjacent block has already been derived, the difference of the pixels of the adjacent block is Data is read out from the buffer 5 and the sum-of-products operation described above is executed.

Note that, for example, as described in Japanese Patent Application Laid-Open No. 2021-019257, the above-described band-pass filter processing is a DoG (Difference of Gaussian) filter processing.

Next, operation of the image processing apparatus according to Embodiment 1 will be described.

This image processing apparatus moves a target pixel along a predetermined scanning pattern for each color plane of each component color of one image, and sequentially derives an output pixel value of the target pixel.

At that time, for the pixel of interest, based on the above-described differences already derived and stored in the buffer 5, the filtering unit 1 (processing element 11) executes the above-described filtering process for a plurality of blocks in parallel. , a filter processor 1 (processing element 11) and a quantizer 2 derive and output an output pixel value. 5.

The value stored in the buffer 5 is a value obtained by adding the input pixel value to the difference between the input value and the output value of the quantizer 2 (that is, the quantization error). The filtering operation of the processing unit 1 is performed, and the filtering operation of the filtering unit 1 is performed on the quantization error, and the sum of the results of both filtering operations becomes the output of the filtering unit 1 .

That is, one filter processing unit 1 performs filtering processing for input pixel values of peripheral pixels and filtering processing for quantization errors of peripheral pixels, the former realizing clustering of output dots, and the latter Gradation preservation before and after quantization (corresponding to error diffusion) is achieved.

In this way, for all the component colors (for example, CMYK), after obtaining binary images based on the above output pixel values, these binary images are developed with respective color toners and output as color output images. be done.

As described above, according to the first embodiment, the quantizer 2 quantizes the pixel values after filtering by the filtering unit 1 to generate output pixel values. The buffer 5 stores the difference between the sum of the pixel value after filtering by the filtering unit 1 and the input pixel value and the output pixel value for each pixel. The filter processing unit 1 includes a plurality of processing elements 11, and the plurality of processing elements 11 sequentially select a target pixel in each of a plurality of blocks obtained by dividing a target image in the main scanning direction. For pixels, bandpass filtering is performed in parallel based on the differences stored in the buffer 5 . The size of the block in the main scanning direction is equal to or greater than the value obtained by adding 1 to the value obtained by converting half the size of the filter window in the main scanning direction in the filtering process into an integer.

As a result, output dots can be clustered in a relatively small storage area, and filtering can be performed at high speed by parallel processing. Due to parallel processing, error propagation for a plurality of pixels is performed in parallel, so quantization processing for the entire image is performed in a short time.

Various changes and modifications to the above-described embodiments will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of its subject matter and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the claims.

For example, the image processing apparatus according to the above embodiments may be incorporated in an image forming apparatus. In that case, the image forming apparatus further includes a printing device, and the printing device outputs the above output pixel values. Print the target image based on

Further, in the above embodiment, a plurality of quantizers 2, a plurality of adders 3, and a plurality of subtractors 4 are provided, and the plurality of quantizers 2, the plurality of adders 3, and the plurality of subtractors 4 are , quantization, addition operation, and subtraction operation may be performed in parallel on filtered pixel values generated by parallel processing. For example, the multiple processor cores of the GPU described above may also be used as these multiple quantizers 2, multiple adders 3, and multiple subtractors 4. FIG.

Furthermore, in the above embodiment, an image rotation unit is provided, and when the size of the target image in the main scanning direction is larger than the size in the sub-scanning direction, the image rotation unit rotates the target image by 90 degrees or −90 degrees. , the above-described processing may be executed. In this case, the size of the target image in the main scanning direction is reduced, and the size of the buffer 5 can be reduced.

The present invention is applicable to, for example, an image forming apparatus.

1 filter processor 2 quantizer 5 buffer 11 processing element

Claims (3)

In an image processing device that generates and outputs binarized output pixel values from input pixel values of a target image,
a filtering unit;
a quantizer for generating the output pixel value by quantizing the pixel value after filtering by the filtering unit;
a buffer for storing, for each pixel, the sum of the pixel value after filtering by the filtering unit and the input pixel value, and the difference between the output pixel value;
The filtering unit comprises a plurality of processing elements,
The plurality of processing elements sequentially select a pixel of interest in each of a plurality of blocks obtained by dividing the target image in the main scanning direction, and for the pixel of interest, the difference stored in the buffer. performs bandpass filtering in parallel based on
the size of the block in the main scanning direction is equal to or greater than a value obtained by adding 1 to a value obtained by converting half the size of the filter window in the filtering process in the main scanning direction into an integer;
An image processing device characterized by: the input pixel values are sequentially input along a predetermined scanning order;
the buffer stores the difference for the output pixel values that have already been generated in the scan order;
The plurality of processing elements perform the bandpass filtering of the pixel of interest based on the difference already stored in the buffer when performing the bandpass filtering of the pixel of interest;
2. The image processing apparatus according to claim 1, characterized by: an image processing apparatus according to claim 1 or claim 2;
a printing device that prints the target image based on the output pixel values;
An image forming apparatus comprising:

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