JPH0351967A - Adaptive sharpness increasing device for image - Google Patents

Abstract

PURPOSE:To make the image sharp adaptively by dividing the image into small areas, and determining the suitable size of a differential operator according to the density distribution in each area and performing differential processing. CONSTITUTION:A differential operator size determining circuit 3 reads image data on a specific area out of an image memory 2, detects the change point of the density distribution, and determines the size of the differential operator matching the area and a differentiation circuit 4 performs the differential processing with the size of the differential operator determined for each small area by the circuit 3 to make the image sharp. Consequently, the image can be made sharp adaptively.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an image sharpening device, and more particularly to an adaptive image sharpening method when sharpening an image. BACKGROUND OF THE INVENTION Conventionally, differential calculation has been known as a method for making an image more grainy or sharp.

Among differential operations, the Labradian is a linear differential operator that is particularly useful, and can sharpen an image by subtracting the Labradian from the image. Problems to be Solved by the Invention However, when there is no information about the properties of the image, a differential operator of a fixed size is usually used, and it is not clear that the differential operator is optimal for sharpening the image. Not exclusively. For example, when differential processing is performed on an image of small characters using a large-sized differential operator, the image is smoothed and the outlines of the characters deteriorate, resulting in a blurred image. Furthermore, when differential processing is performed on an image such as a photograph using a small-sized differential operator, fine noise contained in the image is emphasized, resulting in deterioration of image quality. The present invention has been made in order to solve the above-mentioned problems inherent in the conventional technology.Therefore, an object of the present invention is to divide an image into small areas, and to calculate a density distribution suitable for each small area from the density distribution within each small area. An object of the present invention is to provide a novel sharpening device that can adaptively sharpen an image by determining the size of a differential operator and performing differential processing.

Means for Solving the Problems In order to achieve the above object, an image adaptive sharpening device according to the present invention divides an image into small regions and uses a differential operator according to the state of density distribution within the small regions. The size is determined for each small region, that is, when the density change is small, a small-sized differential operator is used, and when the density change is large, a large-sized differential operator is used to perform the differential processing,
It is characterized by adaptively sharpening images. Embodiment Next, a preferred embodiment of the present invention will be specifically explained with reference to the drawings. FIG. 1 is a block elliptical diagram showing an embodiment of the image adaptive sharpening device according to the present invention. Referring to Figure 1,
1 is image data, and for example, when the number of gradations is set to 256, it is represented by levels from 0 to 255. In the following, the case where the number of gradations is 256 will be explained. 2 is an image memory, into which the above image data 1 is input. Reference numeral 3 designates a differential operator size determining circuit which reads image data of a predetermined area from the image memory 2, detects a change point in density distribution, and determines the size of a differential operator suitable for that area.

The differentiation circuit 4 is the differentiation operator size determination circuit 3 described above.
Differential processing is performed using the size of the differential operator determined for each small region to sharpen the image. 5 is the sharpened image data. Below, we explain the operation of the adaptive image sharpening method described above. (1>. First, image data 1 is stored in image memory 2. (2>. Next, as shown in FIG. 2, image data 1 is stored in image memory 2. Divide into 6 small head regions of pixel size. (3). Above (2)
For the small head regions 6 divided in , the differential operator size determining circuit 3 determines the size of the differential operator suitable for each small region by the following procedure. ■． In each small area 6, horizontal direction (row) and vertical direction (column)
Find the concentration distribution of. Figure 3 (a) shows the horizontal density distribution of a row with a small region, and Figure 3 (b) shows the vertical density distribution of a certain column, where g is the density value, and j and i are the horizontal direction of the row. represents the vertical position of the column.

■． Detect the changing points of the density value in the density distribution obtained in step ① above, and find the interval (number of pixels) between the changing points. Third
Figure (a). In (b), 7 to 19 represent the changing points of the density value, and 20 to 30 represent the intervals between the changing points. ② Perform the process ② above for all rows and columns of each small head region 6, and find the frequency of intervals between change points for each small region. ■． ! ! The size of the differential operator is determined for each region as follows based on the value of the interval between the points of change in the frequency of t. i). When the frequency of l & large is less than 4 pixels, Fig. 4 (a
) 3×3 pixel differential operator 31i). When the frequency of large R is 5 to 7 pixels, the differential operator 32i of 6×6 pixels in FIG. 4(b)>. When the frequency of It is 8 to 10 pixels, the differential operator 3 of 9×9 pixels in FIG. 4(C)
3ν). ! When the frequency of 1 is 11 pixels or more, Fig. 4 (
Using the 12×12 pixel differential operator 34 (4) in d) and the size of the differential operator determined for each small head area 6 in (3) above, the differential circuit 4 performs differential processing as follows to obtain an image. Sharpen the image. In other words, when the differential operator (digital Labrasian) is 2 and the image data is G, the G-h ma”G

(1) (h is an arbitrary constant) and obtain sharpened image data 5. At this time,
Negative values give 0, and values over 255 give 255. Effects of the Invention As described in detail above, according to the present invention, image data is divided into small regions, the change point of the density distribution in each small region is detected, and the change point of the density distribution in each small region is detected based on the value of the interval. By determining the appropriate size of the differential operator and performing differential processing, images can be sharpened adaptively.

[Brief explanation of drawings]

FIG. 1 is a block composition diagram showing an embodiment of an image adaptive sharpening device according to the present invention, FIG. 2 is an explanatory diagram of image division, and FIG. 3(a). (b) is a diagram showing the concentration distribution of a certain row and a certain column of a small region, and FIGS. 4(a) to (d) are diagrams of differential operators of each size. 1... image data, 2...
...Image memory, 3. Differential operator size determination circuit, 4. Differential circuit, 5. Sharpened image data, 6. Small area, 7 to 19. Point of change, 20~
30... Interval between change points, 3l... 3x3 pixel differential operator, 32... 6x6 pixel differential operator, 33... 9x9 pixel differential operator, 34...
12x12 pixel differential operator

Claims (1)

[Claims] an image memory that stores image data; a differential operator size determining circuit that reads image data of a predetermined area from the image memory, detects a change point in density distribution, and determines a differential operator size suitable for the area; An apparatus for adaptively sharpening an image, comprising: a differentiation circuit that performs differentiation processing using the size of a differentiation operator determined for each small region by an operator size determination circuit to sharpen an image.