JPS6024776A - Half tone picture compression system - Google Patents

Abstract

PURPOSE:To obtain the matching characteristics with MH system and enlarge the compression ratio by flattening and smoothening the forecasting picture element per bit plane and by marking the half tone data for forecasting. CONSTITUTION:The picture data B and C for 1 picture element of the front line is read out of the register 12. Picture elements X, A, B and C are inputted to ROM14. In the ROM14, the data in order showing in what number the value of the picture element X is easy to appear in accordance with the value of the referring picture elements A to C is written beforehand. The bit corresponding to the forecasting order is divided and written in the memories 15 to 17. The multiplexor 18 reads out the data for 1 scanning line per bit plane from the memories 15 to 17. Further, it smoothens the output bit 39 at FF19. And it executes the run length coding with MH coder 20.

Description

Detailed Description of the Invention (a) Technical Field of the Invention The present invention relates to a halftone image compression method that compresses halftone image data by allocating bits using a predictive coding method and smoothing bits for each bit plane. It is something.

(b) Prior art and problems Conventionally, various methods for compressing multi-tone image data have been used, such as level plane coding, bit plane coding, differential pulse code modulation, and prediction order coding. There is a way. On the other hand, the compression methods for two-dimensional images include the modified Huffman method (hereinafter referred to as the MH method) and the modified two-mode method (hereinafter referred to as the MH method).
R method) has been established as an international standard data compression method. The level plane encoding and bit plane encoding of the compression method of the multi-tone halftone 1+lii image are M
Several methods have been tried that are compatible with the H method and transmit data after being compressed using the M H method. (For example, refer to Proceedings of the 1981 Institute of Image Electronics Engineers National Conference 1, G■ encoding via bit-plane representation of halftone images.) Therefore, if the MH method can be used to encode halftone images, the facsimile encoder This is advantageous because it can be used. However, bitplane encoding and level I replane encoding have the disadvantage that they cannot achieve a higher compression ratio than predictive encoding methods.

(Q) Object of the Invention The object of the present invention is to provide a halftone image compression method that can increase the compression ratio of multi-case halftone images and is compatible with the international standard M f (method).

(5) Structure of the invention and its purpose is to encode l! ! ! a prediction means for predicting an image set to be encoded by referring to a predetermined reference pixel in the vicinity of the l element, and obtaining a prediction error; an encoding means for allocating bits of the prediction error; A storage means for writing bits in units of words and reading bits for each bit plane, and a smoothing means for smoothing an output bit signal from the storage means, encodes a predicted pixel, and reads the encoded signal. This is achieved by a halftone image compression method characterized by smoothing the image and inputting it to a modified Huffman encoder.

(e) Embodiment of the Invention An embodiment of the halftone image compression method according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a predictor diagram for explaining the halftone image compression method according to the present invention.
, O indicates a reference pixel, and X indicates a coded pixel. FIG. 2 is a block diagram of a halftone image compression method according to the present invention, in which 10°11.18 is a register, 12 is a
o (Fastin Fast out) v Jinwoo p, 1
4 is ROM (Read-OJy-Memory)
, 15.16.17 is memory, 18 is multiplexer,
19 is a trigger flip-flop (TFF), 20 is MH
Encoder, 30 is 8 for one pixel, corresponding signal, 31 is pixel X,
82 indicates pixel A, 33 indicates pixel C, 184 indicates pixel data of pixel B, and 39 indicates an output bit signal.

In this embodiment, considering the case where an 8-level halftone image is compressed, the three reference pixels shown in FIG. 1 are used as predictors, and the block diagram of the halftone image compression method of the present invention is shown in FIG. The operation will be explained.

An octad signal 80 for one pixel is set in the register 10. At the same time, the contents of register 10 are moved to register 11 and written to Fj-Fo register 12. The lli'iFo register 12 stores the image signal of the previous line as a reference line. B”iF
Image data for one pixel of the previous line is read out from the O register 12. At the same time, the image data that had been read out from the F'x F'o register 12 is transferred to the register 13.
is set to As a result, the signal 81.82.84.8
8 is the pixel X in FIG. 1, respectively.

The image signals correspond to A, B, and C, and these are RO,
It is input to the address of M14. Pixel A in ROM14
, B, and C, ranking data indicating which position of pixel X is most likely to appear is written in advance, and the pixel is predicted according to the order of The prediction rank is obtained as an error. Furthermore, bit allocation is performed in the ROM 14 in accordance with the predicted order. As shown in Table 1, the bits in the higher rankings have fewer bit changes, and serve to enhance the compression effect of image data. Each bit of the next read order is a memo')15. Written on '16 and 17. The following operations are operations until a prediction error for one pixel is obtained. This operation is repeated for at least the number of pixels in one scanning line. Then, the predicted pixels for the scanning line are written into the memory 15, 16, and 17. Next, the written one scanning line data is read out from the memory 15 bit by bit, including the most significant bit of the prediction error, via the multiplexer 18, and when the reading is finished, the most significant bit of the prediction error is read out one bit at a time from the memory 16, 17, and so on. Data for one scanning line is read out for each plane. The read output bit signal 89 is applied to the trigger flip-flop 19. The trigger flip-flop 19 has a signal 39 of 1
'', the output bit signal 39 is smoothed by inverting its state from ``0'' to 111'' or from ``L'' to ``O''. The output 40 of the trigger flip-flop 19 is M
The signal is input to the H encoder 20 and run-length encoded. In the embodiment shown in FIG. 2, an 8-tone halftone image is shown, but the present invention can be similarly applied to images with 16 or more shades. Furthermore, in the embodiment shown in Fig. 2, the bit allocation to the ranks is fixed as shown in Table 1, but it is also possible to dynamically allocate the bits by cyclically shifting the ranks for each pixel or by using some algorithm. be.

(f) Effects of the Invention According to the present invention, it is possible to increase the compression ratio by predictively encoding halftone data and smoothing the predicted pixels for each bit plane, and it is also compatible with the international standard MH method. The effect of gaining sex is great.

[Brief explanation of the drawing]

FIG. 1 is a preliminary predictor diagram for explaining the halftone image compression method according to the present invention, and FIG. 2 is a block diagram of the halftone image number compression method according to the present invention. In the figure, A, B, and O are reference pixels, X is a coding pixel, and t
o, tt, 18 are registers, 12 is F: LFO register % 14 is ROM (Read Only Memory
), 15.16.17 is memory%, 18 is multiplexer, 19 is trigger flip-flop, 20 is Mf (encoder, 80 is 81 direct signal for one pixel, 31 is pixel data of pixel X, 82 is pixel A's 1-time element data, 8B is pixel C
34 is the pixel data of pixel B. 39 indicates an output bit signal. Figure 1 397 Attachment Table 1 Bit allocation table for prediction error

Claims (1)

[Claims] a prediction means for predicting a pixel to be encoded by referring to a predetermined reference pixel in the vicinity of the pixel to be encoded to obtain a prediction error; an encoding means for allocating bits of the prediction error; and an output from the encoding means. a storage means for writing bits in units of words and reading bits for each bit plane, and a smoothing means for smoothing an output bit signal from the storage means, and a smoothing means for smoothing the output bit signal from the storage means. A halftone image compression method characterized by smoothing the signal and inputting it to a modified Huffman encoder.