JPS62183672A - Picture processor - Google Patents

Abstract

PURPOSE:To output an input picture signal in which the change in density is steep and isolated without emphasizing an edge by providing an edge emphasis discriminating means for discriminating whether an edge emphasis means is selected or not from plural density difference values calculated by a density difference calculating means. CONSTITUTION:An original 1 is projected on a CCD 3 through a lens 2. The analog picture signal outputted from the CCD 3 is amplified by an amplifier 4 and converted into, for instance, a digital picture signal of 6 bits by an A/D converter 5. Thereafter, the shading correction of the picture is carried out in a shading correction circuit 6. Then, whether the edge is emphasized or not is discriminated in the edge emphasis discriminating circuit 7a, and when the edge is emphasized, the edge is emphasized in the edge emphasis circuit 7b and when it is not emphasized, the signal is fed to a picture processing circuit 8.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an image processing device that performs image processing on an input image to obtain an output image.

[Prior Art] This type of device converts a digital image signal into an analog signal in order to obtain halftone gradation when forming an image using, for example, a laser beam printer based on an input digitized image signal. The applicant has previously proposed a method of generating a pulse width modulated signal by converting the signal and comparing the converted signal with a pattern signal such as a triangular wave.

However, according to this method, when converting to an image signal with fine density changes such as 64 gradations, it is necessary to convert images such as characters or symbols in which density changes from white to black or from black to white are unnecessary. There was a problem in that when inputting data, the density change from white to black or from black to white becomes gradual, the boundaries become unclear, and the contrast deteriorates.

In order to solve this problem, conventional methods have been used to emphasize the edges of image information. For example, this method involves subtracting the second-order differential of a human-powered image signal from the source signal. As a result, the density change from white to black or from black to white becomes steep,
Sharpness and contrast of characters are improved.

[Problems to be Solved by the Invention] However, if image processing is performed only by the method of emphasizing edges as described above, for example, images with steep density changes and isolated points about the diameter of a laser spot may be produced. If there is a signal or noise, there is a problem in that by edge-emphasizing the signal, the density change is emphasized even more, which has the opposite effect of making it unnecessarily noticeable.

The present invention has been proposed in order to improve the above-mentioned problems, and it is an object of the present invention to provide an image processing apparatus that outputs isolated input image signals with steep density changes without edge enhancement.

[Means for Solving the Problem] In order to solve this problem, for example, the image processing apparatus of this embodiment includes an edge emphasis circuit that emphasizes edges for human image information, and a circuit that determines whether or not to emphasize edges. and an edge emphasis discrimination circuit for discrimination.

In the image processing apparatus of this embodiment, when it is detected that the pixel of interest is an isolated pixel from the difference between the pixel of interest of the input image signal and surrounding pixels within a predetermined distance range from the pixel of interest, edge enhancement is performed. The output image is formed by processing isolated pixels without highlighting them.

[Embodiments] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram of the image information processing apparatus of this embodiment.

In the figure, 1 indicates the original that becomes the input image, 2 indicates the lens, and 3
is a COD which is an image sensor.

4 is an amplifier that amplifies the signal output from the CCD 3, and 5 is an A/D converter that converts the analog electrical quantity into digital.
It is a D converter. 6 is a shading correction circuit, and 7a is an edge emphasis discrimination circuit. This edge discrimination circuit 7a discriminates whether or not to emphasize the edge portions of the input image, and if the edge portion is to be emphasized, the human-powered image signal is passed to the next edge enhancement circuit 7B, and if the edge portion is not to be emphasized, the human-powered image signal The image signal is passed to the image processing circuit 8. In addition,
The criterion for this judgment is that the input image signal is passed to the image processing circuit 8 without passing through the edge emphasis circuit 7b only when the judgment conditions described later are satisfied. In addition, the image processing circuit 8
For example, a 6-bit digital signal is subjected to γ conversion. 9 is a D/A converter that converts a digital signal into an analog signal. 10 is a triangular wave generator that generates a triangular wave synchronized with the beam detection signal, and 11 is a comparator that compares the triangular wave generated from the triangular wave generator 10 with the output image level signal of the D/A converter 9. A laser driver 12 causes the laser diode to emit light based on the pulse width output from the comparator 11. 14 is a scanner composed of a polygon mirror or the like for scanning a laser beam, and 15 is an optical system such as a toric lens for exposing the photosensitive drum 17 with an optical signal from the scanner 14. In addition, 16 is a primary charger, 18 is a developer, 19 is a registration roller, 2° is paper, 21 is a transfer charger, 22 is a separation charger, 23 is a cleaner, 2
4 is a transport unit for paper 20; 25 is a fixing unit; 2
6 is a pre-exposure light emitting element that equalizes the potential on the surface of the photosensitive drum.

In this configuration, the document 1 is transferred to the CCDB via the lens 2.
projected on top. The analog image signal output from the CCD 3 is amplified by an amplifier 4 and then sent to an A/D converter 5.
The signal is then converted into, for example, a 6-bit digital image signal. Thereafter, the shading correction circuit 6 performs shading correction on the image. Next, an edge emphasis determination circuit 7a determines whether or not to perform edge emphasis. If edge emphasis is to be performed, an edge emphasis circuit 7b performs the edge emphasis, and if not, a signal is passed to an image processing circuit 8. The details of this process will be explained below.

FIG. 4 is a diagram showing the principle of edge enhancement, where signal a is the original signal, signal S is the first differentiated signal of signal a, and signal C
is the second-order differential of the signal a (the first-order differential of the signal a). Signal d shows [signal a - number C], and it can be seen that the final change from white to black is steep and the edges are emphasized. This process is actually performed digitally as shown below.

In the 3×3 pixel matrix shown in FIG. 2, the density difference between the density of the pixel of interest X and the density of adjacent pixels y1 to y4 is defined as Laplacian Δ for each main scan and sub-scan.

Δ main scanning = (yt-x) + (yt-x) Δ sub-scanning =
(y3-x) + (y4-x) When the amount of emphasis in the main scanning direction is α and the amount of emphasis in the sub-scanning direction is β, and if the density of the pixel of interest X is the edge-emphasized density X', then X' is It can be expressed by a formula.

x'=x-(α・Δ main scanning + β・Δ sub-scanning)=x+2
(αX+βX) -α(y1+y2)−β(y3+y4) Therefore, α=
When β=1, x' = 5X-(yx +372 +y3+y4).

When the A/D converter 5 performs A/D conversion to 64 gradations, the white level becomes (00)H() (represents a hexadecimal number), and the black level becomes (3F)H.

For example, if α=β=1, Focused pixel density X=(21)H.

yz=(IE)H, y2=(IE)H.

y3 = (20)H, y4 = (IF)H
In this case, X'=(2A)H, and the density is emphasized.

However, for example, if there is an isolated gray spot with a very small area on a barely foggy white background, or if there is an isolated gray spot with a very small area on a gray background, these The edges of each image are emphasized, and the former becomes black and the latter becomes white, resulting in a large change in density relative to the background, making it very noticeable.

In order to prevent such a problem from occurring, an edge enhancement determination circuit 7a is provided before the edge enhancement circuit 7b for determining whether or not edge enhancement is to be processed. This determination criterion is used to perform the determination, for example, by implementing the process shown in FIG.

That is, there is little variation in the density of the pixel of interest X and the density of the adjacent pixels y1 to y4. In other words, the following first condition is set as a condition that the background has a uniform density. (However, Δα is the absolute value of the maximum and minimum density difference among the adjacent pixel densities y1 to y4.) Δα≦A ... First condition Here, A is (00)H to (05)H Set it to a fairly small value. Next, the pixel density of interest X is the adjacent pixel density y1
The following second condition is provided as a condition indicating that the difference in density is large compared to the maximum density or minimum density in ~y4.

α1. The larger value compared to α2 ≧ B... Second condition However, α1 is the concentration of the pixel of interest X and the concentration of adjacent pixels y1 to y4
α2 is the absolute value of the density difference between the pixel density of interest X and the minimum pixel density among the adjacent pixel densities y1 to y4.

Here, the value of B is empirically set as a density difference in which the density of an isolated point becomes noticeable when edge enhancement is performed.

As shown in FIG. 3(a), when the pixel density X of interest is close to the black level, α1≦α2.

Further, when the pixel density X of interest is close to the white level, that is, when the pixel density X is close to the white level, that is, as shown in FIG. 3(b), α1≧α2.

Therefore, it is sufficient to compare α1 and α2 and compare the larger value with the value of B.

In this embodiment, only when the first condition and the second condition are satisfied at the same time, it is determined that an isolated image signal (singular point) with a steep density change exists, and edge enhancement is not performed. There is a particular thing.

The image signal processed by the edge emphasis circuit 7b is further converted into a digital image signal by γ-converting the 6-bit digital image signal, for example, by an image processing circuit 8. This image signal is again converted into an analog image level signal by the D/A converter 9.

On the other hand, the triangular wave generator 8 generates a triangular wave synchronized with the beam detection signal.

The comparator 11 compares the analog image level signal and the triangular wave signal. Only when the triangular wave signal is larger than the image level signal, the output signal of the comparator 11 becomes HIGH. Therefore, as the image level goes from "low" (black) to "high" (white), the pulse width of the output signal of the comparator 11 becomes smaller. The laser driver 12 is driven in proportion to this pulse width, and the laser diode 13 emits light.

A beam spot of a laser beam emitted from a laser diode 13 is scanned on a photosensitive drum 17 by a scanner 14 and an optical system 15. This forms a static N<M image. Next, a developer 1 is placed on the area irradiated with the laser beam.
8 adheres to the toner, and a visible image is formed on the surface of the photosensitive drum 17 (however, in the case of image scanning)
.

On the other hand, the paper 20 is sent to the transfer charger 21 via the registration rollers 19. Here, the toner adhering to the surface of the photosensitive drum 17 is transferred to the paper 20, and the paper 20 is electrostatically separated from the photosensitive drum 17 by the separation charger 22.

Next, the paper 20 is transported by the transport unit 24, and is fixed in the fixing unit 25. on the other hand,
The toner adhering to the surface of the photosensitive drum 17 is removed by the cleaner 23, and the electric charges on the surface of the photosensitive drum 17 are eliminated by the pre-exposure light emitting element 26.

As a result, a series of electrophotographic processes is completed.

In the above electrophotographic process, the longer the light emission time of the laser diode 13 on the photosensitive drum 17, the lower the surface potential due to optical attenuation. In reversal development, the lower the surface potential, the higher the density of the copied image.

Therefore, the density of the copy image and the pulse width of the output signal of the comparator 11 are proportional, and a copy image with gradation is obtained.

As explained above, by comparing a signal obtained by converting a digital image signal into an analog image signal and a pattern signal of a predetermined period according to this embodiment, in a pulse width modulated signal output device, it is possible to detect isolated areas with steep density changes. image signal (
If a singular point (singular point) exists, edge enhancement is not performed, so it is possible to prevent the problem that the singular point stands out due to edge enhancement.

Furthermore, in this embodiment, the density of the pixel of interest X shown in FIG. 2 and the neighboring pixel densities y1 to y4 were compared to determine whether the first and second conditions were satisfied.
The density of the pixel of interest X and the neighboring pixels y1 to y4 are set as shown in FIG. 5 or 6, and the densities are compared to see if they satisfy the first and second conditions. Also good.

[Effects of the Invention] As explained above, according to the present invention, edge enhancement processing is not performed when an isolated image signal with a steep density change exists, so that the problem of conspicuous singular points can be avoided, and a good result can be obtained. You will be able to get the output image.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the image processing device of this embodiment. FIG. 2 is a diagram showing the position of the pixel density of interest and its surrounding pixel density. FIGS. 3(a) and (b) are the concentrations of the pixel of interest. Figure 4 is a diagram showing the waveform conversion processing that is the standard for edge enhancement processing, and Figures 5 and 6 are diagrams showing the positions of other pixel densities of interest and their surrounding pixel densities. FIG. In the figure, 1... Original, 2... Lens, 3... CCD
. 4...Amplifier, 5...A/D converter, 6...
shading correction circuit, 7a... edge emphasis discrimination circuit, 7b... edge emphasis circuit, 8... image processing circuit, 9... D/A converter, 1o... triangular wave generator, 11... Comparator, 12... Laser driver, 14... Scanner, 15... Optical system, 17...
It's a drum. Patent applicant: Canon Co., Ltd. Figure 2 Main Lid direction Figure 3 (a) White (00) 16 Figure 3 (b) White (00) + 6 Black (3Fh6)

Claims (2)

[Claims] (1) In an image information processing device equipped with an edge part emphasis means for enhancing an edge part of input image information, the density of a pixel of interest in the input image information and a plurality of surrounding pixels within a predetermined distance range from the pixel of interest. a concentration detection means for detecting;
density difference calculating means for calculating the difference between the density of the pixel of interest detected by the density detecting means and the density of the plurality of surrounding pixels, and detecting the edge from the plurality of density difference values calculated by the density difference calculating means. An image processing apparatus characterized by comprising an edge emphasis determining means for determining whether or not to select an emphasizing means. (2) The determining means detects that the difference between the maximum density difference value and the minimum density difference value among the plurality of density difference values is within a predetermined range, and the maximum density difference value is greater than or equal to a predetermined value. 2. The image processing apparatus according to claim 1, wherein the image processing apparatus does not select the edge enhancement means when .