JPS61237577A - Shading-distortion correcting circuit - Google Patents

Abstract

PURPOSE:To correct a shading distortion of large variation with an A/D converter of bits small in number by D/A-converting a reference signal stored in a storage device then synchronizing it with each picture element of original- reading signal, and by inputting it to an A/D converter. CONSTITUTION:The reference signal is generated prior to the reading of the original, which is converted to a digital signal by an A/D converter 1 and is stored in a memory 2. The reference signal Vs stored in the memory 2 has a shading variation of DELTAV in the direction of a line l. When the reading of the original is started, the reference signal in the memory 2 is converted to an analog value by a D/A converter 3, and the resulting analog voltage is synchronized with the original-reading signal, and is supplied to the A/D converter 1 as a reference input Vref. In such way, the A/D converter 1 corrects the shading distortion of the original-reading signal VIN based on the reference signal Vref, and outputs it.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a shading distortion correction circuit capable of correcting shading distortion with large fluctuations without using an A/D converter with a large number of bits.

[Prior art]

As a conventional shading distortion correction circuit, for example, A/
The reference analog signal is digitized by a D converter and then stored in memory (RAM). Then, each pixel of the line sensor is synchronized with the reference signal in the memory, and the digital calculator calculates the following equation. There is a method in which a corrected output Z is obtained by doing so.

(where, Shading distortion caused by irregularities in the response characteristics of the sensor system is stored in advance as a reference signal in the memory. This reference signal and the sensor output signal are synchronized for each pixel using a digital calculator.

By executing the calculation of equation (1), it is possible to obtain an output signal Z with shading distortion corrected. In this case, assuming that the conversion precision of the A/D converter is n bits, the numerical value expressed by digital calculation is 2'''.

Regarding the correction of shading distortion, there is Japanese Patent Application Laid-Open No. 59-175279 (compensation is made by comparing an accurate shading distortion stored in advance with a document reading signal).

[Problem that the invention seeks to solve]

However, in the conventional shading distortion correction circuit,
The range of values that can be expressed is limited depending on the variation included in the reference signal (for example, if the shading variation is ±2□, the value that can be expressed is 211-2), that is, the number of effective bits is limited (n In order to correct shading distortion with large fluctuations, it is necessary to use an A/D converter with a capacity several bits larger than the effective number of bits, which increases the cost of the circuit. There is a problem.

[Means and effects for solving the problems] The present invention has been made in view of the above, and is an A/D with a small number of bits.
In order to be able to correct shading distortion with large fluctuations using a converter, a reference signal is stored in a storage device, then D/A converted to create a reference signal, and this reference signal is converted to A/A. The present invention provides a shading distortion correction circuit that inputs a document reading signal to a D converter in synchronization with each pixel.

〔Example〕

Hereinafter, the shading distortion correction circuit according to the present invention will be explained in detail.

Figure 1 shows an embodiment of the present invention, in which reading information from a line sensor (described later) that reads an image of a document, etc. is manually input as an analog value for each pixel, and this analog value is converted into a digital value. an A/D converter 1 that converts and outputs;
When the line sensor reads the reference surface, the A/D converter 1
a memory (RAM or ROM) 2 that stores a reference signal output from the memory 2; and a D/A converter 3 which converts the reference data read from the memory 2 into a D/A and supplies it to the A/D converter 1 as a reference signal. It consists of

FIG. 2 shows a reading section including a line sensor 11, which includes a reference surface 13 (for example, a white surface) placed at a reading position on a platen 15, a light source 14 such as an LED or fluorescent lamp that illuminates the reading position, and a reading section. A SELFOC lens (rod lens) captures the reflected light from the position reference plane 13 or the original (not shown).
A line sensor 1 receives a read signal via 12 and outputs a read signal.
1.

In the above configuration, a reference signal is created prior to reading an image of a document or the like. That is, the reference plane 13 is read by the line sensor 11, converted into digital data by the A/D converter 1, and then stored in the memory 2.

The reference signal v1 stored in the memory 2 has a shading variation of Δ■ in the direction of line β, as shown in FIG. Stored. When the reading of the reference surface 13 is completed, reading of the original (not shown) sent to the reading position of the platen 15 is started. When the reading of the original is started, the reference data stored in the memory 2 is changed into an analog value by the D/A converter 3.

This analog voltage is applied to the A/D converter 1 as a reference human power □ while being synchronized with the original reading signal.

The A/D converter source reading signal VIN is used as the reference signal VR@
The shading distortion is corrected based on f and a read signal is output.

That is, Z = VIN/V□,・-----1・----
---(2'').In equation (2), VI
When N=VIlof, the maximum number of effective bits for A/D conversion can be obtained. At this time, in the case of an A/D converter with a resolution of n bits, the minimum resolution is V*-r/2fi.

In the present invention, when a 6-bit flash A/D converter is used, a signal of 64 levels can be obtained, taking a sensor with a variation of ±30% as an example. By the way, with the conventional method, you can only take 16 levels. In other words, while the conventional system requires an 8-bit A/D converter, the present invention requires only 6 bits.

〔Effect of the invention〕

As explained above, according to the shading distortion correction circuit of the present invention, after storing the reference data in the memory, the digital value obtained by D/A converting the reference data is given to the A/D converter as the reference signal. Shading distortion with large fluctuations can be corrected using an A/D converter with a large number of bits.

Furthermore, since the number of signal lines can be reduced by reducing the number of bits, the circuit can be made smaller.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention. FIG. 2 is an explanatory diagram showing the reading section. FIG. 3 is an explanatory diagram showing fluctuations in the reference signal. Explanation of symbols 1-----A/D converter 2...Memory 3--D/A converter 11--Line sensor 12--Selfox lens 13.
------・Reference plane 14-・-・-Light source 15
−−−−−・−Platen Patent Applicant Fuji Xerox Co., Ltd. Agent Attorney Shin Matsubara 2 Same as Seiji Muraki Same Same as Tadao Hirata Same Same as Jun Ueshima−

Claims (1)

[Scope of Claims] A shading distortion correction circuit that corrects shading distortion of an image reading signal based on a reference symbol created in advance and outputs a distortion-corrected image signal, comprising: input the reference signal, and convert the image reading signal to A/D based on the reference signal.
An A/D converter converts and performs shading distortion correction;
A memory for digitizing the digital signal by a D converter and storing it as the reference signal, and a D/A conversion circuit for D/A converting the reference signal read from the memory and outputting it to the A/D converter. A shading distortion correction circuit characterized by: