JPS59141874A - Coder for color dot picture - Google Patents

Abstract

PURPOSE:To improve the estimating efficency by estimating a noticed picture element to each of color dot pictures having different screen angles by means of an array of reference picture elements suited to each screen angle. CONSTITUTION:Picture signals 10 are stored in a line memory 1 in the number equal to the lines which are used as reference picture elements. The values of reference picture elements of arrays which are accordant with screen angles of four types of dot pictures (cyan, magenta, yellow and black) respectively are read out of the memory 1 in the form of reference picture element patterns 11- 14 and sent to estimation table memories 2-5. Then the estimated values of noticed picture elements which are previously written with the reference picture element patterns used as addresses are read out of the memories 2-5. Each of these estimated values 15-18 is selected by a selecting circuit 6, and an estimated error signal 21 is produced to a picture signal. This signal 21 is coded by a coder 8.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a color halftone image encoding device that predicts a pixel of interest from a plurality of reference pixels for a plurality of color halftone images having different screen angles, and encodes the prediction error. It is something.

Generally, in color printing for magazines, newspapers, etc., cyan,
Multicolor plate making is performed in which halftone images of the four colors of magenta, yellow, and black are printed overlappingly.1 In this multicolor platemaking, "moiré" is created by overlapping halftone images of each color.
In order to prevent this (unstable pattern that changes in a variety of ways) from occurring, the screen angle of the halftone dot image for each color (the angle between the halftone dot lattice and the horizontal direction of the image) is different.

Figure 1 shows the case where the screen angle blur is 45° to prevent fly spots. 'When predictively encoding a color halftone image with multiple screen angles like this, if prediction is performed using one type of reference pixel arrangement tailored to a specific screen angle, the prediction efficiency will decrease. However, this results in an increase in the amount of code.

For example, the screen angle of white and black halftone images (45 degrees and 0
If a color halftone dot image is encoded using a reference pixel arrangement that is adjusted to a high degree of compression, a high compression ratio cannot be obtained.

SUMMARY OF THE INVENTION An object of the present invention is to provide an encoding device for color halftone images that eliminates the drawbacks of the conventional encoding devices described above.

The color halftone image encoding device of the present invention predicts a pixel of interest from a plurality of reference pixels for a plurality of color halftone images having different screen angles, and encodes this prediction error. Selecting B number of submeasurement means whose reference pixel arrangement is changed according to the screen angle of the input halftone image, and a prediction means whose reference pixel arrangement is adjusted to the screen angle of the input halftone image from among the plurality of submeasurement means. and means for encoding a prediction error signal obtained from the selected prediction means.

The color halftone image encoding device of the present invention uses a reference pixel arrangement suitable for each screen angle for each color halftone image having a different screen angle, and selects a pixel of interest (the object currently being predicted). Since prediction is performed for each pixel), the prediction efficiency is high and the amount of code can be significantly reduced.

The present invention will be described below with reference to drawing r showing an embodiment.

FIG. 2 is a block diagram showing an embodiment of the color halftone image encoding apparatus of the present invention. The image signal 10 is one of four types of color halftone images (two-color image) of cyan, magenta, yellow, and black used in multicolor plate making for color printing. This image signal 10 is a reference pixel (
The number of lines used as the pixel to be referred to in order to predict the current pixel of interest to be encoded is stored in the line memory 1. The value of the reference pixel in the line memory 1 is set according to the screen angle of the four types of halftone images (cyan, magenta, yellow, black) respectively. (for magenta), reference pixel pattern 13 (for yellow), and reference pixel pattern 14 (for black) and sent to prediction table memories 2 to 5 (for cyan-magenta, yellow, and blank, respectively).

Each of these four prediction table memories is comprised of a read-only memory, etc., and a predicted value (0 or 1) of the target pixel for each reference pixel pattern is written therein. By inputting the reference pixel pattern as an address of the read-only m-memory, the predicted value stored at that address is output. This predicted value is calculated by examining the probability that the pixel of interest becomes 1 for 21 reference pixel patterns separately for each of the cyan, magenta, yellow, and black images, when the number of reference pixels is n. When the probability exceeds O,S@, the predicted value is set as 1K1, and when it does not exceed, the predicted value is set as 1lon.

Prediction table memory 2 for cyan has a predicted value of 15 for cyan, prediction table 3 for magenta has a predicted value of 16 for magenta, prediction table 4 for yellow has a predicted value of 17 for yellow, and prediction for flick. A predicted value 18 for black is output from the table 5 and sent to the selection circuit 6. The selection circuit 6 receives from the outside a selection signal 19 indicating which of the four color halftone images the currently input image signal is, and according to this signal, generates a predicted value corresponding to the color of the input image. Output as selected predicted value 20.

This selected predicted value 20 and image 48 No. 1° (target pixel value) are input to the exclusive OR circuit 7, and when these signal values match, It□II is output, and when they do not match, 11111 is output as the prediction error signal 21. be done.

The encoder 8 encodes the prediction error signal and outputs a code 22. The encoder 8 used here may be a CCITTi-compliant MH (Monified Huffman) encoder or an MR (Modified Read) encoder, or may still be a patented Intercondylar 5 encoder.
3-115357, in which the prediction error signal is divided into several groups and encoded based on the prediction state signal. However, when using the latter encoder, the prediction table memories 2 to 5 output a prediction value as well as a status signal indicating whether the pixel of interest is likely to match the reference pixel pattern or not, and select circuit 6
It is necessary to select a predicted state signal corresponding to the input color halftone image in the same way as the predicted value.

Figure 3 shows an example of the reference pixel arrangement with high prediction efficiency for each color halftone image O screen angle shown in Figure 1.
Shown below. (I3) is for the magenta halftone dot, (C) is for the yellow halftone dot, and (L) is the reference pixel arrangement for the black halftone dot. ~C
) and 9 pixels (d to I) separated from the pixel of interest by the halftone dot pitch (P) depending on the screen angle, which are M+12 pixels. The positions of the respective reference pixels are also shifted by the difference in the screen angle of each color halftone dot. For color halftone dot images having different halftone dot pitches, it is necessary to use different reference pixel arrangements that are matched to each other.

Further, for a color halftone image having a screen angle different from that shown in FIG. 1, a reference pixel arrangement different from that shown in FIG. 3 must be used in accordance with the screen angle.

As explained above, the color halftone image encoding device of the present invention has the most predictable 311
By using a highly efficient reference pixel arrangement, efficient encoding is performed.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of the screen angle of four types of color halftone images, FIG. 2 is a block diagram showing the configuration of an embodiment of the present invention, and FIG. 3 is a screen showing the color halftone image of FIG. 1. 1 is a diagram showing an example of the reference pixel arrangement of four branches according to the angle. Each number in the diagram indicates the following, respectively. 1 Line memory 2 -/An prediction table memory 3 Magenta prediction table memory 4 Yellow prediction table memory 5 Plaque prediction table memory 6 Selection circuit 7 Exclusive OR circuit 8 Encoder 10 Image Signal 11・Reference pixel pattern (for cyan) 12・Reference pixel pattern (for magenta) 13
Reference pixel pattern (for yellow) 14 - Reference pixel pattern (for plaque) 15 - Predicted value (for cyan) 16 -
・Predicted value (for magenta) 17 ・Predicted value (for yellow) 1
8 Pre-order! II value (for black) 19...Selection signal 2〇-selection prediction (i 21...Prediction ζ1 error conversion bone 22 Signed again (A) (C) (D)

Claims (1)

[Claims] In a color halftone image encoding device that predicts a feature of interest from a plurality of reference pixels for a plurality of color halftone images with different screen angles, and encodes this prediction error, a plurality of screens of each color halftone image are used. a plurality of sub-measurement means whose reference pixel arrangement is changed according to the respective angles, and a means for selecting a prediction means having a reference pixel arrangement according to the screen angle of the input halftone image from among the plurality of sub-measurement means; and a means for encoding a prediction error signal obtained from the selected prediction means.