JPS59219069A - Reader of original - Google Patents

Abstract

PURPOSE:To improve the correction of shading distortion even just after the lighting of a light source by changing over the lower limit of the correcting range of shading distortion into >=2 stages in a reader used for a facsimile device. CONSTITUTION:A voltage Vr is set so that the relation of voltage Vp proportional to a peak value < reference voltage Vr is obtained when a peak value of a pictue signal is less than a threshold value lower than the peak value at steady-state value at normal temperature and the relation of Vp>=Vr when the peak value exceeds the threshold value, the lower limit value of the correcting range is changed over to C1 just after lighting and to C2 after the lighting. When the calculation and storage of the correcting coefficient is finished, an original 2 is fed in front of a white reference plate 1 and scanned by a CCD image sensor 4, and an original picture signal and the correcting coefficient read from a memory 10 are multiplied. Since the correcting coefficient of the correcting range with the low lower limit value C1 just after the lighting of a fluorescent light 3 and that of a high lower limit value C2 at steady-state at normal temperature are outputted respectively from the memory 10, a picture signal applied with proper correction for shading distortion at all times is outputted from a multiplier 9.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a document reading device that can be used in a facsimile machine, etc., and more specifically, it corrects shading distortion by reading a white reference plate prior to reading the document. The present invention relates to an original reading device that calculates a coefficient and uses the correction coefficient to correct shading distortion of an image signal when reading an original.

Structure of a conventional example and its problems FIG. 1 is a schematic block diagram showing a conventional example of a document reading device used as a document reading section of a facsimile machine.

In this figure, reference numeral 1 denotes a white reference plate, in front of which the original 2 passes.Although there is a means for moving the original 2, it is not shown in the figure. Reference numeral 3 denotes a fluorescent lamp that illuminates the surface of the document 2 on which the white reference plate 1 is placed.

This is a COD image sensor that scans the original 2 by one inch on a 4fd white reference plate and outputs an image signal. Light (image) emitted from the fluorescent lamp 3 and reflected by the white reference plate 1 or the surface of the original 2
is imaged on the light receiving surface of the CCD image sensor 4 via the lens system 5, and photoelectrically converted into an image signal. This image signal is amplified by an amplifier 6, and further converted into a digital signal by an analog/digital converter (ADC), and then
It is input to ROM8 and multiplier (MLY)9.

The ROM 8 functions as a calculation means for calculating a correction coefficient for shading distortion correction, and the correction coefficient M is calculated from the address specified by the input image signal using the following formula.
Output i.

I i X M i /2N=C, -=- (1) Here, 19 is the number of quantization bits, and 1 is the level of the first same pixel of the input image signal. Since C is a constant value, the shading distortion correction described later acts effectively on image signals above this level. That is, C is the lower limit value of the shading distortion correction range.

10 is a RAM having a storage capacity capable of storing correction coefficients for one scanning line. Before the document 2 is sent, the white reference plate 1 is scanned by the CCD image sensor 4.
During this period (+-learning mode period), the RAM 10 operates in the write mode, reads the correction coefficient Mi output from the ROM 8, and stores it at address i. When the storage of the correction coefficient M1 for one scanning line is completed, the training mode ends and the RAM 10 switches to the read mode.

Next, the feeding of the original 2 starts, and the CCD image sensor 4 starts scanning the original. The RAM 10 sequentially reads the correction coefficient M1 in synchronization with the output timing of both signals, and the multiplier 9
Enter. This multiplier 9 multiplies the image signal by the correction coefficient M1, and outputs an image signal whose shading distortion has been corrected.

Here, since Ml/2N≦1, the above multiplication is essentially a division, and the image signal level output from the multiplier 9 is always equal to or lower than the input image signal level.

That is, the level of an image signal below the lower limit value C of the shading distortion correction range cannot be raised by the above multiplication. Note that the upper limit value of the shading distortion correction range is the reference voltage of the analog/digital converter 7.

Conventionally, the shading distortion correction range is always fixed, and the lower limit C is generally set to a level approximately 6Q related to the upper limit. As a result, immediately after the fluorescent lamp 3 is turned on, there is a problem in that the aging distortion correction of the image signal cannot be performed satisfactorily.

This is a fluorescent light immediately after it is turned on compared to when it is stable at room temperature.

This is because the level of the image signal, which is the photoelectric conversion output of the CCD image sensor 4, falls below the lower limit value C of the correction range due to insufficient light quantity.

In order to deal with this problem, it is conceivable to set the lower limit value C of the correction range to a sufficiently small value (for example, to 25% of the upper limit value). If this is done, the problem regarding the 7 aging distortion correction immediately after lighting will certainly be solved. However, on the other hand, since the calculation error (C/2N) increases, a new problem arises in that when the fluorescent lamp 3 is stable at room temperature, the image quality after correction becomes unstable and the readout value decreases. It will happen.

In this specification, the term shading distortion is used as a general term for image signal distortion caused by uneven light intensity of the fluorescent lamp 3, distortion of the lens system 6, sensitivity variation among pixels of the CCD image sensor 4, etc. ing.

OBJECT OF THE INVENTION The present invention solves the above-mentioned problems of the conventional art.It is an object of the present invention to correct the aging distortion without degrading both read values when the light source for document illumination is stable at room temperature, and even immediately after the light source is turned on. It is an object of the present invention to provide a document reading device that can obtain such image signals.

Structure of the Invention The present invention is configured such that the correction coefficient calculation means is configured to switch the lower limit value of the correction range of shading distortion in two steps, 1 and 4J, and the peak value of both signals obtained by scanning a white reference plate. The above object is achieved by providing means for detecting the peak value detected by this means, and means for switching and specifying the lower limit value of the correction range for the correction coefficient calculating means according to the peak value detected by this means. DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 2 is a schematic block diagram showing a document reading device according to an embodiment of the present invention. In this figure, the same parts as in FIG. 1 are given the same reference numerals.

A peak hold circuit 11 detects and holds the peak value of the amplified image signal by the amplifier 6 and supplies a voltage vP proportional to the peak value to one input of the comparator 12. This comparator 12 functions as a means for switching and specifying the lower limit value of the correction range, and a reference voltage Vr is applied from a reference power supply 13 to the other input. The output signal of the comparator 12 is applied to the address input of the ROM 14 together with the image signal digitized by the analog/digital converter 7.

The ROM 14, like the RO'M8 in FIG. 1, functions as a calculation means for calculating the correction coefficient Mi for shading distortion correction. However, this ROM 14 differs from the ROM 8 of FIG. 1 in that the lower limit value of the correction range switches between 01 and 02 depending on whether the output signal of the comparator 12 is logic "o" or logic "1".

In other words, when the Lebel image signal is input, the comparator 12
When the output signal is logic “o”, I i xMi
/2N= C1-=, when the correction coefficient M1 calculated by the formula (2) is output and the output signal of the comparator 12 is logical °°1°', -IiXMi/2 -C2... The correction coefficient M i f calculated by the equation (3) is output.

The above-mentioned C1 and C2 have a relationship of C1<C2, and for example, C1 is selected at a level of 26% and C2 is selected at a level of 60% with respect to the upper limit of the correction range.

Next, the operation will be explained.

Prior to reading the original, the peak hold circuit 11 is reset, and then the white reference plate 1 is scanned twice or more by the CCD image sensor 4, and the peak value of the image signal is detected and held by the peak hold circuit 11. . The comparator 12 outputs a logic "o" when V p (V rO), ■P
When ≧Vr, a logic pulse 1°' is output. The ROM 14 outputs the correction coefficient Mi determined by the above equation 2 or 3 from the address specified by the image signal input from the analog/digital converter 7 and the output signal of the comparator 12.

However, until the first scan is completed, ■P is not determined, so the correction coefficient k output from RO1vi14
l i is invalid and is not written to RAM1o.

When the white reference plate 1 is scanned for the second time, the RAM 1° is switched to the write mode, and the correction coefficients 1vli output from the ROItf 14 are sequentially written to addresses lK. When the writing of the correction coefficient Mi for one scanning line is completed in this way, the RAM 10 is switched to the read mode.

Here, the relationship between the reference voltage Vr and the peak value of the image signal will be explained.

FIG. 3 is a characteristic diagram showing temporal changes in the image signal peak value when the white reference plate 1 is continuously scanned from the time when the fluorescent lamp 3 is turned on. The horizontal axis indicates elapsed time (seconds), and the vertical axis indicates the peak value of the image signal relative to the peak value when the temperature is stable at room temperature.

As is clear from this figure, the light intensity of the fluorescent lamp 3 does not rise sufficiently for several minutes immediately after lighting, so the peak values of both signals are considerably lower than when the temperature is stable at room temperature. For this reason, as mentioned above, if the lower limit of the correction range is set and fixed to the stable Tobehata conditions, shading distortion of the image signal will occur immediately after lighting.
(il- This means that it could not be corrected appropriately.

In order to solve this kind of inconvenience, a false death occurs when the peak value of the image signal or the peak value when stable at room temperature is less than a certain threshold value, and when the same threshold value is exceeded, P≧V
The reference voltage Vr is set to be r, and the lower limit of the correction range is set to d, c1 immediately after lighting, and the harpoon is switched to C2.

If) u: The operation will be explained with full reference to FIG.

After completing the calculation and storage of the correction coefficient as described above,
A document 2 is sent in front of a white substrate 1 and scanned by a CCD image sensor 4, and a multiplier 9 multiplies both signals for the document image with a correction coefficient read out from a RAM 10 in synchronization with the output timing. be done. If it is immediately after the fluorescent lamp 3 is turned on, the lower limit value C1 as described above is set.
A correction coefficient for the correction range of C2 is output from the RAM 10, and if it can be considered as a stable state at room temperature, a correction coefficient for the correction range with the higher lower limit value C2 is output from the RAM 10. Therefore, irrespective of the state of the -C1 fluorescent lamp 3, an image signal that has undergone appropriate shading distortion correction is always outputted from the multiplier 9. Ilc, the lower limit value C2 of the correction range at a time point that can be considered stable at room temperature can be determined according to the image signal level at that time, so the image quality can be fixed at a lower lower limit value according to the moxibustion condition immediately after lighting. There is no problem of deterioration.

Note that in this practical example, the lower limit value of the correction range was changed to two levels, but by providing two or more comparators 12, for example, the lower limit value of the correction range could be changed to three levels depending on the image signal peak value.
Cut more than the stage! ll may be changed. Further, an arithmetic circuit may be used instead of the ROM 14 as a stage for calculating the correction coefficient.

Furthermore, shading distortion correction operations are not limited to multiplication. To further clarify, the image sensor is not limited to a CCD image sensor.

Effects of the Invention As described above, the present invention detects the peak value of an image signal when a white reference plate is scanned prior to scanning a document using a peak value detection means, and performs shading using a lower limit value switching means to set the peak value to the peak value. The lower limit value of the distortion correction range is switched, the correction coefficient corresponding to the lower limit value is calculated by the correction coefficient calculation means and stored in the storage means, and the correction coefficient is used to perform shading distortion correction on both signals when scanning the original. First, read the light source for document illumination when it is stable at room temperature! This has the effect that good signals free of 7+ distortion can be obtained immediately after the light source is turned on without deteriorating the 7+ value.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram showing a conventional example of a document reading device;
Fig. 2 is a schematic block diagram (not showing a document reading device) according to an example of the present invention, and Fig. 3 is a blank image that appears when the white reference plate is continuously scanned from the time when the light source for illuminating the document is turned on. FIG. 3 is a characteristic diagram showing temporal changes in signal peak values. 1... White reference board, 2... Manuscript, 3 Old...
Fluorescent lamp, 4... CCD image sensor, 5... Lens system, End... Analog/digital converter,
9... Multiplier, 10... RAM, 11...
...Peakhold circuit, 12...Comparator, 14...FtOM.

Claims (1)

[Claims] a light source that illuminates the white reference plate or a document sent in front of the white reference plate; an image sensor that scans the white reference plate or the document and outputs an image signal; A peak value detection means for detecting the peak value of the image signal output from the sensor, and a lower limit for specifying the lower limit value of the shading distortion correction range of the image signal by switching it to two or more levels according to the peak value detected by the peak value detection means. a value switching means, and a correction for correcting shading distortion of an image signal having a level equal to or higher than the lower limit specified by the lower limit value switching means from the image signal output from the image sensor while scanning the white reference plate. During the scanning of the white reference plate, the correction coefficient calculation means calculates the coefficient. a rewritable storage means for reading and storing the calculated correction coefficients and reading out the stored correction coefficients in synchronization with the output of an image signal from the image sensor during scanning of the original document; shading distortion correction calculation means for outputting an image signal with soning distortion corrected by executing a specific calculation using the image signal output from the image sensor and the correction coefficient read out from the storage means; A document reading device included.