JPH0662251A - Image processor - Google Patents

Abstract

PURPOSE:To automatically correct gamma correcting characteristics corresponding to the characteristics of an output device to be used by reading printed-out images and detecting the image density characteristics. CONSTITUTION:In a gamma correction mode, a switching circuit 9 is activated under the control of a switch 10 and supplies a switching signal to a selector 2. At the same time, a test pattern generation circuit 11 is activated and outputs the test pattern of a prescribed pattern as an image signal to a gradation processing part 7 and further to a printer A. The temporarily printed-out image is read by a CCD or the like and inputted to a density measuring circuit 12, at this circuit 12, the density of the image is judged as a digital signal, and the density characteristic of the used printer is calculated. Although this result is supplied to a CPU 14, the data of a reading part are previously stored in the CPU 14, and the correction information of gamma correction is calculated from these kinds of information, calculated result and original/copy density characteristics and stored in a memory circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus, and more particularly to a function for correcting gamma correction characteristics according to the characteristics of a printing apparatus such as a printer to be connected, and gamma correction corresponding to the characteristics of an image to be processed. The present invention relates to an image processing apparatus that improves the quality of a print image by providing a function of correcting a correction characteristic and further correcting a gamma characteristic for each processed image area.

[0002]

2. Description of the Related Art Some image processing apparatuses such as copying machines are provided with means for improving the image quality by converting a read image signal into a digital signal and performing various processes. Gamma correction is one of these processes, and this process is to perform gradation correction of image density. Examples of the gradation correction of the density include a process of uniformly extending or contracting the range of possible density values, a non-linear conversion of expanding or compressing a specific density region from other parts, and the like. These processes are also used in particular to create a density value distribution suitable for the characteristics of an image reading sensor, a display device, or an output device such as a printer. As a correction characteristic for density gradation correction, a gentle S-curve with saturated upper and lower parts (Hurt)
What uses an er-Drift curve) is generally called gamma correction. In practice, digital gamma correction is generally performed by performing dither processing according to the above-described characteristic curve and calculating from the scanner characteristic of the image reading unit, the printer characteristic, and the original / copy density characteristic.

However, in the conventional image forming apparatus, since the above-mentioned gamma correction means is provided with only one preset gamma correction characteristic, when an output device such as a printer having different characteristics is connected, When the image processing process is different, the gamma correction may not be suitable and the image quality may be deteriorated. Further, some of them have a gamma correction characteristic that can be changed, but the adjustment is complicated because they are manually corrected. Further, in the image processing apparatus, in addition to gamma correction for an output device such as a printer, correction of filter characteristics and correction of gamma correction with respect to differences in characteristics of images to be processed are effective from the viewpoint of improving image quality.

Generally, there are three types of images to be processed: a character original, an original having continuous gradation like a silver halide photograph, and an original having a minute halftone dot structure like a printed matter.
Conventionally, there is one that separates edges and halftone dots by detecting density continuity, density peak detection, and halftone dot position detection, and performs filter processing suitable for each. However, in the conventional device, the gamma correction is performed only by manually changing the characteristics, and the algorithm for changing the filter processing for each image area is complicated and takes a lot of processing time. There was a drawback to

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the conventional image processing apparatus, and automatically corrects the gamma correction characteristic in accordance with the characteristic of the output device such as a printer to be used. It is an object of the present invention to provide an image processing device configured to perform a filtering process and a gamma correction correction suitable for the characteristics of a document image to be processed.

[0006]

To achieve this object, the first invention of the present application is an image processing apparatus for converting input image information into a digital signal and performing various kinds of signal processing, which is equipped with a gamma correction means. Switch means for switching between normal processing and gamma correction processing, means for generating a predetermined test pattern, means for reading an image printed based on image information output from the image processing apparatus, and means for reading the read image. It is characterized in that it is provided with means for measuring the density and means for correcting the correction characteristic of the gamma correction means based on the measurement result. A second invention of the present application is an image processing apparatus which similarly converts input image information into a digital signal and performs various kinds of signal processing, and includes a filter processing means, and obtains a histogram of a read image. Means, a means for separating an image area based on the histogram, and a means for switching the characteristics of the filter processing means for each area separated by the image area.
Furthermore, a third invention of the present application is an image processing apparatus which converts input image information into a digital signal and performs various signal processing, which is provided with a filter processing means and a gamma correction means. Means to ask,
The present invention further comprises means for separating an image area based on the histogram, means for switching the characteristics of the filter processing means for each area separated from the image area, and means for correcting the characteristics of the gamma correction means based on the histogram. And

The communication system control method of the present invention will be described in detail below. FIG. 1 is a processing block diagram of an image processing apparatus according to an embodiment of the present invention. The apparatus shown in this example is a shutter for performing a grayscale image boundary processing of an image signal input from an image reading unit such as a CCD. -Ding correction unit 1
And a selector 2 for switching and outputting a signal as described later.
A filter unit 3 for performing various processes on the image signal, a scaling unit 4 for enlarging / reducing as necessary, a gamma correction unit 5 for performing density gradation correction as described above, and a second selector. 6, a gradation processing unit 7 for performing density gradation, image processing /
A processing / editing processing unit 8 for editing, a switching circuit 9 connected to the first selector 2 and having a function of switching between a normal mode and a correction mode, and a switch 10 added to this switching circuit. , A test pattern generation circuit 11 that is activated by the output of the switching circuit to generate a test pattern, and
The density measuring circuit 12 to which the output of the first selector 2 is supplied, the calculating circuit 13 for calculating the correction value of the density of the image read based on the output of the measuring circuit, and the gamma correction value is corrected by the calculation result. The CPU 14 is provided as a main block.

The processing method and operation in this configuration will be described. In the normal operation, the switch 10 is in the open state, and the switching circuit does not operate in response to this, and the image forming processing known in the related art is performed. Output to a printer, etc.
On the other hand, when connecting to a printer having a different process as described above, the gamma correction mode is set by closing the switch 10. In this gamma correction mode, switch 10
The control circuit 9 activates the switching circuit 9 to supply a switching signal to the first selector 2. At the same time, the test pattern generating circuit 11 is activated, and the test pattern having a predetermined pattern is used as an image signal to the gradation processing unit 7 via the second selector 6.
Further, the data is output to the printer connected via the processing / editing unit 8.

Next, the image once printed out is read by the CCD or the like, subjected to shading processing, and then input to the density measuring circuit 12 through the first selector 2, where the density of the input image is digitally displayed. Expressed as a signal, the density characteristics of the printer used are calculated. The result is supplied to the CPU 14, which stores data such as the CCD characteristics of the CCD and the optical reading unit in advance. Based on these information, the calculated result, and the original / copy density characteristic. The correction information for gamma correction is obtained and stored in the memory circuit provided. When this series of processing is completed, the switch 10 is returned to the original state, and thereafter, the same image forming processing as the conventional one is executed. If the above-described control is performed by such a configuration, optimum gamma correction can be obtained even if printers having different characteristics are connected, so that it is possible to always obtain the best image quality.

FIG. 2 is a block diagram showing another embodiment of the present invention. The image processing apparatus shown in FIG. 2 is a sheer for performing a grayscale image boundary processing of an image signal input from an image reading unit such as a CCD. A photograph provided with a Ding correction unit 21, a filter unit 22 for performing various kinds of processing on an image signal, a scaling unit 23 for enlarging or reducing as necessary, and a means for performing gamma correction for performing density gradation correction. Mode gamma correction unit 2
4 and a character gamma correction unit 25, a gradation processing unit 26 that performs gradation processing of the output of the photograph mode gamma correction unit 24, an output of the character mode gamma correction unit 25, and an output of the gradation processing unit 26. Of the output of the shading unit 21, and a selector 27 that outputs any one of the output signals, a processing / editing processing unit 28 that processes / edits an image signal as needed and then outputs the processed image / processing to the printer. A density histogram detection unit 29 for detecting a density distribution of a read image signal by inputting a part thereof, and a characteristic of the read image based on the histogram are detected, and the original is a character image or a printed halftone image. A character detection unit 30 and a halftone dot detection unit 31 that detect whether there is any
And a determination circuit 32 that determines which one is based on the outputs of the two detection units and controls the filter 22 according to the determination result.

To explain the operation in this configuration, first, the image of the set original is read by the CCD, and the density histogram of the shading-corrected output is obtained. This processing is executed by the density histogram unit 29, and the result is the character detection unit 30 and the halftone dot detection unit 31.
Then, the density distribution value (histogram) of each reference is compared, and from the result, it is determined whether the image read by the determination circuit 32 is a character original or a halftone image of a printed matter or the like. The determination result is input to the filter 22 and set to the optimum filter or the optimum filter is selected according to whether the original is a character original or a halftone original. On the other hand, the image signal processed by the filter 22 is subjected to enlargement / reduction processing in the scaling unit 23 as necessary, and then input in parallel to the two different gamma correction mode units 24 and 25. However, either the photographic mode or the character mode is selected based on the signal output from the above-mentioned determination circuit by the selector 27 after the respective processes are performed, and the printer is passed through the processing / editing unit 28. Is output to.

According to such a configuration and control, even if the original to be processed is a text original or a photographic original, the characteristics of the filter and the gamma correction are automatically and optimally selected and set. It is possible to prevent the deterioration of the copied image due to the difference in the characteristics of the original to be processed as described above. In the above embodiment, the case where both the filter characteristic and the gamma correction characteristic are automatically controlled at the same time has been described, but the control of only one of them is effective in improving the image quality. Further, if the halftone dot portion and the edge portion of the image are separated based on the density histogram and the optimum filter processing and gamma correction are corrected for each area, the image quality improving effect becomes more remarkable. For example, every time one line of the read image is scanned, the halftone dot portion and the character portion may be separated and the above processing may be executed. Further, the means shown in FIG. 2 and the means explained in FIG. 1, that is, the image once printed out is read, the quality of the image density is judged, and the gamma correction is corrected so that the optimum density gradation can be obtained. It is also very effective to improve the image quality by using the above means together.

[0013]

As described above, according to the first means of the present invention, the image printed out is read, and the gamma correction characteristic is corrected by detecting the image density characteristic. The gamma correction characteristic can be set, and the image quality can be improved significantly. Further, according to the second means of the present invention, the filter characteristic or the gamma correction characteristic is switched according to the original image to be processed and further according to the partial characteristic of the original image. Is effective in bringing about.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram showing another embodiment of the present invention.

[Explanation of symbols]

1, 21 Shading correction unit, 2, 6, 27 selector, 3, 22 filter, 4, 23 scaling unit,
5 gamma correction unit, 7, 26 gradation processing unit, 8, 28
Processing / editing section, 9 switching circuits, 10 switches,
11 test pattern generation circuit, 12 density measurement circuit, 13 calculation circuit, 14 CPU, 24 photo mode gamma correction unit, 25 character gamma correction unit, 29
Density histogram detection unit, 30 character detection unit, 31
Halftone dot detector, 32 determination circuit.

Claims (3)

[Claims] 1. An image processing apparatus for converting input image information into a digital signal and performing various signal processing, comprising a gamma correction means, comprising: switch means for switching between normal processing and gamma correction processing; A means for generating a test pattern, a means for reading an image printed on the basis of image information output from the image processing apparatus, a means for measuring the density of the read image,
An image processing apparatus comprising: means for correcting the correction characteristic of the gamma correction means based on the measurement result. 2. An image processing apparatus for converting input image information into a digital signal and performing various kinds of signal processing, comprising filter processing means, means for obtaining a histogram of a read image, and the histogram An image processing apparatus comprising: means for separating an image area based on the image area; and means for switching a characteristic of a filter processing means for each area separated from the image area. 3. An image processing apparatus for converting input image information into a digital signal and performing various signal processing, comprising a filter processing means and a gamma correction means, and means for obtaining a histogram of a read image. A means for separating an image area based on the histogram, a means for switching the characteristics of the filter processing means for each area separated from the image area, and a means for correcting the characteristics of the gamma correction means based on the histogram. A characteristic image processing device.