JPS59175279A - Method for correcting shading distortion - Google Patents

Abstract

PURPOSE:To obtain an accurate binary-coded output by providing a memory storing in advance accurate shading distortion in addition to a memory A/D- converting a peak value of initial input and storing it. CONSTITUTION:An ROM 5 to which shading distrotion not including picuture information is stored in advance is provided in addition to an RAM 4 storing the shading distortion A/D-converted. If accurate shading distortion is not obtained, that is, if a video signal including pictue information is inputted as the initial value input 1, the memory is changed over from the RAM 4 to the ROM 5 and the information is read from the ROM 5 storing the accurate shading distortion. The data of read shading distortin is D/A-converted by a D/A converter 6 to obtain a reproduced shading distortion, its slice level and a signal of a video input 7 are compared by a comparator circuit 8 to obtain a binary-coded output 9.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a shading distortion correction method, and more particularly to a shading distortion correction method during image reading by a facsimile machine or the like.

BACKGROUND OF THE INVENTION Correction of shading distortion in conventional facsimile machines has been carried out by a correction circuit as shown in FIG.

In Fig. 1, the symbol l indicates the initial value input, and this input signal is input to the peak hold circuit 2 which detects the peak value, detects the peak value of the input video signal, and uses this peak value as a reference. The signal is converted into a digital signal by the A/D converter 3 and stored in the memory 4.

The shading distortion stored in the memory 4 is read out in synchronization with the bidet intervention cuff number, converted into an analog signal by the D/A converter 6, and input to the comparison circuit 8.

Through this process, shading distortion corresponding to the background density of the original is reproduced, and compared with the video input signal in a comparator circuit 8 to obtain a binarized output 9.

However, in the past, as shown in FIG. 2, when initializing, the white back plate 13 is
CD (Charge Coupled Device
) Since the element 12 was reading and initial values were being set, the original! If 0 is inserted deeply so as to block the white back plate I3, image information such as rABcJ will also be read, and this image information will be included in the video signal, making it impossible to set accurate initial values, and the image Therefore, facsimile machines were unable to transfer parts of the document from the middle.

Purpose The present invention has been made in order to eliminate the above-mentioned drawbacks of the conventional technology, and it is possible to obtain accurate shading distortion even if a video signal containing image information is input without initial value setting. It is an object of the present invention to provide a shading distortion correction method configured in such a manner that an accurate binary output can be obtained.

EXAMPLES Hereinafter, the present invention will be explained in detail based on examples shown in the drawings.

FIG. 3 explains one embodiment of the present invention.
The same parts as those in the figures are given the same reference numerals, and their explanations will be omitted.

In this embodiment, in addition to a RAM (Random Access Memory) 4 that stores A/D-converted shading distortion, there is also a ROM ('J-only memory) that stores shading distortion that does not include image information in advance. A structure with 5 is adopted.

Since this embodiment is configured as described above, when accurate shading distortion cannot be obtained, that is, when a video signal containing image information is input to the initial value 1, the memory is switched from RAM4 to ROM5. Read out accurate shading distortion from the ROM 5 that stores it. Then, the read shading distortion data is D/'A converted by the D/A converter 6 to obtain reproduced shading distortion, and the comparison circuit 8 compares the sono slice level and the bidet cuff signal. A binarized output 9 can be obtained.

To switch from RAM4 to ROM5, for example, a document sensor such as a microswitch shown in FIG. All you have to do is switch it.

- By adding the ROM 5 in which accurate shading distortion is stored in advance, images can be binarized accurately, and even when a document is inserted halfway through a facsimile machine, partial transfer is possible. can be done.

Furthermore, since the shading distortion of the fluorescent lamp that is the light source does not vary greatly, even if the shading distortion is corrected using the shading distortion stored in ROM 5, there is no significant change, and it is possible to accurately correct the kneading distortion according to the ground density. Even without this, it is possible to obtain a binarized output that is suitable for practical use.

Effects As is clear from the above explanation, according to the present invention, in addition to the memory for A/D converting and storing the peak value of the initial input, a memory is provided in which accurate shading distortion is stored in advance, so that the original is When the initial value input includes an image signal, the memory is switched and the accurate shading distortion is read out to obtain the reproduced shading distortion. Therefore, this reproduced shading distortion is compared with the video signal. Accurate binarized output can be obtained.

[Brief explanation of the drawing]

Figures 1 and 2 are for explaining the conventional structure, Figure 1 is a block diagram of a control circuit, Figure 2 is an explanatory diagram showing an initial value setting method, and Figure 3 is an embodiment of the present invention. FIG. 2 is a block diagram of a control circuit. l...Initial value manually 2...Peak hold circuit 3...A/D converter 4...RAM...RO,
M 6...D/A converter 7...Video power 8...Comparison circuit 9...Output 1
0・Pa Original 12...CCD 13...Back plate 14...Original sensor Fig. 1 Fig. 2 0 Fig. 3 437

Claims (1)

[Claims] It is equipped with a memory that detects a predetermined value of the initial value input, converts it into A/D and stores it, and another memory that stores accurate shading distortion in advance, so that the original is inserted deeply into the edge removal position. , the shading distortion correction method is characterized in that the shading distortion is detected and pre-stored accurate shading distortion is read out, this data is compared with a video input signal, and a binarized output is obtained.