JPS61238176A - Half tone facsimile signal processing system - Google Patents

Abstract

PURPOSE:To convert and to process the half tone facsimile signal to the signal suitable for coding by replacing respective picture elements in the block by the signal level at the block which is decided to be a network point, so that the signal level difference can be smaller, and processing to use the signal level in the block at the block which is not decided to be the network point. CONSTITUTION:A network deciding device 14 decides the network point part by the value of counters 131 and 132. When it is decided at a character, etc., deciding circuit 17 that as the result of a network deciding device 14, the part is not the network point, it is decided whether or not the character part is obtained by the value of a substracter 16. A comparator 18 compares the relation of the size of the block average signal level and respective picture elements, a P1 calculating circuit 191 and a P2 calculating circuit 192 calculate the average value of the P1 and the P2. At a picture element information memory 20, the information to show which picture element is included in the P1 and which picture element is included in the P2 is stored, and at a signal level replacing circuit 21, the signal level in the block is replaced and processed based upon the deciding information, and the processing signal is outputted to an output terminal 22.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Description of the field to which the invention pertains The present invention converts a halftone facsimile signal obtained by scanning a document with mixed halftones, halftone dots, etc. into a halftone signal suitable for encoding. This relates to a halftone facsimile signal processing method that processes and converts into halftone facsimile signals.

(2) Description of the Prior Art Most of the halftone and color paintings around us are printed materials using halftone photographs. Halftone photographs are used in the printing field to express the shading of manuscripts, and the size of the ink dots gives the impression of shading to the human eye. Currently, halftone photographs are used for most of the printed materials that contain shading, such as photographs, and the period of ink dots varies from very fine to coarse. When scanning a printed matter that is a collection of dots with such periodicity using a facsimile machine, etc. 1. In the case of documents such as ordinary photographs, the gradation changes are sufficiently large compared to the sample density, so the gradation changes between adjacent pixels. However, in a halftone photograph, since the image signal is a collection of minute black dots having a density approximately equal to the sample density, the obtained image signal has a sharp change in gradation almost for each pixel. For image signals that do not include halftone dots, such as text and photographs, the image signal is divided into areas with sharp gradation changes such as outlines and characters, and other areas with gentle gradation changes, and then averaging processing is performed. However, for image signals that include halftone dots, due to the nature of gradation changes in halftone dots, it is necessary to remove redundancy without sacrificing definition. This has the disadvantage that it is difficult to average the processed image signal, and that it is not compatible with existing encoding methods, which assume that the image signal after processing changes in gradation like a normal photograph.

(3) Purpose of the Invention The present invention, in order to solve the above-mentioned drawbacks, identifies the halftone dot part in a single image signal by simple processing, and then identifies it.

The present invention relates to a halftone facsimile signal processing method for converting into a halftone signal suitable for encoding without impairing definition, and will be described in detail below with reference to the drawings.

(4) Description of structure and operation of the invention As a specific example, one embodiment will be described in detail using figures.

FIG. 1 is an example of the position of a block for determining the average signal level difference between adjacent blocks in order to identify the contours of halftone dots and halftone portions. In the figure * Po, PAt
Pg represents the average signal level of each block, 1Pa
If either Pal or 1Pa-PaI is larger than a predetermined value, the block having Po as the average signal level is determined to be the contour portion. For example, if the threshold value for this contour determination is 4.

IPo Pal”16-121”6≧4,
In the case of FIG. 1, a block with +Pl) is determined to be a contour. As a result of this determination, in the block determined to be 1 contour,
Divide the pixels in the block into groups of pixels smaller and larger than the average signal level P0, find the average signal levels P r and Pg of each group, and calculate the signal levels of the pixels in each group as p, , p, respectively. Change it with

Furthermore, among the blocks that are determined to be not one contour, there are still blocks where the gradation changes are severe and the fineness should be preserved, such as in the 9-character portion. Therefore, it is necessary to identify blocks in which gradation changes are severe within a block. Figure 2 is a schematic drawing of an example of level changes within a block when an image with periodic density changes is viewed as a block with a size of 4 pixels square. A pixel with a relatively high density level is represented, and a white portion represents a pixel with a relatively low density level. There are various other patterns, but they are omitted here. In the patterns shown in Figure 2, the value of gradation change within the block is large, but among these patterns, the numbers in Figure 9 are (1, 3), (3, 1).
, (1, 4), (4, 1) patterns are likely to appear in 9 characters, line drawings, etc., and the fineness should be preserved. Conversely, patterns with large numbers (i, j) are This is a pattern of halftone dots that has an adverse effect on encoding, etc., as described in the technical description, and it is necessary to perform averaging processing even if the gradation change is large unless it is in one contour area.

FIG. 3(A) shows an example of the order in which pixels within a block are accessed in the main scanning direction in subsequent processing.
B) also shows an example of the order of access in the sub-scanning direction. Pixels in a block having a density level distribution as shown in FIG. 2 are accessed in the main scanning direction and sub-scanning direction in a predetermined order as shown in FIG.
Calculate the level difference between two consecutive pixels. If the level of the first accessed pixel is LJ, and the level of J+1st pixel is Li, the difference is Dll-Lit-Li
Similarly, the level difference between the z+1st pixel and the z+2nd pixel is D l +r= L 14t L 12-! becomes.

Paying attention to the successive positive/negative changes of D, D, I, in the order shown in Fig. 3, the number (x) in Fig. 2.

j) is larger, the number of changes from positive to negative and from negative to positive becomes thicker in both the main scanning direction and the sub-scanning direction.For the 16 level patterns in FIG. 2.

In the signal of the level difference obtained as a result of accessing the main scanning direction and the sub-scanning direction in the order shown in Fig. 3, the number of positive/negative changes in the main scanning direction and the sub-scanning direction [changes in the main scanning direction] and the number of changes in the sub-scanning direction] is shown in FIG. However, the number of changes shown in FIG. 4 includes the access order from 4 to 5, from 8 to 9, which is the access order shown in FIG. The number of changes from 12 to 13 was not measured.

As can be seen from the figure, in the block (1, 1), there is no positive/negative change even once in both the main scanning direction and the sub-scanning direction, that is, (0, 0).

In the block (4, 4), there are 12 changes in both the main scanning direction and the sub-scanning direction. By focusing on this number of times, it is possible to detect the complexity of the concentration distribution in the block.For example, in the example of FIG. 2, (2, 2).

(2,3), (2,4), (3,2), (
3,3), (3,4), (4,2), (4
, 3), (4゜4) When trying to identify the nine types of patterns caused by halftone dots, from Fig. 4, for example, the number of positive/negative changes is 4 in both the main scanning direction and the sub-scanning direction. If this is used as a threshold value, it is possible to identify a block that has occurred four times or more in both the main scanning direction and the sub-scanning direction.

Therefore, the previous halftone dot identification is performed on blocks that are determined not to be two contours, etc., and in blocks that are identified as halftone dots, all pixels in the block are replaced with the average signal level P0. For blocks that are not determined to be halftone dots, the maximum signal level Lmax and minimum signal level Lmin within the block are
is calculated, and the difference (Lmax-Li+in) is calculated. If the difference (Lmax - Lmin) is larger than a predetermined value.

The block is determined to be a character part, etc., and the pixels in the block are replaced with P, , P, in the same way as for 2 contours, etc.

Furthermore, if (Lma -L+win) is smaller than a predetermined value, the pixels in the block are replaced with the average signal level P0. For example, if the threshold value for one tone difference is set to 100 for a block with a signal level as shown in FIG. 5, then in this block.

Lmax=140, Ln+in=30 and 1, w
ax-L+5in=110≧100, and pixels within the block are pt-40 for pixels below PO=80.
Pixels larger than pH are replaced with Pg-120 and converted as shown in the figure.

FIG. 6 shows an embodiment of the present invention. 1 is an input terminal for a halftone facsimile signal. A signal memory 2 stores one block or a plurality of blocks of signals input from the input terminal 1. Reference numeral 3 denotes an average signal level calculator which calculates the intra-block average based on the signal from the signal memory 2 and sends it to the register. Average signal level register 4
1.42 and the values of the one block line delay device 43, the subtracters 51 and 52 calculate lPo-Pa1. l Pa
Pal is calculated. Depending on the value, 1 contour etc. judgment circuit 6
Then, it is determined whether to replace the pixels of the block with P,,P,. If the determination circuit 6 determines that the signal is not a contour, etc., the signal is called out from the signal memory 2 by the memory address condolence, and is stored in the signal register 81.8.
Sent to 2. The difference between adjacent pixels is calculated by the subtracter 9 and sent to difference signal registers 101 and 102. A positive/negative change detector 11 detects a positive/negative change, and the counter selector 12 sends the result to the main and sub-scanning direction counters 131 and 132, and the counter indicates that a positive/negative change has been detected. It operates only when the indicated signal is input. The halftone dot determination unit 14 determines the halftone dot portion based on the values of counters 131 and 132. Maximum value detector 156 and minimum value detector 157.

Detect the maximum and minimum values within the block, respectively.

A subtracter 16 calculates the difference between them. Character determination circuit 17
If the halftone dot determination device 14 determines that there is no halftone dot, it is determined whether or not it is a character portion based on the value of the subtractor 16.

The comparator 18 compares the magnitude relationship between the block average signal level and each pixel, and the +PI calculation circuit 191 and the P2 calculation circuit 192 calculate the average values of pt and pg. Also 9
The pixel information memory 20 stores information indicating which pixels are included in P and which pixels are included in P2, and the signal level replacement circuit 21 replaces the signal level within the block based on the 2 determination information. Processing is performed, and a processed signal is output to the output terminal 22.

(5) Description of Effects As explained above, according to the present invention, it is possible to convert a halftone facsimile signal into a signal suitable for encoding by simple processing without impairing definition. In the description, a square area of 4×4 pixels is used, but of course other numbers of pixels and shapes may be used. Furthermore, the identification process can be simplified by changing the order of accessing two pixels and the number of pixels to be accessed in the halftone dot identification area. In this halftone dot identification, if the change is measured using a predetermined signal level, it will be less susceptible to the effects of image signal noise and the like. The signal level used to measure this change may be set to a constant value for all blocks.

It can also be changed for each block. For example, the signal level for measuring this change can be the average level of each block; in this case, the first accessed pixel is lower than the average level.

Assume that there is a change when the z+1th accessed pixel is higher than the average level, or vice versa, when the 1st is high and the 11th is low. in this way.

When the average level of each block is used, it is possible to follow the difference in partial shading of the document and identify the halftone dot area with high accuracy. In addition, in the description, in blocks where the signal level difference is small, all pixels are replaced with the average signal level P0, and in blocks where the signal level difference is large, the average signal level P0 of the group of pixels is replaced with the average value, which is smaller than the average value.

Although this is replaced with the average P2 of a group of large pixels, it is of course possible to replace it with a signal level other than this. Furthermore, the number of signal levels to be replaced may be changed.

In addition, when replacing +PO with P+ and Pz as in the second text, if you assign "0" to the pixel replaced by +PO and the pixel replaced by P, and 11" to the pixel replaced by P2, A facsimile signal can be divided into gradation information of Po, P+, and Pt, and resolution information of "0" and "1" indicating whether the pixel is represented by Po, Ps, or Pz. By encoding each piece of resolution information, it is also possible to efficiently transmit facsimile signals.

In addition, in order to further improve the efficiency of encoding, r
p, I + in the block replaced by Pg
If the number of pixels to be replaced by Pl or the number of pixels to be replaced by +Pt is smaller than a predetermined value, the block to be replaced by Po or the block to be replaced by + P l + Pg is Po is extremely large within the possible level range of IP+1.

If the block is extremely small, the block may be replaced with Po.

[Brief explanation of drawings]

Figure 1 is a diagram showing the position of the block for which the difference in the average signal level within the block is calculated, Figure 2 is a diagram schematically showing an example of the density change within the block, and Figure 3 is the pixel within the block. Figure 4 is a diagram showing an example of the order in which the data are read out. Figure 4 is a diagram showing the number of density changes when the density changes in Figure 2 are processed in the order shown in Figure 3. Figure 5 is a diagram showing the signal level within a block. P
FIG. 6, which is a diagram showing the case of replacing with + and Pz, shows an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Input terminal, 2... Halftone facsimile signal memory, 3... Intra-block average signal level calculator, 41
．． 42...Average signal level value register, 43...Average signal level value 1 block line delay device, 51°52.
. . . Subtractor, 6 . . . Contour etc. judgment circuit, 7 . . . Memory address controller, 81.82 . . . Signal register, 9 . . . . Positive/negative change detector, 12 . . . Counter selector, 131 . . . Main scanning direction counter, 132.
. . . Sub-scanning direction counter, 14 . . . Halftone dot judge, 15
6... Intra-block and large value detector, 157... Intra-block minimum value detector, 16... Subtractor, 17... Character etc. determination circuit, 18... Comparator, 191... P: calculation circuit; 192: Pg calculation circuit; 20: pixel information memory; 21: signal level replacement circuit; 22: processed signal output terminal.

Claims (3)

[Claims] (1) In a halftone facsimile signal processing method in which a halftone facsimile signal obtained by scanning a document that may have halftone dots is divided into blocks each consisting of multiple pixels, 2 spatially continuous
For several pairs of pixels, the change in signal level between the two pixels is measured, and the sum of the measured amounts only between the pairs that are continuous in the main scanning direction and the changes in the signal level between the two pixels that are continuous in the main scanning direction are calculated. Calculate the sum of the measured values only between the pairs that are connected, compare them with predetermined values, and use the results to identify whether a certain position on the screen is a halftone dot area. For blocks that are determined to be dots, each pixel in the block is replaced with some signal level so that the signal level difference between adjacent pixels is small; for blocks that are not determined to be halftone dots, the signals in the block are replaced. A halftone facsimile signal processing method characterized by processing using levels. (2) In a halftone facsimile signal processing method in which a halftone facsimile signal obtained by scanning a document that may have halftone dots is divided into blocks each consisting of multiple pixels, the maximum signal level within a block is Find the difference between the minimum signal level and the minimum signal level, and compare the value of the difference with a predetermined value. If a block is determined to have a moderate change in signal level, each pixel in the block is changed to several signal levels so that the difference in signal level between adjacent pixels is reduced. A halftone facsimile signal processing method characterized in that, in a block determined to be an intense portion, processing is performed to identify whether or not a certain position of the block on the screen is a halftone dot portion. (3) In a halftone facsimile signal processing method in which a halftone facsimile signal obtained by scanning a document that may have halftone dots is divided into blocks each consisting of multiple pixels, the average signal level of each block is After calculating the average signal level of the adjacent block, the difference value is compared with a predetermined value, and the signal level of the block including the halftone or halftone area outline is calculated. It identifies whether or not it is a part where the change is rapid, and in blocks that are judged to be a part where there is a large change, each pixel in the block is replaced with several signal levels with a large signal level difference, and in the block judged to be a part where the change is not large, the subsequent pixels are replaced. 1. A halftone facsimile signal processing method, characterized in that the processing includes processing for identifying whether or not a certain position of a block on a screen is a halftone dot portion.