JPH01194670A - Picture processor - Google Patents

Abstract

PURPOSE:To shorten the time necessary for pre-scanning by pre-scanning the range of a special original picture and preparing the concentration histogram of an original. CONSTITUTION:A pre-scanning time is set within the warming-up time of a copying machine, the prescribed area of about 1/5-1/6 of the maximum original size is made into the range of the pre-scanning and picture data detected within the range are used for concentration histogram preparation. When the pre- scanning is completed, the concentration histogram based on the concentration data in a pre-scanning area is stored into a memory. The data of the prepared concentration histogram are referred to by address data from a CPU at the time of threshold calculation and this is fetched through a driver 111 to a CPU 160.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an image processing device that can be applied to color copying machines that record on plain paper, and in particular to a threshold value that automatically calculates a threshold value for multi-value conversion. The present invention relates to an image processing device having a calculation function.

[Background of the Invention] In an image processing device, such as a color copying machine using a laser beam, a latent image of a predetermined object is formed on a photoreceptor drum by modulating the laser beam based on final image information. However, in this case, it is necessary to create binary or multivalued image data for laser beam modulation.

Recently, beams have been modulated using multivalued image data in order to display halftones.

An example of a color image processing apparatus that performs such multi-value processing to record images is shown in FIG. 8 and subsequent figures.

Color image information (optical properties) of a subject 2 such as a document passes through an optical system 3 and is separated into two color-separated images by a dichroic mirror 4. In this example, the color separation image of red R and the color separation image of cyan cy are divided i! I will be treated. Therefore, the cutoff of dichroic mirror 4 is 540 to 600 nm.
A certain degree is used.

The color separated images of red R and cyan Cy are supplied to image reading means such as CCDs 6 and 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 CM are supplied to an A/D converter 10.11, where they are converted into digital signals having a predetermined number of bits, 6 bits in this example. Shading correction is performed simultaneously with A/D conversion. 12 and 13 indicate shading correction circuits.

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 generation circuit 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 a configuration is possible in which the signal is 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, helmet, and black. When this process is performed, each part of the document is recognized as a red, helmet, or black color part.

In addition, it is possible to use other colors than red, helmet, and black.
This color discrimination process also includes the use of colors.

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.
bit data).

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

FIG. 9 shows an example of this color discrimination map.

The image data that has undergone color discrimination is transferred to a color image processing step.

First, the signal is supplied to the next-stage color ghost correction circuit 30, and color ghosts in the main scanning direction (horizontal scanning direction) and sub-scanning direction (drum rotation direction) can be corrected.

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

FIG. 10 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. 11A to 11C, 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.

This color ghost correction circuit is a circuit for correcting such color ghosts as much as possible.

Color ghost processing applies only to color code data.

In addition to color ghost correction, image processing includes resolution correction, partial color conversion processing, scaling processing, multi-value processing, and the like.

First, the image data (color code data and density data) after color ghost correction is sent to the subsequent resolution correction circuit 40.
At , the density data is processed to determine its resolution (MT
F) is corrected.

Deterioration of resolution includes deformation of the beam shape of the laser beam, deterioration of the development characteristics of toner on the photoreceptor drum, and the like. Among these, the optical system (original reading device) and its traveling system directly affect resolution deterioration.

FIG. 12 shows the MTF values (before correction) in the main scanning direction and the sub-scanning direction when the optical system is driven. This characteristic is 2~l
6d□ts/mI! This is the measured value when scanning a black and white pattern with a spatial frequency up to +.

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, make the correction in the sub-scanning direction relative to the main-scanning direction.

The amount of correction in the direction may be set to 2 to 4 times.

In order to correct the main and sub-scanning directions to the same degree while not degrading the reproducibility of fine line areas, a convolution filter that uses 3 x 3 pixel image data is used as the resolution correction circuit. can do.

FIG. 13 shows the correction results when using the convolution filter.

The resolution-corrected density data and color code data are each supplied to a color data selector 50, and when the partial color conversion mode is selected, the image area is recorded in a specific color.

The partial color conversion mode is a mode in which an area surrounded by a marker (color marker) on a black and white document is recorded in the color of the color marker.

For example, as shown in FIG. 14, in this mode, the area a surrounded by the helmet color marker is recorded in blue.

To do this, it is necessary to detect the chroma and force and extract the area.

For this reason, an area extraction circuit 60 is provided to detect the area of the color marker on the document, and supply the area signal to the data filler 50.

The region extraction circuit 60 outputs region signals QR and QB corresponding to the color marker region, as shown in FIG. 15, for example.

In addition to these '3' numbers, the data selector 50 also contains a scan code signal B indicating which color is currently being copied.
BR and partial color conversion signal CC are supplied, respectively.

This is a multi-color copying machine that can record multiple specific colors. One color is developed each time the photoreceptor drum rotates, and once all colors are developed, one transfer is performed. In Type 6, which records color images by performing separation processing, the scan code (No. 3 BBR) indicates how many colors are currently in production.

Therefore, when the helmet color marker is detected, if the corresponding color data is output when the blue copy sequence is obtained and the area (a) is obtained, it is possible to output the corresponding color data within the blue color marker. Images can be recorded in blue.

When not performing partial color conversion processing, scan code signal BB
Density data is output only for color code data that matches H. 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 that has been 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, the 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, this is an enlargement process.

In this example, the color code data is also enlarged/reduced at the same time.

The density data that has been 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.

The threshold data is manually or automatically set as described below.

When automatically calculating the threshold value, before the original is scanned and recorded, density data is detected by bliscanning, and a density histogram as shown in Figure 16 is created based on the output. . A threshold value for the document is determined from this density histogram.

The 3-bit multi-value data subjected to multi-value processing is supplied to the driver 140 via the interface circuit 130.

The driver 140 modulates the laser beam in accordance with the multilevel data. In this example, PWM modulation is performed.

The driver 140 may be built into the multi-value conversion circuit 80.

Output device 150 by a PWM modulated laser beam
A photoreceptor drum installed in the photoreceptor drum is used for development.

As the output device 150, a laser recording device or the like can be used.

And the YLL steamer and electrophotographic color copying machine can be used. In this example, two-component non-contact jumping development is used.
And reversal development is adopted.

That is, the transfer drum used in conventional color image formation is not used. In order to reduce the size of the device, three colors of blue, red and black are developed on an OPC photoreceptor (drum) for image formation in three rotations of the drum, and transfer is performed once after development to print on plain paper. I try to transfer it to recording paper such as.

170 is a processing timing signal generation circuit for obtaining various processing timings, which includes a clock CLK, horizontal and vertical synchronization signals HV in the main scanning direction and sub-scanning direction obtained from the output device 150 side, V
An index signal IDX indicating the start of laser beam scanning is supplied to the V-coat.

[Problems to be Solved by the Invention] In the above-described configuration, when converting density data into multiple values,
As described above, it is possible to consider both cases in which the threshold value for multilevel quantization is automatically set and cases in which it is manually set.

Therefore, as shown in FIG. 8, in addition to an automatic threshold determination circuit (EE circuit) 163 to which concentration data is supplied, a threshold table (ROM configuration) 164 in which pre-calculated threshold values are tabulated is provided.

One of the respective threshold data is selected by the selection circuit 165. This selection is made by a mode select signal obtained when specified on the operating section side.

The density data is multivalued based on the selected threshold value data.

By the way, in the case where the threshold value is automatically set in consideration of the density of the original, it is necessary to perform a bliscan to detect the density information of the original before the main scan for recording the image of the original.

Briscanning is performed on the entire manuscript.

Therefore, an image processing apparatus having such an automatic threshold value determination means has a drawback that it takes a long time for blisscanning. This means that the initial copy time will be longer.

In addition to this drawback, since a memory is required to store image data obtained by blisscanning the entire document, there are other problems such as the need to prepare a large-capacity memory.

Therefore, the present invention solves these problems and proposes an image processing apparatus that reduces the time required for blisscanning.

[Technical means for solving the problem] In order to solve the above problems, the present invention provides an image processing device that performs image processing on image information converted into an electrical signal. The present invention is characterized in that a density histogram of the document is created by bliscanning a specific range of the document image.

[Operation] In this configuration, whether the threshold value is set automatically or manually is processed by software in accordance with an external mode selection.

When the manual mode is selected, data in a threshold table attached to the CPU 160 is referred to and used as threshold data.

The threshold data used during manual operation is a fixed threshold calculated in advance, and the number of threshold data is divided into about seven levels.

On the other hand, when the automatic threshold value setting mode (EE mode) is selected, an appropriate threshold value is determined by the CPU 160 based on the density histogram from the histogram creation circuit 100.
Calculated with the intervention of

As the density data, data obtained by blisscanning a specific range of the document is used. Since the range of blisscanning is a specific area, the time required for blisscanning is shortened.

If the briscan is completed within the warm-up time of the copying machine, the initial copying time will not become longer than before even if a means for briscanning and automatically determining the threshold value is adopted.

[Embodiment] Next, an example of the image processing device according to the present invention, when applied to the above-mentioned color image processing device, will be described in detail with reference to FIG. 1 and subsequent figures.

In this invention as well, a color image processing apparatus 1 as shown in FIG. 8 is used, so a description of the same parts will be omitted.

In the present invention, the creation and selection of threshold data for multi-value processing is performed by the CPU 160.

Therefore, a histogram creation circuit 100 is provided, and the CPU 160 processes the creation of a density histogram and the threshold values (multiple threshold values in multi-value conversion) calculated for each color from the data of this density pistogram.

Therefore, the data bus of the CPU 160 is also connected to the multi-value conversion circuit 80.

In this example, the histogram creation circuit 100 performs optimal multi-value processing for each color, so a density histogram is also created for each color, and q threshold value data are output for each color. Therefore, color code data is also supplied to this histogram creation circuit 100 in addition to density data.

When creating a density histogram, a predetermined image area (
Image data is obtained by bliscanning a partial area of the entire image.

The purpose of detecting density data by blisscanning only a predetermined area is to allow the density data necessary for creating a density histogram to be collected from a predetermined area without requiring a significant amount of bliscan time. .

This briscan time can be set within the warm-up time of the copying machine. The reason why a copier requires warming up is as follows.

First, a copying machine has a rotating polygon mirror that deflects and scans an optical signal (a signal modulated by a multivalued signal, such as a laser beam) in the main scanning direction to irradiate the photoreceptor drum. (such as a polygon mirror).

This is because some warming-up time is required to stabilize the rotation of this rotating polygon mirror.

Secondly, it is necessary to pre-rotate the photosensitive drum (within one rotation) to stabilize the copying process.

Since one quartering up time is about 2 to 3 seconds, the bliscan is set to end at a time close to this one quartering up time, preferably within the warming up time.

However, if such a time is set as the blisscan time, the area of the predetermined region to be blisscanned becomes extremely narrow.

To avoid this drawback, in the main scanning direction (horizontal direction in Figure 3)
The image information necessary for threshold calculation is extracted by sampling the image information while thinning it out, and by making the scanning speed of the optical system faster in the sub-scanning direction (tJ1 direction) than during normal recording.

For example, if the resolution is 16 dots/mta,
Samples are taken in the horizontal direction while being thinned out to about 1 dot/mm.

In this example, the scanning speed in the sub-scanning direction is selected to be approximately 4 times the speed. By setting the speed to 4 times, image information is sampled once every four lines. Furthermore, by setting the speed to 4 times, the image data within the predetermined area has been completely averaged and detected as the density data.

With this selection, assuming that the maximum original size is 84 size, in the embodiment, as shown in FIG. becomes.

Then, image data that can be detected within this range is used to create a density histogram.

Therefore, the histogram creation circuit 100 is configured as shown in FIG.

In the figure, reference numeral 101 indicates a memory, which stores density histogram data (a value indicating the frequency of occurrence) based on density data obtained by Briscan.

In the case of a color original, an image with good color reproducibility can be recorded by calculating an optimal threshold value for each color and performing multi-value conversion based on this.

In order to determine a plurality of threshold values for each color in this way, a density histogram is created for each color. In that case, memory 1
As shown in FIG. 4, 01 has a memory area for each color.

For this reason, color code data for distinguishing memory areas can also be used as address data for about 1 L of memory 101 (see FIG. 4).

An example of color code data is shown in FIG.

In this example, the frequency for the density histogram is immediately calculated from the read image data, and when the Briscan is finished, the density histogram data is stored in this memory 10.
It is configured to be stored at 1.

Moreover, since the density pistogram data is necessary for threshold value determination, the memory 101 is configured so that it can be referenced not only by image data but also by address data sent from the CPU 160.

Therefore, the peripheral circuit of the memory 101 is configured as follows.

First, a latch circuit 102 is provided on the address side of the memory 101.
and an address selector 103, the image data (fA degree data and color code data) read out by the briscan is once latched by the latch circuit 102, and this image data is transferred to the address data via the address selector 103. The data can be supplied to the memory 101 as follows.

Similarly, address data completely sent out from the CPU 1.60 is also supplied to the memory 101 via this address selector 103.

As described above, the image data is used when creating the density histogram, and the address data of CPU] and 60 are used during the threshold value calculation mode.

The latch pulse applied to the latch circuit 102 is created as follows.

As mentioned above, at a disintegration level of 16 dots/ml 11, relative to the basic clock CLK (Fig. 6E).

Then, the sampling clock 5 is divided into 1716.
CLK (FIG. F) is used as a latch pulse.

The sampling clock 5CLK and the like can be generated in a timing generation circuit 108 for creating a histogram.

Therefore, the basic clock CLK is supplied to this generating circuit 108.

Further, as will be described later, this generation circuit 108 further includes a bliscan signal HPS that determines the blisscan width in the horizontal direction and a blisscan signal PS that determines the blisscan width in the vertical direction (see FIG. 6B).

C) is supplied.

The address selector 103 is supplied with a vertical bliscan signal VPS as a selection signal as shown in FIG.

Note that the selector 109 is a selector for switching the read enable No. 43 and write signal for the memory 101 between the density pistogram creation time and the threshold value calculation mode. Therefore, the readout and Ml-containing signals m, Tff”T (Fig. 7c) created at the generation port v8108
, F) is supplied to the case selector 109, and
Similar signal tiles U and Wm are supplied from the CPU 160.

Respective signal selection is performed by a briscan signal VPS.

In order to immediately create a density histogram from the image data supplied to the memory 101, the following method may be employed.

In this example, an adder 1 that increments the read data by "1" is installed on the I10 port side of the memory 101.
05 and a latch circuit 106 for latching the output thereof, and the latch output is stored in the memory area of the same address of the memory 101 via the I10 port again.

In order to control latch timing and the like, the latch circuit 106 is supplied with a latch output enable signal r shown at H in FIG. 7 and a latch clock LCLK.

When creating a density histogram, a memory area of the memory 101 is selected using color code data of the image data, and its address is set based on the value of the density data.

When image data is supplied, the read enable signal m
(FIG. 7F), the memory 101 enters the read state, the data (value indicating the frequency) stored at the referenced address is read, and this data is sent to the adder 101.
is incremented.

The addition output is latched particularly at the rising timing (time tl) of the latch clock LCLK (E in the figure). Thereafter, since the latch circuit 106 is enabled by the enable signal 77, the write signal T
The latch output can be completely rewritten at the rising edge point t2 of 'rWT (C in the figure).

Note that the period from reading to writing in the memory 101 is a period during which the latch circuit 102 is in an active state by the sampling clock 5CLK (see FIG. 7).

In this way, by repeating rewriting while incrementing the data at the referenced address, data indicating the frequency of the same density data has been stored at the same address.

Therefore, when the Briscan is completed, a density histogram as shown in FIG. 16 based on the density data in the Briscan area is stored in the memory 101.

This makes it possible to read out image data and create a density histogram at the same time.

Therefore, there is no need to store the density data itself, and the capacity of the memory 101 can be significantly reduced.

The created density histogram data is used for threshold calculation.
-1 CPU is referred to by address data, and this is taken into the CPU 160 via the driver 111. Then, the CPU 160 calculates the optimal threshold value for each color for the image from the calculated density histogram.

The calculated threshold value data is sent to a value converting circuit 80, and the density data is subjected to multivalue processing based on this.

In FIG. 1, reference numeral 180 is a timing signal generation circuit for generating the timing (g) used during the scaling process.

[Effects of the Invention] As explained above, according to the present invention, only a specific area of a document is bliscanned, and a density histogram necessary for threshold calculation is created from the image data that is not te3 by this bliscanning. It was designed to do so.

According to this, because only a specific area is blisscanned,
This blisscan takes very little time. In particular, if the briscan time is set within the time required for warming up the copying machine, the initial copy time will not change even if the briscan is performed.

In other words, it has the feature of being able to eliminate the problem of longer copying time due to bliscanning.

Furthermore, since the density histogram is created at the same time as the image data is read, there is a practical benefit in that the memory capacity for creating the density histogram can be significantly reduced.

Therefore, the present invention is extremely suitable for application to the color image processing apparatus as described above.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing an example of an image processing device according to the present invention, FIG. 2 is a system diagram showing an example of a density histogram creation circuit, FIG. 3 is a diagram showing a Briscan area, and FIG. 4 is a diagram showing image data. FIG. 5 is a diagram showing the relationship between color and color code data, FIGS. 6 and 7 are waveform diagrams used to explain how to create a histogram, and FIG. 8 is a diagram showing the relationship between color and color code data. A system diagram of a color image processing device used to explain the present invention, FIG. 9 is a diagram of a color discrimination map, FIGS. 10 and 11 are illustrations of color ghosts, and FIGS.
The figure is an explanatory diagram of resolution correction, FIGS. 14 and 15 are explanatory diagrams of partial color conversion, and FIG. 16 is a diagram of a density histogram. 1... Color image processing device 20... Color discrimination circuit 30... Color ghost correction circuit 40... Resolution correction circuit 50... Color data selector 60... Area extraction circuit 70... Magnification change Circuit 80...Multi-value conversion circuit 100...Histogram creation circuit 101...Memory 105...Adder 106...Latch circuit 108...Timing generation circuit 140 ports/driver 150...Output device 160...CPU 170...Processing timing signal generation circuit Fig. 3 57mm Fig. 4 Fig. 5 Fig. 9 Fig. 16 DL Power, -,, V DH Fig. 10 Fig. 11 A B C Ward guard Ku 0

Claims (1)

[Claims] (1) An image processing device that processes the image information based on the image information converted into an electrical signal prescans a specific range of the original image to create a density histogram of the original. An image processing device characterized in that: