JPH06225129A - Picture processor - Google Patents

Abstract

PURPOSE:To attain the pseudo halftone expression with high picture quality and high gradation reproducibility by setting/clearing dots in a picture display device. CONSTITUTION:A 3-dimension dither ROM section 11 outputs a three-dimension dither signal vibrated by 4-picture element period in the main scanning direction and the subscanning direction and vibrated for a 4-frame period in a time base direction by using each 2-bit output from a picture element counter 2, a line counter 3 and a frame counter 10 as an address signal A comparator 6 binarizes a picture signal pix by using the signal as a threshold to execute pseudo halftone expression in 64 gradation in white/black texture is not eminent.

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 a process (pseudo-halftone process) for artificially expressing a halftone of a multivalued image by turning dots on and off in an image display device.

[0002]

2. Description of the Related Art Conventionally, as an image processing apparatus for this type of pseudo halftone processing, an apparatus based on a so-called systematic dither method as shown in FIG. 5 is known.

In FIG. 5, 1 is a terminal to which a multi-valued image signal pix is serially input pixel by pixel, and 2 is an image signal pi.
2 bits (modulo 4) for counting the pixel transfer clock pc of x and resetting with the line synchronization signal lc of the image signal
The pixel counter 3 is a 2-bit (modulo 4) line counter that counts the line synchronization signal lc of the image signal and resets with the frame synchronization signal fc of the image signal. 5
Is a two-dimensional dither ROM section storing a 4 × 4 dither signal table as shown in FIG.
The dither signal having the value stored at the address designated by the two-dimensional address signal composed of the bit output signal and the 2-bit output signal of the line counter 3 is output. 6 is 2
A comparator 7 which binarizes the input image signal pix using the dither signal output from the dimensional dither ROM unit 5 as a threshold.
Is an output terminal of the binarized output signal.

In this conventional example, when an image display device or an image printing device for expressing an image by turning dots on and off is connected to the output terminal 7, a pseudo intermediate of maximum 16 gradations (level 0 to level 15) is obtained. Key expression is possible.

[0005]

However, the image signal is binarized by using the dither signal that vibrates only in the spatial (two-dimensional) direction as described above, and the gradation is expressed by the local area ratio of black / white. According to the configuration for reproducing, if the number of gradations is increased (the dither signal table is increased) in order to improve the gradation reproducibility, a black / white texture (pattern) on the binarized output image.
However, there was a problem that the image quality was deteriorated due to visual problems.

That is, when the image area of 50% gradation level is binarized, according to the above-mentioned conventional example, the 4 × 4 dot pattern shown in FIG. 7 appears periodically on the binarized output image. When the number of gradations is increased to 64, the same pattern of 8 × 8 dots appears periodically, which visually deteriorates the image quality considerably.

The present invention has been made in view of the above problems, and enables an image output apparatus to turn on and off dots to achieve high-quality pseudo-halftone representation with higher gradation reproducibility. It is an object of the present invention to provide an image processing device for.

[0008]

In order to solve the above-mentioned problems, the present invention provides a means for generating a vibration signal vibrating in both space and time directions and a binary image signal using the vibration signal generated by this means. And a means for converting the same.

[0009]

The present invention has a space (two-dimensional) by the above configuration.
Direction dots on, off time dots on,
Since three-dimensional dither processing with OFF added is realized, when the binarized output image according to the present invention is output to an image display device capable of dot ON / OFF, the number of gradations is higher than that of the conventional white image. / Enables high-quality pseudo-halftone expression with no black texture.

[0010]

(First Embodiment) FIG. 1 is a block diagram of an image processing apparatus according to a first embodiment of the present invention. In FIG. 1, reference numerals 1, 2, 3, 6 and 7 denote image signal input terminals, pixel counters, line counters, and the like similar to those shown in FIG.
An output terminal for a comparator and a binarized output signal.

Reference numeral 10 denotes a 2-bit (modulo 4) frame counter, which is a frame synchronization signal f of the image signal pix.
c is counted and reset by the reset signal rst.
Each frame of the image signal pix is input in synchronization with the frame synchronization signal fc.

Reference numeral 11 vibrates in the space and time directions 3
It is a three-dimensional dither ROM unit that generates a three-dimensional dither signal. The three-dimensional dither ROM section 11 stores 4 × 4 tables T0, T1, T2, T3 as shown in FIG. The three-dimensional dither ROM unit 11 is addressed by a three-dimensional address signal including a total of 6-bit output signals from the pixel counter 2, the line counter 3, and the frame counter 10, and the two-bit output signal of the frame counter 10 causes tables T0 to T3. Is selected, the positions in the main scanning direction and the sub scanning direction on the selected table are selected by the output signals of the pixel counter 2 and the line counter 3, and the dither signal of the value stored in that position is output. It

In the above structure, during the period when the image signal pix of the first frame (frame 0) is input, the dither signal oscillating in the spatial direction is read out from the table T0, and this is used as the threshold signal by the comparator 6 to generate the image signal. pix is binarized. In the image signal input period of the next frame (frame 1), the dither signal vibrating in the spatial direction is read from the table T1, and the image signal pix is binarized using this as a threshold signal. In the image signal input period of the next frame (frame 2), binarization is performed using the dither signal oscillating in the spatial direction on the table T2, and in the image signal input period of the next frame (frame 3), the table T3. Binarization is performed using the above dither signal. In the next frame, the dither signal on the table T0 is used.

In this way, in each frame, the dither signal oscillates in the main scanning direction and the sub scanning direction at a period of four pixels. Further, the tables T0 to T3 are sequentially selected for each frame in the 4-frame cycle, and the dither signal for the same pixel vibrates in the time direction in the 4-frame cycle. Therefore, when the binarized output signal output to the output terminal 7 is displayed on the image display device, the average of the white / black area ratios of the four frames is visually perceived as a gradation, and therefore according to the present embodiment. For example, a pseudo halftone representation of 64 (= 4 × 4 × 4) gradations is possible.

For example, for a region of 50% gradation level on the input image, four kinds of 4 × 4 dot patterns as shown in FIG. 3 appear in sequence on the binarized output image for each frame. The dot pattern of each frame is different,
The black / white area ratio is 50%, and the black / white area ratio obtained by averaging four consecutive frames is also 50%, which is visually perceived as a gradation level of 50%.

As can be understood from the example shown in FIG. 3, the size of the dot pattern for the area of the same gradation level is the same as that of the conventional example shown in FIG. Since it is 4 × 4 dots and this changes for each frame, white / black texture is not visually noticeable. Therefore, according to the present embodiment, it is possible to realize high-quality pseudo-halftone representation with a higher number of gradations than ever before.

(Second Embodiment) FIG. 4 is a block diagram of an image processing apparatus according to a second embodiment of the present invention. 4, the same reference numerals as those in FIG. 1 denote the same parts.

In this embodiment, an adder 12 is added before the comparator 6, a three-dimensional dither signal output from the three-dimensional dither ROM section 11 is added to the input image signal pix, and this added signal is sent to the comparator 6. The threshold value signal of the fixed value generated by the threshold value generator 13 is input to the comparator 6.

A fixed threshold value is used in the comparator 6, but since the three-dimensional dither signal oscillating in the space direction and the time direction is added to the image signal to be compared with the fixed threshold value, it is equivalent to the space in the same manner as in the first embodiment. As a result of the image signal being binarized by a threshold value that vibrates temporally and temporally, it is possible to realize a high-quality 64-gradation pseudo-halftone representation with inconspicuous white / black texture.

The size and the number of tables (T0 to T3) of the dither signal values stored in the three-dimensional dither ROM section 11 are changed, and the number of bits of the address signal generating counters 2, 3 and 10 is changed accordingly. By changing the, the high-quality pseudo-halftone representation with a gradation number larger or smaller than 64 gradations is possible.

[0021]

As is apparent from the above description, the present invention has means for generating a vibration signal vibrating in both space and time directions, and means for binarizing an image signal using the vibration signal. With the configuration, the three-dimensional dither processing in which the dots in the spatial (two-dimensional) direction are turned on and off and the dots in the temporal direction are turned on and off is realized, and the image display device capable of turning the dots on and off is This has the effect of enabling high-quality pseudo-halftone expression in which the white / black texture is not noticeable at a high number of gradations.

[Brief description of drawings]

FIG. 1 is a block diagram of an image processing apparatus according to a first embodiment.

FIG. 2 is a diagram showing an example of dither signal data stored in a three-dimensional dither ROM unit.

FIG. 3 is a diagram showing a dot pattern obtained in four consecutive frames for a 50% gradation level.

FIG. 4 is a block diagram of an image processing apparatus according to a second embodiment.

FIG. 5 is a block diagram of a conventional image processing device.

FIG. 6 is a diagram showing a dither signal table used in the conventional apparatus.

FIG. 7 is a diagram showing a dot pattern of 50% gradation level obtained in the conventional device.

[Explanation of symbols]

 1 image signal input terminal 2 pixel counter 3 line counter 6 comparator 7 binarized image signal output terminal 10 frame counter 11 three-dimensional dither ROM section 12 adder 13 threshold generation section pix input image signal pc pixel transfer clock lc line synchronization Signal fc frame sync signal

Claims (1)

[Claims] 1. An image processing apparatus comprising: means for generating a vibration signal that vibrates in the spatial and temporal directions; and means for binarizing an image signal using the vibration signal generated by this means.