JPS5972863A - Output control method of photosensor - Google Patents

Abstract

PURPOSE:To decide accurately the white and black levels on the basis of a held signal, by detecting the peak value of a video signal sent from a CCD photosensor by holding the signal sent from a reference reflecting plate in case no original exists, and discontinuing said detection of the peak value if an original exists. CONSTITUTION:A reading detector 19 detects the position of an original to decide a reading mode or non-reading mode and then feeds a signal G to a control circuit 10. Then the peak detecting action of a peak holding circuit 6 is turned on and off by a signal G1 in response to the signal G. When an original is not set at its reading position, the light of a fluorescent lamp 1 is reflected by a reference reflecting plate 18. A CCD photosensor 4 detects the peak value of a picture signal, and the circuit 6 performs a detection to control the peak value at a constant level. While an original is read, the detector 19 stops the working of the circuit 6 with the signal G and via the circuit 10. Then the black and white levels are set by the peak value set by the plate 18. Thus the correct decision is possible despite of the continuous black levels.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling the output of a CCD photosensor.

In a COD photo sensor used for facsimiles, etc., the reading time of the sensor output is controlled so that the output peak value is constant, and the black and white level of the target paper surface, etc. is identified based on the reference level corresponding to the peak value.

FIG. 1 shows an example of the configuration of an output control circuit for a CCD photosensor. Information on a document 2 illuminated by a fluorescent lamp 1 is input to a CCD photosensor 4 via a lens 3. The image signal photoelectrically converted by the photosensor 4 is amplified by the amplifier 5 and taken out from the video signal terminal 20. At the same time, the peak value vP of the video signal X is detected and stored by the peak hold circuit 6. A voltage Vr proportional to the difference between this peak value yp and a reference voltage vO set by the resistor R1°R2 is outputted from the differential amplifier 7 and inputted to the comparator 8. The comparator 8 is further inputted with the output of an integrating circuit composed of a resistor R3 and a capacitor C, and its output is FRI.

It is input to the reset terminal of the PUFRO and TUB circuit 9.

The control circuit 10 controls these operations.

FIG. 2 is a time chart showing the operation of this circuit. When the start signal S is output from the control circuit 10, the photosensor 4 starts outputting a photoelectric conversion signal, the transistor TR discharges the capacitor C, and And then, flop 9 is set. The peak hold circuit 6 detects the peak value vp of the video signal X 7, and the differential amplifier 7 detects the voltage Vp.
Output r. On the other hand, after the start signal S turns off, the capacitor C starts charging and its terminal voltage VC increases in proportion to time.

When the comparator 8 becomes vC and Vr, the comparator 8
, the control circuit 10 receiving the reset signal R8 outputs the start signal S again. below,
Repeating the above-mentioned operation, one accumulation time T of the capacitor C at this time is approximately equal to the period of the start signal S. Moreover, when the amount of light from the lens 3 decreases, the peak value vp decreases, and therefore the voltage Vr increases, so that vc>vr
The operation is performed so that the time T for which , , is increased, the amount of light input to the photosensor 4 during one readout is increased, and the peak value vp is increased.

When the amount of light from the lens 3 increases, the opposite operation is performed, and in any case, control is performed such that the peak value of the output of the photosensor 4 is kept constant. Therefore, terminal 20
The black and white level of the video signal X extracted from the video signal can be determined reliably using a fixed standard.

However, this conventional output control method causes a problem when the black level continues for a long time. That is the third
As shown in the figure, during scanning 11 to read the white part of the original 2, the video signal
The peak value is VW in the same figure. However, at the time of scanning 12 to read the dot portion 13 of the original, the black original waveform 16 appears, and the peak value VB at that time must be below the black and white level judgment standard 15, but in reality, the black level is If it continues for a long time, the above-mentioned control will work and the accumulation time T will increase, and the peak value at that time will be the same VW signal 17 as in the white part, and it will be judged as white even though it is at the black level. It will be done.

An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to provide a method for controlling the output of a photosensor that can always perform black and white determination faithfully to the original.

The present invention detects the peak value of the video signal from the CCD photosensor only during the period when a reflector serving as a reference reflecting surface is being read, and controls the output of the CCD photosensor by controlling the accumulation time. The present invention is characterized in that the peak detection is stopped and the black and white judgment level is set based on the reflector reading and the peak value at various times.

Hereinafter, the present invention will be explained in detail using the embodiments shown in FIGS. 4A to 4C. In these figures, the reading detector 19 is
It detects the position of the original and determines whether it is between reading and υ, and its detection signal G is input to the control circuit 10 shown in FIG. The overall circuit in Figure 1 is the same as the conventional one, but
A function has been added to turn on or off the peak detection operation of the peak hold circuit 6 according to the signal G1 using the signal G1. Therefore, Figure 4A before the first two manuscripts are read, and manuscripts 2 and 4.

When the state shown in FIG. 4C is reached after the reading of document A is completed and before the reading of the next document 2B is started, this state is detected by the detector 1.
9 detects and notifies the control circuit 10 by signal G. At this time, the control circuit 10 operates the peak hold circuit 6 using the signal G1 to detect the peak value of the image signal from the CCD photosensor 4 according to the light reflected by the reference reflector 18, thereby keeping the peak value constant as described above. Control is performed to hold this value. On the other hand, the two manuscript authors
When the data is being read as shown in Figure B, the detector 19 notifies the control circuit 10 of this with the signal G, and the control circuit 10
stops the operation of the peak hold circuit 6 by the signal G1. Therefore, when reading a document, the black and white judgment level is set based on the peak value determined by the reflection plate 18.
Correct judgment is possible even if the black levels are continuous.

According to this embodiment, even if there is a completely black part in the middle of the document, it will not be erroneously marked as white, and the document can be read faithfully.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a CCD photosensor output control circuit, and FIG. 2 is a time chart showing the operation of the circuit in FIG. 1.
FIG. 3 is an explanatory diagram of an example of document reading, and FIGS. 4A, 4B, and 4C are explanatory diagrams of an embodiment of the present invention. 1...Fluorescent light, 2...Manuscript, 4...C
OD photo sensor, 6...Peak hold circuit, 10...Control circuit, G...Reading increase detection signal.・ 7 ・ No. 2 wJ No. 3 / 4

Claims (1)

[Claims] 1. Detect the peak value from the CCD photosensor output when the detection target surface is not on the reference reflector, control the peak value to be constant, 2. Hold the constant value, and make sure that the detection target surface is When it is on the reference reflector above,
A photo sensor output control method characterized in that the peak value detection is stopped and the black and white level of the detection target surface is determined based on a determination standard set using the held constant peak value as a basis.