JP2656561B2 - Color image processing equipment - Google Patents

Description

The present invention relates to a color image processing apparatus suitable for application to an image processing apparatus such as a color copying machine for recording on plain paper, and more particularly, to accurately determine the light distribution state of a light source. The present invention relates to a color image processing device capable of distinguishing.

BACKGROUND OF THE INVENTION In a color image processing apparatus, for example, a color copying machine using a laser beam, a color original is separated into a plurality of colors to obtain color image information, and a color image is recorded based on the color image information. I am trying to do it.

When a color image is recorded, various image processing such as scaling processing and partial color conversion processing can be performed by a built-in CPU.

The partial color conversion process refers to an image editing process in which image information inside or outside a designated area can be recorded in, for example, a color used for area designation.

In such a color copying machine, a linear light source such as a halogen lamp or a commercially available fluorescent lamp is used as a light source for reading an image.

When a linear light source is used, it is necessary to determine the light distribution state of the light source. This is because if the light distribution state is poor, the image of the document cannot be correctly converted into a color signal.

Conventionally, at the factory shipment stage, the light distribution state of the light source was checked using a synchroscope. The light distribution state is checked based on conversion data at one point of the light source, for example, at the center of the light source.

[Problems to be Solved by the Invention] However, it is very difficult to check the light distribution state of the light source by bringing the synchroscope to a place where the user actually uses the light source.

Therefore, when the lens provided in the optical scanning system or the CCD as the optical reading means is replaced during maintenance or inspection, the light distribution adjustment cannot be easily confirmed.

Also, since the light distribution state is inspected only at the center of the light source,
The light distribution over the entire area of the light source cannot be confirmed.

Therefore, the present invention proposes a color image processing apparatus in which the light distribution state of a light source can be easily checked over the entire area.

[Means for Solving the Problems] In order to solve the problems described above, in the present invention,
Means for decomposing the color image information into a plurality of color separation images and converting them into a plurality of color signals; means for obtaining a digital color signal having been subjected to distortion correction from the plurality of color signals; The image processing apparatus includes a color separation unit that separates the color signals into bits, and an image processing unit that processes the color separated multi-bit color signals.

In the adjustment mode, the level is determined based on the digital color signal, and the sampling position in one line of the digital color signal used for the determination can be changed. is there.

[Operation] In the adjustment mode, the light distribution state of the light source is detected based on the levels of a plurality of digital color signals supplied to the color discriminating means, and the result is displayed. In detecting light distribution, a digital color signal obtained from one line is sampled without bias to detect the light distribution state of the entire light source.

This makes it possible to know the light distribution state over almost the entire area of the light source without requiring a detection device such as a synchroscope.

The plurality of digital color signals are image signals obtained by reading a reference white plate with a CCD, and A / D conversion of the image signals.
It is a converted output signal that has been subjected to shading correction.

[Embodiment] Next, a case where an example of the color image processing apparatus according to the present invention is applied to the above-described color copying machine will be described in the first embodiment.
This will be described in detail with reference to the drawings.

FIG. 1 is a system diagram showing the outline of this color image processing apparatus. The color image information (optical image) of a copy body 2 such as an original is separated into two color separation images by a dichroic mirror 4 via an optical system 3. Is done. In this example, the color separation image is separated into a red R color separation image and a cyan Cy color separation image. for that reason,
The cutoff wavelength of the dichroic mirror 4 is 540 to 600 nm
Some are used.

Each color separation image of red R and cyan Cy is supplied to image reading means, for example, CCDs 6 and 7, and an image signal of only red component R and cyan component Cy is output from each.

The image signals R and Cy are supplied to the A / D converters 10 and 11 to be converted into digital signals of a predetermined number of bits, in this example, 6 bits. Shading correction is performed simultaneously with A / D conversion. Reference numerals 12 and 13 denote shading correction circuits.

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

Here, assuming that the shading-corrected digital image signals are VR and VC, respectively, these image signals VR and VC are supplied to the color discrimination circuit 20 and separated into a plurality of color signals.

In this example, a case is described in which the color signals are separated into three color signals of red, blue, and black.

That is, regardless of the color of the document, the color is assigned to one of red, blue, and black for each pixel. When this process is performed, each portion of the document is recognized as a portion of any of red, blue, and black.

It should be noted that the use of red, blue, and black as other colors, and the use of four or more colors, are also included in the color discrimination processing.

Each of the color-separated color signals is composed of color code data (2-bit data) indicating the color information and density data (6-bit data). As the data of these color signals, for example, those stored in a conversion table (map) for color discrimination having a ROM configuration are used.

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

A plurality of color discrimination conversion tables may be prepared, and these may be selected according to, for example, the type of document. In this case, a microcomputer for image processing described later
The table selection process is executed based on the command from 160.

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

First, the color ghost is supplied to the next-stage color ghost correction unit 300 to correct the color ghost in the main scanning direction (horizontal scanning direction) and the sub-scanning direction (drum rotation direction).

This is because unnecessary color ghosts (color ghosts) occur around the black characters at the time of color discrimination.

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

This figure shows a color ghost appearing after color discrimination by capturing a kanji character of the black character "sex".

As can be seen from this example, as color ghosts, as shown in FIGS. 4A to 4C, red and blue are shown at the edge of a black line, black are shown at the edge of a blue line, and red Black appears at the edge portion of.

It is clear that the appearance of color ghosts differs in other color combinations.

A circuit for correcting such a color ghost as much as possible is the color ghost correction means 300. The color ghost processing is performed only on the color code data.

In this example, the color ghost is corrected by the color pattern method. This is because the color ghost color that appears is determined for the original color, such as the original black → red, blue ghost original red, blue → black ghost. According to the color pattern method, the color of the original image can be relatively easily identified by examining the appearance (pattern) of the color of the target pixel and the surrounding pixels in determining the color of the target pixel.

As an example, FIG. 5 shows the relationship between the target pixel and the surrounding color pattern and the color of the target pixel 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 black color ghost. Therefore, in both the first and third examples, the target pixel 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 it is.

Such processing is difficult to achieve with an arithmetic circuit,
In this example, it is converted to ROM and used in LUT (lookup table) format. As the color pattern, a one-dimensional or two-dimensional method can be considered. However, when the number of colors is N and the number of peripheral pixels including the pixel of interest is M, the size of the color pattern is N ^M. Therefore, when a two-dimensional pattern is used, the number of Ms suddenly increases, and becomes unpractical. In other words, in a two-dimensional pattern, each dimension direction (main scanning direction / sub scanning direction)
Although only a large number of peripheral pixels cannot be obtained, only the number of patterns increases. FIG. 6 shows the relationship between the size and the number of color patterns.

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

At this time, since there is no difference in the appearance of the color ghost in the image between the main scanning direction and the sub-scanning direction, the same color pattern is used in the main scanning direction and the sub-scanning direction in this example.

As the color pattern size, a size of 1 × 7 is selected, but a color pattern of a smaller size such as 1 × 5 can be used if the degree of appearance of color ghost is small. A color ghost of 1 pixel can be removed from a 1 × 5 color pattern, and a color ghost up to 2 pixels can be removed from a 1 × 7 color pattern.

The image data (color code data and density data) after the color ghost correction is processed by the resolution correction circuit 40 at the subsequent stage to process the density data, and the resolution (MTF) is corrected.

Factors of the resolution degradation include problems such as an optical system, an optical traveling system, a signal processing system, and a recording system. Of these, the optical system and its traveling system directly affect the resolution degradation.

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 2-16 dots /
This is a measurement value when a black-and-white pattern having a spatial frequency of up to mm is inspected.

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.

MTF degradation is more pronounced in the sub-scanning direction. To make the same correction, the correction amount in the sub-scanning direction with respect to the main scanning direction is set to 2
It may be set up to 4 times.

In order to correct the main and sub-scanning directions to the same extent, and not to degrade the reproducibility of the fine line part, use a convolution filter or the like that uses 3 × 3 pixel image data as the resolution correction circuit. can do.

FIG. 8 shows a correction result when the convolution filter is used.

The resolution-corrected density data and color code data are respectively supplied to the color data selector 50, 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 the 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 to extract the area.

For this reason, an area extracting circuit 60 is provided to detect the area of the color marker on the document, and the area signals QR 'and QB' (see FIG. 11) obtained from the area are supplied to the data selector 50. You.

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

A multi-color copying machine capable of recording a plurality of specific colors as a color copying machine, wherein one color is developed for each rotation of the photosensitive drum, and after all the colors are developed, transfer separation is performed. In the type in which a color image is recorded by processing, a scan code signal indicates which color is currently being developed.

Therefore, when the blue color marker is detected, the corresponding color data is output at the time of the blue copy sequence, and when the area signal is obtained, the image in the blue color marker is output. Can be recorded in blue.

When the partial color conversion process is not performed, the density data is output only when the color code data matches the scan code signal. That is, in the case of a red copy sequence, while the red color code is obtained, the corresponding density data is selectively output.

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

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

If the scanning speed is increased, sampling data in the sub-scanning direction is thinned out, so that a reduction process is performed. Conversely, if the scanning speed is reduced, an enlargement process is performed.

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

The density data that has been subjected to the enlargement / reduction processing
In, multi-value processing is performed. For example, by using four threshold values, density data having a 6-bit configuration is converted into quinary values.

 The threshold data is set manually or automatically.

To automatically determine threshold data, a histogram creation circuit 100 is provided.

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

The multi-valued data of the 3-bit configuration subjected to the multi-value processing is supplied to the host computer 160 via the interface 130.

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

As the 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 are employed.

That is, the transfer drum used in the conventional color image formation is not used. In order to reduce the size of the apparatus, a three-color image of blue, red and black is developed on the OPC photosensitive member (drum) for image formation by three rotations of the drum as described above, and transfer is performed once after development. The image is transferred to recording paper such as plain paper.

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

Reference numeral 170 denotes a processing timing signal generation circuit for obtaining various processing timings, which forms a timing signal for starting reading of the CCDs 6 and 7 and the like. Numeral 180 denotes a timing signal generating circuit for obtaining a variable power timing.

In the present invention, the light distribution state of the light source is determined based on the digital color signal obtained when the reference original, in this example, the reference white plate, is read out of the digital color signals obtained immediately before the color discrimination circuit 20. Is done.

Therefore, the digital color signal obtained from a predetermined area is latched by the latch circuit 200, and the digital color signal is captured by the CPU 160 for image processing. A center pulse CSP described later is used as the latch pulse.

The digital color signal captured by the CPU 160 is further captured by a CPU (master CPU) 250 that controls an optical scanning system (scanner), and a light distribution state display process is performed.

FIG. 12 shows the image processing CPU 160 and the scanner CP described above.
An excerpt of the signal transfer relationship between the U250 and the printer CPU 150A is shown.

Timing signal generation circuit 170 from CPU 150A for printer
Are supplied with horizontal and vertical effective area signals H.V, V.V, an index signal IDX indicating the start of each horizontal scan, and an external synchronization signal such as a clock CLK.

This timing generation circuit 170 is sent from the CPU 250 for the scanner.
, An index switching signal IDX / EX is supplied. This is a control signal for switching between the internal synchronization signal generated inside the timing generation circuit 170 and the above-described external synchronization signal.

In addition, a signal COR, a reference signal REF, and a pre-scan signal PRE that determine the timing to start sampling the shading data are supplied. Reference signal REF
Is a control signal for switching the reference voltage of the A / D converters 10, 11. The pre-scan signal PRE is a pre-scan control signal for creating a histogram prior to document reading.

The index switching signal IDX · EX, the signal COR for determining the sampling start timing, the reference signal REF, and the prescan signal PRE are all active “L”.

The following serial communication signals are exchanged between the CPU 160 for image signals and the CPU 250 for scanning.

The request signal REQ used in the light distribution adjustment confirmation mode or the like is a signal for controlling transmission and reception of serial data between the scanner CPU 250 and the image processing CPU 160. This is synchronized by the serial lock SCK.

RxD indicates serial data (received data) transmitted from the scanner, and TxD indicates serial data (transmitted data) transmitted from the image processing side. These transmission / reception data RxD,
Specific examples of TxD are shown in FIG. 13 and FIG. A specific example will be described later.

In FIG. 12, the CPU 250 for the scanner and the CPU 1
The following signal transmission / reception is performed with 50A.

Of the pulses sent from the printer CPU 150A, SST
ART is a pulse designating the start of scanning with respect to the scanner.

The transmission data TxD1 is the data when the magnification is specified,
The scanning speed in the sub-scanning direction is specified for the scanner.
These are all synchronized by the serial clock SCK1.

Image data (reception data) RxD1 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, and thereby the lighting state of the light source (eg, a halogen lamp) 370 is controlled.

Further, the drive circuit 380 is controlled by the motor drive signal, whereby the drive motor 390 for the scanner is controlled.

Now, in the present invention, in the adjustment mode such as maintenance and inspection, the light distribution adjustment is confirmed at the same time.

In the light distribution adjustment confirmation mode, as shown in FIG.
When the scanner 370 is turned on and the optical system of the scanner is at the home position, information on the reference white plate is read.

The received data RxD is transferred to the image processing CPU 160 by the request signal REQ (A and B in FIG. 4).

The CPU 160 performs a determination process for each sampling location based on the received data RxD. The 2-byte determination result is the transmission data TxD. The determination is made for each color signal.

The determination result is sent to the scanner CPU 250 on the transmission data TxD for each color signal (FIG. 15C), and the result is displayed.

Display is performed for each sampling position and further for each color signal (FIG. 16). As the display element, an LED or the like can be used. The display element can be displayed such as turned off at a low level, turned on at a normal level, and blinked at an overflow.

In the light distribution adjustment confirmation mode, the level of a digital signal obtained by scanning one line is determined for each color. In the present invention, a plurality of sampling positions are set so that the light source can be confirmed over almost the entire area.

It is assumed that the effective area of one line is divided into seven parts, and data is extracted from each of the seven areas. The effective area is composed of 5000 bits. In this case, as shown in FIG. 17, the center pulse CSP (CSP1 to CSP
By shifting 7), the position of the pixel to be latched, that is, the sampling position is changed.

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

Now, the reception data RxD shown in FIG. 13 has a 7-byte configuration, and the lower 3 bits of the first byte are I / O.
O Check data CHKIP. This check data CHKI
FIG. 18 shows the relationship between P0 to CHKIP2 and the transmission mode selected thereby.

The light distribution adjustment mode is shown as mode II. Mode II is 2
The channel configuration is such that the first is a light distribution adjustment confirmation mode for cyan, and the next channel is a light distribution adjustment confirmation mode for red.

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

Mode III is also a light distribution adjustment, but this mode is used to detect the maximum level position of the linear light source. Also in this mode, the center pulse CSP is used for changing the image reading position.

An example of another code addressed to each byte of the reception data RxD is shown below.

1. SC0 to SC2: Scan code 2. CHANG: Partial color conversion code 3. EE: Automatic threshold selection code 4. CHKPRE: Prescan code 5. RD0 to RD3: Red density level 6. BL0 to BL3: Blue density level 7. BK0 to BK3: Black density level 8. HZ0 to HZ8: Magnification in the main scanning direction (50 to 400%) Of the transmission data TxD shown in FIG. PxB is 2-byte transmission data indicating a level determination result in the light distribution adjustment confirmation mode I.

Here, x indicates a sampling position in the horizontal scanning direction, and in this example, there are seven positions. The same bit at the same sampling position indicates the determination result at that sampling position.

FIG. 19 shows the relationship between the level determination condition, the determination result, and the transmission data PxA and PxB representing the determination result. And
For example, when the determination result at the sampling position x is normal, the transmission data TxD is coded as PxA = 1, PxB = 0.

FIG. 20 is a flowchart 400 showing an example of a light distribution adjustment confirmation control program.

When the rising edge of the request signal REQ is detected, the input of the received data RxD is started. When all the data input (7 bytes) is completed, the received data inserted in the first byte is received.
RxD is decoded (steps 401 to 404).

As a result of the decoding, if the mode is not the transmission mode II, the process proceeds to another processing routine 405. If the mode is the transmission mode II, the center pulse CSP1 is set (step 40).
6). Then, the color signal specified by the check data CHKIP0 to CHKIP2 is checked (step 407).
Since the color is cyan at first, a digital color signal related to cyan is first taken in, and thereafter, the same processing is performed by changing the sampling position of the center pulse CSP. When the input has been completed for all sampling positions, the input level is determined (steps 408 to 410). This determination process is performed in the same order as the number of samplings (step 411).

When all the determination processes are completed, the determination result is coded as shown in FIG. 19, and this is transmitted as transmission data TxD (step 412). And this transmission data T
When xD becomes 2 bytes, the transmission mode ends.

Similar processing is performed on the red digital color signal (step 420).

[Effects of the Invention] As described above, according to the present invention, in the adjustment mode, the level is determined based on the digital color signal obtained immediately before the color discriminating means, and is used for this determination. The sampling position in one line of the digital color signal can be changed.

According to this, the light distribution state of the light source can be known without using a device such as an oscilloscope. Further, since the light distribution state can be known over almost the entire area of one line, there is a benefit that the deterioration state of the light source can be accurately grasped.
Therefore, the presence or absence of light distribution adjustment can be accurately determined from these data.

Therefore, the present invention is very suitable when applied to a color image processing apparatus such as the above-described color copying machine.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an example of a color image processing apparatus according to the present invention, FIG. 2 is a diagram of a color discrimination map, FIGS. 3 and 4 are explanatory diagrams of a color ghost, and FIGS. FIGS. 7A and 7B are explanatory diagrams of color ghost correction, FIGS. 7 and 8 are characteristic diagrams showing MTF correction, FIG. 9 is a diagram of a density histogram, FIG.
FIG. 11 is an explanatory diagram of a change mode of a color marker, FIG. 11 is a system diagram of an area extracting circuit, FIG. 12 is a diagram showing a relationship between CPUs, FIG. 13 is an explanatory diagram of received data, and FIG. Illustration of,
FIG. 15 is an explanatory diagram of a light distribution adjustment confirmation mode, FIG. 16 is a diagram showing a light distribution display example, FIG. 17 is a diagram showing a relationship between a center pulse and a sampling pixel, and FIG. 18 is a diagram showing I / O check data. FIG. 19 is a diagram showing a relationship with a transmission mode, FIG. 19 is a diagram showing a relationship between a light distribution determination result and transmission data, and FIG. 20 is a flowchart showing an example of a processing procedure in an image processing CPU. DESCRIPTION OF SYMBOLS 1 ... Color image processing apparatus 20 ... Color discrimination circuit 40 ... Resolution correction circuit 50 ... Color data selector 60 ... Area extraction circuit 70 ... Scaling circuit 80 ... Multi-value conversion circuit 100 ... Histogram creation circuit 150 Output device 160 Image processing CPU 200 Latch circuit 250 Scanner CPU

Claims (1)

(57) [Claims] A means for decomposing color image information into a plurality of color separation images and converting the color image information into a plurality of color signals; a means for obtaining a distortion-corrected digital color signal from the plurality of color signals; And a color discriminating means for discriminating the color signal of a plurality of bits, and an image processing means for the color signal of the discriminated plural bits. In the adjustment mode, the level is determined based on the digital color signal. And a sampling position in one line of the digital color signal used for the determination can be varied.