JPS61239778A - Picture signal processing device - Google Patents

Abstract

PURPOSE:To automatically obtain density level correction with high precision by controlling the input picture signal at constant amplitude by making shading correction to manuscript reading picture signal and controlling variable amplifier according to the maximum white density and maximum black density. CONSTITUTION:When reading the input manuscript, selection switch 22 is connected to (b) side, and correction factor is read from white reference memory 17 of correction ROM 18. This correction data is connected to variable amplifier 12 for shading correction through a D/A converter 19, and the shading correction is made between picture signal 11' of input manuscript which is amplified by pre-amplifier 11. Furthermore, by setting gain and offset values corresponding to the maximum white density and maximum black density at terminals 23, 24 when the reading of white reference is finished, D/A converters 20, 21 control the output voltage level of variable amplifier 13 and amplifier 14. Thus, even when the input picture signal 11' fluctuates according to the change of density of manuscript, it is possible to control up to the range of input voltage of an A/D converter 15.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an image signal processing device that corrects the density level of an image signal read by scanning a continuous tone original such as a photograph.

2. Description of the Related Art Recently, solid-state scanning devices such as COD have come to be widely used in image input devices such as 71-inch millimeter devices and document reading devices. The image signal having density information photoelectrically converted by such a solid-state scanning element is once converted into digital values by an A/D converter, and then various image signal processing is performed in a multivalued state.

Conventionally, image reading devices for the purpose of reading manuscripts such as photographs,
As an image signal processing means for applying density level correction to the density level of a document, especially for the purpose of gradation, a configuration described in Japanese Patent Laid-Open No. 147562/1983 is known. ing.

The configuration of a conventional image reading section will be described below with reference to FIG.

In FIG. 3, 1 is a solid-state scanning device such as a COD, 2 is an amplifier, 3 is an A/D converter that converts the analog signal output from the amplifier 2 into a digital signal, and 4 and 6 are A/D converters, respectively. This is a resistance dividing section that provides upper and lower reference voltages to the D converter 3.

In the above configuration, the output from the COD solid-state scanning device 1 that has read the original is amplified to an appropriate level by the amplifier 2 and applied to the input terminal vi of the A/D converter 3. At this time, the range determined by the upper and lower reference voltages V and vRB is output as an 8-bit digital image signal to the output terminals oUT0 to 0UT7 by determining whether it matches the voltage divided by A266, for example, and outputs an image (not shown) to the output terminals oUT0 to 0UT7. After passing through a signal processing unit and a modem, the signal is sent via a transmission line to, for example, a recipient's receiving facsimile device or computer device.

Now, the resistor divider 4 determines the conversion range of the A/D converter 3.
, 6, this corresponds to the reference voltages RA and RB, respectively.
is set to be equal to the analog signal output voltage of the amplifier 2 corresponding to the whitest part (maximum white density) and the blackest part (maximum black density), assuming the expected type of original to be read. If the density level of the input original varies widely, such as a dark photo original or a light photo original, depending on the method of use, which is adjusted and fixed in advance, the maximum white density and maximum black density as described above may be changed. A large number of reference voltages vRA and vRB corresponding to the density are prepared, and the operator has to readjust the settings of the reference voltages vRA-vRH each time according to the density level of the input document, which is inconvenient to operate. Met. Further, in the above-described conventional method, when converting into a highly accurate multi-level digital image signal, the linearity of the conversion level is poor and there are problems with image quality in terms of density gradation.

On the other hand, when reading images with a solid-state scanning device such as a COD, there are variations in the sensitivity of the solid-state scanning device, vignetting of the peripheral part of the optical lens interposed between the document and the COD solid-state scanning device, non-uniformity of the light source that illuminates the document, etc. A shading phenomenon occurs due to the following causes.

Therefore, when reading the document, it is necessary to first perform shading correction and then perform density level correction. In order to reverse this number, it is necessary to perform shading correction according to the density level of the photoelectric conversion signal output for each pixel from the solid-state scanning element, which makes the control circuit system complicated and makes it difficult to obtain the appropriate density. The accuracy of level correction will also decrease.

In view of the above problems, the present invention provides an image signal processing device capable of correcting density levels suitable for reading continuous tone originals such as photographs. The invention includes reading means for reading white reference information and original image information to obtain an analog image signal, and amplifying the analog image signal sent from the reading means.

a first variable amplification means for performing shading correction processing; a second variable amplification means for variably amplifying the level of the analog image signal sent from the first variable amplification means;
analog/digital conversion means for converting the analog image signal sent from the variable amplification means into a digital image signal according to the signal level;

shading correction data is obtained from the image signal of the white reference information in the analog/digital conversion means, and the first variable amplification means amplifies the analog image signal of the original image information according to the shading correction data; a first amplification rate control means for controlling the amplification rate of the first variable amplification means; and a first amplification rate control means for controlling the amplification rate of the first variable amplification means; The above object is achieved by providing a second amplification rate control means for controlling the amplification rate of the second variable amplification means according to parameters of maximum white reference density and maximum black reference density. It is something.

According to the above configuration, the present invention stores the read data for each pixel of the white reference plane for shading correction when reading the original, and at the time of reading the image of the original surface, the white reference signal is stored. Based on the information for each pixel, the original reading image signal is corrected by shading, and the gain and offset of the variable amplifier are controlled according to the maximum white density and maximum black density level of the original. By controlling the image signal level to a constant amplitude value, that is, to the maximum quantization voltage of the A/D conversion means, highly accurate density level correction can be automatically obtained.

Embodiment Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of an image signal processing device according to an embodiment of the present invention.

1 In FIG. 1, 10 is a solid-state scanning device such as a COD, and 11 is a preamplifier for amplifying the analog signal of the solid-state scanning device 1o. Reference numeral 12 denotes a variable amplifier for shading correction, which is composed of, for example, a multiplier, etc., one terminal of which is connected to the output of the preamplifier 11, and the other terminal connected to the output of the D/A converter 19 for shading correction. It is connected to the. A variable amplifier 13 controls the gain determined from the maximum white density and maximum black density levels of the original. Reference numeral 14 denotes an amplifier for controlling an offset determined from the maximum white density level and the maximum black density level. Here, the maximum white density and the maximum black density are density levels that the original has, and are used to widen the image signal of the original to a certain amplitude level, and both are parameters instructed by the operator. . These can give a gain parameter through a terminal 23 and an offset parameter through a terminal 24, and the gain parameter 23 can be sent to the other terminal of the variable amplifier 13 through the D/A converter 2o, and Offset parameter 24
is connected to the other terminal of the amplifier 14 via the D/A converter 21. 16 is an A/D converter, and 17 is a white reference memory in which read data for each pixel of the white reference plane is stored. On the 1st, there is a correction R in which an inverse coefficient correction value for converting the correction data from the white reference memory 17 is stored.
It's OM.

Also, at this time, when reading the white reference, the selection switch 22 is set to a.
is connected to R, and at this time constant data is always sent to R for correction.
A constant voltage is output from the OM 18 and connected to one terminal of the variable amplifier 12 via the D/A converter 19.

During normal image reading of the document surface, the selection switch 22 is connected to b, and the COD solid-state scanning element 10
The read image signal of the original that has been amplified is subjected to shading correction by the variable amplification device 12 .

The operation of the above embodiment will be described in detail below.

The relationship between the input image signal level and the output image signal level when performing density level correction processing will be explained with reference to FIG.
The density level correction is performed according to the equation shown below.

This i relational expression is expressed by the formula %, where vin is the input image signal shown by curve 30, and vo is the input image signal shown by curve 30.
ut indicates the output image signal corrected by the above equation. ) child;! At knee, Lw=0.70, LB=1. OO
Considering the case of scanning an input document having maximum white density and black density (both values are expressed as optical density), the above equation is as follows: VOut= 10.047606 Vin-1,004
7606 will be given. Here, 10.047606 is the gain parameter of the variable amplifier 12, and 1.0047
Reference numeral 608 is an offset parameter, and it can be seen that the variable amplifier may be configured to provide gain and offset from the outside.

Therefore, the analog signal level of the preamplifier 11 is Lw,
Depending on LB, o, 1■ to 0.2 V (0,1995
Considering that the signal level is up to 262V), the output voltage is controlled within the range of oV to 1V by the gains of the variable amplifier 13 and the amplifier 14 and offset control. At this time,
The above gain and offset parameters are applied to the D/A converter 2.
By appropriately setting the coefficients 0 and 21, it is possible to control the output signal level to a constant amplitude.

When reading the white reference, the selection switch 22 connected to the correction ROM 18 is connected to the a side, constant data is always read from the correction ROM 18, and a constant voltage is variably increased through the D/A converter 19. By applying data to the width filter 12, white reference data is stored in the white reference memory 7 for each pixel.

That is, in the white reference reading state, shading correction by the variable amplifier 12 is not performed, and the variable amplifiers 13 and 14 are simply controlled to bypass the analog image signal 11', and the analog image signal 11' is Level 11' is oV~
If the amplitude is up to 1V, the image signal level of each amplification part is 12',
13' and 14' are also controlled to the same level. That is,
The gains and offsets given to the variable amplifier 13 and the amplifier 14 may be set at the terminals 23 and 24, respectively, so that they become 1 and 0, respectively.

On the other hand, when reading an input document, the selection switch 22 connected to the correction ROM 18 is connected to the b side, and the correction coefficients corresponding to each pixel are transferred to the correction ROM 18 from the white reference memory 17.
It is controlled so that it is read out. These correction data are D/A
Since it is connected to the variable amplifier 12 via the converter 19, shading correction is performed with the image signal 11' of the input document read by the solid state scanning element 10 and amplified by the preamplifier 11. It will be done. Furthermore, when the white reference reading state is completed, the maximum white density of the input document is input to terminals 23 and 24.
By setting the gain and offset value according to the maximum black density, D/A converters 2o and 2 can be adjusted according to this parameter.
1 is capable of controlling the output voltage level of the variable amplifier 13 and the amplifier 14, respectively, as described above.

According to the above configuration, even if the voltage level range of the input image signal 11' changes depending on the density level of the original, the A
When inputting to the A/D converter 15, it is possible to always correct up to a certain level range up to the input voltage range of the A/D converter 16, so image quality due to multi-level A/D conversion can be improved. The linearity is well reproduced, and the gain of the variable amplifier is kept constant during image reading, so even if noise occurs, image reproduction will not be adversely affected.

Effects of the Invention As described above, according to the present invention, the read data for each pixel of the white reference plane is stored for shading correction before reading the original, and when reading the image of the input original, the white The shading correction of the original reading image signal is performed based on the information for each pixel of the reference data, and the gain and offset of the variable amplification means are controlled according to the maximum white density and maximum black density level of the original. Since the image signal level of the original can always be controlled up to the maximum quantization voltage of the A/D conversion means, it is possible to simplify the circuit configuration for image reading, and achieve a remarkable effect in correcting the density level of the original. I can do that.

[Brief explanation of drawings]

FIG. 1 is a block wiring diagram of an image signal processing apparatus according to an embodiment of the present invention, FIG. 2 is a processing characteristic diagram of the main parts thereof, and FIG. 3 is a block wiring diagram of a conventional image signal processing apparatus. 1o...solid-state scanning element, 11...preamplifier. 12.13...Variable amplifier, 14...
Amplifier, 16...A/D converter, 17...
...White reference memory, 18...Correction ROM, 1
9,20.21...D/A converter, 22...
...Selection switch. Name of agent: Patent attorney Toshio Nakao and 1 other person 2nd
Illustrated Kai Saill (V)

Claims (1)

[Claims] a reading unit that reads white reference information and original image information to obtain an analog image signal; and a first unit that amplifies the analog image signal sent from the reading unit and performs shading correction processing.
a second variable amplification means for variably amplifying the level of the analog image signal sent from the first variable amplification means; an analog/digital conversion means for converting an analog image signal into a digital image signal according to a signal level;
The first variable amplification means obtains shading correction data from the image signal of the white reference information in the digital conversion means and amplifies the analog image signal of the original image information according to the shading correction data. a first amplification rate control means for controlling the amplification rate of the variable amplification means; and a first amplification rate control means for controlling the amplification rate of the variable amplification means; An image signal processing device comprising: second amplification rate control means for controlling an amplification rate of the second variable amplification means according to parameters of a reference density and a maximum black reference density.