JPH04185076A - Shading correction device - Google Patents

Abstract

PURPOSE:To make a high tension side digital finely at the time of obtaining the data for shading correction and to improve the accuracy of shading correction by varying the range of the reference voltage of an A/D converter. CONSTITUTION:At the time of storing data for correction in a RAM4, a variable gain amplifier 2 is turned to a through state, and a switch 5 is on a +2.5V side. When a white original is read by a CCD1, a reference voltage is turned to +5 to +2.5V for digital in an A/D converter 3. In short, the data for fine correction for high-tension side easily causing shading distortion is obtained. Then, when the reading of the original is performed while returning the variable gain amplifier 2 to a normal mode and being the switch 5 on an OV side, the data for correction to be outputted from the RAM 4 changes finely to attain high accuracy shading correction.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a shading correction device in an image reading device such as a facsimile machine or an electronic copying machine.

(Prior Art) Conventionally, in an image reading apparatus, a document is irradiated with a light source such as a fluorescent lamp, and the reflected light is photoelectrically converted by an image sensor such as a CCD. However, the amount of light from the light source is not uniform in the length direction, and when reading a white document, the conversion characteristics have shading distortion as shown in Figure 3, where the light source is low at both ends and high in the center. can get.

Therefore, conventionally, a shading correction device as shown in FIG. 4 has been provided. In other words, white originals etc. are CC
The signal V1 read by the D image sensor 1 is
First, the variable gain amplifier 2 is put into a through state (VI=■o) and is applied to the A/D converter 3. A reference voltage of OV, +5V is applied to the A/D converter 3, and 4-bit digitization is performed within this range. The digitized data is stored in RAM4. By sequentially performing the above operations in the main scanning direction, correction data for each bit in the main scanning direction is stored in the RAM 4.

The output of RAM4 is 4 bits. On the other hand, the variable gain amplifier 2 divides the output of the CCD image sensor 1 using the data given from the RAM 4 as a divisor, changes the gain, and performs shading correction. Then, the position in the main scanning direction of the signal output from the CCD image sensor 1 (the i-th bit) and the position in the main scanning direction of the correction data read from the RAM 4 (the i-th bit)
A clock is given to each part so that the clocks match.

Incidentally, the input terminal for the divisor data of the variable gain amplifier 2 has 5 bits, which is more than the 4 bits output from the RAM 4.

Therefore, as shown in the figure, data "0" is given to the least significant bit to perform division. For example 1, D=10110 (2)
=22(10) then vo=32/22 VI.

D ” 11011 (2) When =26(1o), V
A conversion called o=32/26 VI is performed. As mentioned above, since division is performed by giving data "0" to the least significant bit, if the data in RAM 4 is as shown in FIG. ) is simply used as a divisor, and the resolution is 4 bits despite the variable gain amplifier 2 having 5 bits.

(Problems to be Solved by the Invention) As described above, according to the conventional shading correction device,
The number of bits of the input terminal of the divisor data of the variable gain amplifier is A
/D converter output bits, the resolution is A.
Since the method of use is adapted to match the output bit number of the /D converter, a problem has arisen in that shading correction cannot be performed with high accuracy.

The present invention was made in view of the problems of the conventional shading correction device as described above, and an object thereof is to provide a shading correction device that can perform shading correction with high precision.

[Structure of the invention]

(Means for Solving the Problems) The present invention includes a memory in which shading correction data is stored, a variable gain amplifier that divides and amplifies the output of an image sensor based on the output of the memory, and this variable gain amplifier. digitizes the output and provides it to the memory,
A shading correction device was constructed by including an A/D converter that outputs an output signal from the device, and voltage variable means that varies the reference voltage range of the A/D converter.

Furthermore, the present invention includes a memory in which shading correction data is stored, and a variable gain amplifier that divides and amplifies the output of the image sensor based on the output of the memory, the lower bit side of the divisor data input terminal A variable gain amplifier to which the output of the memory is given from and data "1" is given to the remaining upper bits; /D converter to constitute a shading correction device.

(Function) According to the shading correction device having the above configuration, since the reference voltage range is variable, the reference voltage range is set to the high potential side when reading a white original, etc. in order to obtain data for shading correction. do,
Perform fine A/D conversion on the range where shading distortion occurs,
The accuracy of correction can be improved.

Furthermore, according to the shading correction device according to the present invention,
The output of the memory storing the shading correction data is applied from the lower bit side of the input terminal of the divisor data of the variable gain amplifier, and the data r1. , so to speak, the shading correction data is provided with a raised level, and can approach the resolution of the bit number of the input terminal of the divisor data.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 shows the configuration of an embodiment of the present invention, and the components used are a CCD image sensor 1, a variable gain amplifier 2.
A/D converter 3. The configuration of RAM 4 is the same as that shown in FIG. However, although the maximum value of the reference voltage of the A/D converter 3 is fixed at +5V, the minimum value of the reference voltage can be selected between 0■ and ±2.5■ by the switch 5. It is configured.

Furthermore, the 4-bit output of the RAM 4 is allocated from the lower bit side of the divisor data input terminal of the variable gain amplifier 2,
The remaining bits of the divisor data input terminal of variable gain amplifier 2 (
Here, data "1" is given to the most significant bit.

In the shading correction device configured as above,
Initially, in order to store the correction data in the RAM 4, the variable gain amplifier 2 is set to the through state, and the switch 5 is set to +.
Set it to the 2.5V side. In this state, hold a white original, etc.
It is read by the CD image sensor 1. Then, A/D
The converter 3 sets the reference voltage to +5V to +2.5V and performs 4-bit digitization within this range. That is,
As shown in Figure 3, shading distortion occurs on the high voltage side (at least in the 50% range), so by narrowing the range to this range, narrower correction data can be obtained, and this correction data is stored in RAM4.

Next, the variable gain amplifier 2 is returned to the normal mode, the switch 5 is turned to the 0■ side, and the document is read. Then, the 4-bit correction data outputted from the RAM 4 is data that changes in the main scanning direction as shown in FIG.
), the part shown by the broken line is raised (because the most significant bit is set to "1"). Therefore, conventionally (10)' (10),...
The correction data changed by 3129 is 3130 (10) = (10)・”°to' I J tsutsu,
The shading changes more precisely, and this correction data is used to perform more accurate shading correction.

Note that the number of bits in the embodiment is only an example, and the value of the reference voltage is also only an example. Therefore, other numerical values may be used. Further, in the embodiment, a -dimensional image sensor is assumed, but a two-dimensional image sensor may be used. In this case, reading in the main scanning direction as explained using FIG. The data read by the cell may be corrected with a variable gain amplifier.

Further, it is effective to use either the switch 5 or the configuration in which data "1" is given to the upper bit side of the divisor data input terminal.

〔Effect of the invention〕

As explained above, according to the present invention, since the range of the reference voltage of the A/D converter can be made variable, the high voltage side can be finely digitized when obtaining data for shading correction, and highly accurate shading correction can be performed. It can be done.

In addition, correction data is applied from the lower bit side of the input terminal of the divisor data of the variable gain amplifier, and the remaining upper bits are
1'', shading correction can be performed with higher precision than before without reducing resolution.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is a diagram showing how divisor data changes depending on the embodiment, Fig. 3 is a diagram showing shading distortion, and Fig. 4 is a diagram showing conventional shading correction. FIG. 5, a block diagram of the apparatus, is a diagram showing how divisor data changes according to a conventional example. 1... COD image sensor 2... Variable gain amplifier 3... A/D converter 4
...RAM 5...Switch agent Patent attorney Book 1) Takashi Figure 1 Figure 3

Claims (2)

[Claims] (1) A memory in which shading correction data is stored, a variable gain amplifier that divides and amplifies the output of the image sensor based on the output of the memory, and digitizes the output of the variable gain amplifier and provides it to the memory. With,
A shading correction device comprising: an A/D converter that outputs an output signal from the device; and voltage variable means that varies a reference voltage range of the A/D converter. (2) a memory in which shading correction data is stored; and a variable gain amplifier that divides and amplifies the output of the image sensor based on the output of the memory, the memory starting from the lower bit side of the divisor data input terminal. a variable gain amplifier to which an output is given and data "1" is given to the remaining upper bits, and an A/D conversion which digitizes the output of the variable gain amplifier and supplies it to the memory, and also makes it an output signal of the device. A shading correction device comprising: