JPH0722328B2 - Image processing device - Google Patents

Description

The present invention relates to an image processing device.

In a recording apparatus that forms an image based on recording data obtained by electronic or mechanical scanning such as electrophotography and thermal recording, as a conventional halftone expression method, (A) the amplitude is modulated based on the recording data to obtain a gradation property. And (B) a method of performing gradation processing digitally by performing dither processing on the basis of the recording data. However, (A) has the instability of recording due to the environment dependency, and (B) has a drawback that the resolution is deteriorated because the gradation expression is expressed by the two-dimensional recording area ratio.

An object of the present invention is to improve the quality of a reproduced image by eliminating the above drawbacks and performing an appropriate process according to the type of an input image.

According to the embodiments of the present invention described below, an image processing apparatus that achieves such an object is provided.

That is, there are high resolution areas such as characters and symbols in an original and areas in which halftones are emphasized, such as photographs. Even in the high resolution region, there are many cases where halftones such as characters and symbols are expressed. In the present invention, in order to meet such requirements, digital halftone is expressed in a region where gradation is expressed in a relatively large region, environment resistance is improved, and recording is performed by pulse width modulation or brightness modulation in a high resolution region. Satisfy both high resolution and gradation. Therefore, in the high resolution area of characters, symbols, etc., even if the gradation is changed, it has little effect on the overall image quality, and character slash due to the disconnection of the connecting part by the dither of the characters, symbols, etc. Higher image quality can be realized.

FIG. 1 shows an example of a concrete embodiment of the present invention. In the figure, 1 is an image data line from an input source, and data is input in parallel by 6 bits of 1 pixel with gradation weighting. 2A and 2B are switches for buffer line memory switching. In this figure, 3A is currently acting as an image input buffer memory, and 3B is acting as an output buffer memory. Four
Is a buffer memory for storing input data of N × M pixels necessary for identification among the information from the line memory.
Reference numeral 5 is a discriminator for discriminating whether the N × M pixel region is a high resolution region or a high resolution region from the data of 4 N × M pixels, which can be realized, for example, by Japanese Patent Application Laid-Open No. 57-185446. . 6
Is a switch controlled by the control signal α of the output line 10 from the discriminator of 5. Reference numeral 7 is a pulse width modulator for recording or an energy controller which controls, for example, voltage, brightness and the like according to the input amount. The output 11 in this case produces the analog recorder control signal. Reference numeral 8 denotes a binary halftone expression circuit, which may be a dither method or a systematic density pattern method. Reference numeral 9 is an OR circuit that passes either of the control signals from 7 and 8. Reference numeral 11 is an input signal line to the recording unit for receiving and recording the pulse width modulated signal, the analog modulated or binarized recording image signal. The recording unit is a scanning type recording apparatus capable of controlling the recording density by the intensity of energy for recording, that is, the size of dots, the voltage, the brightness, etc., for example, an electrophotographic method in which a laser beam is radiated onto a photoconductor to form a latent image. Alternatively, there is a heat-sensitive method or an electrostatic recording method.

To explain the operation, the image data transmitted from the image input source 1 is stored in the line memory 3A for N lines, and the switch 2A
Is switched and data for the next N lines is written in the line memory 3B. Switch 2B is the opposite of 2A, and 2B accesses 3B when 2A is accessing 3A. In the figure, M pixels of N line image data in 3B, that is, N ×
M pixel data is transferred to 4. The discriminator 5 is 4 N × M
It is determined from the pixel data whether the image area is a high resolution area or a high gradation area. This obtains an image density gradient within N × M pixels, that is, grad. When grad is larger than a certain value, it is determined as a high resolution area, and when grad is less than a certain value, it is determined as a gradation area. In the high resolution area based on this identification result, all the 4 × N pixel data are transmitted to the recording unit by pulse width modulation of the recording unit or analog modulation of the modulation circuit according to the pixel density. On the other hand, when the discrimination result is the gradation region, all the N × M pixel data of 4 are digitally converted into a binary recording signal through the binary halftone circuit 8 and transmitted to the recording unit.
As an example of the binary halftone circuit, binarization can be performed by the N × M systematic dither method. The OR circuit of 9 may be a switching switch synchronized with 6 because an analog signal comes from 7 and a digital signal comes from 8. In the case of laser electrophotography, for example, the signal from 7 that has passed 9 is transmitted to a laser light source drive current circuit, amplitude-modulated by an image control signal, and the surface potential is determined on the photoconductor according to the image recording signal strength. The adhesion amount is controlled in an analog manner. In the case of binary recording, the laser light source only swings between the maximum brightness and the minimum brightness.

FIG. 3 shows one example of a circuit for switching the halftone reproduction. LB
Is the laser light source, 20 to 22 are comparators for comparing the input signal Video with threshold levels L1 to L3, 23 to 25 are line memories, 26 to 28 are AND gates for output control, and 29 is a pulse width controlled waveform. , Or an analog halftone reproducing means 7. 30
Is a comparator for comparing the input data Video with the threshold value array of the dither ROM 35, 31 is a line memory, 32 is a gate which is turned on in all time zones of φ1 to φ3, and these constitute the binary halftone reproducing means 8. . 33 and 34 are switches for selecting either the analog means 7 or the binary means 8 and are controlled by the identification signal α shown in FIG.

The operation will be described. It is assumed that the analog means 7 is selected now. Image data signal Vide with 6-bit gradation weight
When o is input, the level of L
1 to L3, and if the pixel has a density of L3 or higher, the comparators 20 to 22 all output 1, and between L3 and L2, the comparators 20 and 21 output 1 and 22 output 0, and L2 Between L1 and L1, 20 outputs 1 and the others output 0, and below L1 outputs all 0s. Each of the above output data is stored in each line memory in the order of pixels, and when one line is stored, each memory is output for each pixel. The time division signals φ1 to φ3 are shown in FIG. The signals .phi.1 to .phi.3 correspond to the output control gates 26 to 28 for the data from the memories 23 to 25, respectively. Therefore, the data output from the OR gate 29 in the case of the density of the above-described example is as shown by the one-pixel pattern in FIG. The output of the OR gate 29 modulates the pulse width of the laser beam.

Next, when the binary means 8 is selected, the video signal
It will be successively compared with the 36 patterns, and as described above, the output only turns the laser on and off.

When it is known that high gradation or high resolution is achieved over the entire area of the input signal, for example, the signal α is detected by the pre-scanning of the document or by a command from the host or manually.
Can be output to switch the means 7, 8.

From the above description, if the image processing method of the embodiment of the present invention is used, the high definition area of the original image is recorded by analog recording,
It has been found that the relatively large area of uniform density is represented by digital halftone, so that the recording image quality is improved and the instability during recording is eliminated by binarization. This image processing method has been described for the case of a single color, but it is obvious that in the case of reproducing a multicolor image, it is possible to sufficiently apply each color component by performing the same processing as described above and superposing them.

The input image data to 1 is not limited to the one obtained by reading the original, and the same effect can be obtained even with the color B, G, R signals transmitted from the host computer.

The following effects are produced by the embodiment of the present invention.

(1) High-gradation image information or a partial area thereof can be expressed in a stable digital halftone, and the image quality is stable without environmental dependence.

(2) In the high resolution image information or a partial area thereof, the connecting line of the fine line portion is not divided by a dither or the like, and the fine line portion is clearly expressed, so that the image quality improving effect is large.

A color image may not require high resolution as compared with a monochrome image, and in that case, binary halftone reproduction can be selected regardless of the identification result. It determines that the level of each color separation signal is not above a certain value,
In other words, if it is not black, it is possible to consider it as color.

As described above, according to the present invention, input means for inputting an image signal (image data line 1 in the embodiment) and the image signal input from the input means represent a character / symbol area or a halftone area. Identification means for identifying a water mark (also an identifier 5)
And when the image signal is identified by the identifying means as representing a character / symbol area, the image signal input from the input means is recorded at a resolution higher than one pixel, A means for outputting a multi-gradation pulse width modulated image signal corresponding to the signal level of the pixel per pixel (similarly analog halftone processing means 7), and identifying that the image signal represents a halftone region. In the case where the image signal input from the input unit is output, an intermediate unit including a unit that outputs a binary pseudo-halftone image signal of one pixel (also a binary halftone reproducing unit 8) By including the tone processing means, the input image in which the character / symbol and the halftone image are mixed is 1 for the character / symbol.
It can be played at a higher resolution than the pixel resolution,
The quality of characters / symbols is improved, and a high-gradation reproduced image can be obtained for a halftone image by performing binary pseudo-halftone processing for each pixel.

[Brief description of drawings]

FIG. 1 is an image processing block diagram in the present invention, FIG. 2 is a pixel block diagram, FIG. 3 is a halftone reproduction switching circuit diagram, and FIG.
The figure is a time chart. 7: Analog halftone reproduction means 8: Binary halftone reproduction means

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-57-130064 (JP, A) JP-A-58-3374 (JP, A) Actually developed 55-91260 (JP, U)

Claims (1)

[Claims] 1. An input unit for inputting an image signal, an identifying unit for identifying whether the image signal input from the input unit represents a character / symbol region or a halftone region, and the image by the identifying unit. When it is determined that the signal represents a character / symbol area, the signal of one pixel per pixel is recorded so that the image signal input from the input unit is recorded at a resolution higher than that of one pixel. Means for outputting a multi-tone pulse width modulated image signal according to the level, and when the image signal is identified as representing a halftone region, with respect to the image signal input from the input means,
An image processing apparatus comprising: a halftone processing unit including a unit for outputting a binary pseudo halftone image signal for each pixel.