JPS60114086A - Picture profile emphasis system - Google Patents

Abstract

PURPOSE:To obtain a good picture-quality image with less noise and with natural contrast by deciding whether a density level of a noted picture element is situated within a predetermined range, prohibiting correction of the density level designed for profile emphasis for the noted picture element whose density level is decided to be out of the range, and providing sufficient profile emphasis while preventing unnecessary emphasis of local density change. CONSTITUTION:A density level decision circuit 11 is devised to decide whether the value of a picture signal (a) (density level) is within a correction execution range or not to change an output signal (e) into a logic ''1'' level only when said value is out of the correction execution range. This signal (e) is latched by a latch circuit 12 at clock timing synchronized with picture element reading of an image sensor 1. A latch signal f and picture signals (a), (b), and (c) are inputted as addresses signals in an ROM13, the circuit 11 performs correction of the density level for profile emphasis. The circuit 11 prohibits correction of the density level for profile emphasis for the noted picture element of the density level which is out of the correction excution range.

Description

[Detailed description of the invention] Industrial applications The present invention relates to an edge enhancement method for multivalued quantized images.

Conventional configurations and their problems In image processing apparatuses such as facsimile machines, edge enhancement processing is often performed on multi-level quantized images to improve image quality. Such a conventional image contour enhancement method will be explained below using a document reading system of a facsimile machine as an example.

FIG. 1 is a block diagram of a document reading system of a facsimile machine.

In this figure, reference numeral 1 denotes an image sensor for reading a document, which scans the document and outputs an analog image signal. After this image signal is amplified by an amplifier 2, it is multivalued quantized pixel by pixel by an analog/digital (AID) converter 3 and converted into a digital image signal. Since this digital image signal has a value proportional to the reflectance of the document surface, it is converted by the reflectance/a degree conversion circuit 4 into a digital image signal (hereinafter abbreviated as image signal) proportional to the density. This image signal indicates the density level of each pixel of the multi-level quantized original image.

Image signal ail- output from the reflectance/density conversion circuit 4
j: latched by the latch circuit 5 at a clock timing synchronized with pixel reading of the image sensor 1, and at the same time, the excitation Ab output from the latch circuit 5 is latched to the next latch circuit 6. Image signals a, b and latch circuit 6
The image signal C output from the ROM (read-only memory) 7 is input as an address signal. Here, image signal a
, b, and c respectively indicate the density levels of three consecutive pixels on the same scanning line.

The ROM 7 functions as a type of arithmetic unit that performs density level correction for edge enhancement, and outputs a signal d having a value expressed by the following equation from the address specified by the image signals a, b, and c.

If 1b-al≧t1 and 1b-cl≧t1, then d=a
@b-β1m(a+C) 1 b' a l < t 1 or l b c
If 7 < t 1 then d=b where tl, α1. β1 is a constant.

That is, if the difference between the density level of the pixel of interest indicated by image signals b:c and the density level of each adjacent pixel indicated by image signals a and c is 11 or more, the density level of the pixel of interest is determined by the density level of the adjacent pixels. By the way, according to conventional image contour enhancement methods like this, ■light levels in dark fabrics (ink unevenness, etc.) and ■dark levels in light fabrics (granular noise, etc.) are emphasized unnecessarily. , there was a problem that the image quality of the processed image deteriorated.

FIG. 2 is a density pattern diagram for explaining such a problem. Figure 2a is an example of a density pattern corresponding to the above ■.If the difference in density level between the central pixel and the pixels on both sides is 11 or more, the density after contour enhancement processing is performed for the central pixel. The pattern will be as shown in Figure 2. Further, FIG. 2C is a density pattern corresponding to the above-mentioned (■).If the difference in density level between the center pixel and the neighboring pixels on both sides is 11 or more, the density pattern after the edge enhancement process of the center pixel is It will look like Figure 2 d. In this way, local density level changes that should not be emphasized are emphasized, resulting in an unnatural image with a lot of noise.

In order to deal with the above problem, it is conceivable to set the value t1 for determining the density level difference between the pixel of interest and the adjacent pixel to be large. However, in that case, a new problem arises in that density level correction is not performed on pixels that require density level correction, making it impossible to obtain a sufficient edge enhancement effect.

OBJECTS OF THE INVENTION The present invention solves the above-mentioned conventional problems, and aims to provide an image contour enhancement method that can achieve a sufficient contour enhancement effect without unnecessarily emphasizing local density changes. 0 Structure of the Invention The present invention determines whether the density level of a pixel of interest is within a predetermined range, and for the pixel of interest that is determined to have a density level outside the range, a density level for contour enhancement is applied. DESCRIPTION OF EMBODIMENTS OF THE INVENTION The present invention will now be described in detail with reference to the drawings.

FIG. 3 is a block diagram of a document reading system according to an embodiment of the present invention. In this figure, 11 is a density level determination circuit, 12 is a latch circuit, and 13 is a ROM. In addition,
Blocks 1 to 6 are the same as the blocks with the same reference numerals in FIG. 1, so their explanation will be omitted.

The density level determination circuit 11 determines whether the value (density level) of the image signal a is within the correction range shown in FIG. This signal e is latched into the launch circuit 12 at a clock timing synchronized with the pixel reading of the image sensor 1. Therefore, the latch circuit 1
The output signal f of No. 2 indicates the determination result of the density level determination circuit 11 for the image signal b (the pixel of interest).

The signal f and the image signals a, b, and c are input to the ROM 13 as address signals. This ROM 13 acts as a kind of arithmetic unit that executes density level correction for edge enhancement, and it uses the address specified by the address signal and the signal q1 of the value shown by the following formula, that is, after correction of the target pixel. Outputs the density level of

1 If f = "1°' (The density level of the pixel of interest is 81 or less or 82 or more) q = b 2 If f = "o°' (The density level of the pixel of interest is within the correction range) + 1b-al If ≧t2 and 1b-cl≧t2, then q=amb-β2” (a + C)ii 1b-a
If l<t2 or l b c l <t2, then q=b, where t a and β are constants.

21 2 2 As described above, in this embodiment, for a pixel of interest having a density level within a predetermined correction range, density level correction is performed using adjacent pixels as in the conventional method, but for density levels outside the correction range, the density level is corrected using adjacent pixels. Density level correction for contour enhancement is prohibited for the target pixel of level. Therefore, even if you select a value for t2 that provides the necessary and sufficient contour enhancement effect,
Enhancement of local variations in density levels near "white" or "black" levels can be prevented.

FIG. 6 is a density pattern diagram for explaining an example of edge enhancement processing. In the same figure, ag ' g el q shows an example of the density pattern of three consecutive pixels before contour enhancement processing, and d, f, and h in the same figure are the center pixels (target pixels).
shows the density pattern after contour enhancement processing.

In the case of the density patterns a and g in FIG. 5, the density level of the central pixel is outside the correction range, so no density level correction is performed. In the case of the density turn in FIG. 6C, the density level of the central pixel is within the correction range, but the density level correction is not performed because the difference in density level with the adjacent pixel is less than t2. In the case of the density pattern e, the center pixel is within the density level correction range and has a density level difference of 12 or more with the two edge pixels, so density level correction is applied to enhance the outline.

Incidentally, if noise at the "black level" or "near" level is not a problem, it is also possible to set the correction execution range as shown in FIG. 6. Furthermore, if noise near the "white" level is not a problem, the correction range can be set as shown in FIG. 7.Furthermore, it is possible to set the correction range as shown in FIG.
It is also possible to make t2 variable and adjust it according to the characteristics of the image to be processed.

Furthermore, although the above-mentioned embodiment performs one-dimensional contour enhancement, it is obvious that the present invention can be similarly applied to two-dimensional contour enhancement.

Effects of the Invention As described above, the present invention determines whether the density level of a pixel of interest is within a predetermined range, and sets a density level for edge enhancement for a pixel of interest whose density level is outside the range. Since no correction is applied, it has the effect of preventing unnecessary emphasis on local density changes in the image, applying sufficient edge enhancement, and obtaining a high-quality image with little noise and high contrast. It is.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a document reading system using a conventional image edge enhancement method, FIG. 2 is a density/turn diagram for explaining the problems of the conventional image edge enhancement method, and FIG. A block diagram showing a document reading system to which an image contour enhancement method according to an embodiment is applied, FIG. 4 is an explanatory diagram of the correction execution range, and FIG. 6 is a density diagram for explaining the image contour enhancement process]
6.6.12...Latch circuit, 11...
Concentration level determination circuit, 13...ROM (read-only memory) 0 Name of agent Patent attorney Toshio Nakao and 1 other person 1st
Figure 2

Claims (1)

[Claims] An image contour enhancement method that corrects the density level of an arbitrary pixel of interest (abbreviated as a pixel of interest) by the density level of its adjacent pixels, in order to enhance the edges of an image whose density is multivalued quantized on a pixel-by-pixel basis. , determining whether the density level of the pixel of interest is included in a predetermined range, and prohibiting the above density level correction for the pixel of interest whose density level is determined to be outside the range. Image contour enhancement method.