JPH0241074A - Color picture processing unit - Google Patents

Abstract

PURPOSE:To attain sure A/D conversion processing even when a light source with a biased light distribution state is in use by adjusting the level of a optoelectric conversion signal based on a optoelectric conversion signal obtained from a maximum level position in one line. CONSTITUTION:After an optical image of an object 2 is converted into an electric signal by optoelectric converters 6, 7, the result is converted into a digital signal by A/D converters 10, 11 via level adjusting devices 8, 9 and fed to an effective area circuit 15. In the adjustment mode, a reception data just before a color discrimination circuit 20 is transferred to a picture processing CPU 160, where peak value discrimination processing is applied for each sampling position of the reception data. Then the result of discrimination in 2 bytes representing a maximum value is sent to a scanner CPU 250 as a transmission data for each color signal and the CPU 250 controls the level adjustment circuit 8, 9 so that the peak is made coincident with a reference level (sampling level close to a maximum level).

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a color image processing device suitable for application to an image processing device such as a plain paper recording color copying machine, particularly an A/D
The present invention relates to a color image processing device that eliminates overflow during conversion.

[Background of the Invention] In a powerful color image processing device, such as a color copying machine using a laser beam, a color original is separated into multiple colors to obtain color image information, and a color image is created based on this color image information. I try to record it.

In all such image processing, a photoelectrically converted image signal is first converted into a digital signal, and various signal processing is performed on the digital signal.

Therefore, normally, an analog image signal photoelectrically converted by an image reading means is amplified to an appropriate level by an amplifier and then supplied to an A/D converter where it is sampled and quantized.

In this case, the gain of the amplifier is controlled a1+ so that, for example, the A/D conversion output at the center of one line is maximized.

[Problems to be Solved by the Invention] Incidentally, the level adjustment carried out as pre-processing for A/D conversion is performed by an amplifier so that the A/D conversion output at the center of one line, for example, is maximized. It is sold wholesale.

This means that the light distribution of the linear light source used during photoelectric conversion is
This is based on the empirical rule that the center is larger than the surrounding area. Therefore, there is no particular problem when using such a linear light source in which the central portion becomes the maximum.

However, some light sources exhibit a biased light distribution such that the level is higher at the periphery than at the center.

Conventionally, the level of the photoelectric conversion signal was adjusted based on the photoelectric conversion signal obtained at the center of one line, assuming that the center of the light source was always high, so in the above case, the A/D conversion output was There were cases in which the photoelectric conversion signal could not be correctly A/D converted due to overflow.

Therefore, the present invention proposes a color image processing device that can correctly perform A/D conversion processing without overflowing even when a light source with a biased light distribution is used.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides charging conversion means for converting image information into an electrical signal, and means for obtaining a distortion-corrected digital color signal from this photoelectric conversion signal. and an image signal means for this digital color signal.

The level of the photoelectric conversion signal is adjusted based on the charging conversion signal obtained from the maximum level position in one line.

[Function] In the adjustment mode, the position (horizontal scanning direction) of the maximum level of the light source is detected. This allows the light distribution state of the light source to be determined.

The level is adjusted so that the level of the photoelectric conversion signal obtained from the position of the maximum level of the light source becomes the reference level.

By doing so, A/D conversion processing can always be performed with the highest efficiency. Further, since the level of the photoelectric conversion signal obtained from the maximum level position of the light source is adjusted to the reference level, there is no possibility that the A/D conversion output will overflow.

[Example] Next, an example of a color image processing device according to the present invention will be described.
A case in which the present invention is applied to the color copying machine described above will be described in detail with reference to FIG. 1 and subsequent figures.

FIG. 1 is a system diagram showing the outline of this color image processing device, in which color image information* (optical image) of a subject 2 such as a document is passed through an optical system 3 and then sent to a dichroic mirror 4.
It is separated into two color separation images.

In this example, the image is divided into a color-separated image of red R and a color-separated image of cyan Cy. Therefore, the dichroic mirror 4 used has a cutoff wavelength of about 540 to 600 nm.

The color separation images of red R and cyan cy are supplied to an image reading means, for example, C0D6.7, and image signals of only the red component R and cyan component Cy are output from each image reading means, for example.

The image signals R and cy are level-adjusted in a level adjustment circuit 8.9. This level adjustment is a process to eliminate overflow during A/D conversion and improve A/D conversion efficiency, and as described later, the level of the image signal obtained from the position of the maximum level of the light source is the standard. The level is adjusted to match the level. Details will be described later.

The level-adjusted image signal is supplied to an A/D converter 10.about.11, where it is converted into a digital signal of a predetermined number of bits, 6 bits in this example.

Shading correction is performed simultaneously with A/D conversion. 12.1
3 indicates a shading correction circuit.

The digital image signal subjected to the shading correction is extracted by the effective area extraction circuit 15 for only the signal corresponding to the maximum document size width, and is supplied to the color discrimination circuit 20 at the next stage. When the maximum document width to be handled is 84 size, the size signal B4 generated by the timing signal generating means 170 of the system is used as the gate signal.

Here, if the digital image signals subjected to shedding correction are VR and VC, respectively, these image signals VR.

VC is supplied to a color discrimination circuit 20 and separated into a plurality of color signals.

In this example, a case is illustrated in which the signal is configured to be separated into three color signals: red, blue, and black.

That is, no matter what color the original is, each pixel is assigned to one of red, blue, and black. When this process is performed, each part of the document is recognized as a red, blue, or black color part.

In addition, if these red, blue, and black are other colors, roughly 4
This color discrimination processing also includes the determination of a color or more.

Each color-discriminated color signal is divided into color code data (2 and t data) indicating its color information and density data (6 and 6), respectively.
It consists of

The data for each color signal is stored in a color discrimination conversion table (map) in a ROM, for example.

FIG. 2 shows an example of this color discrimination map.

It is also possible to prepare a plurality of color discrimination conversion tables and select one of them depending on the type of document, for example. In this case, a microcomputer 1 for image processing, which will be described later, is used.
Table selection processing is executed based on instructions from 60.

The color-discriminated image data is transferred to a color image processing step.

First, it is supplied to the next-stage color ghost correction means 300, where color ghosts in the main scanning direction (horizontal scanning direction) and sub-scanning direction (drum rotation direction) are corrected.

This is because unnecessary color ghosts occur during color discrimination, especially around black characters.

FIG. 3 shows an example of appearance of color ghosts.

The figure shows the color ghost that appears after color discrimination is performed by capturing an image of the kanji character "sexuality" written in black.

As you can see from this example, as a color ghost,
As shown in FIGS. 4A to 4C, red and blue appear at the edge of the black line, black appears at the edge of the blue line, and black appears at the edge of the red line.

It is clear that color ghosts appear differently in other color combinations.

The color ghost correction means 300 is a circuit for correcting such color ghosts as much as possible. Color ghost processing applies only to color code data.

In this example, color ghost correction is performed using a color pattern method. This is because the color ghost color that appears is determined for the original color, such as original black → red, blue ghost, original red, blue → black ghost. According to the color pattern method, if the color of a pixel of interest is determined by examining the color appearance (pattern) of the pixel of interest and its surrounding pixels, the color of the original image can be identified relatively easily.

As an example, FIG. 5 shows the relationship between the pixel of interest, the surrounding color pattern, and the color of the pixel of interest determined at that time.

In the first example, since both sides of the pixel of interest are white and black, the blue color of the pixel of interest is determined to be a color ghost appearing at the black edge. Red in the third example is also determined to be a color ghost of black. Therefore, in both the first and third examples, the pixel of interest is changed to black.

On the other hand, in the second and fourth examples, it is not determined that a color ghost has appeared, and the color of the pixel of interest is output as is.

This type of processing is difficult to implement with an arithmetic circuit, so in this example, it is implemented in ROM and LUT (lookup table).
It is used in the format. A one-dimensional or two-dimensional system can be considered as a color pattern, but if the number of colors is N and the number of peripheral pixels including the @-th pixel is M, the size of the color pattern is NM. Therefore, if a two-dimensional pattern is used, the number of M will suddenly increase, making it impractical.

In other words, in a two-dimensional pattern, each dimension direction (main scanning direction/
Although the number of peripheral pixels in the sub-scanning direction (sub-scanning direction) cannot be increased, the number of patterns increases. FIG. 6 shows the relationship between size and number of color patterns.

In this example, the size is 1×7 in one dimension (that is, N
=4. M=7) color pattern is used, and color ghost removal is performed independently in the main scanning direction and the sub-scanning direction.

At this time, in this example, the same color pattern is used in the main scanning direction and the sub-scanning direction, since there is no difference in how ghosts appear in the main scanning direction and in the sub-scanning direction due to color in the image.

The color pattern size is 1 x 7, but if the degree of color ghost appearance is small, 1 x 7 is selected.
It is also possible to use a smaller size color pattern, such as x5. Color ghosts of up to 1 pixel can be removed in a color pattern of size I×5, and color ghosts of up to 2 pixels can be removed in a color pattern of size 1×7.

The image data (color code data and density data) after the color ghost correction is processed in the subsequent resolution correction circuit 40, and the resolution (MTF) is corrected.

Factors contributing to resolution deterioration include problems with the optical system, optical travel system, signal processing system, recording system, etc. Of these, the optical system and its travel system directly affect resolution deterioration.

FIG. 7 shows MTF values (before correction) in the main scanning direction and the sub-scanning direction when the optical system is driven. This characteristic is 2~16d
These are the measured values when scanning a black and white pattern with a spatial frequency up to ots/mm.

The MTF in this case was defined and used as MTF=(W-BK)/(W+BK)(%). Here, W is a white signal and BK is a black signal.

The deterioration of MTF is more significant in the sub-scanning direction. To make the same amount of correction, the amount of correction in the sub-scanning direction should be 2 times that of the main-scanning direction.
You can set it to ~4 times.

In order to correct the main and sub-scanning directions to the same degree without deteriorating the reproducibility of fine line areas, use a component filter that uses 3 x 3 pixel image data as the resolution correction circuit. be able to.

FIG. 8 shows the correction results when using the convolution filter.

The resolution-corrected density data and color code data are each supplied to the color data selector 5o, and when the partial color conversion mode is selected, the image area is recorded in a specific color (see FIG. 10).

When image processing such as this partial color conversion mode is performed, as shown in FIG. 11, it is necessary to detect marker signals RP and BP from color markers written on the document and extract the area.

For this reason, a region extraction circuit 60 is provided to detect the color marker region on the document, and the region signals QR", QB- (see FIG. 11) obtained from this are supplied to the data selector 50. Ru.

In addition to these signals, the data selector 50 is supplied with a scan code signal indicating which color is currently being copied and a partial color conversion signal CC.

It is a multi-color copying machine that can record multiple specific colors, and it develops one color per rotation of the photoreceptor drum, and after all colors are developed,
In a type of printer that records a color image by performing transfer separation processing, the scan code signal indicates which color is currently being developed.

Therefore, when the -kamori color marker is detected, if the corresponding color code is output at the end of the blue copy sequence and when the area signal is obtained, the image within the blue color marker can be output. can be recorded in blue.

When not performing partial color conversion processing, density data is output only when the color code data matches the scan code signal. That is, during the red copy sequence, while the red color code is being obtained, the corresponding density data is selectively output.

The image data output from the color data selector 50 (
The density data) is subjected to enlargement/reduction processing in a scaling circuit 70.

Enlargement/reduction processing is performed by interpolating the density data in the main scanning direction, and by controlling the scanning speed in the sub-scanning direction (rotation direction of the photosensitive drum).

If the scanning speed is increased, sampling data in the sub-scanning direction is thinned out, resulting in a reduction process; on the other hand, if the scanning speed is made slower, an enlargement process is performed.

In this example, the color code data is also subjected to enlarging/reducing processing at the same time, and is then supplied to the multi-value conversion circuit 80.

The density data subjected to the enlargement/reduction processing is sent to the multi-value conversion circuit 80.
, multi-value processing is performed. For example, by using four threshold values, 6-bit density data is quinarized.

Threshold data can be set manually or automatically.

A histogram creation circuit 100 is provided to automatically determine threshold data.

The histogram creation circuit 100 creates a density histogram as shown in FIG. 9 from certain captured image data, and calculates optimal threshold data for the image based on the created density histogram.

A density histogram may be created for each color, and multi-value processing may be performed for each color using threshold data calculated based on the density histogram.

The 3-bit multi-value data that has been subjected to multi-value processing is supplied to the postcomputer 160 via the interface 130.

The multi-level signal passed through the host computer 160 is supplied to a laser beam printer 150 that constitutes an output device, and the laser is PWM-modulated by this multi-level signal. The photosensitive drum provided in the laser beam printer 150 is completely developed by the laser beam.

As a developing device provided in the laser beam printer 150, an electrophotographic color copying machine is used. In this example, two-component non-contact jumping development and reversal development can be adopted.

That is, the transfer drum used in conventional color image formation is not used. In order to downsize the device, three-color images of blue, red, and black are developed on the ○PC photoreceptor (drum) for image formation in three rotations of the drum as described above, and transfer is performed once after development. It is then transferred onto a recording medium such as plain paper.

The various image processing commands and image processing timings described above are all controlled by the host computer 160.

Reference numeral 170 is a processing timing signal generation circuit for obtaining various processing timings, and generates a timing signal for starting reading for C0D6°7, and the like. 180 is a timing signal generation circuit for obtaining scaling timing.

In the present invention, among the digital color signals obtained immediately before the color discrimination circuit 20, the A/D converter 10 uses the digital color signals obtained when reading a reference document, in this example, a reference white plate. The level of the image signal input to .11 is adjusted in advance.

Therefore, the digital color signal obtained from a predetermined area is latched by the latch circuit 200, and this is sent to the CPU for image processing.
160. A center pulse C8P, which will be described later, is used as the latch pulse.

The digital color signals taken into the CPU 160 are roughly
CPU (master CPU) that controls the optical scanning system (scanner)
U) 250, and the level of the level adjustment circuit 8.9 is adjusted based on the image signal corresponding to a specific sampling position.

At the same time, the maximum level position of the light source is displayed.

FIG. 12 shows an excerpt of the signal exchange relationship among the image processing CPU 160, scanner CPU 250, and printer CPU 150A described above.

The printer CPU 150A sends horizontal and vertical effective area signals H, ■, ■ to the timing signal generation circuit 170.
- External synchronization signals such as (1), an index signal IDX indicating the start of each horizontal scan, and a clock CLK are supplied.

The scanner CPU 250 sends an index switching signal IDX-E to the timing generation circuit 170.
X is supplied. This is a control signal that switches between the internal synchronization signal generated inside the timing generation circuit 170 and the external synchronization signal described above.

In addition, a signal COR that determines the sampling start timing of shading data, a reference signal REF, and an O reference signal REF to which the prescan signal PRE can be supplied are control signals for switching the reference voltage of the A/D converter 10 and 11. It is. Briscan signal PRE
is a pre-scan control number m+= for creating a histogram prior to reading the original.

The index switching signal IDX-EX, the signal COR determining the sampling start timing, the reference signal REF, and the bliscan signal PRE are all active "L".

CPU160 for image signals and CPU250 for scanning
The following serial communication signals are exchanged between the terminal and the terminal.

The request signal REQ used in the maximum level adjustment mode is a signal for controlling the transmission and reception of serial data between the scanner CPU 250 and the image tN processing CPU 160.

This is synchronized by the serial clock SCK.

RxD refers to serial data (received data) sent from the scanner, and TxD refers to serial data (transmitted data) sent from the image processing side.

Specific examples of these transmitted and received data RxD and TxD are shown in FIGS. 13 and 14. A specific example will be described later.

In FIG. 12, the following signals are exchanged between the scanner CPU 250 and the printer CPU 150A.

Among the pulses that can be sent out from the printer CPU 150A, 5START is a pulse that specifies the start of scanning for the scanner.

Transmission data TxD 1 is data when a magnification is specified, and a scanning speed in the sub-scanning direction is specified for the scanner. All of these are synchronized by a serial clock 5CKI.

Image data (received data) RxDl to be actually copied is sent from the scanner CPU 250 side.

A sensor output indicating the home position of the scanner is input from the sensor 350 to the scanner CPU 250 .

The lighting control circuit 360 is controlled by the lighting signal generated by the scanner CPU 250, thereby controlling the lighting state of the light source (such as a halogen lamp) 370.

Further, a drive circuit 380 is controlled by the motor drive signal, and thereby a drive motor 390 for the ski V is controlled.

According to the present invention, when in an adjustment mode such as maintenance or inspection, adjustment processing of the level adjustment circuit 8.9 is performed.

In this adjustment mode, as shown in FIG.
When 0 is lit and the scanner optical system is at the home position, the information on the reference white plate is read.

Rifnis! The received data RxD is transferred to the image processing CPU 160 by the signal REQ (A and B in the figure).

The CPU 160 performs peak value determination processing for each sampling location based on the received data RxD. The 2-byte determination result indicating the maximum value becomes the transmission data TxD. Peak value determination is performed for each color (g number).

The determination result is sent to the scanner CPU 250 on the transmission data TxD for each color signal (FIG. 15C). Thereby, the level adjustment circuit 8 adjusts the peak value to match the reference level (sampling level close to the maximum). , 9 are controlled. Additionally, the peak value position of the light source is displayed (FIG. 16).

In particular, in the level adjustment mode, multiple sampling positions are set so that the level adjustment mode can be checked over almost the entire area of the light source.

Assume that the effective area of one line is divided into seven parts, data is extracted from each part, and the effective area is made up of 5000 bits. In that case, as shown in FIG. 17, the center pulse CSP (C
5PI to C5P7) to change the position of the pixel to be latched, that is, the sampling position.

Therefore, when the first pixel is the 480th bit,
Next, the 1152nd bit pixel becomes the sampling position, and the final sampling position becomes the 4592nd bit pixel.

The received data RxD shown in FIG. 13 consists of 7 bytes, and the lower 3 bits of the first byte are I10 check data CHKIP. FIG. 18 shows the relationship between the check data CHKIPO to CHKIP2 and the transmission mode selected thereby.

The level adjustment mode is shown as mode Ill. Mode I
II has a two-channel configuration, where the first channel is a level adjustment mode for cyan, and the next channel is a level adjustment mode for red.

In this example, there are modes I and 11 in addition to mode I11. Mode I is a mode in which image data (digital color signals) necessary for determining the quality of parts is transmitted as transmission data TxD, and this is also a normal reading mode.

Mode TI is a light distribution adjustment confirmation mode, and in this mode, the light distribution state of the entire linear light source is detected, and the state can be displayed at each sampling position. Even in this mode, the center pulse C8P can be used for changing the image reading position.

Examples of other codes assigned to each byte of received data RxD are shown below.

1, SCO~SC2...Scan code 2, CI
(AHG...Partial color conversion code 3, EE/
...Automatic threshold selection code 4, CHKPRE
...φ... Prescan code 5, RDO ~ RD3.
... Red density level 6, BLO to BL3... Blue density level 7.8 KO to BK3... Black density level 8, H2O to H28... Magnification in the main scanning direction (50 to 4
00%) Of the transmission data TxD shown in FIG.
xB is 2-byte transmission data indicating the peak value determination result in level adjustment mode Ill.

Here, X indicates sampling positions in the horizontal scanning direction, which are seven in this example. The same bit at the same sampling position indicates the peak value determination result at that sampling position. For example, let the pixel position of the peak value be rl, 1. Then, any pixel position at a level lower than this is ro,
o, yell.

FIG. 19 is a flowchart 400 showing an example of a control program for peak value detection.

In the Briscan mode, when the rising edge of the request signal REQ is detected, input of reception data RxD is started, and when all data input (7 bytes) is completed, 1
The received data RxD inserted into the byte is decoded (steps 401 to 404).

As a result of decoding, if the transmission mode is not III, a transition is made to another processing routine 405;
If so, the center pulse C3PI is set (step 406). And check data CHKI
The color signal specified by IF5 to P'0-CH is determined (step 407). Since the color is cyan at first, a digital color signal related to cyan is first taken in, and then similar processing is performed by changing the sampling position of the center pulse C8P (step 408).

When input for all sampling positions is completed,
Next, peak value determination is performed from the seven sampled color signal levels (steps 409 and 410).

When the maximum peak value is calculated from the seven color signal levels, transmission data TxD including data indicating the sampling position is output (step 411). Then, when this transmission data TxD becomes 2 bytes, the transmission mode ends (step 412).

Similar processing is performed for the red digital color signal (step 407).

The level adjustment circuits 8 and 9 described above are controlled so that the output at the sampling position showing this peak value becomes the reference level. In this way, the peak value on one line will be at least below this reference level, so that A
There is no overflow during /D conversion.

[Effects of the Invention] As described above, according to the present invention, the light distribution state of the light source is detected, and the level is adjusted based on the output level of the sampling position where the peak value is obtained.

According to this, since the peak value in one line is at least below the reference level, it is possible to eliminate the problem of overflow during A/D conversion, which prevents image signals from being correctly A/D converted. Therefore, even when using a light source whose light distribution is biased towards the periphery rather than the center, the A/D conversion accuracy can be improved.

From the above, the present invention is extremely suitable for application to a color image processing apparatus such as the above-mentioned color copying machine.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing an example of a color image processing device according to the present invention, FIG. 2 is a diagram of a color discrimination map, FIGS. 3 and 4 are explanatory diagrams of color ghosts, and FIGS. The figure is an explanatory diagram of color ghost correction, and Figures 7 and 8 are MTF.
A characteristic diagram showing correction, FIG. 9 is a diagram of a density histogram, FIG. 10 is an explanatory diagram of how color markers are changed, FIG. 11 is a system diagram of an area extraction circuit, and FIG. 12 is a diagram showing the relationship between CPUs. , Fig. 13 is an explanatory diagram of received data, Fig. 14 is an explanatory diagram of transmitted data, Fig. 15 is an explanatory diagram of light distribution adjustment confirmation mode, Fig. 16 is a diagram showing an example of light distribution display, and Fig. 17 is an explanatory diagram of transmitted data. A diagram showing the relationship between the center pulse and sampling pixels, Figure 18 is I
FIG. 19 is a flowchart showing an example of a processing procedure in the image processing CPU. 8.9 ・Color image processing device ・Level adjustment circuit ・Color discrimination circuit ・Resolution correction circuit ・Color data selector ・Area extraction circuit ・Scaling circuit ・Multi-value conversion circuit 20.0 ・Histogram creation circuit ・Output device ・Image processing CPU for latch circuit, CPU for scanner Figure 12 Figure 15 Figure 16 Figure 16 C3P2 Figure 17 Figure 18 Figure 19

Claims (1)

[Claims] (1) comprising a photoelectric conversion means for converting image information into an electrical signal; a means for obtaining a distortion-corrected digital color signal from the photoelectric conversion signal; and an image signal means for the digital color signal; A color image processing device characterized in that level adjustment is performed based on a photoelectric conversion signal obtained from a maximum level position in one line.