JPH0330575A - Shading corrector - Google Patents

Abstract

PURPOSE:To provide a shading corrector, which is profitable in the manner of cost and does not reduce the dynamic range of a signal by conversion even in the case of coarse adjustment, by executing shading correction along data stored in a RAM by utilizing a D/A converter for a video band. CONSTITUTION:An analog signal is amplified by an amplifier 2 and level- converted. Then, the signal is converted to a digital signal by an A/D converter 3, picture-processed and edited by processing blocks in rear steps. Further, the signal is transmitted, recorded and stored. A control part 9 applies the output of a constant voltage source 6 as a converting reference voltage to the A/D converter 3 by a synchronizing signal to be generated when reflected light is made incident from a reference white board 12 to a CCD 1. At such a time, a digital converting output from the CCD 1 is stored in a RAM 7 for one line. When the synchronizing signal is inactive, sampled data are applied as a reference voltage from the RAM 7 through a D/A converter 5 to the A/D converter 3. Thus, the nonuniformity of the output caused by the dispersion of CCD picture element sensitivity and the nonuniformity of an optical system can be corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a shading correction device in an image reading section of a facsimile machine, digital copying machine, etc.

[Conventional technology]

Conventionally, as a shading correction device, correction data for each pixel is stored in RAM, and during operation, the pixel output value and the correction value of the corresponding pixel obtained from RAM are used to access the memory that stores the converted value and obtain the correction data. The technology is known.

This conversion table memory usage method is common and cost-effective, so it is currently employed in the majority of devices on the market.

[Problem that the invention aims to solve]

However, in a digital copy machine, etc., if 20CPS40
In a 0 dpi (7) device, a high-speed conversion ROM with an access time of about 80 ns is required, and an 8-bit conversion ROM requires a somewhat large capacity.

In addition, according to this method, when calculating the value to be stored in the conversion memory, when the maximum value of the stored data (value when reading the reference white board) deviates from the planned value, the dynamic range of the converted data will decrease. do.

In other words, if the initial adjustment (for example, setting the output value when reading the reference white board to the target value) is not performed accurately, the performance of the device itself will deteriorate.

An object of the present invention is to provide a high-performance shading correction device that allows easy initial adjustment work.

[Means to solve the problem]

The above object includes a first conversion means for converting an analog output of a photoelectric conversion element into a digital value, a storage means for storing one line of digital conversion output of the photoelectric conversion element, and a storage means for storing digital data stored in the storage means. This is achieved by a second conversion means for converting into an analog signal, and a control means for supplying the output of the second conversion means as a conversion reference voltage to the first conversion means.

[Effect]

One line of digital data stored in the storage means is stored in the second
It is converted into an analog signal by the conversion means, and fed back again as a conversion reference voltage of the first conversion means that converts the analog output of the photoelectric conversion element into a digital value.

Therefore, since the correction operation is performed according to the value stored in the storage means, there is no reduction in the dynamic range of the signal due to conversion even with coarse adjustment.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

Figure 2 is a configuration diagram of the optical system of a copying machine, where I is a CCD.
(photoelectric conversion element), 11 is a movable contact glass, 12 is a reference white plate provided in the non-image area of contact glass II for density adjustment, and 13 is contact glass 1
1 with a two-page spread! ! 2 The manuscript placed, work 4 is the light source, 1
5, 16, and 17 are mirrors; 18 is an imaging lens; the original image is projected onto the CCD 1 and converted into an analog voltage by photoelectric conversion;

FIG. 1 is a block diagram of a shading correction device according to the present invention, in which a CCD 1 is driven by a clock;
Outputs an analog signal according to the amount of light received. This analog signal is amplified and level-converted by amplifier 2, and A/
The digital signal is converted into a digital signal by the D converter (first conversion means) 3, subjected to image processing 9 and edited by a subsequent processing block (not shown), and further transmitted, recorded, and stored.

5 is a D/A converter (second conversion means), 6 is a constant voltage source,
7 is a RAM (storage means) that stores one line of digital data from the CGDI.

Further, the control unit (control means) 8 controls the blocks within the dotted line as follows using a synchronization signal generated when the contact glass 11 reaches the position shown in FIG. 2 and the reflected light from the reference white plate 12 enters the CCD 1. to control.

Mode ■ Correction data sample when the synchronization signal is active) The control unit 8 sets the switches 31 and 32 to the positions shown in the figure (the signal flow is on the ■ side), and sends the output of the constant voltage source 6 to the A/D converter 3. The digital conversion output from the CCD 1 at this time is stored in the RAM 7 for one line.

Mode ■ When the synchronization signal is inactive (correction operation) Switch 3
1. With S2 on the opposite side of the figure (the signal flow is on the ■ side), data sampled in mode ■ is applied from the RAM 7 to the A/D converter 3 through the D/A converter 5 as a reference voltage.

Writing and reading operations to and from the RAM 7 in the above modes (1) and (2) are performed in synchronization with the CCD drive clock.

Assuming that the output of pixels PI and P2 when reading the reference white board is a digital value of 100.120, the conversion reference voltage given to the A/D converter 3 during actual image reading will be Since the P1 reading is 120/100°, that is, 20% increased, the A/D conversion value becomes 100/120, and it is possible to correct COD pixel sensitivity variations and output non-uniformity due to optical system unevenness.

Note that a line memory may be used as the RAM 7 by providing a rewrite loop during reading.

Furthermore, the conversion reference voltage supplied by the latch S2 in mode (2) may be supplied to the D/A converter 5 as a fixed digital value.

〔Effect of the invention〕

As explained above, according to the present invention, R
Since shading correction is performed according to the data stored in the AM, it is advantageous in terms of cost, and even with 111 adjustment,
It is possible to provide a shading correction device that does not reduce the dynamic range of a signal due to conversion.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of a shading correction apparatus according to the present invention, and FIG. 2 is a configuration diagram of an optical system of a copying machine. 1...CCD, 3...A/D converter, 5...D/
A converter, 7...RAM, 8...control unit.

Claims (1)

[Claims] a first conversion means for converting an analog output of the photoelectric conversion element into a digital value; a storage means for storing one line of digital conversion output of the photoelectric conversion element; and a conversion means for converting the digital data stored in the storage means into an analog signal. 1. A shading correction device comprising: a second conversion means for converting the second conversion means; and a control means for supplying the output of the second conversion means as a conversion reference voltage to the first conversion means.