JPS60223377A - Method for generating pseudo half tone picture data - Google Patents

Abstract

PURPOSE:To improve the picture quality of a reduced picture by selecting a pseudo half tone slice corresponding to a reduced ratio among plural pseudo half tone slices to reduce the difference between a pseudo half tone picture before reducing and a reduced half tone picture after interleaving. CONSTITUTION:The pseudo half tone slice level data is stored in a memory 15 and the pseudo half tone slice is considered to be close to the pseudo half tone picture before reducing when the slice is interleaved and reduced by 1/2. Plural sets of the slice level data are stored in advance in a fixed memory such as an ROM and grouped into addresses by using signals S1, S2 designating the reduced ratio easily. The circuit in the figure is synchronized by using a horizontal clock T1 and a vertical clock T2. The horizontal clock T1 and the vertical clock T2 are generated easily by a pulse oscillator. The address information by the signals S1, S2 designating the reduced ratio is generated by an operating switch or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method for generating pseudo halftone image data, and in particular, the present invention relates to a method for generating pseudo halftone image data, and in particular, a method for generating pseudo halftone image data that is input from an image input device to an image processing device by thinning out an image. The present invention relates to a method of generating pseudo halftone image data suitable for reduction.

[Background of the invention]

The principle of pseudo halftone is explained in [Image Digital Signal Processing (pp2a6) J, published by Nikkan Kogyo Shimbun, May 25, 1980 (written by Hikotaka Fukieda), and detailed explanation will be omitted here. However, with reference to FIGS. 6 to 9, the disadvantages of pseudo halftones seen in reduced images will be explained.

FIG. 6 is a block diagram of a pseudo halftone image data generation circuit, FIG. 7 is a diagram showing a pseudo halftone slice in which a plurality of slice levels for binarization are arranged periodically, and FIG. 8 is a block diagram of a pseudo halftone image data generation circuit. A diagram showing the relationship between an analog image signal and a plurality of slice levels of pseudo halftone slices. FIG. 6 is a diagram illustrating a thinned-out and reduced output. In FIG. 6, an analog image signal A as an image input signal is converted into a multivalued digital image signal by an A/D converter 1, and is inputted to one side of a comparator 2. The output of the slice level generation circuit 5, which generates slice levels using the outputs of the horizontal period counter 4 and the vertical period counter 3 as addresses, is sent to the comparator 2.
The digital image signal is compared with a plurality of slice levels and binarized, and the pseudo half 1--
This is output as image data D. The pseudo-1-ftone slice is a pattern in which slice levels of 16 values are periodically arranged, as shown in FIG. 7, for example. Further, the relationship between the analog image signal A and the slice level of the pseudo halftone slice is as shown in FIG.

Now, if the halftone image input as an analog image signal increases in density linearly in the horizontal scanning direction as shown in FIG. 9, the slice level of the first scanning line is Lo
, Ls , L2 , Ll O, LO, Ls , L2
, LI O . . . are repeated, and the shaded portion in FIG. 9(1) is output as black in the dithered image output, and the other portions are output as white. Similarly, the slice level of the second scan line is L12. L4. Ll4. L6, L12. L
4. Ll4. L6... is repeated, and the slice levels of the third scanning line are L3, Ll 1, Ll
, L9, L3. Lll, Ll, L9, etc. are repeated, and the slice level of the fourth scan line is Lls,
L? , Ll 3. Ls, Ll5. L7. Ll3. L5
...is repeated. The slice level of the fifth scan line is the same as the slice level of the first scan line, and the same is repeated periodically thereafter. Here, if the dithered image output of Figure 9 (Sun) is thinned out to 1/2, Figure 9 (2)
.

The image shown in (3) is significantly different from (1) in FIG. 9, and is difficult to be regarded as a halftone image. In other words, Figure 9 (2)
With this data, the image becomes extremely black, and one solution (Fig. 9)
With data 3), the image becomes extremely white. It is clear that in any case, the reduced images obtained by thinning out show a significant deterioration in image quality compared to the pseudo halftone image before reduction.

[Purpose of the invention]

An object of the present invention is to provide a new method for generating pseudo-halftone image data that improves the extreme deterioration in image quality of pseudo-halftone images that occurs when conventional dithered images are thinned out and reduced.

[Summary of the invention]

When converting to pseudo halftone image data, the present invention specifies thinning/reduction conditions in advance and selects an appropriate pseudo halftone slice from among a plurality of pseudo halftone slices prepared in advance. It is intended to be applied. This reduces the difference between the pre-reduction pseudo halftone image and the reduced pseudo halftone image after thinning out, thereby improving the image quality of the reduced image.

In the present invention, for example, slice levels with periodicity as shown in FIGS. 3 and 4 are prepared as pseudo halftone slices applied to 1/2 thinning reduction.
The 2-thinned reduction data is for obtaining pseudo halftone image data to which the slice level marked with a circle is applied.

Similarly, in the case of 1/3, 1/4 reduction, etc., a pseudo halftone slice suitable for the reduction ratio is prepared in advance.

[Embodiments of the invention]

An embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an example of the configuration of a pseudo halftone image data generation circuit. The image input signal A is quantized to 4 bits and 16 levels by the A/D converter 11 and becomes one input of the digital 9 comparator 12. On the other hand, the outputs of the horizontal period counter 4 consisting of an 8-bit binary counter that determines the period of the slice level in the horizontal direction scan and the vertical period counter 3 consisting of the 8-bit binary counter that determines the period of the slice level in the vertical direction scan are as follows. It is input to the memory 15 as an address of the memory 15. Output n of memory 15
It becomes the other input of the digital comparator 12 as one slice level. For example, pseudo halftone slice level data as shown in FIG. 5 is stored in the memory 15 in advance, and the slice level data shown in FIG.
The data includes the values shown in FIG. The pseudo halftone slices shown in FIGS. 3 and 4 are
The cycle is determined so that when the data is thinned down to 1/2, the data to which the slice level marked with a circle is applied is output. This period was designed so that when the image is thinned down to 1/2, it becomes close to the pseudo halftone image before reduction.

A plurality of sets of slice level Φ data are stored in advance in a fixed memory such as a ROM, and can be easily addressed using signals 81 and 82 specifying the reduction ratio.

The synchronization of the circuit in FIG. 1 is based on the horizontal clock T1 shown in FIG.
and vertical clock T2. Although not shown, the horizontal clock Tl and vertical clock T2 can be easily generated from a pulse oscillator. Furthermore, address information based on the signals S1 and 82 specifying the reduction ratio can be easily generated using an operation switch or the like.

Now, when the signal 5x=Q, the signal S, and 2WQ, the address of the memory 15 where the pseudo halftone slice shown in FIG. 4 is stored is selected, and the digital comparator 12
/-When the input signal from the D converter 11 is higher than the slice level from the memory 15, a 'H' level signal (
At other times, a 1L" level signal (white signal) is output.

° Since the pseudo halftone data output from the digital comparator 12 is data to which the pseudo halftone slice shown in FIG. 3 or 4 has been applied, when this is thinned out to 1/2. , 3 or 4 to which the slice levels marked with circles are applied, and a reduced image close to the pseudo halftone image before reduction is obtained. As described above, according to the embodiments of the present invention, it is possible to create a pseudo halftone image that can avoid significant deterioration in image quality when thinned out and reduced.

〔Effect of the invention〕

According to the present invention, it is possible to generate pseudo halftone image data that can prevent deterioration in image quality when a pseudo halftone image is reduced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a pseudo halftone image data generation circuit according to an embodiment of the present invention, FIG. 2 is a waveform diagram of a clock that synchronizes the circuit in FIG. 1, and FIG. 4 and 4 illustrate pseudo-halftone slices according to one embodiment of the present invention - FIG. 5 shows the pseudo-halftone slices of FIG.
FIG. 6 is a block diagram showing a conventional pseudo halftone image data generation circuit, FIG. 7 is a diagram showing a conventional pseudo halftone slice, and FIG. 8 is a diagram showing how rice is stored in memory. A diagram showing the relationship between an analog image signal and a slice level. FIG. 9 is a diagram showing a dithered image output in which pseudo halftone image data is binarized by pseudo halftone slices, and an output in which pseudo halftone image data is decimated to 1/2. It is. 11...4-bit A/D converter 12''°Digital comparator 13...Vertical period counter 14...Horizontal period counter 15...Memory agent Patent attorney Akira Takahashi Husband 1st Part 2 -Figure ゛-------L
1lt7oshi Figure 3 →χNote Figure 10 -〇Dirty

Claims (1)

[Claims] 1. A method of converting an analog image signal into a multivalued digital image signal, and converting the digital image signal into pseudo-halftone image data in which a plurality of slice levels are arranged periodically and using pseudo-halftone slices. The pseudo halftone slices are provided in the memory in accordance with the reduction ratio of the image, and each pseudo halftone slice is a plurality of periodic slices that display pseudo halftones of the image according to the reduction ratio. has an array of slice levels, and selects a pseudo halftone slice corresponding to a reduction ratio from among the plurality of pseudo halftone slices when generating pseudo/%-tone image data of an analog image signal. A method of generating pseudo-h-tone image data characterized by: