JPS6098765A - Shading correcting device - Google Patents

Abstract

PURPOSE:To attain the shading correction at reading of original in high speed by providing a mode selector and a clock selector and decreasing the clock period at original reading less that that at correcting data write. CONSTITUTION:When the correction data write mode is selected by the mode selector 11 before reading an original, the selector 11 feeds a selection signal to a clock selector 12. The selector 12 selects a clock phi1 having a comparatively longer period and it is fed to an address counter 7, a control circuit 5 and an image sensor drive circuit 13. The circuit 13 drives an image sensor 14 and a light source lighting signal generating circuit 16 by using a drive pulse (f). The circuit 16 lights a light source 17 for a prescribed time, irradiates an original, and the sensor 14 extracts white original information being a reference, amplifies (15) it and inputs it to a programmable attenuator 2. Then a shading correction data is fetched to a memory 6. A picture signal correcting mode is selected from the selector 11 at reading of original, the selector 12 selects a clock phi2 having a short period and the reading of original is performed in high speed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Application) The present invention relates to a shading correction device, and particularly to a shading correction device that can perform shading correction at high speed when reading a document.

(Prior Art) A conventional shading correction device will be explained with reference to FIG. In the shading correction device, the image signal corresponding to the photoelectrically converted reference white portion is compared with the reference level before reading the original, and the correction data for changing the gain 4q for each pit in the main scanning direction is stored in the memory. An operation of writing to (RAM) is performed.

As shown in the figure, when the input image signal of the reference white part is input, the input image signal is transferred to the peak hold circuit 1.
is input to the programmable attenuator 2. The peak hold circuit 1 holds the peak value of the input image signal. The held peak value is subjected to a predetermined attenuation by an attenuator 3, and is set as a reference level. This reference level is input to the comparator 4.

On the other hand, both signals that have passed through the programmable attenuator 2 are input bit by bit to a comparator 4, and compared bit by bit with the reference level from the attenuator 3.

If the bit of the image signal is larger, the control circuit 5 writes a signal of, for example, "1" into the area of the memory 6 corresponding to the bit controlled by the address counter 7. On the other hand, if the bit of the image signal is smaller, a signal of 0'', for example, is written in the area of the memory 6 corresponding to the bit.

The control circuit 5 and the address counter 7 for determining the address of the memory 6 operate in synchronization with the clock output from the clock generation circuit 8.

As described above, the first correction data is written into the memory 6. Next, the second correction data is written into the memory 6 using this correction data.

That is, the first correction data is set in the programmable attenuator 2, and the input image signal is corrected using the correction data. Subsequently, the corrected image signal and the reference level from the attenuator 3 are compared again to determine the magnitude of each bit of the corrected image signal. Then, like the first time, if the corrected image signal is larger, 1'' is written in the area of the memory 6 corresponding to that bit, and if the corrected image signal is smaller, then
Write “O”.

The above operation is repeated a necessary number of times to write data for shading correction into the memory 6.

When the writing of the correction data is completed, the original is read, and the image signal thereof is subjected to shading correction by the programmable attenuator 2 in which the correction data is set. Therefore, the programmable attenuator 2 outputs a corrected image signal that has undergone shading correction.

An example of the timing of writing the above-mentioned correction data into the memory 6 will be explained with reference to the timing chart of FIG. 2. Note that the numbers in FIG. 2 correspond to the numbers in FIG.

In the figure, a is the clock output from the clock generation circuit 8, and b is the output period of the address counter 7. During the period of clock a, programmable attenuator 2 outputs its output C. This output C is compared with a reference level by a comparator 4, and the comparator 4 outputs an output d. Data corresponding to the signal of this output d is written into the memory 6 at the timing of the rise of the memory write signal e.

As described above, the conventional shading correction device has a long cycle time in the correction data writing mode, and requires a relatively slow clock a. On the other hand, in the mode in which the shading of the image signal is corrected using the correction data, only the correction data is read from the memory 6, so the cycle time is shortened.

However, in the past, the same clock was used in the mode for writing correction data before reading the original and in the mode for correcting the image signal after writing the correction data, so when performing high-speed reading, the correction before reading the original The disadvantage was that it was not possible to write the data in time.

(Purpose) The present invention has been made to eliminate the above-mentioned drawbacks, and its purpose is to
It is an object of the present invention to provide a shading correction device that can reliably write data into a memory for shading correction.

(Summary) In order to achieve the above object, the present invention changes the gain for each bit in the main scanning direction while comparing both signals corresponding to a reference white portion photoelectrically converted with a reference level before reading a document. A shading correction device that writes correction data for a memory into a memory and corrects an image signal based on the correction data when reading an original, includes a mode selector and a clock selector that selects a clock based on an output signal of the mode selector. , is characterized in that the clock is slower when writing correction data than when correcting the image signal.

Another feature of the present invention is that the invention further includes means for outputting a light source turn-on signal with a constant pulse width regardless of when writing correction data or correcting an image signal, so that the light source turn-on time is always constant. , the absolute level of the image signal is made equal when writing the correction data and when correcting the image signal.

(Example) The present invention will be described in detail below with reference to the drawings.

FIG. 3 is a block diagram of one embodiment of the present invention.

In the figures, the same reference numerals as in FIG. 1 indicate the same or equivalents. 10 is a main control device, and although only the mode selector 11 and clock selector 12 that are related to the present invention are clearly shown in the figure, it is natural that other circuits are included. The clocks Φ1 and Φ2 selected by the clock selector 12 are sent to the address counter 7 and the control/opening circuit 5, as well as to the image sensor drive circuit 13.

The image sensor drive circuit 13 outputs shift pulses, two-phase drive pulses, reset pulses, etc. to the image sensor 14 composed of a COD, etc.
to drive. The shift pulse [ is a pulse for a shift gate, and during a period when the pulse is at a low level, for example, the gate is closed and a signal charge of the photoelectric conversion unit according to the document information is output to the output circuit 15.

The output circuit 15 consists of an amplifier circuit, and the image signal amplified by the output circuit 15 is sent to the programmable attenuator 2.

The shift pulse "is also sent to a light source lighting signal generation circuit 16. During a period in which the shift pulse f is at a low level, this circuit 16 outputs a light source lighting signal having a constant pulse width shorter than this period. .

Therefore, the light source 17 is always turned on for a certain period of time.

Next, the operation of this embodiment will be explained using FIG. 2.3.4.5. FIG. 4 shows a signal time chart when the correction data stored in the memory 6 is applied to the programmable attenuator 2 to correct the image signal. Figure (b) shows the output 1lI1 of the address counter 7.

Moreover, the same figure (C) shows the output (corrected image signal) of the programmable attenuator 2.

FIG. 5(A) shows the image sensor shift pulse [and the light source turn-on signal Q] when writing correction data, and FIG. 5(B) shows the image sensor shift pulse [when correcting the image signal].
' and a light source lighting signal g' are shown.

Before reading the original, the mode selector 11 selects the correction data writing mode. The mode selector 11 sends a selection signal for the mode to the clock selector 12. As a result, a clock l (clock a in FIG. 2) having a relatively long period is selected. Clock Φ12 is sent to address counter 7, control circuit 5, and image sensor drive circuit 13.

The image sensor 1 drive circuit 13 drives the image sensor 14
Then, the shift pulse t12-phase drive pulse, reset pulse, etc. shown in FIG. 5 (A>) are outputted to drive the image sensor υ14.

The shift pulse is also sent to a light source turn on signal generation circuit 16, which outputs a light source turn on signal with a pulse width T+. As a result, the light source 17 is turned on for a time T1 and illuminates the original.

Before the document is read, as described in the related art section, the document corresponding to the reference white portion is irradiated with light from the light source 17. Therefore, the image sensor 14 picks up reference white document information and undergoes photoelectric conversion. Thereafter, the signal is amplified by the output circuit 15, becomes an image signal, and is input to the programmable attenuator 2.

After this, the operation of loading the shading correction data into the memory 6 is the same as described in the section of the prior art, so the explanation will be omitted.

Next, when reading a document, the image signal correction mode is selected by the mode selector 11. The clock selector 12 receives a signal from the mode selector 11 and selects a clock Φ2 having a shorter cycle than the clock Φ1. A in FIG. 4 shows this clock Φ2. Note that Figures 2 and 4 are drawn to the same scale.

This clock Φ2 is input to the address counter 7 and the control circuit 5. The address counter 7 outputs the address to the memory 6 during the period shown in FIG. The correction data stored in the memory 6 is read out using this address and set in the programmable attenuator 2. The programmable attenuator 2 outputs a corrected image signal during the period shown in FIG.

That is, since the image signal is corrected based on the clock Φ·2, the shading correction operation of the image signal is performed at high speed.

On the other hand, the image sensor driving circuit 13 receives the clock 2 and outputs an image sensor → no shift pulse r' having a pulse width shorter than the pulse width shown in FIG. 5(A). The sensor 14 outputs a signal charge to the output circuit 15 during the pulse f'.The shift pulse r' is also input to the light source turn-on signal generation circuit 16.

The circuit 16 outputs a light source turn-on signal g' having the same pulse width Ts as the light source turn-on signal Q shown in FIG. Therefore, the light source 17 is turned on for the same period as when the correction data is taken in before reading the document, that is, for the time T1.

As is clear from the above description, in this embodiment, the clock Φ1 with a relatively long cycle is selected in the correction data writing mode, and the clock Φ2 with a relatively short cycle is selected in the image signal correction mode.

Therefore, it is possible to achieve both high-speed document reading and reliable writing of correction data to the memory.

Furthermore, in this embodiment, the light source lighting signal generation circuit 16 is provided so that the lighting time of the light source 17 is equal in the image signal correction mode and the correction data writing mode, so that the clock signal is Even if the charge integration time in photoelectric conversion of the image sensor 14 differs by switching, the absolute level of the output image signal can be made equal.

(Effects) As is clear from the above description, according to the present invention, the following effects are achieved.

It is possible to speed up shading correction, and to reliably store data for shading correction in memory.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a conventional shading correction device.
Fig. 2 is a time chart when inputting correction data for the main part of the signal, Fig. 3 is a block diagram of an embodiment of the present invention, Fig. 4 is a time chart of the signal when correcting the image signal,
FIGS. 5A and 5B are time charts of the shift pulse and the light source turn-on signal when writing correction data and when correcting both signals, respectively. 10... Main control device, 11... Mode selector, 1
2...Clock selector, 13...Image sensor drive circuit, 16...Light source lighting signal generation circuit Patent attorney Michito Hiraki and 1 other person

Claims (1)

[Claims] (1) Before reading the original, the image signal corresponding to the photoelectrically converted reference white area is compared with the reference level, and correction data for changing the gain for each bit in the main scanning direction is written in the memory. , a shading correction device that corrects an image signal based on the correction data, comprising a mode selector and a clock selector that selects an O according to an output signal of the mode selector,
A shading correction device characterized in that a clock is made slower when writing correction data than when correcting an image signal. (2) Before reading the original, the image signal corresponding to the photoelectrically converted reference white part is compared with the reference level, and correction data for changing the gain for each pit in the main scanning direction is written in the memory, and when reading the original, In a shading correction device that corrects both signals based on the correction data,
A mode selector, a clock selector that selects a clock based on an output signal of the mode selector, and means for outputting a light source lighting signal with a constant pulse width regardless of when correction data is written or when correcting an image signal. A shading correction device characterized in that a clock is set slower during writing than when correcting an image signal, and the lighting time of a light source is always constant.