JP2640661B2 - Image signal processing method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image signal processing method for binarizing an image signal obtained by scanning a projected image on a film with an image sensor.

(Technical Background of the Invention) Conventionally, various methods have been proposed for reading a projected image of a film using an image sensor such as a CCD line sensor or a CCD area sensor and binarizing the image signal. For example, the applicant of the present application has proposed a method of correcting a blur of an image signal and comparing it with a fixed binarization level (Japanese Patent Laid-Open No. 62-1300).
No. 68). Further, in this case, a method has been proposed in which the binarization level is obtained by performing each processing of smoothing, compression, and level shifting on the image signal, that is, a binarization level floating according to the image signal.

Here, the blur correction emphasizes the edges of the image by enhancing the high-frequency components of the image, and a high-frequency emphasis filter using first-order differentiation or Laplacian (secondary differentiation) can be used. However, since such a high-frequency emphasis filter essentially uses a derivative, it is susceptible to noise. On the other hand, when an image is read by projecting a film, it is inevitable that the film is dusty, dusty or scratched. For this reason, when reading a projection image of this type, noise in an area of a white background (white spots) or a black background (closed black) of the image is also emphasized at the same time, which significantly reduces the image quality after the binarization processing. was there.

Further, in this type of apparatus, a shading phenomenon in which a peripheral portion of an image becomes dark occurs due to the influence of non-uniform illuminance of an optical system, characteristics of an image sensor, aberration of a lens, and the like. This shading phenomenon particularly affects the output level of the image signal with respect to a white background portion of the image. If the image signal is subjected to the blur correction processing as it is, the degree of the influence of noise depending on the location in the binarization processing differs. I.e.
As shown in FIG. 7A, the image signal a has the shading characteristic b
When the signal a is subjected to blur correction processing by high-frequency emphasis when the signal is deformed as shown in FIG. 7B, an output c shown in FIG. 7B is obtained. When this signal is binarized at the binarization level d, the signal level becomes low. The left and right end regions 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 that a change in image quality depending on a place becomes large, and it is difficult to obtain a uniform image.

In addition, the projected image of the film often has small scratches on the film, and when the scratches are projected, it becomes noise on a black background. In the conventional image processing, the noise on the black background is also emphasized by the high-frequency emphasis, which causes the image quality to deteriorate.

(Object of the Invention) The present invention has been made in view of such circumstances,
When performing high-frequency enhancement using a high-frequency enhancement filter or the like prior to binarization processing on an image signal obtained by projecting a film, noise included in a white background does not cause non-uniformity depending on the location of image quality, At the same time, an object of the present invention is to provide an image signal processing method capable of removing noise on a black background and maintaining high image quality after binarizing an image.

According to the present invention, there is provided an image signal processing method for binarizing an image signal obtained by scanning a film projection image with an image sensor by comparing the image signal with a predetermined binarization level. The noise included in the image signal corresponding to the white background of the projected image is removed using the upper noise cut level slightly lower than the image signal level corresponding to the white background of the projected image and the shading correction characteristic is superimposed, and included in the black background. After obtaining an image signal by removing noise generated using a constant lower noise cut level, the image signal is subjected to blur correction to sharpen the image signal, and further binarized at a predetermined binarization level. And an image signal processing method characterized by the following. .

(Embodiment) FIG. 1 is a block diagram of one embodiment of the present invention, FIG. 2 is a conceptual diagram of a specific example, FIGS. 3A to 3C are diagrams showing signal waveforms in a processing process, and FIG. It is a figure showing a 3 matrix.

In FIG. 1, reference numeral 10 denotes a light source. Light from the 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 film 14
Is formed on the image sensor 20. The image sensor 20 is formed by a CCD line sensor, a CCD area sensor, or the like, is driven by a pulse 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 the image signal becomes low level, and the area including the image becomes a white background and the signal level becomes high. Here, the image signal a is affected by shading,
The shading characteristic b shown in the figure is superimposed, so that the output level at the center is high and the levels at the left and right ends are low. 3A to 3C, the horizontal axis indicates time or pixel order,
The vertical axis indicates voltage.

This image signal a is input to the background noise cut circuit 22, where the noise contained in the black background (background area for negative film, image area for positive film) is removed. That is, as shown in FIG. 2, the circuit 22 includes a comparator 24 and a switch 26, and the comparator 24 compares the image signal a with the lower noise cut level e. The switch 26 selects the lower noise cut level e when the comparator 24 determines that a <e, and selects the image signal a when a ≧ e. As a result, the output f of the circuit 22 is sliced at the lower noise cut level e, and noise in the background area 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 an upper noise cut circuit 28, which removes noise contained in a white background (image area for negative film, background area for positive film). That is, the circuit 28 includes, for example, a comparator 30 and a switch as shown in FIG.
32 and an upper noise cut level generator 34. The upper noise cut level generator 34 outputs an upper noise cut level g including shading correction and set to 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 with the upper noise cut level g. Switch 32
Selects the output f when the comparator 30 determines that f ≦ g, and selects the upper noise cut level g when f> g. As a result, after being sliced at the lower noise cut level e by the circuit 22, the circuit 28 further slices the upper noise cut level g.
And the noise of the black and white background of the image is cut. As a result, the image signal a becomes a signal h from which noise included in the background area and the image area has been cut as shown in FIG. 3B.

Reference numeral 36 denotes a blur correction circuit that emphasizes the high-frequency component of the signal h using, for example, a high-frequency emphasis filter to perform edge enhancement of an image.

The high-frequency emphasis filter 38 functions to emphasize the center pixel when, for example, the image space is an odd matrix appearing at the center pixel. As shown in FIG. 4, for example, as shown in FIG. 4, when each of the image data of the 3 × 3 matrix is a to i, the high-frequency emphasizing filter 38 uses the data e for the central pixel as the data of the four surrounding pixels. = 5e- (b + d + h + f), and this E is used as a new image signal. In this case US
The mask 38 is set as shown in FIG. 2, and each element of this matrix is integrated with the image data of the four pixels surrounding the central pixel, and the sum E of the integrated values is obtained. The image signal i thus enhanced is compared with the binarization level j in the comparator 40 to obtain a binarization signal k.

As described above, prior to the process of the blur correction by the high-frequency emphasis, the noise of the image signal corresponding to the white background and the black background of the image is removed by the lower noise cut level e and the upper noise cut level g including the shading correction. The fine noise included in the image signal, especially in the white area, is amplified on the ground to be corrected, and the level of the amplified noise fluctuates due to the influence of shading, which may have an adverse effect on the binarization processing. There is no. For this reason, the inconvenience that the influence of noise changes depending on the position of the image can be eliminated. In particular, in a film projection image, an image in a black background area is hardly affected by shading, so that noise can be removed from the black background by a constant lower noise cut level e.

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

In this embodiment, the binarization level is changed using the image signal a. That is, the image signal a (6A
The figure is smoothed in the smoothing circuit 50 and the smoothed signal l (the
6B), and the smoothed signal 1 is compressed by the compression circuit 52. The voltage level of the compressed signal m (FIG. 6C) is further increased by n in the level shift circuit 54. This level-shifted signal o (FIG. 6C) is
The signal is compared with the signal i shown in FIG. 3C in which the blur correction has already been completed, and a binary signal p is obtained.

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

According to this embodiment, the binarization level o itself is the image signal a
Therefore, it is suitable for high-precision binarization processing of an image with low contrast.

(Effect of the Invention) As described above, the present invention uses the upper noise cut level slightly lower than the level of the image signal corresponding to the white background of the projected image of the film and includes the shading correction before the blur correction processing. Since the image signal is sliced and the noise contained in the white background is removed, it is not affected by this noise even if high frequency emphasis processing is performed for blur correction, and the image quality changes depending on the location. There is no.

In a film projection image, an image on a black background is less likely to be affected by shading. Therefore, the noise on the black background is removed by slicing the image signal using a noise cut level below a certain value. Therefore, noise mainly due to dust or dust on a white background and noise mainly due to scratches on a black background can be removed, and high-quality binarization processing can be performed.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of the present invention, FIG. 2 is a conceptual diagram of a specific example, FIGS. 3A to 3C are diagrams showing signal waveforms in a processing process, 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 respective parts, and FIG.
7A to 7B are diagrams showing the effects of shading. 20 ... Image sensor 22 ... Lower noise cut circuit 28 ... Upper noise cut circuit 36 ... Blur correction circuit 38 ... High frequency emphasis filter 40 ... Comparator a ... Image signal b ... Shading characteristics, e. Lower noise cut level g. Upper noise cut level, j, o .. Binarization level.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-121667 (JP, A) JP-A-61-242170 (JP, A) JP-A-62-216477 (JP, A) “FAX , Image signal processing for OA ”(57-10-20), Nikkan Kogyo Shimbun P. 11−12, 23

Claims (4)

(57) [Claims] An image signal processing method for binarizing an image signal obtained by scanning a film projection image with an image sensor by comparing the image signal with a predetermined binarization level, the image signal corresponding to a white background of the projection image The noise included in the image signal corresponding to the white background of the projected image is removed using the upper noise cut level slightly lower than the level and the shading correction characteristic is superimposed, and the noise included in the black background is reduced to a fixed lower noise cut level. An image signal processing method comprising: obtaining an image signal by removing the image signal by using the image processing method; performing image blur correction on the image signal to sharpen the image signal; and further binarizing the image signal at a predetermined binarization level. 2. The image signal processing method according to claim 1, wherein the blur correction is performed using a high-frequency emphasis filter. 3. The method according to claim 1, wherein the binarization level is obtained by smoothing the image signal, compressing the smoothed signal, and further performing a level shift. Image signal processing method. 4. The image signal processing method according to claim 3, wherein the smoothing is performed using a median filter.