JPS63155948A - Processing method for picture signal - Google Patents

Abstract

PURPOSE:To obtain a picture with very excellent quality form by adding a noise signal in response to a level of a picture signal to a picture image signal subjected to sensitivity correction according to a photoelectric conversion characteristic of a line sensor. CONSTITUTION:In adding a modulation noise signal K(Si).N from a noise modulation circuit 24 to picture information Si corrected by a sensitivity correction circuit 20 and converting the result into a digital signal by an A/D converter 26, the uneven picture signal is hardly visualized. In this case, the modulation noise signal K(Si).N is adjusted so as to reduce the effect by the noise signal N is decreased when the level of the picture signal Si is larger and the effect of the noise signal N is large when the level of the picture signal Si is smaller by using a noise modulation function K(Si). Thus, it is avoided that the dispersion in the reproduced picture is made eminent because of the presence of the modulation noise signal K(Si).N applied to the picture signal S.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for processing an image signal, and more particularly, the present invention relates to a method for processing an image signal, and more particularly, it reproduces image information by adding a noise signal of a predetermined level to a document image information signal obtained by photoelectric conversion using a line sensor. The present invention relates to a method of processing an image signal, which makes it possible to improve image quality over time.

For example, in the fields of printing and plate-making, image scanning recording and reproducing systems are widely used to electrically process image information carried on manuscripts and create film masters for the purpose of streamlining work processes and improving image quality. ing.

This image scanning, recording and reproducing system basically consists of an image reading device and an image reproducing device. That is, in the image reading device, image information of a document that is conveyed in a sub-scan direction in an image reading section is main-scanned by a photoelectric conversion element and converted into an electrical signal. Next, the image information photoelectrically converted by the image reading device is subjected to arithmetic processing such as gradation correction and edge enhancement according to plate-making conditions in an image reproducing device, and then converted to an optical signal such as a laser beam and film. Recording and reproduction are performed on a record carrier made of a photosensitive material such as. Note that this recording carrier is developed by a predetermined developing device and used as a film original for printing or the like.

By the way, when the image reading device main scans a document and reads its image information, a COD (charge coupled device) in which a large number of photoelectric conversion parts are arranged along the main scanning direction is mainly used as a photoelectric conversion element. . Here, the CO
The photoelectric conversion characteristics of the photoelectric conversion unit that constitutes D are not constant due to manufacturing errors, and for example, even when scanning an original with uniform density, the photoelectric conversion characteristics are reproduced from the photoelectrically converted image signal. The problem is that the image becomes uneven. In other words, a document carrying image information is main-scanned by the COD in which the photoelectric conversion characteristics of each photoelectric conversion section vary, and is also conveyed in a sub-scanning direction by a conveyance mechanism, so that image information on the entire surface of the document is scanned. In the image reproduced from the photoelectrically converted image signal, streak-like unevenness that is parallel to the main scanning direction and extends in the sub-scanning direction occurs.

Therefore, various correction methods have been proposed to eliminate such defects. An example of this is the correction method disclosed in Japanese Patent Application Laid-Open No. 60-189372. In this conventional technology, a reference original with a uniform density is read by a CCD in advance to obtain a correction coefficient for the photoelectric conversion characteristics of each photoelectric conversion unit, and when the original is main scanned, the COD
The basic idea is to obtain an even reproduced image by correcting the image signal obtained from each photoelectric conversion section using the correction coefficient.

However, since the photoelectrically converted image signal is subjected to arithmetic processing for correction by a predetermined correction circuit, it may be corrected due to rounding errors due to the calculation accuracy of the correction circuit, circuit characteristics, errors in inputting correction data, etc. Unevenness occurs in the reproduced image obtained from the image signal. in this case,
The unevenness that appears in the reproduced image is generally harder to see than the unevenness that arises from the photoelectric conversion characteristics before COD correction, but
Even so, it has been pointed out that there is still a problem in that it is not possible to completely eliminate streak-like unevenness extending in the sub-scanning direction of the reproduced image, making it impossible to obtain a high-quality image.

The present invention has been made to overcome the above-mentioned disadvantages, and by adding a noise signal of a predetermined level to an image signal photoelectrically converted by a line sensor, it is possible to reduce the visibility of unevenness in a reproduced image. An object of the present invention is to provide an image signal processing method that can improve image quality.

In order to achieve the above object, the present invention generates a noise signal of a predetermined level based on an image signal obtained by reading a reference original in advance when main scanning and reading image information carried on an original by a line sensor. The noise signal is created in advance, and the noise signal is added to the image signal obtained from the document during main scanning of the document to form a desired image signal.

Next, preferred embodiments of the image signal processing method according to the present invention will be described in detail with reference to the accompanying drawings.

In FIG. 1, reference numeral 10 indicates a reading unit of an image reading device to which the image signal processing method according to the present embodiment is applied. In this reading section IO, the image information carried on the document S is illuminated by illumination light from a light source 12, and reflected light is transmitted to a condenser lens 16 by a CCD 14, which is a line sensor.
is read out photoelectrically via the In this case, the original S
is conveyed in the sub-scanning direction in the direction of arrow A by a conveyance mechanism (not shown), and main-scanned in the direction of arrow B by the CCD 14, thereby reading image information on the entire surface.

On the other hand, the image information photoelectrically converted by the CCD 14 is subjected to predetermined processing in the processing section 18 to form a desired image signal. In this case, the processing section 18 includes a sensitivity correction circuit 20 that corrects the photoelectric conversion characteristics of each photoelectric conversion section in the CCD 14, a noise signal generation circuit 22 that outputs a noise signal of a predetermined level, and a sensitivity correction circuit 20 that outputs the noise signal.
It basically consists of a noise modulation circuit 24 that modulates the image signal according to the corrected image signal, and an A/D converter 26 that A/D converts the image signal. Note that the image signal corrected by the sensitivity correction circuit 20 and the noise signal modulated by the noise modulation circuit 24 are inputted to the A/D converter 26 in a summed state via a changeover switch SW.

Therefore, next, a method of processing an image signal according to this embodiment in the processing section 18 will be explained.

First, the changeover switch SW is turned off, and the reading section 10 is turned off.
Read a blank document as a reference from .

In this case, the image signal obtained from the CCD 14 is
There are variations depending on the photoelectric conversion characteristics of each photoelectric conversion unit constituting D14. Therefore, the sensitivity correction circuit 2
Set the sensitivity correction coefficient at 0. Note that this sensitivity correction coefficient is initially set to 1.0 in the sensitivity correction circuit 20, and after being calculated from the image signal obtained as a digital signal by the A/D converter 26, the sensitivity correction coefficient is In step 20, the value is set for each photoelectric conversion unit.

Next, an image signal obtained from a reference blank document is corrected using a sensitivity correction coefficient, and the corrected image signal is A/D converted by an A/D converter 26. In this case, the A/D converted corrected image signal is sent to the sensitivity correction circuit 20 as described above.
There are variations that cannot be completely eliminated due to rounding errors due to the calculation accuracy or circuit characteristics.

Therefore, the standard deviation of this variation is determined from the corrected image signal having this variation. Then, the level of the noise signal N output from the noise signal generation circuit 22 is set based on the standard deviation.

Note that the noise signal N is preferably white noise, and its level is preferably set to about two to three times the standard deviation.

On the other hand, in the noise modulation circuit 24, the noise modulation function K(
Si) is set in advance. This noise modulation function K(Si)
As shown in FIG. 2, during main scanning of the original S,
It is set to gradually decrease as the level of the image signal S corrected by the sensitivity correction circuit 20 increases. Here, i indicates the number of the photoelectric conversion unit constituting the CCD 14.

After the above preparation work is completed, the changeover switch SW is turned on and main scanning of the document S carrying predetermined image information is started.

Therefore, the reflected light from the document S illuminated by the light source 12 is imaged on the CCD 14 via the condenser lens 16 and photoelectrically converted. This photoelectrically converted image signal is corrected by a sensitivity correction coefficient corresponding to each photoelectric conversion section of the CCD 14 in a sensitivity correction circuit 20 to form an image signal Si.

On the other hand, the noise signal N corresponding to the standard deviation mentioned above is output from the noise signal generation circuit 22 to the noise modulation circuit 24. In this case, the noise modulation circuit 24 uses the noise signal N
The corrected image signal S output from the sensitivity correction circuit 20
, the noise modulation function K (S i) shown in FIG.
and outputs a modulated noise signal K(Si)·N.

Next, the modulated noise signal K (S f)·N is added to the image signal S through a changeover switch SW, and C
The photoelectric conversion characteristics of each photoelectric conversion unit of the CD 14 are corrected and the image signal S, / is inputted to the A/D converter 26 as an image signal S, / with no unevenness due to circuit characteristics or the like. Therefore, the A/D converter 26 converts the image signals S, / into digital signals to form a desired image signal.

Here, FIG. 3a schematically shows an image signal when only the image signal Si corrected by the sensitivity correction circuit 20 is converted into a digital signal by the A/D converter 26. In this case, the sensitivity correction circuit 20 is used for the image signal.
Due to the characteristics of
Line-like unevenness extending in the direction of arrow A) has occurred. On the other hand, a modulated noise signal K (
It will be easily understood that if the signal is converted into a digital signal by the A/D converter 26 after adding St)·N, the unevenness of the image signal becomes less visible as shown in FIG. In this case, the modulated noise signal K(Si)·N reduces the influence of the noise signal N when the level of the image signal Si is large by the noise modulation function K(St) shown in FIG. When the level of the signal S5 is low, the influence of the noise signal N is set to be large, so that the modulated noise signal K(Si)·N added to the image signal St causes the roughness of the reproduced image. A serious situation is avoided.

As described above, according to the present invention, a desired image signal is formed by adding a noise signal corresponding to the level of the image signal to an image signal whose sensitivity has been corrected according to the photoelectric conversion characteristics of the line sensor. There is. Therefore, in the image reproduced from the image signal to which the noise signal is added, the unevenness caused by the circuit characteristics of the sensitivity correction circuit and the like is made less visible, so that an extremely high-quality image can be obtained. Furthermore, since the level of the noise signal is increased or decreased in accordance with the level of the image signal, there is no possibility that the resolution of the reproduced image will decrease due to the noise signal.

Although the present invention has been described above by citing preferred embodiments, the present invention is not limited to these embodiments, and various improvements and design changes can be made without departing from the gist of the present invention. Of course.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the main part configuration of an image reading device to which the image signal processing method according to the present invention is applied; FIG. 2 is a characteristic diagram of the noise modulation function in the image signal processing method according to the present invention; FIG. 3A is an explanatory diagram of an image signal before correction by a noise signal, and FIG. 3 is an explanatory diagram of an image signal when a noise signal is added in the image signal processing method according to the present invention. 10...Reading section 14...C0D18
... Processing section 20 ... Sensitivity correction circuit 2
2... Noise signal generation circuit 24°... Noise modulation circuit 26... A/D converter SW... Changeover switch S... Original

Claims (3)

[Claims] (1) When reading the image information carried on the document by main scanning with a line sensor, a noise signal of a predetermined level is created in advance based on the image signal obtained by reading the reference document, and the main scanning of the document is performed. A method for processing an image signal, comprising: adding the noise signal to an image signal obtained from the document to form a desired image signal. (2) In the method described in claim 1, the image signal obtained by reading the reference document is corrected according to the sensitivity of the line sensor, and the standard deviation is then determined from the corrected image signal. Furthermore, the image signal processing method comprises setting the level of the noise signal based on the standard deviation. (3) An image signal processing method according to claim 1 or 2, in which the amplitude of the noise signal is modulated according to the level of the image signal obtained from the original.