JPS5853269A - Texture eliminating circuit - Google Patents

Abstract

PURPOSE:To make the reference point of an image signal follow the change of level of the original texture and to secure the offset of the image signal, by detecting the peak value of the image signal on the basis of the black level and subtracting the output of detection from the image signal to convert it into an image signal on the basis of the white level. CONSTITUTION:An image signal A read out through a CCD solid state image pickup element 1 is amplified 2, and the peak voltage of the signal A is detected by a peak holding circuit 3. The difference between the signal A and the peak value B is obtained through an operational amplifier 4. In this case, the signal A is based on the black level in the original image in terms of the zero reference, and the arithmetic output F is based on the peak level of the signal A in terms of the zero reference. Thus the black level information is converted into an image signal emerging at the minus side. Then the output F is inverted by a polarity inverting amplifier 5. As a result, the texture level component is compensated compared with the signal A for an image signal which is based on the white level.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a background removal circuit that removes information at the background level from image information obtained by scanning a single image with a WS.

-ff, the original image placed on the contact glass is scanned by a light-reflecting lamp, the reflected light is received by an image sensor, the image information is captured, and an image is created based on the read image information. The image input/output device is designed to remove the density level of the original background from the image information that has been removed, so that a high-quality recorded image without background stains can be obtained. Image processing is applied to the image.

Conventionally, as a means of background removal, reading n, ta l[11i
The reference point of one-image information is offset by a predetermined background level, but with this method, it is not possible to easily perform appropriate background removal according to the background density, which varies considerably. It is not possible, and especially if there are two
If the background level removed differs locally, it will not be possible to follow the changes and variations will occur in the background removal, leaving partial background stains in the recorded image and deteriorating the image quality. The problem is that you end up doing it.

The present invention has been made in consideration of these points, and provides a background removal circuit that offsets a reference point of image information by following changes in the level of the background of a document.

FIG. 1 shows the basic configuration of the background removal circuit according to the present invention, which detects the peak voltage value in the image signal A removed by the CCD solid-state image element l and amplified by the video amplifier 2. A peak hold circuit 3 for holding, an operational amplifier 4 for performing arithmetic processing based on the following equation based on its hold output B and the image signal A, and a polarity inversion amplifier for inverting the polarity of its operational output F. 5.

F=A-B (1) If the image information shown in the 21st %l (a) is removed by the CCD solid-state image sensor 1 in this configuration, Let's imagine. For the image signal, the black level BL in the original image is used as a zero reference, and the difference W)f-B between the peak voltage value B and the white level voltage value WH is calculated as the background level.

Therefore, the peak voltage value B of the spider image signal gA is detected and held by the peak hold circuit 3, and (3) the operational amplifier 41C calculates the above equation (1) based on the hold output B and the image signal A. When the processing is performed, the calculation output F is as shown in FIG. 2(b),
The black level information BL is converted into an image signal that appears on the negative side with the peak level of the original image signal as a zero reference. Next, when the calculation output F is inverted by the polarity inversion amplifier 5, as shown in FIG. An image signal whose zero reference is the white level WH' from which WH' has been removed is sent to its output terminal OUT.

As described above, in the background removal circuit according to the present invention, even if the background level changes depending on the type of food on the document, and even if the background level of the document changes partially, the background level removal circuit according to the present invention can remove the background level that follows the background level. 1j. 3. Image with background level removed 1
The subsequent image processing circuit 1cE performs quantization, etc. based on the number g (if it has a circuit configuration that can handle the minus 4M number, then, as in the case of the previous embodiment, (4) It goes without saying that it is not necessary to invert the output F of the device 4 using the polarity inverting amplifier 5.

In such a background removal circuit, if the peak level (ground level) of the image signal removed by the CCD solid-state image sensor 1 contains high frequency components and causes variations as shown in FIG. Since optimum background removal cannot be performed, the present invention applies a compensation voltage C to eliminate shadow 1# due to variations in the background level.

At that time, a method of uniformly correcting variations in the background level by adding a compensation voltage C' of a certain magnitude to the hold output B of the peak hold circuit 43 and subtracting the result B + C' from the image signal gh. However, in this type of method, the constant compensation voltage does not correspond to the input level of the image signal A, and therefore, in the case of high reflectance originals as shown in Figures 4(a) and (b), a) and low reflectance original (b)
In this case, there is a problem when the reproducibility near the background density deteriorates.

Therefore, in the background removal circuit according to the present invention, the high frequency component of the background of the original is changed depending on the reflectance of the original to improve the reproducibility near the background density.

FIG. 5 shows an embodiment of the background removal circuit 1 according to the present invention.
A multiplier 6 is provided for multiplying 8 by the peak hold times Nr30 and the hold output B, and the multiplier output is applied as a compensation voltage C to the operational amplifier 4, where the CCDCD solid acid 1-quadrant element 1
Based on the original image signal A amplified by the video amplifier 2 and the peak value B of the image signal A detected by the peak hold circuit 3, the calculation process of the following equation is executed. The calculated output F is supplied to the polarity inversion amplifier 5.

F=A-B+C (2) Here, the compensation voltage C (given by a linear equation) corresponds to the high-frequency fluctuation of the background portion of the original.

C=-VR-B-(3) where k is a constant and VR is a constant voltage determined by the compensation voltage.

In addition, since the compensation voltage C=0 does not exist, it is also possible to add the offset voltage Vof to equation (3) and use it as the compensation voltage I:F, C, as shown in the following equation. be.

C=k-V,+!・B + Vof”・(
4) fj'Oj6, the background removal circuit according to the present invention is not limited to the embodiment shown in FIG. 6
Instead of using , it can be easily achieved by using other means that can be controlled by the output of the peak hold circuit 3, such as an attenuator using a photocoupler or a multiplier using an analog multiplier. F.

As described above, the background removal circuit according to the present invention includes a peak hold circuit that detects the peak value of an image signal read by an image sensor and used as a black level reference, and a constant voltage at an output level of one peak hold cycle. Means for creating a compensation voltage according to the high frequency fluctuation of the skin by making it variable; an arithmetic circuit that subtracts the peak value from the captured image signal and adds the compensation voltage value; and the arithmetic output thereof. and a means for inverting the polarity of the signal and converting it into an image IT signal based on a white level, thereby effectively removing the background level by following high frequency fluctuations in the background level of the original. It has the excellent advantage of being able to

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the basic configuration of the background removal circuit according to the present invention, FIGS. 3
The figure shows an example of an input image signal and is a T% characteristic diagram, FIG. 4(a). (b) shows an example of the image reproduction signal in the case of a high-reflectance original and the case of a low-reflectance original when the compensation voltage is constant; FIG. FIG. 2 is a block configuration diagram showing an example of a background removal circuit. 1... CCD solid-state image sensor 2... Video amplifier 3... Peak hold circuit 4... Operational amplifier (
8) 5...Amplifier for polarity reversal 6...Multiplier Applicant's agent Suzuki Torii Figure 1 Figure 2

Claims (1)

[Claims] A peak hold circuit detects the peak value of the image signal read by the image sensor and is used as a black level reference, and a constant voltage is varied by the output level of the peak hold circuit to adjust the compensation voltage according to high frequency fluctuations in the background. an arithmetic circuit that subtracts the first peak value from the read image signal and adds a compensating pressure value; and a means that inverts the polarity of the arithmetic output to convert it into an image signal based on a white level. A background removal circuit configured by.