JPS63126367A - Pseudo intermediate tone processing device - Google Patents

Abstract

PURPOSE:To obtain a sharp intermediate tone picture by using a data quantized into 2<n> gradation from a noticed picture element and adjacent reference picture element respectively, calculating the density difference to apply positive/negative judgement to a difference, adding a prescribed reference value accordingly and converting it into binary information and outputting the result. CONSTITUTION:A picture element data storage section 11 consists of a RAM 22 storing picture data K of 2 lines and a picture element counter 21 counting picture element number in the main scanning direction synchronously with the picture element data K, and the output of a counter 21 is used as an address signal and inputted to the RAM 22, a timing signal (b) is used for write/read and the read data is sent sequentially to a picture element data extraction section 12. The extraction section 12 consists of 2-stage of FFs 23, 24 synchronized by the timing signal (a), a dither pre-processing section 13 consists of a ROM 25 and a dither processing section 14 consists of a dither counter 26 and a ROM 27, they are used to aply quantization of 2<n> gradation to the noticed picture element and the reference picture element and the result is outputted to the processing section 14.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a pseudo halftone processing device that binarizes halftone image data to express halftones in a pseudo manner.

2. Description of the Related Art A conventional pseudo-halftone processing device generally includes a main scanning counter 1 for counting the number of pixels in the main scanning direction and a sub-scanning counter 1 for counting the number of lines in the sub-scanning direction, as shown in FIG. a decoder 8 which inputs the count values of the counter 2, the main scanning color/reference counter 1, and the sub-scanning counter 2, and generates a 4×4 Bayer type dither pattern m as shown in FIG. 9 according to the input data; A comparator 4 inputs the digital turn m generated by the decoder 3 and the multivalued image data k obtained by a predetermined image reading means, and compares the magnitude of both.
It had Then, in the comparator 4, if the multivalued image data k is equal to or greater than the threshold value (k≧m), the image data k becomes blank, and on the other hand, if the multivalued image data k is less than the threshold value (k≧m),
kpm), it was binarized by setting it to "black") to express a pseudo-halftone (Takahiko Fukinuki, "Image Signal Processing for FAX and OA", Nikkan Kogyo) Newspaper company).

For example, input image data k having a 16-gradation halftone pattern as shown in FIG.
When binarized according to the dither pattern m shown in the figure (the dither pattern m in Fig. 9 is superimposed within the dotted line frame in Fig. 11), the binarized processing data as shown in Fig. 10 (in the figure, the circles are A black pixel and a frame without a circle mark are white pixels.) are obtained.

Problems to be Solved by the Invention However, although such a configuration can represent a halftone image in a pseudo manner, for example, as shown in FIG. There was a problem with this.

Furthermore, when halftone photographs, etc. are expressed in a pseudo-halftone manner using binary information, periodic density changes that do not exist in the original image, so-called moiré noise, occur, making the same image as described above difficult to read. There was a problem.

The above-mentioned problem arises for the following reasons. That is, in the former case, the threshold value for binarization is, for example, 4×4 as shown in FIG.
This occurs because the white/black pattern obtained by binarizing each pixel in the area is dispersed, and the latter is
This occurs because the line densities of the halftone photograph and the reading device (halftone expression means) are different.

The present invention has been made in view of the above-mentioned problems, and it is possible to improve the quality of characters, characters, and
Pseudo-halftone processing that improves the resolution of binary images such as drawings, and that can clearly reproduce halftone images such as halftone photographs without generating noise such as moiré. The purpose is to provide equipment.

Means for Solving the Problems In order to achieve the above object, the present invention provides a pixel data storage that sequentially stores data obtained by quantizing a pixel of interest and a pixel adjacent to the pixel of interest (reference pixel) to 2n gradations. a pixel data extraction section that extracts pixel data of interest and reference pixel data from the pixel data storage section; and a pixel data extraction section that takes in pixel data of interest and one or more reference pixel data from the pixel data extraction section and calculates the density difference between the two. The absolute value of this density difference and the first set value are compared in magnitude, and the difference between this density difference and the second set value is determined to be positive or negative.

A dither preprocessing section adds a predetermined reference value to the pixel data of interest according to the determination result to calculate new pixel data of 21 gradations and outputs this as pixel data, and The present invention is characterized by comprising a dither processing section that takes in tone pixel data, converts it into binary information, and reproduces halftone pixels in a pseudo manner.

Operation With the above-described configuration, the present invention compares whether the absolute value of the density difference between the pixel of interest and the reference pixel is greater than or equal to the first set value, and if there is a reference pixel that exceeds the first set value, the pixel of interest is removed. When it is determined that the edge is a white or black edge and this edge determination is made, a white or black pattern is output to the dither processing section to emphasize the white or black edge, regardless of the pixel data of interest. While improving the resolution of binary images such as characters, the difference between a predetermined number of density differences and a second set value is determined to be positive or negative, and if the predetermined number of density differences are in the same direction, positive or negative, When a pixel is determined to be an isolated point and the isolated point determination is performed, a reference value is added to the pixel data of interest and output to the dither processing section. As a result, isolated points are smoothed, making it possible to remove moiré from halftone images such as halftone photographs.

Embodiment FIG. 1 is a block diagram showing a pseudo intermediate processing device according to an embodiment of the present invention. In FIG. 1, 11 is a pixel data storage unit that sequentially stores pixel data k quantized to 2n gradations, and 12 is a pixel data storage unit 11, which is arranged in a positional relationship as shown in FIG. A certain pixel of interest px, a reference pixel pi(i
A pixel data extraction unit 13 that appropriately extracts desired pixel data from the data of =l to 8) performs the processing described below on the pixel of interest px based on the relationship between the extracted pixel of interest PX1 and the reference pixel Pi. This is a dither preprocessing section that outputs the pixel data as pre-dithered pixel data PXI.

Note that in this embodiment, the dither preprocessing unit 13
and a reference pixel pi (i=l
Let us take as an example the case where the data in ~3) is input as an address. Further, 14 is a dither processing unit that takes in pre-dither pixel data PXI and converts it into dither data D.

Note that in this embodiment, the pixel data is provided by the pixel data extraction unit 12.
The pixel data is taken into the pixel data storage section 11 via the pixel data storage section 11.

The configuration of the pseudo halftone processing device described above will be explained in more detail with reference to FIG. The pixel data storage section 11 shown in FIG. 8 includes a RAM 2 that stores pixel data k for two lines.
2, and a pixel counter 21 that counts the number of pixels in the main scanning direction in synchronization with pixel data k. pixel counter 2
The output of 1 is the address signal for RAM22.
2. The RAM 22 receives the timing signal ■ and performs writing and reading, and the RA
The read data of M22 is sequentially input to the pixel data extraction section 13.

The dither processing unit 14 is a main scanning counter 1 shown in FIG.
and a dither counter 26 consisting of a sub-scanning counter 2;
It is equipped with a ROM 27 having the functions of the decoder 3 and comparator 4 shown in FIG. The ROM 27 takes in the output of the dither counter 26 and the output data RXI of the dither preprocessing section 13 as address data, and also stores the above-mentioned dither data D in correspondence with these address data.
is written.

The dither preprocessing unit 13 inputs data of a pixel of interest px and a reference pixel pi (i=1 to 3) having a positional relationship as shown in FIG.
It is equipped with 25. In this case, as for the data of the reference pixel Pi, the upper two bits of the pixel data quantized to 4 bits are inputted to the address of the ROM 25.

The pixel data extracting unit 12 includes a two-stage flip-flop (F/F) synchronized with the timing signal ■ shown in FIG.
)28.24, the target pixel px and the reference pixel P1. P2. Each data of P9 is extracted.

In FIG. 6, n indicates the n-th pixel, and an asterisk (*) indicates data that is invalid in the processing of the ROM 25. Furthermore, only the upper two bits of the reference pixel data are extracted as described above.

The ROM 25 contains a pixel of interest px and a reference pixel PI.

P2. Using each data of P3 as an address signal, pre-dither pixel data P which is the result of the procedure shown in FIG. 4 described later
The coefficients for outputting XI are written in advance. In this case, reference pixels PI, P2 . Since P8 is 2-bit data, a conversion such as pie-piX4+2 is performed to make the data of the reference pixel Pi pseudo-4 bits, and then the processing shown in FIG. 4 is performed. The operation of the pseudo halftone processing device configured as above will be explained with reference to FIG.

The multivalued image signal quantized to 2n gradations is stored in the pixel data storage section 11 via the pixel data extraction section 12.

The pixel data extraction unit 12 extracts pixel px data of interest and reference pixel pi (i=l~8) in the positional relationship as shown in FIG.
) The data is extracted as necessary and output to the dither preprocessing section 13. The dither preprocessing unit 13 performs processing as described later on the pixel data of interest, and outputs pre-dither pixel data Rxl to the dither processing unit 14.

The dither preprocessing unit 13 processes the pixel of interest px using the processing procedure shown in FIG.

First, the presence or absence of edge detection is determined based on the density difference Δi (Δ1=pi−px) between the pixel of interest px and the reference pixel Pi (i=1 to 8) (step (hereinafter referred to as ST) 1). Here, the density difference △i and the edge detection value T as the first set value
Between HI (THI≧0), 3PiC1△11≧THI)・・・・・・・・・・・・
If the following relationship is satisfied, the operation proceeds to Sr1 as an edge detection cloth, whereas if the relational expression is not satisfied, the operation proceeds to Sr1 as an edge detection heat. In Sr1, pixel data px is held in data out as data as a candidate for output pixel data.

In Sr1, discrimination between white and black edges is performed. In other words, for pi that satisfies the relational expression ■, Δi≦−THI・・・・・・・・・・・・・・・
・・・・・・・・・・・・■If the relationship is satisfied,
The edge is set to white, and the operation proceeds to Sr1.

And Δi≧THI・・・・・・・・・・・・・・・・・・
If the relationship ■ is satisfied, it is assumed that the edge is black and the operation proceeds to Si2. Sr.
In 1, white data is set as OUT←15, and Si2
Then, set OUT←0 to hold black data.

When any of the processes in Sr1.4.5 is completed, isolated points are detected (Si6). That is, when the isolated point detection threshold as the second setting value is, for example, TH2 (TH2≧0), the following relationship is satisfied: Pi [Δi≦−TH2]・・・・・・・・・■ Or, picΔi> TH2)・・・・・・・・・・・・■
If the relationship is satisfied, it is assumed that there is an isolated point and the operation is Sr1
Proceed to. On the other hand, if the relational expressions ■ and ■ are not satisfied, the operation proceeds to 5TIO as an isolated point heat and the data is already out.
The data held in is output as pre-dither pixel data PXI (STIO).

In this case, if TH2=O is set, the positive or negative of the concentration difference Δi will be directly compared.

In Sr1, when the relational expression (2) is satisfied, it is assumed that a white isolated point has been detected, and the operation proceeds to Sr1, where the smoothing process of PX14-PK-(X (, α≧0) is performed on the pixel data px. Here α is a smoothing coefficient. Also, Sr
1, when the relational expression (■) is satisfied, it is assumed that the firing point has been detected, and the operation proceeds to Si9, where the smoothing process of PXI←px+α is performed on the pixel data px. The data PXI of the pre-dithered pixel PXI obtained through the above procedure is outputted to the dither processing section 14 as pixel data.

Then, the dither processing unit 14 calculates binary image data obtained by dithering the captured pre-dithered pixel data PXI, and outputs this as dither data D.

In this example, when edge detection threshold: TH1 = 7, isolated point detection threshold TH2 = 4, and smoothing coefficient α = 2, when pseudo halftone processing is applied to 16 gradation data as shown in Fig. 11, the result is As shown in Figure 7, the first
The results are clearer than the conventional processing results shown in Figure 0.

In addition, in this embodiment, all the reference pixels P are
Although the processing requirement is set when the condition is satisfied over i, it may be set so that the processing is performed when any reference pixel Pi satisfies the condition.

By doing so, a wide range of image processing can be performed.

Effects of the Invention As is clear from the above explanation, the present invention can easily enhance edges, improve the resolution of binary images such as characters, and smooth density changes in halftone images. This has the effect of removing noise such as simian marks.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram showing a pseudo halftone processing device according to an embodiment of the present invention, FIG. 2 is a conceptual diagram showing the positional relationship between a pixel of interest and a reference pixel processed by the pseudo halftone processing device,
3 is a block diagram showing the configuration of the pseudo halftone processing device shown in FIG. 1, FIG. 4 is a flowchart showing the processing procedure performed in the dither preprocessing section of the device shown in FIG. 3, and FIG. 6 is a time chart of each signal in the device of FIG. 3, and FIG. 7 is an example of the processing results of the device of FIG. 3. FIG. 8 is a block diagram showing an example of a conventional pseudo-halftone processing device; FIG. 9 is a schematic diagram showing a Bayer r-type dither pattern used in the device shown in FIG. 8; FIG.
The figure is a schematic diagram showing an example of the processing result by the apparatus of FIG.
FIG. 11 is a schematic diagram showing pixel data input to each of the devices shown in FIGS. 3 and 8. 11... Pixel data storage section, 12... Pixel data extraction section, 13... Dither pre-processing section, 14... Dither processing section. [Ku → To ■ 砺C( Admittedly ゞFigure 4Figure 5 □The Lord's favor - ゛To times; -0 Ine AnimalFigure 7Figure 8Figure 9Figure 10Figure 11

Claims (1)

[Claims] Pixel of interest and pixels adjacent to this pixel of interest (reference pixel)
a pixel data storage section that successively stores data quantized to 2^n gradations, a pixel data extraction section that extracts pixel data of interest and reference pixel data from this pixel data storage section, and a pixel data extraction section that extracts pixel data of interest and reference pixel data from this pixel data storage section; Focused pixel data and 1
The above reference pixel data is taken in, the density difference between the two is calculated, and the absolute value of this density difference is compared with the first setting value, and the difference between this density difference and the second setting value is determined to be positive or negative. a dither preprocessing unit that calculates new pixel data of interest with 2^n gradations by adding a predetermined reference value to the pixel data of interest according to the comparison and determination results, and outputs this as pixel data; A pseudo-halftone processing device comprising: a dither processing section that takes in 2^n gradation pixel data from a dither pre-processing section, converts it into binary information, and reproduces a pseudo halftone image.