JPH057913B2 - - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for correcting shading distortion, and more particularly to a method for correcting shading distortion during image reading by a facsimile device or the like.

PRIOR ART Correction of shedding distortion in conventional facsimile apparatuses was performed by a correction circuit as shown in FIG.

In Fig. 1, the reference numeral 1 indicates an initial value input, and this input signal is input to a peak hold circuit 2 that detects the peak value, detects the peak value of the input video signal, and uses this peak value as a reference. It 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 video input 7, converted into an analog signal by the D/A converter 6, and input to the comparison circuit 8.

In this way, the shading distortion corresponding to the ground density of the original is reproduced, and compared with the video input signal in the 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, a CCD (Charge Coupled Device)
Since the device 12 reads the data and sets the initial values, if the document 10 is inserted deeply so as to block the white backing plate 13, image information such as "ABC" will also be read, and this image information will be lost. Since it is included in the video signal, it is not possible to set accurate initial values, and it becomes impossible to accurately binarize the image.
With facsimile machines, it is not possible to partially transfer a document from the middle.

Purpose The present invention was made in order to eliminate the above-mentioned drawbacks of the conventional technology, and it is possible to obtain accurate shading distortion even when a video signal containing image information is input when setting initial values. It is an object of the present invention to provide a shading distortion correction method configured to obtain an accurate binarized output.

Embodiments Hereinafter, details of the present invention will be explained based on embodiments shown in the drawings.

FIG. 3 illustrates an embodiment of the present invention.
Components in the figure that are the same as those in FIG.

In this embodiment, a ROM (read only memory) 5 is provided in which shading distortion that does not include image information is stored in advance, along with a RAM (random access memory) 4 that stores A/D converted shading distortion. The structure has been adopted.

Since this embodiment is configured as described above,
If accurate shading distortion cannot be obtained, that is, if a video signal containing image information is input to initial value input 1, the memory can be moved from RAM4 to ROM.
I switched to 5 and memorized the exact shading distortion.
Read from ROM5. The read shading distortion data is then D/A converted by a D/A converter 6 to obtain reproduced shading distortion, and the slice level and the signal of the video input 7 are compared by a comparison circuit 8 and binarized. Output 9 can be obtained.

Switching from RAM4 to ROM5 uses a document sensor such as a micro switch shown in FIG. Just do it.

In this way, by adding the ROM 5 in which accurate shading distortion is stored in advance, images can be binarized accurately, and partial transfer can be performed even when a document is inserted halfway through a facsimile machine. can.

Furthermore, since the shading distortion of the fluorescent lamp that is the light source does not vary greatly, even if shading distortion is corrected using the shading distortion stored in the ROM5, there is no significant change, and accurate shading distortion correction that matches the ground density can be performed. Even without this, it is possible to obtain a binarized output that is suitable for practical use.

Effects As is clear from the above description, according to the present invention, in a shading distortion correction method for a reading device that is capable of partially reading a document from the middle, the insertion state of the document is detected and the document is read in a partial manner. If it detects that it has been inserted deeper than the specified position,
The image signal of the read original is corrected for shading distortion based on data in a memory in which data of predetermined shading distortion is stored in advance.On the other hand, if it is not detected that the original is inserted deeper than the predetermined position, Before reading the original, a uniform density reference member at the reading position is read to generate shading distortion data, and based on the obtained shading distortion data, the shading distortion of the image signal of the read original is corrected. Optimal shading distortion correction can be performed when reading the original image from the leading edge of the original, and shading distortion correction can also be performed when reading the original image from the middle of the original, resulting in a high-quality output image in both cases. This excellent effect 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 illustration of an embodiment of the present invention. FIG. 3 is a block diagram of a control circuit. 1...Initial value input, 2...Peak hold circuit, 3...A/D converter, 4...RAM, 5...
ROM, 6...D/A converter, 7...video input, 8...comparison circuit, 9...output, 10...original, 12...CCD, 13...back plate, 14...original sensor.

Claims (1)

[Scope of Claims] 1. In a shading distortion correction method for a reading device that is capable of partially reading a document from the middle, the insertion state of the document is detected, and the document is inserted deeper than a predetermined position for partial reading. If this is detected, the image signal of the read original is corrected for shading distortion based on data in a memory that stores predetermined shading distortion data, and on the other hand, it is determined that the original has been inserted deeper than the predetermined position. is not detected, before scanning the document,
A shading distortion characterized in that shading distortion data is generated by reading a reference member having a uniform density at a reading position, and shading distortion correction of an image signal of a read document is performed based on the obtained shading distortion data. Correction method.