JP2984516B2 - Image sharpness adjustment method - 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 for adjusting the sharpness of an image, and more particularly to a method for adjusting the sharpness of a large-sized convolution, that is, a method for adjusting the sharpness.

[0002]

2. Description of the Related Art Sharpening is used as an edge emphasizing method by restoring high-frequency components, and by taking a large convolution, more global processing can be realized. However, hardware corresponding to a large convolution size has a large overall circuit scale, and is an expensive system. Further, a practical processing speed cannot be obtained by image processing using software.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in order to solve such a conventional problem. A sharpness adjustment capable of realizing a sharpness adjustment of a large convolution with a relatively small circuit scale. It is intended to provide an adjustment method.

[0004]

An image sharpness adjusting method according to the present invention performs smoothing on a reduced image, enlarges the reduced image to its original size, and weights the difference between the enlarged image and the original image. Is added to the original image, and as a result,
Large-size sharpening is performed. Then, the sharpness is continuously adjusted by changing the weight.

[0005]

According to the image sharpness adjusting method according to the present invention, the reduced image is smoothed, enlarged to the original size, and the difference between the enlarged image and the original image is weighted. Can be further added to the original image.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an image sharpness adjusting method according to the present invention will now be described with reference to the drawings. In FIG.
In one example of an image processing apparatus for performing the method,
It has image memories IM1 to IM3 and an input memory INM. One or two of the outputs of these memories are selected by the multiplexer MUX and input to the arithmetic unit CAL. The output of the arithmetic unit CAL is selectively input to one of the memories IM1 to IM3 by the selector SEL. On the other hand, the input camera C is connected to the input memory INM,
The captured image is temporarily held in the memory INM.

FIG. 2 is a flowchart showing a procedure for adjusting the sharpness, which will be described in detail below. [Step 2-1] First, an original image is fetched from the camera C, stored in the memory INM, and then transferred to the memory IM1. At this time, the arithmetic unit CAL passes the data as it is without executing the arithmetic processing.

[Step 2-2] The original image in the memory IM1 is read out one pixel at a time, and is written to the memory IM2 while thinning out to generate a reduced image. FIG. 3 shows the state of this thinning, in which pixels are extracted at regular intervals, for example, every eight pixels (indicated by crosses in the figure), and other pixels are ignored. In the image processing apparatus, this thinning can be executed by writing to the memory IM2 at regular intervals. In the reduction process, the calculator CAL does not perform the calculation but passes the data.

[Step 2-3] The reduced image in the memory IM2 is read out one pixel at a time, and the processing result is written into the memory IM3 while being smoothed by the calculator CAL. The convolution size of the smoothing is a common one such as 3 × 3, and can be executed by a small-scale circuit. The smoothing performed here is the density average of the pixels other than the central pixel, and in the convolution of FIG.

[Step 2-4] The smoothed image in the memory IM3 is read out one pixel at a time, and the processing result is written into the memory IM2 while further smoothing by the calculator CAL. This smoothing is the same as the processing performed in step 2-3.

[Step 2-5] The smoothed image in the memory IM2 is read out one pixel at a time, enlarged, written into the memory IM3, and returned to the original image size. The enlargement process is realized by writing the read pixel a plurality of times and writing the same line a plurality of times. Writing of the same pixel is realized by repeatedly giving the same address in reading of the memory IM2.

[Step 2-6] Weighted addition of the image in the memory IM3 and the original image stored in the memory IM1 is performed, and the result is written to the memory IM2. The pixel density of the original image is Do, the pixel density of the IM3 image is D, the weight is α,
Assuming that the density of the processing result is Dr, the weighted addition is expressed by the following equation. Dr = (1 + α) Do−αD Here, when α = 1, Dr = Do + (Do−D), and the value of D is substantially equal to a smoothed image of 32 × 32 convolution, and Dr is consequently 32 It becomes an image that has been sharpened by a × 32 convolution. As α decreases, the second term on the right side of Dr = Do + α (Do−D) decreases, sharpness decreases, and gradually approaches the original image.

The above-described smoothing of the reduced image has the same effect as the smoothing of the large convolution, and the large-sized sharpening is realized by adding the large-sized smoothed image and the original image. And as hardware, 3 × 3
The goal is achieved on a normal scale of convolution. Furthermore, the sharpness can be adjusted by adjusting the coefficient α,
In digital copiers, facsimile machines, digital photographs, and the like, the sharpness can be set arbitrarily according to the application or the user's preference.

[0014]

As described above, the method for adjusting the sharpness of an image according to the present invention performs smoothing on a reduced image, enlarges the reduced image to its original size, and weights the difference between the enlarged image and the original image. Is further added to the original image to perform the large-size sharpening, so that there is an excellent effect that high-speed processing can be realized by a small-scale circuit.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an image processing apparatus used for implementing a method of the present invention.

FIG. 2 is a flowchart showing one embodiment of the method of the present invention.

FIG. 3 is a conceptual diagram showing a state of thinning in the method of the present invention.

FIG. 4 is a conceptual diagram showing a 3 × 3 convolution.

[Explanation of symbols]

 MUX multiplexer IM1 image memory 1 IM2 image memory 2 IM3 image memory 3 INM memory CAL calculator SEL selector C camera

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-1-194683 (JP, A) JP-A-3-102973 (JP, A) JP-A-58-7710 (JP, A) JP-A-4- 357773 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H04N 5/208 H04N 5/262

Claims (4)

(57) [Claims] 1. An original image is reduced at a predetermined reduction ratio, smoothing is performed on the reduced image, and the smoothed image is enlarged at an enlargement ratio corresponding to the reduction ratio. A sharpness adjustment method for an image, wherein a difference from the original image is added to the original image with a predetermined weight. 2. The method according to claim 1, wherein the reduction ratio is 1/8 and the enlargement ratio is 8. 3. The image sharpness adjusting method according to claim 1, wherein the sharpness of the image is increased by setting the weight to 1. 4. The image sharpness adjustment method according to claim 1, wherein the image is smoothed by setting the weight to 1/2 or less.