JPH0316380A - Picture processor - Google Patents

Abstract

PURPOSE:To execute the intermediate tone processing suitable for a picture by varying the intermediate tone processing of an input picture signal in response to the output destination of the picture signal. CONSTITUTION:An output of an AND gate circuit 9 goes to logical 1 only when a signal whose maximum value is larger than a prescribed value A is given to a comparator 6, a signal whose minimum value is smaller than a prescribed value C is given to a comparator 8, that is, a '1' level output is generated from the comparators 6, 8 respectively in addition to the presence of the output of a comparator 7. Then a multiplexer 10 selects a binary picture data being an output of a dither binarizing circuit 4. Thus, in addition to the density gradient being a conventional image area criterion, the maximum value and the minimum value of the density are used for the discrimination. Then the dither processing to a black level picture or a white level picture is not required, and the compression rate at NH coding is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image processing device that appropriately performs halftone processing on an input image signal depending on the output destination.

The original image is photoelectrically read by an image sensor such as COD or A-Si, and this read signal is converted into 2 signals depending on the level.
It has been proposed to convert the image into a value and reproduce the image using a binary printer such as a laser beam printer or an inkjet printer. It has also been proposed to compress the binarized read signal using a modified Huffman code circuit or the like and store it in a transmission or magnetic or optical memory.

There are two methods for converting a document image into a binary signal: one is to set a threshold value at a fixed level and then compare the threshold value with the read signal, and this is used to determine the lightness and darkness. ) is compared with multiple threshold values corresponding to different white to black, and a block is considered as one unit, and depending on how many pixels in the block are judged to be black (or white), There is a method called the dither method that reproduces tonal images.

The latter dither method is an effective method because it has a relatively simple configuration and can reproduce images with multiple tones. However, a drawback of the dither method is that the resolution of the reproduced image decreases. Furthermore, although the former method of binarization using a fixed threshold provides good resolution, it has the disadvantage that gradation cannot be reproduced.

Therefore, in order to prevent resolution degradation and perform image reproduction with tonality, the original image is divided into a multi-tone reproduction area and a high-resolution reproduction area, the former being binarized by dithering, and the latter being binarized using a fixed threshold. It has been proposed to switch the binarization process automatically or manually depending on the image content.

As a method for automatically and in real time determining the image content on a document, the maximum and minimum values of pixel density in an image area within a block corresponding to the size of a dither matrix consisting of multiple threshold values used in the dither method are used. There is a method that uses the difference between This method is relatively simple and effective using several lines of memory in the main scanning direction, a comparator, and a subtracter.

Then, when the density difference is larger than a predetermined value (generally an intermediate value between black and white), it is considered to be a line drawing or character area, and it is binarized using a constant value (hereinafter referred to as slice binary). Process. Conversely, when the concentration difference is less than the predetermined value,
It is assumed that the image is a halftone image such as a photograph, and binarization processing is performed using the dither method. Therefore, for example, in a region that is almost uniformly black (or white), since the difference in eagleness is approximately equal to 0, it is determined that the image is a halftone image, and binarization processing using the dither method is executed.

At this time, for example, when binarized image data is reproduced using LBP, etc., at most 1 to 2 pixels determined to be white (or black) due to dithering are included in the 4 x 4 image area. Therefore, as long as you look at the reproduced image, it is not that disturbing.

However, when this binary image data is encoded and transmitted, or when it is stored in a page memory prepared in advance, the compression rate of the data is extremely reduced, resulting in a longer transmission time or when storing it in a page memory prepared in advance. The problem arises that images cannot be stored effectively.

The present invention has been made in view of the above points, and an object of the present invention is to more reliably judge the content of an image and thereby execute halftone processing suitable for the image. The present invention provides an image processing device that performs halftones of an image.

The present invention will be further explained below using the drawings. Explain in detail.

FIG. 1 is a diagram showing a circuit configuration of an embodiment of the present invention,
The image signal of the document read by the image sensor is converted into a 6-bit digital image signal by an A/D converter (not shown), and then applied to the manual terminal IN. The digital image signal is processed by the minimum value detection block, maximum value detection block,
The signal is supplied to a dither binarization circuit and a slice binarization circuit. l is an area (0
．． This circuit detects the maximum density value within 5 mm), and when the main scanning direction is 4B short side, the maximum value (black) of each image area is detected and stored by an IK x 6 bit memory. Similarly, the minimum value detection block 2 detects and stores the minimum value (white) in each area block, and is read out in synchronization with the main scanning reading of the 9th line.

The maximum and minimum values within each block 1.2 are subtracted by the subtractor 5.
The concentration gradient is calculated by subtracting . When this value is smaller than the 6-bit constant value B, that is, when the density is close to uniform density, the converter 7 inputs an output of the "l" level to the AND gate 9.

Conventionally, the output of the comparator 7 was used to select either the output of the binarization process by the dither binarization circuit 3 or the fixed slice binarization circuit 4. In addition to the output, the AND gate is applied only when the maximum value is larger than the constant value A and the minimum value is smaller than the constant value C, that is, when the comparator 6 and the comparator 8 output a '1'' level, respectively. The output of circuit 9 is “l”
``, the output binary image data of the dither binarization circuit 4 is selected by the multiplexer IO.

1l is an MH decoder that encodes binary data, l3 is a page memory that stores encoded data, and l4 is a transmitter such as a FAX.

Table 1 shows examples of binarization method selection between the present embodiment and the conventional method in various cases.

Here, the image density signal input to the input terminal IN is 6 bits.
(0 to 63) signal, level 0 is pure white, and level 63 is pure black. Also, the above-mentioned constant values A are 6, B are 32, and C
is 58.

In Table 1, the maximum value is 50. Since the minimum value lO is 50>A (=6), the output of the comparator 6 is "1", and since the minimum value is No>58, the output of the comparator 8 is "1", and similarly, the output of the comparator 7 is "1". The output of the AND gate 9 becomes O, and the multiplexer 10 selects the output of the slice binarization circuit 4.

In the cases of (1) and (2), the density gradient is small and the maximum and minimum values are fairly halftones, so the output of the dither binarization circuit 3 is selected.

However, in the case of ■ and ■, the concentration gradient was small, so the conventional method would have determined that it was a dither, but the minimum and maximum values were C = 58 and A. = 6 and is biased toward the black and white sides, so it is determined to be a slice binary value. When considering compression and encoding, it is preferable to binarize the entire area into black or white.

In this way, in this embodiment, in addition to the density gradient, which is the conventional image area judgment criterion, the maximum and minimum values of the density are taken into consideration to perform dither processing on a black image or a white image. This makes it possible to improve the compression rate during NH encoding, for example. To give an example of the compression rate of encoding, in the case of ■ in Table 1, if binarization is performed using the dither method according to the conventional example, the dither threshold value is O.
If there are 64 pixels from 63 to 63, there will always be three pixels that are determined to be white, so if the area is ■ in the main scanning direction, white data will periodically appear in the middle of consecutive data determined to be black. It appears in For example, MH (ModifiedH
u f m a n ) When performing encoding, B41
In the case of a completely black line, one line information is represented by 40 to 50 bits, but when one white pixel is inserted in the center, about 20 bits are immediately added. Therefore, the image area determination and binarization method selection means according to the present invention is highly effective in improving the compression rate during image signal encoding.

In addition, if processing such as compression is not required and the appearance of black or white dots is not a big problem, use the converter 7.
The binarization process may be selected only based on the output of .

That is, a multiplexer l2 is provided which manually outputs both the outputs of the dither binary circuit 3 and the slice binary circuit 4, and the multiplexer l2 is driven by the output of the comparator 7, and the binary printer 15, such as a laser beam printer, outputs a binary value. It is designed to supply an image signal.

Furthermore, in this embodiment, a signal that has undergone two types of binarization processing is selected as the output of the AND gate 9, but a fixed slice level is also stored in the ROM that stores a dither pattern to be output in a combo barrette, for example. Seshime, And Gate 9
It is also possible to select the output of the ROM based on the output of the ROM. It can also be used for data other than document reading, for example, for binarization processing of transmitted data.

Furthermore, it goes without saying that the slice level of each converter is not limited to that of this embodiment.

As explained above, according to the embodiments of the present invention, it is possible to eliminate the inconvenience caused by dithering a wide range of black or white areas of a document, and to achieve binarization processing according to the image content. be able to. In addition, especially when compressing binary data, it is effective in improving compression efficiency and, for example, shortening transmission time.

As described above, according to the present invention, an input image signal can be appropriately subjected to halftone processing depending on the output destination.

[Brief explanation of drawings]

FIG. 1 is a circuit block diagram of an embodiment of an image processing apparatus according to the present invention, where l is a maximum value detection block, 2 is a minimum value detection block, 3 is a dither binarization circuit, and 4 is a slice 2
Value conversion circuit, 5 is a subtracter, 6, 7.8 is a combiner, 9
is an andgame-1-, '10 is a multi-build noxa, and 11 is a MH encoder. Table 1

Claims (1)

[Claims] An image processing device that performs halftone processing on an input image signal and outputs the resultant image signal, the image processing device changing the halftone processing of the input image signal depending on an output destination of the image signal.