JPH01160171A - Picture signal processing method - Google Patents

Abstract

PURPOSE:To attain binarization processing with high picture quality by using a specific noise cut level, slicing a picture signal in preceding over blur correction processing, and eliminating noise included in white and balck background. CONSTITUTION:An image sensor 20 consists of a CCD line sensor or a CCD area sensor and is driven by a pulse supplied from a pulse circuit and outputs a picture signal (a). A noise corresponding to the white and balck background of the picture is eliminated from the picture signal (a) by using an upper noise cut level slightly lower than the picture signal level corresponding to the white background of the picture and a lower noise cut level slightly higher than the picture signal level corresponding to the black background at a lower noise cut circuit 22 and an upper noise cut circuit 28. Then blur correction is applied to sharpen the picture signal and binarization is applied by a prescribed binarization level. Thus, in the case of high frequency emphasis, the effect of noise included in white and black background is avoided and it is possible to improve the picture quality in applying binarization processing to the picture.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an image 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 an image using an image sensor such as a CCDjCD sensor or a COD area sensor and 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, there is also a method in which the binarization level is obtained by subjecting the image signal to smoothing, compression, and level shifting processing, so that the binarization level floats according to the image signal. Proposed.

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 this type of high-frequency emphasis fusilta uses differentiation in a woody manner, it is susceptible to noise, especially when white areas 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.

(Objective of the Invention) The present invention has been made in view of the above circumstances, and when performing high frequency enhancement on an image signal using a high frequency enhancement filter or the like prior to binarization processing, it is possible to An object of the present invention is to provide an image signal processing method capable of improving the image quality after binarizing an image without being affected by noise.

(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. Noise contained in the image signals corresponding to the white background and black background of the image is eliminated using an upper noise cut level slightly lower than the image signal level corresponding to the white background and a lower noise cut level slightly higher than the image signal level corresponding to the black background. This is achieved by an image signal processing method characterized in that after the removal, the image signal is sharpened by performing blur correction, and further binarized 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 is a light source, and the light from this light source 10 is guided to an image sensor 20 via a condenser lens 12, a film 14, a projection lens 16, and a mirror 18, and the projected image of the film 14 is sent to the image sensor 20. Form an image. The image sensor 20 is a CCD line sensor or CC
D formed by area sensor etc., pulse circuit (not shown)
It is driven by pulses supplied from , 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. 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 contained in the black background of the image (background area for negative film, image area for positive film) is removed. That is, as shown in FIG.
If it is determined that <b, the output C of the Kujiji 22 is sliced at the background cut level b, and the noise in the black area is cut.

The output C of the lower noise cut circuit 22 is then input to the upper noise cut circuit 28, where noise contained 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. 2, and the comparator 30 compares the output C with the upper noise cut level d. The switch 32 selects the output C when the comparator 32 determines that C≦d, and selects the output C when the comparator 32 judges that C≦d.
At the time of d, the upper noise cut level d is selected. As a result, the circuit 22 slices the image at the lower noise cut level d, and the circuit 28 further slices it at the upper noise cut level d, thereby cutting noise in the black area of the image (background area for negative film, image area for positive film). be done. Therefore, the image signal a becomes the signal e in which the noise contained in the background area and the image area is removed, as shown in FIG. 3B. Here is the lower noise cut level b
is set to a level slightly higher than the image signal level for a black background, and the upper noise cut level d is set to a level slightly lower than the image signal level for a white background.

Reference numeral 34 denotes a blur correction circuit, which emphasizes the high frequency components of the signal C using, for example, a US mask 36 as a high frequency emphasis filter, thereby emphasizing the edges of the image.

This US mask 36 functions to emphasize the central pixel, for example, when the image space is an odd matrix in which the central pixel appears. For this US mask 36, 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 36 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 f thus emphasized is sent to the comparator 38.
It is compared with the binarized level g at , and a binarized signal 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 b and the upper noise cut level d, when performing blur correction processing, the noise in the image signal that corresponds to the white background and black background of the image is removed. Fluctuations caused by fine noise contained in the image are not excessively magnified, so it is less susceptible to background noise, and it is possible to eliminate inconveniences such as dark areas appearing white.

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 by the smoothing circuit 5o and the smoothed signal i
(FIG. 6B), and this smoothed signal i is transmitted to the compression circuit 52.
is compressed. The voltage level of this compressed signal j (FIG. 6C) is roughly increased by k in the level shift circuit 54. This level-shifted signal sentence (FIG. 6c) is compared in a comparator 38 with the signal f shown in FIG. 3c, which has already undergone blur correction, to obtain a binary signal m.

Note that as the smoothing circuit 5o in this embodiment, for example, a median filter can be used that employs the median value 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 itself varies depending on the image signal a, it is suitable for highly accurate binarization processing of images with low contrast.

Although each of the above embodiments uses the US mask 36 in the blur correction circuit, the present invention is not limited to this.

(Effects of the Invention) As described above, the present invention has a lower noise cut level that is slightly higher than the level of the image signal corresponding to the black background of an image, and an upper noise cut level that is slightly lower than the level of the image signal that corresponds to the white background of the image. is used to slice the image signal prior to the blur correction process and remove the noise contained in the white and black backgrounds, so even if high frequency enhancement processing is performed during the blur correction process, the influence of this noise cannot be ignored. This enables high-quality binarization processing.

[Brief explanation of the drawing]

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 during processing, FIG. 4 is a diagram showing a matrix, FIG. 5 is a block diagram of another embodiment, and FIGS. 6A to 6D are output waveform diagrams of each part. 20... Image sensor, 28... Lower noise cut circuit, 34... Blur correction circuit, 36... Unsharp mask, 38... Comparator, a... Image signal, b... Lower noise cut level, d...Upper noise cut level, g, fL...Binarization level. Patent applicant: Fuji Photo Film Co., Ltd. Agent: Patent attorney Yama 1) Yu Fumi (1 other person) Figure 3A Figure 4 Figure 5 Figure 6 AI! Procedure 7 City official document (spontaneous) January 25, 1988 Director General of the Patent Office Kunio Ogawa 1. Aqueous indication Patent Application No. 317356 of 1988 2. Name of the invention Image signal processing method 3. Make amendments. Relationship with the case Patent applicant address 210 Nakanuma, Minamiashigara City, Kanagawa Prefecture Name (520
) Fuji Photo Film Co., Ltd. Representative: Minoru Ohnishi 4, Agent Address: Yamato Bank Toranomon Building, 1-6-21 Nishi-Shinbashi, Minato-ku, Tokyo (Telephone: 591-75511i) Name:
(8222) Patent attorney Yama 1) Bun Yu 5, Date of amendment order (1 other person) Voluntary action 6, Number of inventions increased by amendment 07, Subject of amendment 8, Contents of amendment (1) Ibid., page 5, No. 13 Row, correct [Base noise cut circuit] to "Bottom noise cut circuit". (2) Correct Figure 2 as attached. (with p person)

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 signals corresponding to the white background and black background of the image using the upper noise cut level and the lower noise cut level that is slightly higher than the image signal level corresponding to the black background, blur correction is performed and the image signal is An image signal processing method characterized by sharpening the image signal and further binarizing it 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.