JP2646888B2 - Image processing device - Google Patents

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 performing processing such as gradation correction on image data of a photograph or the like optically read and outputting the processed data.

[0002]

2. Description of the Related Art In recent years, with the development of image processing technology, an image processing apparatus capable of reading image data such as a photograph and performing various kinds of processing such as pasting on a document has been developed. Further improvement in operability is required.

A conventional image processing apparatus is provided with a function of gradation correction for converting the gradation of read image data into an arbitrary gradation of an operator. In this case, as shown in FIG. 10, the horizontal axis represents the density gradation of the input image data, and the vertical axis represents the density gradation of the output image data after the gradation correction, and a graph of the gradation correction ratio (hereinafter referred to as a tone curve). ), The tone curve is deformed using input means such as a mouse, and a desired gradation correction ratio can be set. In the case of FIG. 10, tone curve 1 is input image data = output image data,
Since the tone curve 2 is located entirely below the tone curve 1, the output image is brighter than the input image, and the tone curve 3 is located entirely above the tone curve 1. The output image is darker than the input image. In a portion where the gradient of the tone curve is steep, the change in the gradation in that portion is emphasized, and in a portion where the gradient is gentle, the change in the gradation in the portion is weakened.

When setting a tone curve, information such as the image density at an arbitrary position of the original image and the image density distribution of the original image is required. At the same time, the multivalued data subjected to the tone correction is binarized and displayed on the CRT,
It is stored on M as it is.

Hereinafter, a conventional image processing apparatus will be described.

FIG. 11 is a block diagram of a conventional image processing apparatus. Reference numeral 21 denotes a central processing unit (hereinafter, referred to as a CPU) for controlling the apparatus and performing data processing. A random access memory (hereinafter, referred to as a RAM) for storing as multi-valued tone data; 23, an image input device for optically reading an original such as a photograph, performing gradation correction, and then transferring it to the RAM 22; 24, a CRT display device , 25 are printers.

FIG. 12 shows the image input device 2 shown in FIG.
3 is a block diagram of FIG. 3, 26 is a CCD image sensor (hereinafter referred to as CCD) for optically reading a document image and converting it into an electric signal, and 27 is an A / D converter for converting an analog output from the CCD 26 to a digital signal. Bowl, 28
Is a shading correction circuit that performs shading correction,
Reference numeral 29 denotes a gradation correction circuit that performs gradation correction based on the setting from the CPU 11.

[0008] The operation of the conventional image processing apparatus configured as described above will be described below.

First, the image data optically read by the CCD 26 and converted into an analog electric signal is A
After being converted into a digital electric signal of 8 bits (256 gradations) by the / D converter 27, the electric signal is corrected by the shading correction circuit 28. The data subjected to the shading correction is subjected to gradation correction at a preset ratio by a gradation correction circuit 29 and written into the RAM 22. RAM
The image data of 8 bits per pixel stored in the pixel 22 is CP
The data is binarized (dotted) by U21 and written into the page memory. The binarized image data is output to the CRT 24 or the printer 25.

The ratio of the gradation correction can be set to a desired ratio by the operator by setting the tone curve of the gradation correction described above. In a conventional image processing apparatus, read image data is stored as multi-valued data (here, 8 bits, 256 gradations). Therefore, a desired point of an image displayed on a CRT is specified, and By examining the tone at the point and examining the image density (tone) distribution of the image data, the tone curve is set as a reference for tone correction.

[0011]

However, in the above-mentioned conventional image processing apparatus, a memory of many bits is required for each pixel, and in order to store a read image,
There is a problem that an enormous amount of memory is required.
For example, a 5 cm square document is read at 1000 dpi,
Approximately 4 MBytes of memory is required to store. For this reason, pixel data extracted for each predetermined pixel is stored, and this data is sometimes used as a reference for density data. In this case, the number of pixels to be extracted is determined by the number of pixels with respect to the number of pixels. Or the number of pixels corresponding to
More extraction was done than that. However,
The size of one halftone dot of the halftone-processed image is small,
It is practically impossible to individually specify each halftone dot of the halftone-processed image displayed on the display screen by using a coordinate input device or the like. Having the concentration data every time led to waste of storage capacity.

[0012]

According to the present invention, in order to solve the above-mentioned problems, the ratio of the number of pixel data extracted by the extracting means to the number of pixel data is determined by the halftoning means with respect to the number of pixel data. It is configured to be smaller than the ratio of the number of halftone dots.

[0013]

According to the present invention, reference data for setting a tone curve for gradation correction can be obtained with a memory having a small capacity by extracting and storing a substantially effective number of pixel data with the above configuration. be able to.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an image editing apparatus according to an embodiment of the present invention. Reference numeral 1 denotes a central processing unit (hereinafter referred to as a CPU) for controlling the apparatus and processing data. A magnetic disk drive for storing data, 3 is a page memory, 4 is a display memory, 5 is a CRT display device (hereinafter referred to as CRT), 6 is an image input device, 7 is a printer, 8 is a keyboard, and 9 is a mouse. .

FIG. 2 is a block diagram of the image input device 6 in FIG.
U and 11 are image sensors (hereinafter referred to as CCDs) for converting the intensity of light into high and low voltage (analog voltage), and 12 is an A / D converter for converting an analog voltage output from the CCD 11 into an 8-bit digital signal. , 13 is the CCD 11
A shading correction circuit 14 corrects the variation in reading caused by the image data, a gradation correction circuit 14 converts the density of the read image data, and a halftone conversion process 15 converts the 8-bit digital signal corrected by the gradation correction circuit 14 into a halftone dot. go,
A binarizing circuit 16 for converting into a binary signal of 0/1 counts a preset value "36", and counts 1 at the end of counting.
A counter for repeating the operation of outputting a positive signal of a pixel cycle, a gate circuit 17 for selecting digital image data according to an output signal from the counter 16, and a memory 18 for one line of image data selected by the gate circuit 17 A buffer 20, which is selected by the gate circuit, stores image data temporarily stored in the buffer 18, and is a memory readable and writable by the CPU 10, and 19 is a buffer 18 according to a control signal from the CPU 10.
Is a transfer circuit for transferring one line of image data temporarily stored in the memory 20 to the memory 20.

The processing performed by the image editing apparatus of the present embodiment configured as described above will be described in detail below.

1. First, when the CPU 1 issues reading conditions such as setting of a tone curve to the CPU 10 of the image input device 6 and a reading command, the CPU 10 sets the tone curve to the gradation correction circuit 14 and reads the image. To start. When reading of an image is started, the original is irradiated with light, and the reflected light is imaged on the CCD 11 by a lens (not shown). The formed light is converted into an electric signal by the CCD 11 and converted into an 8-bit digital signal by the A / D converter 12, and then corrected by the shading correction circuit 13. The 8-bit image data after the shading correction is supplied to the gradation correction circuit 14.
, And also to the gate circuit 17.

The counter 16 synchronizes with the output of the image data from the shading correction circuit 13 (basic clock A and digital image signal B in FIG. 3) and counts a predetermined value "36" every time the gate circuit counts. A signal is output to the counter 17 (FIG. 3, output signal C of the counter 16). The gate circuit 17 opens the gate according to the signal from the counter 16, and samples the image data from the shading correction circuit 13 into the memory 20 via the buffer 18 and the transfer circuit 19 at a predetermined rate (FIG. 3, the gate circuit 17).
Output image signal D). At this time, the transfer circuit 19
Sampling is performed in the sub-scanning direction, that is, in line units, at the same rate as the rate of sampling in the line direction performed by the gate circuit 17 based on an instruction from the CPU 10. on the other hand,
The 8-bit image data after the gradation correction is output to a binarization circuit 15.
Is converted to a binary signal and transferred directly to the page memory 3. After the reading of the document image is completed, the CPU 1 enlarges / reduces the image data in the page memory 3 in accordance with the resolution of the CRT 5 and transfers the image data to the display memory 4 so that the read image is displayed on the CRT 5.

As described above, the read image data is binarized (halftone dots) and displayed on the CRT 5, and is sampled at a predetermined ratio while being multi-valued and stored in the memory 20.

2. Tone Correction The tone correction circuit 14 is provided with a 256-byte RAM as shown in FIG. 4, and uses the tone level of the input image data as an address to output the corrected output image data at the initial setting before image reading. It is set by the CPU 10. For example, when the tone curve is set as shown in FIG. 5, the tone levels 100 and 1 of the input image data are set.
Addresses 100 and 10 in the RAM of FIG.
1 is stored in the address 200 for the gradation levels 200 and 201 of the input image data.
190 and 192 stored in the image data 201 and 201 are output as image data. As described above, by fetching the data stored at the address indicated by the gradation level of the input image data and using the fetched data as output image data, gradation correction is performed according to the set tone curve.

3. Setting of Tone Curve In the magnetic disk 2, there is provided an area having the same configuration as the RAM in the gradation correction circuit 14 as shown in FIG.
An initial value for displaying a tone curve is set. CP
U1 reads this initial value, and sets the gradation level of the input image data (address in the area) as the horizontal axis and the gradation level of the output image data (data in the address) as the vertical axis. When the graph is drawn in FIG. 4, the initial state of the tone curve for gradation correction as shown in FIG. When the tone curve is transformed into a desired shape using the mouse 9, the CPU 1 sends the coordinate values on the tone curve to the CPU 10 of the image input device 6 as the set value of the tone curve, and the CPU 10 Is set in the RAM.

4. Binarization (Half Dot) The binarization circuit 15 converts the multi-valued image data having undergone the gradation correction into binary (half tone) data. Here, the image data output from the gradation correction circuit 14 is
5 and the value set at the corresponding position in the halftone dot pattern table as shown in FIG. 6 for each pixel, and if the gradation of the pixel is larger than the value in the table. The pixel becomes black (1), and if smaller, it becomes white (0). The same dot pattern table is used repeatedly according to the number of pixels of the image data. FIG. 7 schematically shows the relationship between each pixel of the image data and the dot pattern table.

As described above, in the halftoning process, the halftone is artificially represented by the ratio of the black pixels occupying a unit area (the size of the halftone dot pattern table). If you use a large pattern table, you will get an image with many gradations.
If a small pattern table is used, an image having a small number of gradations is obtained. The binarization circuit 15 is 4 × 4 to 36
It has 33 types of dot pattern tables of × 36, and a desired table can be used in accordance with instructions from the CPU 1 and the CPU 10 based on designation by the operator from the keyboard 8.

[5] Display of Density When the position of the image displayed on the CRT 5 is designated by the mouse 9, the CPU 1 calculates the coordinates in the page memory 3 (corresponding to the coordinates of the read original image) from the coordinates on the CRT 5, and Issue a command requesting the image density of the coordinates.

The CPU 10 calculates the address of the image data sampled in the memory 20 based on the coordinates received from the CPU 1 and stores the address data in the CP.
Send to U1. As shown in FIG. 8, the CPU 1
CPU 1 near the position specified by mouse 9 above
The density data sent from 0 is displayed.

6. Relationship between the size of the halftone dot pattern table and the sampling period When halftones are expressed by a binary output device, halftones are simulated by performing halftone processing as in this embodiment. In this method, halftone is expressed by the ratio of black pixels for each unit block composed of a plurality of pixels. In other words, since one density is represented by a block of a predetermined size, the position of the data displayed as a halftone dot is designated, the multi-valued data stored in the memory is acquired, and the When obtaining the density, even if a plurality of multi-value data are stored for a unit block, it has no special meaning.

Since the data output to the CRT 5 and the printer 7 is data that has been subjected to halftone dot processing, if the sampling period is set to be equal to or greater than the maximum value of the halftone dot pattern table as in this embodiment, It can be said that it is sufficient to know the image density at a desired point by looking at the display screen.

As described above, in this embodiment, the read image data is binarized and stored in the image memory, and simultaneously, the multi-valued data before binarization is sampled and stored in the memory. With a small memory capacity, easily obtain the image density at the desired position of the read image data,
It can be used as reference data for setting a tone curve for gradation correction.

Further, in the present embodiment, the sampling period of the image data is set to be equal to or larger than the size of the halftone dot pattern table. Can be sampled. In the case of the present embodiment, 1 / (36 × 36) = 1/1 compared with the case where multi-value data of all images is stored.
A memory having a capacity of 296 times may be used.

If the sampled multi-valued image data is stored as in this embodiment, it is possible to obtain a rough density distribution of the original image. It is useful reference data for setting.

[0032]

According to the present invention, the read image data is binarized by performing a halftone process and stored in an image memory, and at the same time a halftone process is performed when the multivalued data before the binarization is subjected to the halftone process. Sampled at a ratio smaller than the ratio for all pixels, and stored in the memory, the image density at a desired position of the read image data can be easily obtained with a small memory capacity, and a tone curve for gradation correction can be obtained. Can be used as reference data for setting. In addition, since density data having a smaller number of pixels than each halftone dot of the halftone-processed image is stored, wasting of memory capacity can be prevented.

[Brief description of the drawings]

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

FIG. 2 is a block diagram of the image input device in FIG. 1;

FIG. 3 is a timing chart showing an image data sampling operation in the image input device of FIG. 2;

FIG. 4 is a schematic diagram of a RAM for gradation correction.

FIG. 5 is a diagram showing a display example of a graph for setting a tone curve for gradation correction.

FIG. 6 is a schematic diagram of a dot pattern table.

FIG. 7 is a schematic diagram illustrating a relationship between original image data and a dot pattern table.

FIG. 8 is a diagram showing a display example of image density acquisition.

FIG. 9 is a diagram showing a display example of a tone curve for gradation correction.

FIG. 10 is a block diagram of a conventional image processing apparatus.

FIG. 11 is a block diagram of an image input device in a conventional image processing apparatus.

Claims (1)

(57) [Claims] A reading means for dividing an image on a document into a plurality of pixels and outputting multi-value density data for each pixel; and an extracting means for extracting the plurality of density data from the reading means at a predetermined ratio. Means, first storage means for storing the density data extracted by the extraction means, and a halftone dot which is composed of a predetermined number of pixels of the density data from the reading means, and which becomes one dot per block. Doting means, second storage means for storing data of each halftone dot obtained by the halftone conversion means, and display means for displaying an image based on the data stored in the second storage means. Designation means for designating a position in the image displayed on the display means; density stored in the first storage means corresponding to the position designated from the coordinates of the position designated by the designation means Data Means for calculating an address and displaying the density data stored at the address on the display means, the ratio of the number of density data extracted by the extraction means to the number of density data read from the reading means, the image processing apparatus characterized by being smaller than the percentage of the halftone number which is halftoned by the network epilepsy means for pixel number data read from said reading means.