JP3302060B2 - Area discriminating method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for discriminating between a multi-tone area and a single-tone area in one image, and more specifically, to a multi-tone image such as a photograph and a character or graphic. The present invention relates to a method and an apparatus for determining a multi-tone region and a single-tone region of an image in which a single-tone image such as a graph is mixed.

[0002]

2. Description of the Related Art Multi-tone images such as photographs, characters and figures,
For a single-tone image such as a graph, there are image processing methods suitable for each, as can be understood by considering, for example, print output and compression encoding. Accordingly, there is a demand that even when processing an image in which a multi-tone image and a single-tone image are mixed, it is desired to apply processing suitable for each of the images.

For example, taking a page printer as an example,
A print mode with many gradations and low resolution and a print mode with low gradation and high resolution can be selected in a single page.
A configuration is considered in which a multi-tone image portion is printed out in the former print mode, and a single-tone image portion is printed out in the latter print mode. For this purpose, it is necessary to separate a multi-tone image portion and a single-tone image portion into regions, and the following two methods have been proposed as region determination methods.

In the first method, an edge of an image is detected by a change in the level of a luminance signal or a luminance comparison between screens.
A region is separated by the detected edge. The change of the pixel value in each area is examined, and if it is a single tone, it is determined that the area is a single tone area,
The other area is assumed to be a multi-tone area.

In a second method, an edge is determined for a specific color of RGB or CMYK, a region determined to be an edge portion is defined as a single tone region, and the other portion is defined as a multi-tone region.

[0006]

However, in such an area discriminating method, the discriminating accuracy is not so high. For example, one pixel between edges should be recognized as a single tone, and a single tone between edges should be recognized as a single tone. I sometimes recognized it.

An object of the present invention is to provide an area discriminating method and apparatus which can discriminate a single tone area and a multi-tone area with higher accuracy.

[0008]

An area discriminating method according to the present invention is a method of scanning pixels in a predetermined direction and discriminating a multi-tone area and a single-tone area in one image based on an edge judgment result. When the pixel adjacent to the target pixel in the direction intersecting the predetermined direction is not an edge and the pixel values of the target pixel and the adjacent pixel do not substantially match, the target pixel is multi-tone. A first step of determining that the pixel belongs to the region; and a comparison pixel that is located in the same scanning direction as the pixel of interest and has a gradation instead of an edge in a direction that intersects with the predetermined scanning direction. A second step is provided for determining that the target pixel belongs to the multi-tone area when the values match.

An area discriminating apparatus according to the present invention is an area discriminating apparatus that scans pixels in a predetermined direction and discriminates a multi-tone area and a single-tone area in one image based on an edge judgment result.
Edge determination means for determining whether the designated pixel is an edge, pixel value comparison means for substantially comparing pixel values of two pixels, pixel value storage means for storing at least one pixel value, When the pixel adjacent to the pixel in the direction intersecting with the predetermined direction is not an edge and the pixel value of the pixel of interest and the pixel value of the adjacent pixel do not substantially match,
It is determined that the pixel of interest belongs to the multi-tone region, and a comparison pixel that is on the same scanning direction as the pixel of interest and has a gradation instead of an edge in a direction intersecting the predetermined scanning direction and a pixel value And determining means for determining that the target pixel belongs to the multi-tone area when the values substantially match.

[0010]

According to the first and second steps or the determination means, one pixel between edges can be reliably determined, and it is not uniformly recognized as a single tone. In addition, when pixel values of two or more pixels between edges coincide with each other, they are not recognized as a single tone.

[0011]

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

FIG. 1 is a schematic block diagram showing the configuration of an embodiment of the present invention. Reference numeral 10 denotes an image memory in which color image data to be subjected to region determination is stored. RGB data or
The luminance / color difference data is stored. Reference numeral 12 denotes a target pixel value storage circuit that stores a target pixel value, and reference numeral 14 denotes an edge determination circuit that determines whether a designated pixel is an edge. In the present embodiment, the edge determination circuit 14 calculates the amount of change (absolute value) from the pixel value at the same horizontal position that is n lines away, and determines that the edge is an edge when it is equal to or greater than a predetermined threshold.

Reference numeral 16 denotes a pixel value comparison circuit for comparing two specified pixel values. This comparison is made for all the color components. If any one of the color components is different, it is determined that they do not match. Needless to say, the pixel value comparison circuit 16 determines that the pixel values are equal when the pixel values match within a certain error range.

Reference numeral 18 denotes an area storage circuit for storing a result of discrimination between a multi-tone area and a single-tone area. For example, one bit may be assigned to one pixel, and “1” may be stored in an address of a pixel belonging to a multi-tone area, and “0” may be stored in an address of a pixel belonging to a single-tone area. Further, two image memories may be used, and the image data of the multi-tone area and the image data of the single-tone area may be stored in each image memory.

Reference numeral 20 denotes a main control circuit for controlling the whole.
The image memory 10, the target pixel value storage circuit 12, the edge determination circuit 14, the pixel value comparison circuit 16, the area storage circuit 18, and the main control circuit 20 are mutually connected via a bus 22.
The main control circuit 20 is composed of, for example, a microcomputer, and realizes some functions of the target pixel value storage circuit 12, the edge determination circuit 14, the pixel value comparison circuit 16 and the area storage circuit 18 by the control software of the microcomputer. Obviously it is good.

The operation of this embodiment will be described in detail with reference to the flowcharts shown in FIGS. 2, 3 and 4. In addition,
Here, it is assumed that one screen is 640 pixels × 480 lines. i is a variable that scans a pixel on one line, j is a variable that indicates a line, and indicates the address of the pixel of interest on the screen. The pixel value located at (i, j) is represented by I (i, j).

First, i and j are initialized (S1). The first pixel value I (0, j) of the line (S2) is stored in the target pixel value storage circuit 12 (S3), and the process # 2 shown in FIG. 3 is executed (S4). When the target pixel is an edge other than the first pixel of the line, the target pixel value I (i, j) is stored in the target pixel value storage circuit 12 (S
6), the process # 3 shown in FIG. 4 is executed (S7). The edge determination circuit 14 determines whether the edge is an edge.

While incrementing i (S8), 1
S2 to S7 are repeated until the end of the line is reached (S9). When one line is completed, the same processing is repeated for the next line. That is, j is incremented, i is cleared (S10), it is confirmed that the processing of the last line has not been completed (S11), and the process returns to S2.

The process # 2 shown in FIG. 3 will be described. In the process # 2, the comparison pixel is scanned from a position adjacent to the target pixel (i, k) to the end of the line, and a pixel that does not match the target pixel value is detected. That is, i + 1 is substituted for a variable k indicating the position of the comparison pixel on the line (S21), and the target pixel value I is maintained until k reaches 640 (end of line) (S22).
(I, j) is compared with the comparison pixel value I (k, j) (S2
3). This comparison is performed by the pixel value comparison circuit 16. If they substantially match, k is incremented (S
24) Compare with the next comparison pixel value.

If the pixel value of the comparison pixel does not substantially match the pixel value of the target pixel (S23), the edge determination circuit 14 checks whether or not the comparison pixel has an edge (S25). Is determined to belong to the single tone area (S2
6) If it is not an edge, it is determined that the target pixel belongs to the multi-tone area (S27). Each determination result is stored in the area storage circuit 18.

When the comparison pixel reaches the end of the line while the target pixel value and the comparison pixel value match (S2
2) It is determined that the target pixel belongs to the single tone area (S2
6), the determination result is stored in the area storage circuit 18.

In the process # 2, whether a pixel is a multi-tone area or a single-tone area is determined based on whether a pixel value changes between edges on the same line.

The process # 3 shown in FIG. 4 will be described. First, the edge determination circuit 14 determines whether the pixel above or below the target pixel is an edge (S31). If it is an edge, the target pixel is close to the edge, and the area can be determined by process # 2, which is a conventional determination routine. That is, if it is an edge (S31), the target pixel value I (i, j) is stored in the target pixel value storage circuit 12 (S32), and the process # 2 is executed (S33).

If neither the pixel above nor below the target pixel is an edge (S31), the pixel value comparison circuit 16 determines the target pixel value I (i, j) and the pixel values I (i, j) above and below it. ±
1) is compared (S35). If the target pixel value does not match at least one of the upper and lower pixel values (S35),
This pixel of interest has a gradation in the direction crossing the line. Therefore, it is determined that the target pixel belongs to the multi-tone area (S35).

According to S31 and S34, it is possible to appropriately classify a case where the target pixel is close to the edge and a pixel having a gradation in a direction intersecting the line.

If the pixel value of interest matches the pixel values above and below it (S34), the pixel next to the pixel of interest is set as the comparison pixel (S36) and the end of the line is reached (S3).
7), the target pixel value I (i, j) and the comparison pixel value I (k,
j) does not match (S38) or the target pixel value I
(I, j) and pixel values I (k, j ± 1) above and below the comparison pixel
The comparison pixels are sequentially moved to the next position until (S40) does not match (S40).

If the end of the line is reached without anything (S3
7), it is determined that the target pixel belongs to the single tone area (S4)
1).

When the target pixel value and the comparison pixel value do not match (S38), it is checked whether or not the comparison pixel is an edge (S42). If the comparison pixel is an edge, it is determined that the target pixel belongs to the single gradation area (S41). If the comparison pixel is not an edge (S42), since the gradation has changed, it is determined that the target pixel belongs to the multi-gradation area (S42).
43).

When the pixel value of interest I (i, j) does not match at least one of the pixel values I (k, j ± 1) above and below the comparison pixel (S39), the pixel above or below the comparison pixel becomes It is checked whether or not it is an edge (S44). If the pixel above or below the comparison pixel is an edge (S44), the target pixel value is stored in the target pixel value storage circuit 12 (S45), and the process #
2 is executed (S46). If neither the upper nor lower pixel of the comparison pixel is an edge (S44), it is determined that the target pixel belongs to the multi-tone area (S43) because the tone is changing in the direction intersecting the line.

In this embodiment, a single gradation area or a multi-gradation area is determined from the pixel values of the line including the target pixel and the three lines above and below it. It goes without saying that this may be done. Further, in this embodiment, first, the comparative pixels are scanned in the line direction, but it goes without saying that the comparative pixels may be scanned in the direction orthogonal to the line.

As shown in FIG. 5, the edge determination circuit 14 compares the pixel X to be edge-determined with the immediately preceding pixel F as a pre-process, as well as a plurality of pixels adjacent to the previous line, for example, three pixels. The pixel values of the pixels A, B, and C are compared, and the value change between the target pixel X and the previous pixel F is small, and
If the pixel value of the target pixel X substantially matches any of the pixel values of the pixels A, B, and C, the threshold value for edge determination is reduced. In this way, an edge that is overlooked when a certain edge determination threshold is used can be correctly detected as an edge, and therefore, the area determination of the multi-tone area and the single-tone area becomes more accurate.

Further, when one of the upper and lower pixels of the target pixel belongs to the single gradation area, and the pixel values match, even if the target pixel is an edge, it is continued from the pixels having the same pixel value. Since it can be considered an edge,
It is determined that the area is a single tone area. That is, the target pixel is continuous with the upper and lower single tone areas, and has an isolated edge in the line direction.

In the above embodiment, the area discrimination result is stored in the area storage circuit 18, and when the image stored in the image memory 10 is printed out, for example, the print mode is controlled based on the information stored in the area storage circuit 18. Will be
For example, in a case where images of one or more multi-tone areas (or single-tone areas) of one page are collectively printed, after the area determination processing according to the above-described embodiment, the information of the area storage circuit 18 is stored. With reference to this, the image data of the multi-tone area (or the single-tone area) is read out from the image memory 10 and applied to the print circuit system.

Also, without storing the area determination result in the area storage circuit 18, for example, image data determined to belong to a multi-tone area is sequentially printed for each pixel following the area determination processing.
The area determination may be performed once more, and the image data determined to belong to the single tone area may be sequentially printed for each pixel. In this case, the area storage circuit 18 becomes unnecessary, and it is also necessary to separately provide an image memory for storing image data in a single-tone area and an image memory for storing image data in a multi-tone area, separately from the image memory 10. Disappears.

[0035]

As can be easily understood from the above description, according to the present invention, a multi-tone image and a single-tone image are mixed from one image or one page into a multi-tone image and a single-tone image. The tone regions can be properly separated.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram of an embodiment of the present invention.

FIG. 2 is a main operation flowchart of the embodiment.

FIG. 3 is a flowchart of a process # 2 of FIG. 2;

FIG. 4 is a flowchart of a process # 3 in FIG. 2;

FIG. 5 is an explanatory diagram of another edge determination method.

[Explanation of symbols]

10: Image memory 12: Target pixel value storage circuit 14:
Edge determination circuit 16: Pixel value comparison circuit 18: Area storage circuit 20: Main control circuit 22: Bus

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-40752 (JP, A) JP-A-2-196564 (JP, A) JP-A-3-207164 (JP, A) JP-A-2-207 162477 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H04N 1/40-1/409

Claims (2)

(57) [Claims] 1. A method of scanning a pixel in a predetermined direction to determine a multi-tone area and a single-tone area in one image based on an edge determination result, wherein the multi-tone area and the single-tone area in one image are determined in a direction intersecting the predetermined direction. When the adjacent pixel is not an edge and the pixel value of the pixel of interest and the pixel value of the adjacent pixel do not substantially match, a first determination is made that the pixel of interest belongs to the multi-tone region.
A step and a comparison pixel in the same scanning direction as the pixel of interest, the pixel having a gradation instead of an edge in a direction intersecting the predetermined scanning direction, when the pixel value substantially matches the pixel of interest. Is determined to belong to the multi-tone area.
An area discriminating method comprising a step. 2. An area discriminating apparatus that scans a pixel in a predetermined direction and discriminates a multi-tone area and a single-tone area in one image based on an edge judgment result, and determines whether a designated pixel is an edge. , A pixel value comparison unit that substantially compares the pixel values of two pixels, a pixel value storage unit that stores at least one pixel value, and a direction intersecting the target pixel with the predetermined direction. When the adjacent pixel is not an edge and the pixel value of the pixel of interest and the pixel of the adjacent pixel do not substantially match, it is determined that the pixel of interest belongs to the multi-tone region, and the same scanning as the pixel of interest is performed. When the pixel value substantially coincides with a comparative pixel on the direction that has a gradation instead of an edge in a direction intersecting the predetermined scanning direction, the pixel of interest belongs to the multi-gradation area. Judgment means is provided. An area discriminating apparatus characterized by the following.