JPH01160172A - Picture signal processing method - Google Patents

Abstract

PURPOSE:To attain binarization processing with uniform and high picture quality by using a specific upper noise cut level, slicing a picture signal in preceding over blur correction processing, and eliminating the noise included in white background. CONSTITUTION:An image sensor 20 consists of a CCD line sensor or a CCD area sensor and outputs a time series picture signal (a). The picture signal (a) is given to an upper noise cut circuit 28, where after eliminating the noise included in the picture signal (a) corresponding to the white background of the picture by the upper noise cut level set slightly lower than the picture signal level with respect to the white background and including shading correction and the picture signal is sharpened by applying blur correction and binarization is applied by a prescribed binarizing level. In the case of high frequency emphasis, the noise included in the white background does not cause ununiformity depending on the location in the picture quality and it is possible to keep high picture quality after binarization processing of the picture.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an image signal processing method for binarizing an image signal obtained by scanning an image with an image sensor.

(Technical Background of the Invention) Various methods have been proposed in the past for reading out an image using an image sensor such as a CCD line sensor or a CCD area sensor, and for binarizing this image signal. For example, the applicant of the present application proposed a method in which after correcting the blur of an image signal, it is compared with a fixed binarization level (Japanese Patent Laid-Open No. 62-130068
In this case, we also proposed a method in which the binarization level is obtained by subjecting the image signal to smoothing, compression, and level shift processing, so that the binarization level floats according to the image signal. did.

Here, blur correction is a method of emphasizing the edges of an image by emphasizing the high frequency components of the image. ,
(hereinafter referred to as US mask) can be used. However, since such high-frequency emphasis filters essentially use differentiation, they are susceptible to noise, and are especially susceptible to white backgrounds (blank spots) in images.
There is a problem in that the noise in the black background (closed black) area is also emphasized at the same time, and this significantly deteriorates the image quality after the binarization process.

Furthermore, in this type of apparatus, a shading phenomenon occurs in which the peripheral part of the image becomes dark due to the effects of non-uniform illuminance of the optical system, characteristics of the image sensor, aberration of the lens, and the like. This shading phenomenon particularly affects the output level of the image signal for the white background portion of the image, and if this image signal is subjected to blur correction processing as it is, the degree of influence of noise will differ depending on the location during the binarization processing. That is, the seventh
As shown in Figure A, when image signal a has been transformed by the shading characteristics, if this signal a is subjected to blur correction processing by high-frequency emphasis, the output C in Figure 7B will be obtained. When the signal is binarized at the binarization level d, the left and right edge regions where the signal level is low are greatly affected by noise, and the central region where the signal level is high is hardly affected by noise. For this reason, there is a problem in that the image quality varies greatly depending on the location, making it difficult to obtain a uniform image.

(Objective of the Invention) The present invention has been made in view of the above circumstances, and it is an object of the present invention to eliminate noise contained in a white background when high-frequency emphasis is applied to an image signal using a high-frequency emphasis filter or the like prior to binarization processing. It is an object of the present invention to provide an image signal processing method capable of maintaining high image quality after binarizing an image without causing unevenness in image quality depending on the location.

(Structure of the Invention) According to the present invention, it is an object of the present invention to provide an image signal processing method for binarizing an image signal obtained by scanning an image with an image sensor by comparing it with a predetermined binarization level. After removing the noise contained in the image signal corresponding to the white background of the image using a noise filter (level) that is slightly lower than the image signal level corresponding to the white background and on which the shading correction characteristics are superimposed, blur correction is performed. This is achieved by an image signal processing method characterized by sharpening the image signal and further binarizing it at a predetermined binarization level.

(Example) Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is a conceptual diagram of a specific example thereof, Figs. 3A to 30 are diagrams showing signal waveforms in the processing process, and Fig. 4 is a 3 3 is a diagram showing a matrix.

In FIG. 1, reference numeral 10 indicates a light source, and the light from this light source 10 is transmitted through a condenser lens 12. The image is guided to the image sensor 20 via the film 14, the projection lens 16, and the mirror 18, and the role l1 image of the film 14 is formed on the image sensor 20. The image sensor 20 is a CCD line sensor or C
It is formed by a CD area sensor or the like, is driven by pulses supplied from a pulse circuit (not shown), and outputs a time-series image signal a. This image signal a has an output waveform as shown in FIG. 3A when the film 14 is negative. That is, at this time, the background area becomes a black background and its image signal becomes low level, and the area including the image becomes a white background and its signal level becomes high. Here, the image signal a is affected by shading, and the shading characteristics shown in FIG. 7A are superimposed, so that the output level at the center is high and the output level at both left and right ends is low. In FIGS. 3A to 3C, the horizontal axis represents time or pixel order, and the vertical axis represents voltage.

This image signal a is input to the background noise cut circuit 22, where noise included in the black background of the image (background area for negative film, image area for positive film) is removed. That is, this circuit 22 is composed of, for example, a comparator 24 and a switch 26 as shown in FIG.
A comparator 24 compares the image signal a and a lower noise cut level e, and a switch 26 indicates that the comparator 24 compares a < e
When it is determined that the background cut level e is selected, and when a≧e, the image signal a is selected. As a result, the output C of this circuit 22 is sliced at the lower noise cut level e, and background noise is cut. Here, the lower noise cut level e is set to a level slightly higher than the image signal level for a black background.

The output f of the lower noise cut circuit 22 is then input to the upper noise cut circuit 28, where noise included in the white background of the image (image area for negative film, background area for positive film) is removed. That is, this circuit 28 is composed of a comparator 30 and a switch 32, for example, as shown in FIG. The upper noise cut level generator 34 outputs an upper noise cut level g that includes shading correction and is set at a level slightly lower than the image signal level for a white background in synchronization with the scanning position of the image sensor 20. The comparator 30 compares the output f and the upper noise cut level g. The switch 32 is connected to this comparator 3.
2 selects the output f when f≦g, and selects the upper noise cut level g when f>g. As a result, after the image is sliced at the lower noise cut level e in the circuit 22, it is further sliced at the upper noise cut level g in this circuit 28, and the noise on the black background and white background of the image is cut. As a result, the image signal a becomes a signal in which noise contained in the background area and the image area is removed, as shown in FIG. 3B.

Reference numeral 36 denotes a blur correction circuit, which emphasizes the high frequency components of the signal C using, for example, a US mask 38 as a high frequency emphasis filter, thereby emphasizing the edges of the image.

For example, when the image space is an odd matrix in which a central pixel appears, the US mask 38 functions to emphasize the central pixel. For this US mask 38, for example, when each pixel data of a 3×3 matrix is ai as shown in FIG. -(b+d+h+f) and use this E as a new image signal. In this case U
The S mask 38 is set as shown in FIG. 2, and each element of this matrix is integrated into the image data of four surrounding pixels around the center pixel, and the sum E of the integrated values is determined. The image signal i emphasized in this way is transmitted to the comparator 4.
0 is compared with the binarization level j, and a binarization signal k is obtained.

In this way, prior to blur correction processing by high-frequency emphasis,
Since the noise in the image signal corresponding to the white background and black background of the image is removed by the lower noise cut level e and the upper noise cut level g that includes shading correction, fine details included in the image signal, especially in the white areas, are removed during blur correction processing. Noise is amplified, and the level of this amplified noise does not vary due to the influence of shading, which does not adversely affect the binarization process. Therefore, it is possible to eliminate the inconvenience that the influence of noise changes depending on the position of the image.

FIG. 5 is a block diagram of another embodiment, and FIGS. 6A to 6D are output waveform diagrams of each part.

In this embodiment, the binarization level is varied using the image signal a. That is, image signal a (6th A
) is smoothed in the smoothing circuit 50 and the smoothed signal sentence (
6B), and this smoothed signal sentence is compressed by the compression circuit 52. The voltage level of this compressed signal m (FIG. 6C) is further increased by n in level shift circuit 54. This level-shifted signal 0 (FIG. 6C) is compared in a comparator 40 with the signal i shown in FIG. 3C, which has already undergone blur correction, to obtain a binary signal p.

Note that as the smoothing circuit 50 of this embodiment, for example, a median filter can be used that uses the median of a 3×3 matrix centered on the center pixel as the image data of the center pixel.

According to this embodiment, since the binarization level 0 itself varies depending on the image signal a, it is suitable for highly accurate binarization processing of images with low contrast.

In each of the embodiments described above, not only the noise on the white background is cut at the upper noise cut level g, but also the noise on the black background is cut at the lower noise level e, making it even less susceptible to the influence of noise. However, the present invention also includes a method in which black background noise is not cut by the lower noise cut level e.

Although each of the above embodiments uses the US mask 38 in the blur correction circuit, the present invention is not limited to this.

(Effects of the Invention) As described above, the present invention uses an upper noise cut level that is slightly lower than the level of the image signal corresponding to the white background of the image and includes shading correction to generate the image signal prior to the blur correction process. Since it slices and removes the noise contained in the white background, even if high-frequency enhancement processing is performed to correct blur, it will not be affected by this noise, and the image quality will not change depending on the location. This enables homogeneous, high-quality binarization processing.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, FIGS. 2 and 2 are conceptual diagrams of a specific example thereof, FIGS. 3A to 30 are diagrams showing signal waveforms in the processing process, and FIG. 4 is a diagram showing a matrix. FIG. 5 is a block diagram of another embodiment, FIGS. 6A to 6D are output waveform diagrams of each part, and FIGS. 7A to 7B are diagrams showing the influence of shading. 20... Image sensor, 28... Upper noise cut circuit, 36... Blur correction circuit, 38... Unsharp mask, 40... Comparator, a... Image signal, b... Shading characteristics, g...upper noise cut level, J+O...binarization level. Patent Applicant Fuji Photo Film Co., Ltd. Agent Patent Attorney Yama 1) Yu Fumi (1 other person) Figure 1 Figure 2 Figure 3A Figure 30 Figure 4 Figure 51! I Figure 7A Figure 73 Procedural amendments stamped) January 25, 1985 Kunio Ogawa, Commissioner of the Patent Office 1, Indication of the case Patent Application No. 317357 of 1988 2, Name of the invention Image signal processing method 3. Relationship with the case of the person making the amendment Patent applicant address 210 Nakanuma, Minamiashigara City, Kanagawa Prefecture Name (520
) Fuji Photo Film Co., Ltd. Representative: Ohnishi Sho 4, Agent address: Yamato Bank Toranomon Building, 1-6-21 Nishi-Shinbashi, Minato-ku, Tokyo (Telephone: 591-7556) Spontaneous initiative: 6, Number of inventions increased by amendment: 07 , Subject of amendment 8, Contents of amendment L (1) Page 1 of the specification, the scope of claims shall be amended as shown in the attached sheet. (2) In the same book, page 5, line 3, "shading correction characteristics" is corrected to "shading correction characteristics." (3) Ibid., page 7, line 2. The "base cut level e" is corrected to the "bottom noise cut level e". (4) Correct Figure 2 as attached. (1 Kari 2) Attached Claims (1) An image signal processing method for binarizing an image signal obtained by scanning an image with an image sensor with a predetermined binarization level, comprising: After removing the noise contained in the image signal corresponding to the white background of the image using a noise cut level of 1 which is slightly lower than the image signal level corresponding to the shading correction characteristic and superimposed with the shading correction characteristic, blur correction is performed and the image signal is An image signal processing method characterized by sharpening and further binarizing at a predetermined binarization level. (2) The image signal processing method according to claim 1, wherein the blur correction is performed using an unsharp mask. (3) The binarization level is determined by smoothing the image signal,
Claim 1 characterized in that the smoothed signal is obtained by compressing the smoothed signal and further level-shifting the smoothed signal.
Image signal processing method described in section. (4) The image signal processing method according to claim 3, wherein the smoothing is performed using a median filter.

Claims (4)

[Claims] (1) In an image signal processing method in which an image signal obtained by scanning an image with an image sensor is binarized by comparing it with a predetermined binarization level, the image signal level is slightly lower than the image signal level corresponding to the white background of the image. After removing the noise contained in the image signal corresponding to the white background of the image using the upper noise cut level on which the shading correction characteristics are superimposed, the image signal is sharpened by performing blur correction, and then the image signal is sharpened to a predetermined binarization level. An image signal processing method characterized by binarizing the image signal. (2) The image signal processing method according to claim 1, wherein the blur correction is performed using an unsharp mask. (3) The binarization level is determined by smoothing the image signal,
Claim 1 characterized in that the smoothed signal is obtained by compressing the smoothed signal and further level-shifting the smoothed signal.
Image signal processing method described in section. (4) The image signal processing method according to claim 3, wherein the smoothing is performed using a median filter.