JPH08149295A - Dot area decision device - Google Patents

Abstract

PURPOSE: To provide a dot area decision device in which a peak/dip picture element is surely detected independently of the size of dots and then a dot area is accurately decided. CONSTITUTION: The roughness of a dot area is judged by detecting the regularity of pitches p0 , p1 , p2 ,... of dots and the peak/dip picture element is detected by using two kinds of wide/narrow dot areas. Thus, even when dots are coarsers, a wide detection area is used to detect the peak/dip picture element accurately.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a halftone dot area judging device for reading a manuscript image and judging whether or not the read manuscript image is a halftone dot area manuscript image.

[0002]

2. Description of the Related Art In a color digital copying machine, a color original is read by a scanner composed of a CCD (charge coupled device) or the like and converted into red (R), green (G) and blue (B) electric signals. , The original area is the character / line drawing area, halftone dot
It has a function of determining whether it is a (screen) area or a photographic area and performing image processing according to the type of the area.

Then, in the case of a character / line drawing area, edge emphasis or black character emphasis is performed, and in the case of a halftone dot area, smoothing or blurring processing is performed. The halftone dot area is determined as follows. Attention is paid to each pixel in the digital image information which is read from the document and temporarily stored, and the pixel of interest is surrounded by a fixed number of pixels (for example, 3 pixels × 3 pixels) that are continuous around the pixel of interest. It is determined whether the density is higher than that of the surroundings or lower than the surroundings. If the density is higher than the surroundings, this pixel is set as a peak pixel, and if the density is lower, this pixel is set as a dip pixel.

Then, the peak /
By checking whether the intervals between the dips are appropriate, or whether the appearance pitches of the peak pair and the dip pair are constant, it is determined whether or not it is a halftone dot area.

[0005]

By the way, the number of dots per inch (hereinafter referred to as "the number of lines") in the halftone dot area is about 200 lines for a fine texture and for a rough texture. There are up to about 65 lines. In an original with a small number of lines of less than about 100 lines, the size of the halftone dots is larger than the resolution of the scanner, so the detection area of the constant number of continuous pixels is too narrow to determine whether it is a peak / dip pixel. There was a problem that the judgment could not be made accurately, and a false detection was often made.

On the other hand, in the case of an original having a large number of lines of about 100 lines or more, many peak pixels or dip pixels are included in the detection pixels unless a continuous and relatively narrow detection area centered on the pixel of interest is adopted as in the conventional case. , Which makes it virtually impossible to detect peak / dip pixels. Therefore, an object of the present invention is to solve the above-described technical problem, to enable reliable detection of peak / dip pixels regardless of the size of halftone dot dots, and thus to accurately determine halftone dot areas. It is an object of the present invention to provide a halftone dot area determination device capable of achieving the following.

[0007]

In order to achieve the above-mentioned object, a halftone dot area determination device of the present invention collects pixel data in a wider area in addition to the detection area of the fixed number of pixels. It has two kinds of detection areas of wide area detection area, and detects the roughness of the halftone dot area, and detects based on the detection signal of the two kinds of detection areas according to the roughness of the detected halftone dot area. It has a switching means for switching and using any one of the determination results of the halftone dot regions determined by using the determined peak / dip pixel information.

[0008]

According to the above construction, the roughness of the halftone dot area can be accurately determined. Therefore, according to the result of the determination,
It is possible to detect peak / dip pixels using two types of detection areas, wide and narrow. Therefore, it is possible to deal with the case where the halftone dots become coarse, and the peak / dip pixel can be accurately detected.

[0009]

Embodiments will be described in detail below with reference to the accompanying drawings showing embodiments. FIG. 1 is a block diagram showing an electrical configuration of a main part of a color digital copying machine. In this color digital copying machine, a color original is read in one direction (referred to as a main scanning direction) by a scanner 1 composed of a CCD (charge coupled device) or the like, and a yellow (Y), a magenta (M), and a cyan (C) are used. Convert to primary color signal. The resolution of the scanner 1 is about 400 pixels per inch.

The Y, M, and C primary color signals are subjected to correction processing in accordance with the characteristics of toner in the input processing circuit 2,
Only the information of a fixed line (for example, 3 lines) selected for the document type determination is temporarily stored in the FIFO memory 3 and transferred to the character / dot / photo determination circuit 4 and stored in the line memory 41. In, it is determined whether the document area is a character / line drawing area, a halftone dot screen area, or a photograph area.

On the other hand, the Y, M, and C primary color signals are supplied to a black generation circuit 5, where black (BK) data for compensating for the insufficient density of a high-density original is created. Further, the four signals Y, M, C, and BK are taken out by the color selector circuit 6 one by one, and converted by the zoom / movement circuit 7 into signal contents corresponding to the set magnification.

Then, in the filter circuit 8, smoothing or edge sharpening is performed depending on the type of the document whose area has been determined. Finally, halftone display (dithering) is performed by the gradation processing circuit 9 and output to the laser printer through the output control circuit 10. The outline of the signal flow in the color digital copying machine has been described above. The details will be described below centering on the determination function of the dot area in the character / dot / photograph determination circuit 4.

The information for three lines temporarily stored in the line memory 41 of the character / halftone dot / photograph determination circuit 4 includes a matrix of 3 dots × 3 lines (see FIG. 2) and 5 dots spread in the main scanning direction. A matrix of x3 lines (see FIG. 3) is multiplied, and peak / dip pixels are detected in parallel. In the 5 × 3 matrix of FIG. 3, the arrangement of the eight pixels A to H, which are the detection pixels, is devised so that the detection pixels are not arranged in the vertical and horizontal directions as much as possible. The reason is shown in FIG. If the pixels are arranged in a straight line in the vertical and horizontal directions like this, the detection pixels will be missed for the entire row,
This is because there is no detection pixel for a line segment that passes through the target pixel X at an angle of 45 °, resulting in erroneous detection.

The criterion for peak / dip pixel detection is
In the 3 × 3 matrix shown in FIG. 2, the density of the center pixel of interest X is higher than the density of the surrounding pixels B, C, D, and H, and the value obtained by subtracting a predetermined value from the density of the target pixel X is the surrounding pixels. The pixel of interest X is determined to be a peak pixel because it is darker than the densities of A, E, F, and G, and the density of the pixel of interest X at the center is lower than the densities of surrounding pixels B, C, D, and H. The value obtained by adding a predetermined value to the density of the pixel of interest X is the value of the surrounding pixels A,
The target pixel X is determined to be a dip pixel because it is lighter than the densities of E, F, and G.

In the 5 × 3 matrix shown in FIG. 3, the density of the pixel of interest X at the center is higher than the density of the surrounding pixels B, C, D, and H, and the value obtained by subtracting a predetermined value from the density of the pixel of interest X. The target pixel X is determined to be a peak pixel because it is darker than the density of the surrounding pixels A, E, F, and G, and the density of the center target pixel X is higher than the density of the surrounding pixels B, C, D, and H. The pixel of interest X is determined to be a dip pixel because the pixel of interest X has a lower value than the density of the surrounding pixels A, E, F, and G, and the value obtained by adding a predetermined value to the density of the pixel of interest X.

The above processing is performed for each dot (pixel of interest) of the middle line of the information of three lines temporarily stored in the line memory 41. On the other hand, it is necessary to decide which of the results determined by the above two types of matrices should be used. As will be described later, this determination is performed by separately detecting the pitch of the dots that form the halftone dots and depending on the detection result, but in addition to that, it is determined based on both the results determined by two types of matrices. If two halftone dot area detection processes are performed in parallel, and if at least one of them is judged to be a halftone dot area, it is judged to be a halftone dot area. For example, it may be determined that the area is not a halftone dot area.

Next, a method of detecting the pitch of the dots forming the halftone dots will be described. A mask of 3 × 3 matrix as shown in FIG. 4 is assembled, and an average value AVE of the densities of peripheral pixels a, c, f, and h in the diagonal direction of the target pixel x is taken, and the density of the target pixel x is higher than AVE. If it is also dark, the pixel of interest x
To the target pixel x if it is thinner than AVE. Then, the pixel of interest x is moved along the line to form a column of the obtained attributes as shown in FIG. Areas S ₀ , S ₁ , S ₂ , ... Are created by dividing each position in which the numbers forming this row rise from 0 to 1, and the length (pitch) of each area is p ₀ , p ₁ , p ₂ , …
And

The judgment condition is a certain area (for example, area S
₀ )) (this area is referred to as a feedback area), and p ₁ ≦ 10 (1) p ₂ ≦ 10 for the area S ₁ immediately before the area S ₀ and the area S ₂ before the area S _0. (2) If the relationship of | p ₁ −p ₂ | ≦ 1 (3) (p ₁ + p ₂ ) / 2> 4 (4) is established, it is determined that the pitch is coarse, and the pixels constituting the area S ₀ are selected. Is a 5x3 matrix (see Figure 3)
It is decided to adopt the judgment result according to.

If the above expressions (1) to (3) are satisfied, but the relational expression (4) is not satisfied, it is determined that the pitch is fine,
A 3 × 3 matrix (see FIG. 2) is provided for the constituent pixels of the area S ₀ .
It is decided to adopt the judgment result according to the reference). (1) above
~ If the expression (3) is not satisfied, it is determined that the area is not the halftone dot area. In the above equations (1) and (2), the pitch p ₁ and the pitch p ₂ are 1
The condition of 0 pixels or less is shown, and if the resolution of the scanner 1 is about 400 pixels per inch, the number 10 indicates a very coarse halftone dot area of 40 cycles per inch when read at a screen angle of 90 °. It turns out that. If read at a screen angle of 45 °, 60
It becomes a halftone dot area having a line shape. The reason why such a rough halftone dot area is not regarded as a halftone dot area is to prevent a character area from being erroneously detected as a halftone dot area.

In the equation (3), paying attention to the pitch periodicity, if the pitch seems to fluctuate too much, it is not considered as a halftone dot area. The above equation (4) focuses on the pitch itself. The number 4 corresponds to a halftone dot area with a pitch of 100 cycles per inch. If the pitch is larger than 4, the halftone dot area is coarser than 100 lines, and if the pitch is smaller than 4, the halftone dot area is finer than 100 lines.

The above processing is performed for each area of the middle line of the information of three lines temporarily stored in the line memory 41. Then, the result of this decision is
This is transmitted to the switch section (not shown) of the halftone dot / photograph determination circuit 4 to select either of the results determined by the two types of matrices.

As described above, it is determined whether or not it is a halftone dot area based on the selected signal of the results determined by the two types of matrices. When the above process is completed for the line temporarily stored in the line memory 41, the process is similarly performed for the next line. In this way, a column having the attribute of the pixel of interest x is created, and each of the areas S ₀ , S ₁ , S ₂ , ... Length (pitch) p ₀ , p ₁ , p ₂ , ... Based on the mutual relationship, the fineness and roughness of the texture of the halftone dots are detected, and two types of detection matrix regions (see FIGS. 2 and 3) are detected. Since the peak / dip pixels are detected by using the peak / dip pixels, the peak / dip pixels can be surely detected even in the halftone dot area where the texture of the peak / dip array is rough.

The present invention is not limited to the above embodiment. In the above embodiment, the wide area detection matrix area (5 × 3, see FIG. 3) is devised by selecting 8 pixels so that the pixels are not arranged vertically and horizontally as much as possible.
As shown in FIG. 6, even if an array in which pixels are arranged vertically and horizontally is adopted, it is still possible to reliably detect peak / dip pixels in a halftone dot area having a rough texture. Further, although the number of storage lines of the line memory 41 is increased, as shown in FIG.
A × 5 matrix may be used. Other various modifications can be made without changing the gist of the present invention.

[0024]

As described above, according to the halftone dot area judging device of the present invention, it is possible to accurately judge the roughness of the halftone dot area, and depending on the result of the judgment, from a narrow range to a wide range. Since the pixel data in 3) can be collected, it is possible to deal with the case where the halftone dot becomes coarser, and the halftone dot area can be accurately detected.

[Brief description of drawings]

FIG. 1 is a block diagram showing an electrical configuration of a main part of a color digital copying machine.

FIG. 2 is a diagram showing a 3 × 3 matrix area which is an example of a detection area centered on a pixel of interest.

FIG. 3 is a diagram showing a 5 × 3 matrix area which is an example of a wide area detection area centered on a pixel of interest.

FIG. 4 is a diagram showing a mask of a matrix for detecting a pitch of dots forming halftone dots.

FIG. 5 is a diagram showing a column of attributes (0, 1) of a pixel of interest x for detecting the pitch of dots forming halftone dots.

FIG. 6 is a diagram showing another matrix of a wide area detection region.

FIG. 7 is a diagram showing another matrix of the wide area detection region.

[Explanation of symbols]

 1 Scanner 2 Input processing circuit 4 Character / dot / photo judgment circuit 41 Line memory

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location H04N 1/40 C 104

Claims (1)

[Claims] 1. A conversion unit for reading an original image and converting it into image data corresponding to its density, a setting unit for setting a detection region of a fixed number of pixels centering on a pixel of interest, and a detection set by the setting unit. A halftone dot area judging device having a judging means for detecting a peak / dip pixel based on density information of pixel data in the area and judging whether or not the read original image is an original image of a halftone dot area. The setting means has two types of detection areas, a wide area detection area capable of collecting pixel data in a wider area, in addition to the detection area having the fixed number of pixels, and determines the roughness of the halftone dot area. Roughness detecting means for detecting and peak / dip detected based on the detection signals of the two types of detection areas according to the roughness of the halftone dot area detected by the roughness detecting means Halftone dot area determination apparatus characterized by having a switching means using switching one of the determination results of each determination is halftone regions with iodine information.