JP3115065B2 - Image information edge enhancement device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image information edge emphasis processing apparatus for performing edge emphasis processing by correcting the density of an edge pixel which is an outline of an image in multi-value image information.

[0002]

2. Description of the Related Art For example, in a facsimile apparatus, when images such as figures and characters (hereinafter referred to as character images) are read, edge emphasis processing is often performed.

The edge emphasizing process is a process of determining an edge pixel based on a change in density of each pixel and correcting the density of the edge pixel to make the outline of an image clear.

When executing the edge emphasis processing, attention is paid to each pixel in the multi-valued image information of one page, and the density difference between the pixel of interest and the pixels vertically and horizontally adjacent thereto is obtained. If any one of them is higher than a certain threshold level, the pixel of interest is determined to be an edge pixel, and the pixel is corrected to white density or black density.

When image information is read from a document by a facsimile apparatus or the like, if the document is a detailed image in which characters and / or graphics are small with respect to the reading resolution, the obtained image information is obtained when the outline of the image is unclear. become.

Generally, image information whose image outline is unclear is
A clearer image can be obtained by setting the threshold level low and discriminating edge pixels and executing a predetermined emphasis process.

However, when the threshold level is lowered, a portion where the density of the background of the document changes is likely to be erroneously determined as an edge pixel. Therefore, depending on the manuscript,
If the threshold level is lowered as described above, the image quality may deteriorate.

[0008]

As described above, conventionally,
If the threshold level is set low in order to obtain a good image with respect to the detailed image, various original images cannot always be correctly processed because, depending on the original, the density change of the background is erroneously determined as an edge pixel. There was a problem.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and to provide an image information edge enhancement processing apparatus capable of always correctly processing various original images.

[0010]

For this purpose, the first aspect of the present invention is described.
According to the invention, two types of threshold levels, high and low, for density difference determination are stored, and when the image information is emphasized, if the density of the pixel of interest is an intermediate density within a certain range, If the lower threshold level of the two types is selected, but the density is not an intermediate density within a certain range, the higher threshold level is selected, and then, according to a known procedure, the multi-level image information of one page. Each density difference between each target pixel and a plurality of adjacent pixels in is compared with the selected threshold level, and if any one is equal to or higher than the threshold level, the target pixel is regarded as an edge pixel. The determination is made to correct the white density or the black density.

In the second invention, the threshold level is selected based on the average density of each pixel in a certain range around the target pixel, instead of one target pixel as described above. I have.

Further, in the third invention, the threshold level is selected according to whether there are a large or small number of intermediate density pixels among a plurality of pixels around the target pixel, and the same processing is performed.

[0013]

When the image to be processed is a detailed image, the pixel density of each pixel tends to be halftone. Therefore, in each of the above inventions, when the image to be processed is a detailed image, a low threshold level is selected, and for a normal image, a high threshold level is selected. As a result, the threshold level of the normal image is not set low, and the density of the background of the document is prevented from being erroneously determined as an edge. Therefore, various types of document images can always be correctly processed.

[0014]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram of an image processing apparatus according to one embodiment of the present invention. In the figure, an image reading unit 1 reads a document image to obtain multi-valued image information in which each pixel density is indicated by a certain number of gradations. Edge determination unit 2
Is for determining an edge pixel which is an outline of an image. The edge enhancing unit 3 enhances the outline of the image by correcting the density of the edge pixels.

The binarizing unit 4 binarizes the multi-valued image information with the edge emphasized by a simple threshold level at a fixed threshold level or by various known pseudo halftone processes. The image output unit 5 outputs binarized image information, and is a display device that displays an image on a screen, a printer that records the image on recording paper, or the like.

Next, the operation of the image processing apparatus according to the present embodiment having the above configuration will be described.

Assuming that the image processing apparatus is activated, the image reading section 1 reads a document image and sequentially transfers the image information of each line to the edge determining section 2 one pixel at a time.
The edge determination unit 2 sequentially extracts each pixel A to I from the transferred image information according to a template of 3 × 3 pixels shown in FIG. The center pixel E is set as a target pixel, and it is determined whether the target pixel E is a black edge pixel. If the target pixel E is a black edge pixel, the pixel density is corrected.

FIG. 3 shows the operation. When the above-mentioned pixels A to I are extracted, the edge judging section 2 judges whether or not the target pixel E has a certain range of intermediate density. That is, assuming that the image information is represented by 16 gradations and a density of 0 to 15, it is determined whether or not the pixel density of the target pixel E is an intermediate density of, for example, “5” or more and “10” or less. (Process 101).

If the target pixel E has an intermediate density within the above-mentioned fixed range (Y in step 101), the threshold level Th for determining the density difference is set to Th = 4 (step 102). If the density is another value (processing 10
1 N), the threshold level Th is set to Th = 6 (process 103).

Next, the density difference obtained by subtracting the adjacent pixel B from the density of the target pixel E is compared with the threshold level Th (step 104). Similarly, each density difference obtained by subtracting the density of each of the adjacent pixels D, F, and H from the density of the target pixel E is compared with the threshold level Th (steps 105 to 10).
7).

If at least one of the density differences is equal to or greater than the threshold level Th (step 104).
Y of process 105, Y of process 106, or process 1
07, Y), the target pixel E is determined to be a black pixel. And
The edge emphasizing unit 3 corrects the target pixel E to black density “15” (process 108). If each of the above density differences is less than the above threshold level Th (the processing 105 from the processing 104 N and the processing 1 from the processing 105 N)
06, the processing 107 and the processing 107) are not executed.

The edge determination unit 2 and the edge enhancement unit 3
The above-described processing is sequentially performed on all the pixels of one page. The binarizing section 4 binarizes the multi-valued image information processed in this way by a predetermined binarization method. Image output unit 5
Outputs binarized image information to a screen or recording paper.

As described above, in this embodiment, the target pixel E
Is an intermediate concentration, the low threshold level Th
Check the density difference between the target pixel and the adjacent pixel,
It is determined whether or not the target pixel E is an edge pixel.

In the case of a detailed image in which characters and figures of a document are small with respect to the reading resolution of the image reading unit 1, the read image information has a large number of intermediate density pixels. This is because the image reading unit 1 often reads a white portion and a black portion of a document simultaneously as one pixel. When there are many pixels of the intermediate density, the density difference between the pixels at the edge portion of the image becomes small.

In this embodiment, when the target pixel has an intermediate density, the threshold level Th is set low.
Even if the density difference between the pixels is small at the edge portion of the image, the edge pixels can be reliably determined. Thereby, a clear image can be obtained.

On the other hand, in the case of a normal image in which characters and figures of a document are relatively large, the threshold level Th is set high. In this case, contrary to the above, the number of pixels having the intermediate density is reduced, and the density difference between the pixels is increased at the edge portion of the image, so that the edge pixels can be reliably determined. Also, in this case, even if the background of the document has a shading change, the threshold level Th is high, so that the shading change is prevented from being erroneously determined as an edge pixel. This makes it possible to always process various images correctly.

FIG. 4 shows another embodiment of the present invention. That is, in the present embodiment, when each of the pixels A to I is extracted, the edge determination unit 2 calculates an average density J of the extracted nine pixels (process 201). Then, it is determined whether or not the average density J is an intermediate density within a certain range from “5” to “10” (process 202).

If the average density J is an intermediate density in the certain range (Y in step 202), the threshold level Th for determining the density difference is set to Th = 4 (step 202). If the intermediate density is not within the certain range (N in process 202), the threshold level Th is set to Th = 6 (process 204). Thereafter, the operations after the process 104 described in FIG. 3 are executed in the same manner.

As described above, in this embodiment, the level of the threshold level Th is switched according to the average density of the extracted nine pixels. As described above, when the read image is a detailed image, the number of pixels of intermediate density increases,
In this case, the average density also becomes the intermediate density. On the other hand, in the case of a normal image, since the number of pixels having the intermediate density is reduced, it is considered that the average density is biased to either high or low.

Thus, in the case of the normal image and the case of the detailed image, the threshold level T
Since h is switched, various images can always be correctly processed.

FIG. 5 shows still another embodiment of the present invention. That is, in the present embodiment, the edge determination unit 2
When each of the pixels A to I is extracted, the ratio of the number of pixels having an intermediate pixel density is determined in the extracted nine pixels (step 301).

If the number of pixels of the intermediate density is equal to or more than a predetermined ratio (Y in step 301), the threshold level Th is set to Th = 4 (step 302). Also,
If the number of pixels of the intermediate density is less than a certain ratio (N in processing 301), the threshold level Th is set to Th = 6.
(Step 303). Thereafter, the operations after the process 104 described in FIG. 3 are executed in the same manner.

As described above, in the present embodiment, the level of the threshold level Th is switched according to the ratio of the number of pixels of the intermediate density in the extracted nine pixels. As a result, the threshold level Th is switched between the case of the normal image and the case of the detailed image, as in the above-described embodiment, so that various images can always be correctly processed.

In each of the above embodiments, whether or not the read image is a detailed image is determined based on the density of the target pixel E, the average density of the extracted pixels, and the ratio of the intermediate density pixels in the extracted pixels. However, the determination may be made by another determination method, for example, by comparing the density distribution of each extracted pixel with a density distribution pattern stored in advance.

Further, in each of the above embodiments, the black edge pixel is determined and corrected to the black density. However, the present invention is similarly applicable to the case where the white edge pixel is determined and corrected to the white density. Can be applied.

Further, nine pixels are extracted from the multi-valued image information as shown in FIG. 2, but ten or more pixels may be extracted and various determinations may be similarly performed.

Although the image information has been described by taking the case of 16 gradations as an example, it goes without saying that in the case of other gradation numbers, the threshold level may be set according to the gradation number. Absent.

[0039]

As described above, according to the present invention, two types of threshold levels are stored, and the density of the pixel of interest,
Whether the image to be processed is a detailed image or a normal image is determined based on the average density of a plurality of pixels around the pixel of interest or the ratio of the number of pixels of intermediate density in the plurality of pixels. The threshold level is selected, and in the case of a normal image, a higher threshold level is selected, and the edge pixels are determined according to a known procedure to correct the white density or the black density, so that various original images are always correctly processed. Will be able to do it.

[Brief description of the drawings]

FIG. 1 is a block diagram of an image processing apparatus according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of an extracted pixel.

FIG. 3 is a flowchart illustrating a black edge pixel determination and density correction operation.

FIG. 4 is an operation flowchart showing a portion different from FIG. 3 in another embodiment of the present invention.

FIG. 5 is an operation flowchart showing a portion different from FIG. 3 in still another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image reading part 2 Edge determination part 3 Edge enhancement part 4 Binarization part 5 Image output part

Claims (3)

(57) [Claims] 1. Density correction by paying attention to each pixel of multi-valued image information of one page and discriminating an edge pixel which is an outline of an image based on a density difference between the pixel of interest and a plurality of adjacent pixels. In the image information edge emphasizing device for performing the edge emphasizing process, a storage means for storing two kinds of threshold levels, high and low, for density difference judgment, a judgment means for judging the density of the pixel of interest, If the intermediate density is within a certain range, the lower threshold level of the two stored types is selected, while if the density is not the intermediate density within the certain range, the higher threshold level is selected. Selecting means; comparing means for comparing each density difference between the target pixel and a plurality of adjacent pixels with the selected threshold level; and any one of the density differences
An image information edge emphasis processing device, comprising: a density correction unit that determines the target pixel as an edge pixel and corrects the target pixel to white density or black density when at least the threshold level is higher than the threshold level. 2. Density correction by paying attention to each pixel of multi-valued image information of one page and discriminating an edge pixel which is an outline of an image based on a density difference between the pixel of interest and a plurality of adjacent pixels. In the image information edge emphasizing device for performing the edge emphasizing process, a storage means for storing two kinds of high and low threshold levels for density difference determination, and a calculating means for calculating an average density of a plurality of pixels around the target pixel If the average density is in the middle range of the certain range, the lower threshold level of the two stored types is selected, while if the average density is not the middle density in the certain range, the higher threshold level is selected. Means for selecting one of the threshold levels,
A comparing means for comparing each density difference between the target pixel and a plurality of adjacent pixels with the selected threshold level; and setting the target pixel when any one of the density differences is equal to or higher than the threshold level. An image information edge emphasis processing device, comprising: a pixel density correction unit that determines an edge pixel and corrects white or black density. 3. Attention is paid to each pixel of multi-valued image information of one page, and an edge pixel which is an outline of an image is determined based on a density difference between the pixel of interest and a plurality of adjacent pixels. In the image information edge emphasizing device for performing the edge emphasizing process, a storage means for storing two kinds of high and low threshold levels for density difference judgment, and reading for reading each pixel density in a certain area around the above noted pixel. Means for selecting a lower threshold level of the two stored types when the pixels of the intermediate density within a certain range are equal to or more than a certain percentage in the certain area, while the pixels of the middle density are fixed. A selection means for selecting a higher threshold level when the ratio is less than the ratio; and a comparison for comparing each density difference between the target pixel and a plurality of adjacent pixels with the selected threshold level. Means and any one of the above-mentioned concentration differences
An image information edge enhancement processing apparatus comprising: pixel density correction means for determining the target pixel as an edge pixel and correcting the density to white density or black density when the pixel density is at least the threshold level.