JPH04301968A - Image signal processor - Google Patents

Abstract

PURPOSE:To input a voltage close to the maximum output of an image sensor to the reference voltage of an A/D converter with the circuit configuration of reducing cost. CONSTITUTION:An image is read in the state of first inputting a reference voltage V0 of the lowest value among more than the two kinds of reference voltages V0-V3 as the reference voltage of an A/D converter 3. When an overflow signal OF is outputted from the A/D converter 3 in the case of reading the image, the reference voltage V1 of the largest value next to the former reference voltage is inputted as the reference voltage of the A/D converter 3 in the case of reading the next line. Afterwards, the lines are successively read and the reference voltage of the stage not outputting any overflow signals is held as the optimum reference voltage. In the case of shading correction, shading correction reference data corresponding to the current reference voltage are read out of a memory 9, and the shading correction is executed.

Description

[Detailed description of the invention]

0001

FIELD OF INDUSTRIAL APPLICATION The present invention relates to an image signal processing device, and more specifically, an A/D converter that processes an analog image signal.
The present invention relates to an image signal processing device that can effectively use the resolution accuracy of a D converter.

0002

2. Description of the Related Art In image reading devices used in facsimiles, digital copying machines, etc., CCD (Charg
An analog image signal from an image sensor composed of a photoelectric conversion element such as an e-coupled device is converted into a digital image signal by an A/D converter. 2. Description of the Related Art In an image reading device, a phenomenon occurs in which an output image is distorted due to uneven illumination of a light source, characteristics of a lens system, uneven sensitivity of each photoelectric conversion element constituting an image sensor, and the like. Therefore,
This type of image reading device performs so-called shading correction in order to maintain the quality of its output image at a high level. Shading correction reads and scans the white part of the reference (bright reference) and stores the data obtained as correction reference data.
This is performed by correcting image data obtained by reading a document using the correction reference data. When capturing bright reference data for shading correction into memory, in order to effectively use the resolution accuracy of the A/D converter, it is necessary to set a voltage close to the maximum output of the image sensor as the A/D converter reference data. voltage.

As shown in FIG. 4, a conventional device of this type includes an image sensor 31, an amplifier 32, an A/D converter 33, a comparator 34, and a D/A converter 35. be. In this device, an output signal from an image sensor 31 is amplified by an amplifier 32 and then input to an A/D converter 33.
The A/D converter 33 A/D converts the analog image signal inputted to the input terminal pixel by pixel and outputs it as a digital image signal to the comparator 34. The comparator 34 compares the input digital image signal with the peak value stored in a peak value register (not shown), and when the newly read image signal is larger than the peak value detected in the past, the peak value register is used. A command is sent to the register to latch the new image signal value into the peak value register. Therefore, when one line of scanning is completed, the highest peak value of the line data is latched in the peak value register. Then, the peak value is determined by the D/A converter 35.
The signal is taken out and converted into an analog value, and the reference voltage of the A/D converter 33 is changed in accordance with the analog value.

0004

[Problems to be Solved by the Invention] As mentioned above, in the conventional device, a bright reference (white reference) is used for performing shading correction.
A D/A converter and a digital comparator are required in order to set the optimum reference voltage for the A/D converter 33 when taking data into the memory. However, D/A converters are expensive, and digital comparators are also relatively expensive.

The present invention has been made in view of the above problems, and its purpose is to input a voltage close to the maximum output of an image sensor as a reference voltage of an A/D converter using a low-cost circuit configuration. The object of the present invention is to provide an image signal processing device that can perform the following steps.

[0006]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides an A/D that inputs an analog image signal from an image sensor, digitizes it based on a reference voltage, and outputs an overflow signal.
a converter, and reference voltage setting means for setting an optimal reference voltage from at least two types of reference voltages based on an overflow signal of the A/D converter;
A memory storing shading correction reference data corresponding to each of the reference voltages, and reading means for reading out from the memory shading correction reference data corresponding to the reference voltage set by the reference voltage setting means during shading correction. .

[0007]

[Operation] The reference voltage of the A/D converter is selected from at least two kinds of reference voltages determined in advance in correspondence with shading correction reference data. An image is read while the lowest level of the two or more types of reference voltages is first input as the reference voltage of the A/D converter. A when reading the first line image
When the overflow signal is output from the A/D converter, the reference voltage having the next highest value after the previous reference voltage is input as the reference voltage of the A/D converter when reading the next line. Thereafter, the lines are sequentially read, and the reference voltage at the stage when the overflow signal is no longer output is held as the optimal reference voltage. and,
At the time of shading correction, shading correction standard data corresponding to the current reference voltage is read out from the memory and shading correction is performed.

[0008]

[Example] Hereinafter, an example embodying the present invention is shown in Figs.
This will be explained according to FIG. The image sensor 1 is a CCD (C
The device photoelectrically converts the reflected light of the light irradiated onto the document and outputs it to the amplifier 2 as an analog image signal. The A/D converter 3 converts the analog image signal input to the input terminal into an n-bit (for example, 8-bit) digital signal and outputs the digital signal to one input terminal of the arithmetic unit 4 . A
When an analog signal having the same value as the reference voltage input to the reference terminal is input to the input terminal, the A/D converter 3 converts the signal into the digital maximum output signal of the A/D converter 3. ing. Further, the A/D converter 3 outputs an overflow signal OF when the input signal is higher than the reference voltage. Overflow signal OF is input to AND gate 6 via latch 5.

[0009] The reference terminal of the A/D converter 3 has four types of preset reference voltages V0, V1, V2.
, V3 is input via multiplexer 7. The four types of reference voltages V0, V1, V2,
V3 is the four input terminals I0, I of multiplexer 7
1, I2, and I3, and the multiplexer 7 sequentially outputs the reference voltages V0, V1, V2, and V3 according to the output signal from the UP counter 8. The AND gate 6 outputs a signal synchronized with the image sensor drive start pulse IDP to the UP counter 8 when the image sensor drive start pulse IDP is input while the output signal from the latch 5 is being input. The AND gate 6, multiplexer 7 and U
The P counter 8 constitutes a reference voltage setting means.

The memory 9 stores the four types of reference voltages V0.
, V1, V2, and V3 are stored, and their output data lines are connected to the other input terminal of the arithmetic unit 4. And address control circuit 10 as reading means
Based on the address signal outputted from the shading correction reference data stored in the corresponding address, the shading correction reference data is outputted to the other input terminal of the arithmetic unit 4. The address control circuit 10 receives the output signal from the UP counter 8, and the address control circuit 10 receives the output signal from the multiplexer 7.
reads the address where the shading correction reference data corresponding to the reference voltage selected by is stored.

Next, the operation of the apparatus constructed as described above will be explained. Image reading is started with the reference voltage of the A/D converter 3 set to the lowest reference voltage V0 of the four types, that is, with the input terminal I0 of the multiplexer 7 selected. Image sensor 1
To explain the case where the input signal to the A/D converter 3 is the largest when reading the white part of the document, the image sensor 1 sequentially reads the image of the first line of the document in the main scanning direction, and the analog image is The signal passes through amplifier 2 to A/
The signal is input to the D converter 3. The analog image signal input to the A/D converter 3 is converted into a digital signal based on the reference voltage V0 and outputted to the arithmetic unit 4 as a digital image signal. The arithmetic unit 4 performs shading correction on the digital image signal inputted to one input terminal using shading correction reference data outputted from the memory 9 .

When an input signal larger than the reference voltage V0 is input during the reading of the first line, an overflow signal OF is output from the A/D converter 3, which is latched by the latch 5 and output to the AND gate 6. Ru. Then, the next image sensor drive start pulse IDP
When the pulse signal rises, a pulse signal is input from the AND gate 6 to the UP counter 8, and when the pulse signal rises, the input terminal I1 of the multiplexer 7 is selected and the reference voltage V1 is input to the reference terminal of the A/D converter 3. . Reading of the image sensor 1 starts at the falling edge of the image sensor drive start pulse IDP,
When reading the next line, A/D conversion of the analog image signal is performed using a reference voltage V1 higher than that during the previous reading. Similarly, when the A/D converter 3 outputs an overflow signal OF during reading, the reference voltage is changed to a reference voltage one step higher before starting reading of the next line. When the line is read with the largest reference voltage V3 being input to the reference terminal, the overflow signal OF is no longer output. Then, the reference voltage at the stage when the overflow signal OF is no longer output is held as the optimal reference voltage, and thereafter the document is read using that reference voltage.

On the other hand, since the output signal from the UP counter 8 is input not only to the multiplexer 7 but also to the address control circuit 10, the shading correction reference data output from the memory 9 to the arithmetic unit 4 corresponds to changes in the reference voltage. will be changed. That is, shading correction is always performed using shading correction reference data corresponding to the reference voltage input to the reference terminal of the A/D converter 3. When the brightness of the white background part of the document is low, the reference voltage V3 is used as the reference voltage.
The overflow signal OF is no longer output when a reference voltage with a smaller value is input, and that reference voltage is held as the optimal reference voltage, and the document is subsequently read using that reference voltage.

It should be noted that the present invention is not limited to the above-described embodiment; for example, more than four types of reference voltages may be input to the reference terminal, and the shading correction reference data may be increased accordingly. In this case, the image quality accuracy of the output image is further improved. Furthermore, if the image quality accuracy of the output image is not so required, the reference voltages may be reduced to two types.

[0015]

[Effects of the Invention] As detailed above, according to the present invention, D
A voltage close to the maximum output of the image sensor can be generated without using a circuit configuration that requires expensive parts such as /A converters and comparators.
An image signal processing device that can be input to a reference terminal of a /D converter and that can improve the image quality accuracy of an output image after shading correction can be manufactured at low cost.

[Brief explanation of drawings]

FIG. 1 is a block diagram of one embodiment of the present invention.

FIG. 2 is an operation flowchart for determining a reference voltage of an A/D converter.

FIG. 3 is a timing chart of an overflow signal, an input signal of an UP counter, a reference voltage of an A/D converter, etc.

FIG. 4 is a block diagram of a conventional device.

[Explanation of symbols]

1 Image sensor 3 A/D converter 5 Latch 6 AND gate 7 which constitutes reference voltage setting means Multiplexer 8 which constitutes reference voltage setting means UP counter 9 which constitutes reference voltage setting means Memory 10 Address control which constitutes reading means circuit OF
Overflow signal V0 Reference voltage V1 Reference voltage V2 Reference voltage V3 Reference voltage

Claims (1)

[Claims] 1. An A/D converter that inputs an analog image signal from an image sensor, digitizes it based on a reference voltage, and outputs an overflow signal; a reference voltage setting means for setting an optimal reference voltage from two types of reference voltages; a memory storing shading correction reference data corresponding to each of the reference voltages; An image signal processing device comprising: reading means for reading out shading correction standard data corresponding to a reference voltage from the memory.