JP2002094794A - Image processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image processor that conducts gamma correction with high accuracy, without having to use of a lookup table LUT. SOLUTION: A read section 1 reads the side of an original, an amplifier 14 adjusts the amplitude of a read image, an analog/digital converter 15 quantizes the image into digital image data. A shading correction section 16 applies shading correction processing to the generated digital image data and gives the data to an image processing section 2 where the image data are subjected to filter processing, gamma-correction processing and gradation processing or the like, and the resulting data are fed to an image forming section 3. Through the processing of a desired image signal, the processing of converting a quantization value of the digital image signal is conducted according to a tone curve. The tone curve is an approximated tone curve through the combination of linear functions, each having a different gradient. The processing of the image processor approximates the tone curve through the combination of the linear functions with different gradients and can conduct gamma correction with high accuracy, without having to use the LUT.

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, for example, a digital copying machine, a facsimile, a printer, a scanner, and an image processing apparatus which is integrated as a digital multifunction machine.
In particular, the present invention relates to an image processing device to which a quantization value conversion (γ correction) process and a tone curve approximation processing method according to a tone curve performed by the image processing device are applied.

[0002]

2. Description of the Related Art Conventionally, in an image processing apparatus, a gamma correction of digital image data is performed by loading a lookup table (LUT) called a tone curve for data value conversion into a memory in advance and referring to the LUT. This is generally done by: In the case of this method, the size of the LUT must be equal to the number of quantization values that can be taken by the input image data.

On the other hand, JP-A-8-32837 and JP-A-11-196293 approximate a tone curve by linear approximation without using an LUT, and perform gamma correction based on the approximated tone curve. A gamma correction circuit has been invented.

[0004]

However, in the above-mentioned conventional invention, there is no flexibility in the number of divisions and division points when a tone curve is divided and linear approximation is performed, and sufficient accuracy may be obtained depending on the shape of the tone curve. There is a problem that cannot be approximated by Further, since the γ correction is performed by dedicated hardware, when the tone curve is changed, transmission of the tone curve information to the γ correction hardware is not easy.

[0005] In view of the above, a first object of the present invention is to approximate a tone curve by combining a plurality of linear functions having different slopes, and to perform gamma correction with high accuracy without using an LUT. An object of the present invention is to provide an image processing device.

A second object is to provide a programmable SI for an arithmetic processing unit for performing image processing on a digital image signal.
By using the MD type processor, it is possible to easily change the approximate tone curve and reduce the burden on the designer when designing the tone curve.

A third object is to provide an image processing apparatus capable of transmitting information of an approximate tone curve derived on the external device side to the image processing device side through communication between the image processing device and the external device.

A fourth object of the present invention is to provide an image processing apparatus capable of sampling the coordinates of a tone curve to be approximated at n locations, performing linear approximation, and deriving an approximate tone curve with a minimum error.

A fifth object is to extract an arbitrary area of the determined approximate tone curve, sample the coordinates of the nonlinear function at m positions again in the area, and obtain an approximate tone which minimizes the error by linear approximation. An object of the present invention is to provide an image processing device capable of deriving a curve.

A sixth object is to evaluate the error in the determined approximate tone curve, extract a region having the maximum error, and correct the approximate tone curve for the extracted region. Another object of the present invention is to provide an image processing apparatus capable of deriving a tone curve with higher approximation accuracy.

[0011]

According to a first aspect of the present invention, there is provided an image processing apparatus for reading an original document, quantizing the read image signal, and converting the read image signal into a digital image signal. And an image processing device having means for performing image processing on the digital image signal and performing processing to obtain a desired image signal, wherein the means for performing processing to obtain the desired image signal includes a tone curve. In which the tone curve is a tone curve approximated by combining a plurality of linear functions having different slopes.

A second aspect of the present invention is characterized in that the means for performing image processing on the digital signal and performing processing to obtain a desired image signal is a SIMD type arithmetic processor.

According to a third aspect of the present invention, the image processing apparatus includes communication means for communicating with an external device, the external device performs an approximate calculation of the tone curve, and the communication means approximates the image processing apparatus. It is characterized by transmitting the information of the tone curve.

According to a fourth aspect of the present invention, the external device generates means for sampling the coordinates of the tone curve to be approximated at n positions, and an approximate tone curve comprising a plurality of linear functions connecting the coordinates with straight lines. Means for calculating an error between the target tone curve and the approximate tone curve, and means for evaluating the calculated error and determining an approximate tone curve that minimizes the error as a tone curve to be transmitted to the image processing apparatus. It is characterized by having.

According to a fifth aspect of the present invention, there is provided a means for extracting an arbitrary region of the determined approximate tone curve, and a means for sampling the coordinates of the target tone curve at m locations again to approximate the region. And the correction of the approximate tone curve is performed.

In a sixth aspect, the means for extracting an arbitrary area of the determined approximate tone curve includes means for evaluating an error between the target tone curve and the approximate tone curve in the approximate tone curve. And extracting a region having a maximum error.

(Operation) According to the first aspect, an image processing apparatus which approximates a tone curve by combining a plurality of linear functions having different slopes and performs γ correction with high accuracy without using an LUT. Can be provided.

According to the second aspect of the present invention, the approximate tone curve can be easily changed by using a programmable SIMD type arithmetic processor in the arithmetic processing unit for performing image processing on the digital image signal, and the tone curve design can be simplified. The burden on the designer at the time can be reduced.

According to the third aspect, it is possible to provide an image processing apparatus capable of transmitting information on the approximate tone curve derived on the external device side to the image processing device side by communication between the image processing device and the external device. .

According to the fourth aspect of the present invention, it is possible to provide an image processing apparatus capable of sampling the coordinates of the tone curve to be approximated at n points, performing linear approximation, and deriving an approximate tone curve with a minimum error.

According to the fifth aspect, an arbitrary area of the determined approximate tone curve is extracted, and the coordinates of the nonlinear function are sampled again at m points in the area, and the error is minimized by linear approximation. An image processing device that can derive an approximate tone curve can be provided.

According to the sixth aspect, an error is evaluated from the determined approximate tone curve, a region where the error is maximum is extracted, and the approximate tone curve is corrected for the extracted region. Accordingly, it is possible to provide an image processing apparatus that can derive a tone curve with higher approximation accuracy.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of an image processing apparatus according to the present invention will be described in detail with reference to the accompanying drawings. FIG.
10 to FIG. 10, there is shown an embodiment of the image processing apparatus of the present invention.

FIG. 1 shows an embodiment of an image processing apparatus according to the present invention, and shows a configuration of a copying machine. The document surface is read by the reading unit 1. The light emitted from the lamp 11 is reflected on the surface of the document 12, converted into an electric signal by the CCD 13, and the amplitude of the light is adjusted by the amplifier 14.
The image data is quantized by the / D converter 15 to become digital image data.

The generated digital image data is subjected to shading correction processing by a shading correction unit 16, and
The image data is input to the image processing unit 2 and filtered, γ-corrected,
After being subjected to gradation processing and the like, it is sent to the image forming unit 3. The digital image data input to the image forming unit 3 is converted into a laser beam in a writing unit 31 according to the data value.
The photosensitive member 33 charged by the charging charger 32 is irradiated to form an electrostatic latent image on the surface of the photosensitive member.

The developing sleeve 34 adheres toner to the photoreceptor surface in accordance with the formed electrostatic latent image. The toner adhering to the photoconductor surface is transferred onto the paper surface sent from the paper feed tray 35, passes through the fixing unit 36, and is output as a copy original.

FIG. 2 shows a tone curve used in the γ correction process, which is one of the processes performed in the image processing section. According to the tone curve, the quantization value of the input image signal is converted into an output image signal.

FIG. 3 is a block diagram of a gamma correction circuit using an LUT, which is a general method of realizing gamma correction processing. An LUT for quantization value conversion according to the tone curve shown in FIG. 2 is previously formed on the memory. The address generation unit 211 generates an address on the LUT in which the image data value to be converted is stored, based on the input image data value. The memory 212 receives an address and a memory control signal, and outputs output image data.

The graph shown by the solid line in FIG. 4 approximates the tone curve by combining a plurality of linear functions having different slopes. The graph shown by the broken line in FIG. 4 shows the approximation target tone curve of the approximation target. By using the approximate tone curve approximated by the combination of the linear functions, the γ correction processing is realized without using the LUT memory shown in FIG.

FIG. 5 shows a programmable SIMD type arithmetic processor 22 for performing image processing. The SIMD type arithmetic processor 22 has a program loaded into the program RAM 221 from the outside via a global processor, performs image processing on input image data according to the program, and outputs it as output image data.

In the γ correction using the approximate tone curve shown in FIG. 4, the gradients of the linear functions 1 to 8 and the coordinates of the starting point are represented by data RA.
This is realized by loading a program into M222, referring to the data RAM 222, deriving an arithmetic expression from the inclination and the coordinates of the starting point, and executing a program for performing arithmetic processing of γ correction. Here, an example of approximation using eight linear functions is shown, but the number is arbitrary.

FIG. 6 shows a system in which an external device 50 for performing approximate calculation of a tone curve is connected to the image processing apparatus of FIG. The external device 50 is connected to the image processing device via a data bus. The external device 50 performs an approximate calculation of the target tone curve, and obtains the slope of the approximate tone curve and the coordinates of the starting point. The obtained approximate slope of the tone curve and the coordinates of the starting point are stored in the external device 5 via the data bus.
0 is transmitted to the image processing apparatus by communication between the image processing apparatus and the image processing apparatus.

FIG. 7 shows an example in which the coordinates of a tone curve to be approximated are sampled at n points, and an approximate tone curve composed of a plurality of linear functions connecting the coordinates with straight lines is generated. The broken line is the approximate tone curve of interest and the solid line is the approximate tone curve. Here, the start point and end point of the approximate tone curve are fixed points using the start point and end point of the target approximate target tone curve. Here, a case will be described where two arbitrary points are sampled between the start point and the end point (n = 2) to perform approximation.

FIG. 8 is a flowchart showing an algorithm for approximating a tone curve. Of the starting point of the tone curve
The x coordinate is x0 and the x coordinate of the end point is x3 (step S
1). When the tone curve to be approximated is TCorg (x),
2 points from TCorg (x) (d1, TCorg (d1)), (d2, TCorg (d
2)) is sampled, and 4 points (x0, TCorg (x0)), (d
1, TCorg (d1)), (d2, TCorg (d2)), (x3, TCorg (x3)
) Is approximated by a straight line TCaprx ｜ d1, d2
(x) is generated (step S2). Where d1 = x0 + 1, x0 +
, X3-2, d2 = x0 + 2, x0 + 3, ..., x3-1.
The approximate error err (d1, d2) between TCorg (x) and the generated approximate tone curve is calculated according to Equation 1 (step S3).

[0035]

(Equation 1)

In the above equation (1), err (d1, d2)
Is determined as coordinates (x1, x2) that gives an approximate tone curve with the highest approximate accuracy (steps S4 to S10).

FIG. 9 shows an example in which an arbitrary area of the approximate tone curve is extracted, the coordinates of the target tone curve are sampled again at m points, and the area is extracted by a method similar to the method shown in FIGS. The approximation is performed and the approximation tone curve is corrected. Here, a case where an area of the linear function 2 is extracted, two points of the coordinates of the area are sampled (m = 2), and approximation is performed is described. The coordinates indicated by black circles are the newly obtained approximate coordinates for correcting the approximate tone curve.

FIG. 10 shows a procedure for evaluating an error between the approximate tone curve to be approximated and the approximate tone curve in the approximate tone curve and extracting a region where the error is maximum. The approximate error of each area from the area 1 to the area 3 is obtained by Expression 2.

[0039]

(Equation 2)

By comparing the approximation errors, a region where the error is maximum is determined, and the region is determined to be a region where correction should be applied to the approximate tone curve in order to increase the approximation accuracy.

[0041]

As is apparent from the above description, according to the first aspect of the present invention, means for reading a document surface, quantizing the read image signal and converting the read image signal into a digital image signal, An image processing apparatus having means for performing image processing on the digital image signal so as to obtain a desired image signal, wherein the means for performing processing so as to obtain the desired image signal is based on a tone curve. It is possible to provide an image processing apparatus which performs a process of converting a quantized value, and wherein the tone curve is a tone curve approximated by combining a plurality of linear functions having different slopes.

According to the second aspect of the present invention, the means for performing image processing on the digital signal so as to obtain a desired image signal is a SIMD type arithmetic processor. An image processing apparatus according to claim 1 can be provided.

According to the third aspect of the present invention, the image processing apparatus includes communication means for performing communication with an external device, performs an approximate calculation of the tone curve by the external device, and performs image approximation by the communication means. The image processing apparatus according to claim 1 or 2, wherein information of a tone curve approximate to the processing apparatus is transmitted.

According to the fourth aspect of the present invention, the external device samples the coordinates of the tone curve to be approximated at n positions, and an approximation composed of a plurality of linear functions connecting the coordinates with straight lines. Means for generating a tone curve;
Means for calculating an error between the target tone curve and the approximate tone curve, and means for evaluating the calculated error and determining an approximate tone curve that minimizes the error as a tone curve to be transmitted to the image processing apparatus. Item 3 can provide the image processing device.

According to the invention described in claim 5, means for extracting an arbitrary area of the determined approximate tone curve,
5. The image processing apparatus according to claim 4, further comprising: means for sampling the coordinates of the target tone curve again at m points in the area and performing approximation, and correcting the approximate tone curve. Can be provided.

According to the sixth aspect of the present invention, the means for extracting an arbitrary area of the determined approximate tone curve comprises:
6. The image processing apparatus according to claim 5, further comprising means for evaluating an error between the target tone curve and the approximate tone curve in the approximate tone curve, and extracting a region where the error is maximum. it can.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an image processing apparatus according to an embodiment of the present invention.

FIG. 2 illustrates a tone curve used in a γ correction process, which is one of processes performed by an image processing unit.

FIG. 3 is a block diagram of a gamma correction circuit using an LUT, which is a general method for implementing gamma correction processing.

FIG. 4 is a schematic diagram of an approximate tone curve.

FIG. 5 is a block diagram illustrating a configuration example of a programmable SIMD type arithmetic processing processor.

FIG. 6 is a block diagram showing an image processing apparatus to which an external device for performing approximate calculation of a tone curve is connected.

FIG. 7 shows a tone curve obtained by sampling the coordinates of the tone curve at n places and performing approximation.

FIG. 8 is a flowchart showing a procedure for performing approximation by sampling at n places.

FIG. 9 shows a corrected tone curve.

FIG. 10 is a diagram for explaining a method of extracting an area for correcting an approximate tone curve by error evaluation.

[Explanation of symbols]

 DESCRIPTION OF REFERENCE NUMERALS 1 reading unit 2 image processing unit 3 image forming unit 11 lamp 12 original 13 CCD 14 amplifier 15 A / D converter 16 shading correction unit 22 SIMD type arithmetic processing processor 31 writing unit 32 charging charger 33 photoconductor 34 developing sleeve 35 paper feed Tray 36 Fixing unit 750 External device 211 Address generation unit 212 Memory 221 Program RAM 222 Data RAM

Claims (6)

[Claims] 1. A means for reading a document surface, quantizing the read image signal and converting it to a digital image signal, performing image processing on the digital image signal, and performing processing so as to obtain a desired image signal. In an image processing apparatus having predetermined means, the predetermined means for performing processing so as to become the desired image signal performs processing for converting a quantization value of the digital image signal according to a tone curve; An image processing apparatus characterized in that the tone curve is approximated by combining a plurality of linear functions having different slopes. 2. The system according to claim 1, wherein the predetermined means for performing image processing on the digital image signal and performing processing so as to obtain the desired image signal is a SIMD type arithmetic processing processor. The image processing apparatus according to any one of the preceding claims. 3. An image processing apparatus, comprising: communication means for communicating with an external device, performing an approximation calculation of the tone curve by the external device, and calculating a tone curve approximating the image processing device by the communication means. The image processing apparatus according to claim 1, wherein information is transmitted. A means for sampling the coordinates of the tone curve to be approximated at n positions; a means for generating an approximate tone curve comprising a plurality of linear functions connecting the coordinates with straight lines; Means for calculating an error between the target tone curve and the approximate tone curve; and means for evaluating the calculated error and determining the approximate tone curve that minimizes the error as a tone curve to be transmitted to an image processing apparatus. The image processing apparatus according to claim 3, comprising: 5. The apparatus further comprises: means for extracting an arbitrary area of the determined approximate tone curve, and means for sampling the coordinates of the target tone curve at m points again for the area to approximate the area. The image processing apparatus according to claim 4, wherein the correction of the approximate tone curve is performed. 6. The means for extracting an arbitrary area of the determined approximate tone curve further includes means for evaluating an error between a target tone curve and an approximate tone curve in the approximate tone curve, The image processing apparatus according to claim 5, wherein a maximum region is extracted.