JPH08251402A - Image processing unit - Google Patents

Abstract

PURPOSE: To select another content of image processing by converting three- primary R, G, B signal obtained from a read original into a lightness signal, generating the histogram of the signals, analyzing automatically the histogram so as to discriminate the type of the original. CONSTITUTION: A lightness generating section 200 calculates lightness data close to a specific visual sense of human being based on R, G, B data. A 1st histogram memory 202 is used to simply obtain the lightness histogram of an original and 2nd histogram memory 204 is used to obtain the histogram of achromatic dots in the original. A minimum value circuit 212 and a maximum value circuit 214 detect a minimum value and a maximum value of the received R, G, B data, and a subtract circuit 216 obtains a difference between the minimum value and the maximum value. When a comparator 218 discriminates it that the difference is smaller than a prescribed level, the original data are discriminated to achromatic data and the write of the lightness data to the 2nd histogram memory 204 is allowed. Thus, it is identified as to whether an original is a black/white original or a color original and its copy made is automatically decided to increase the copy speed of a black/white original.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus for photoelectrically converting an image of an original to read the image and performing image processing such as background adjustment from the obtained digital image signal.

[0002]

2. Description of the Related Art An image processing apparatus for reading and processing a document image is provided in a full-color digital copying machine or the like and is connected to a digital printer. A variety of originals are targeted by the image processing apparatus, and include full-color originals, single-color originals, character line drawings, photographs, maps, halftone originals, photographic paper photographs, and printed photographs. In order to read and appropriately copy these various originals, it is desirable to switch the image processing contents according to the type of original. Therefore, conventionally, the user selects the document type on the operation panel, and the image processing apparatus performs appropriate image processing according to the selection.

[0003]

However, the manual selection of the document type by the user has a problem that it takes time and effort for the user. Further, when various originals are loaded on the automatic original conveying apparatus, it is not possible to cope with them by manual selection. In addition, it must be able to process both full-color and monochrome color documents.

An object of the present invention is to provide an image processing apparatus capable of automatically discriminating a document type.

[0005]

The image processing apparatus according to the present invention is a device obtained by reading an original with a photoelectric conversion element.
A brightness signal generator for converting the R, G, B signals of the primary colors into a brightness signal, a histogram creating means for creating a histogram from the brightness signal, and an original type from the histogram (preferably a character line drawing, a photograph and a full color or monochrome for each). When the original type determining means for determining the original type of color) and the automatic original type determining mode are selected, the subsequent image processing contents (for example, background adjustment, black character edge) based on the determination result of the original type determining means. Processing switching means for switching the presence / absence of emphasis or gradation reproduction switching).

[0006]

In the image processing apparatus, the types of originals are automatically discriminated for various originals and the optimum image processing is selected. Therefore, by performing a preliminary scan of the original, the brightness (VH) close to the human relative visual sensitivity (brightness) is obtained from the read data, a histogram of the brightness is created, and analyzed to analyze the original type (preferably Is a character line drawing,
Automatically determine photos and their full and monochrome colors). This determination is made based on the histogram. The determination result is preferably displayed by the display means. Then, image processing (for example, background adjustment, presence / absence of black character discrimination, or gradation reproduction switching) suitable for each document type is selected and switched. As a result, image processing such as background adjustment can be uniquely processed in either the full color mode or the monochrome color mode.

[0007]

Embodiments of the present invention will be described below with reference to the accompanying drawings. (1) Overall Configuration of Digital Color Copier FIG. 1 shows the overall configuration of a digital full color copier. The document is read by the image scanner unit 30 and signal processing is performed by the digital signal processing unit 10. Printer unit 20
Outputs an image corresponding to the original image read by the image scanner unit 30 on paper in full color. In the image scanner unit 30, the original placed on the original platen glass 31 is pressed by the pressing plate 39, which is replaced when the automatic original feeding device (not shown) is mounted. A document on the platen glass 31 is indicated by a lamp 32.
And is guided to the mirrors 33a, 33b, 33c, forms an image on the linear full-color sensor (CCD) 36 by the lens 34, full-color information red (R), green (G),
It is converted into a blue (B) component and sent to the signal processing unit 10.
By driving the scanner motor 37, the first
The speed of the slider 35 is V, and the speed of the second slider 40 is V / 2 to mechanically move in the direction perpendicular to the electrical scanning direction of the color sensor to scan the entire surface of the original. A white plate 38 for shading correction is provided at the edge of the platen glass 31.

The signal processing unit 10 electrically processes the read signal, and magenta (M), cyan (C), yellow (Y),
The black (Bk) components are decomposed and sent to the printer unit 20. One component of C, M, Y, and Bk is sequentially sent to the printer unit 20 for each original scanning in the image scanner unit 30, and one printout is completed by a total of four original scanning (surface). Sequential transfer method). Signal processing unit 10
The C, M, Y, and Bk image signals sent from the laser diode drive (PHC unit) drive-modulate the semiconductor laser 214 according to the image signal level. The laser light scans the photosensitive drum 206 via the polygon mirror 215, the f-θ lens 216, and the folding mirrors 217a and 217b.

The developing unit comprises C, M, Y, and Bk developing units 208a, 208b, 208c, and 208d. The developing units 208a, 208b, 208c, and 208d are in contact with the photosensitive drum 206, and the charging charger 207. The electrostatic latent image formed on the photosensitive drum 206 charged by is developed with toner. On the other hand, the paper feeding units 201a, 201
Transfer drum 202 for the paper fed from b, 201c
It is wound around by the suction charger 204 and conveyed to the transfer position by the timing roller 203, and the image developed on the photosensitive drum 206 by the transfer charger 205 is transferred onto a sheet. After the four colors of C, M, Y, and Bk are sequentially transferred in this manner, the separation chargers 209a and 209b are transferred.
The paper is separated and conveyed by the fixing roller 210a,
It passes through 210b and is discharged to the paper discharge tray 211. 218 and 219 are reference position sensors for the transfer drum,
Reference numeral 20 is a separation claw that separates the paper from the transfer drum.

(2) Processing of Image Signal in Signal Processing Unit FIGS. 2 and 3 show the overall configuration of image processing of the signal processing unit 10. The image scanner unit 30 forms an image of the reflected light from the document surface on the linear CCD sensor 36 by the micro optical system, and obtains an analog signal photoelectrically converted into R, G, B color separation information. These signals are sent to the signal processing unit 10. The A / D conversion unit 100 uses the A / D converter to convert the image data of 400 DPI photoelectrically converted by the CCD sensor 36 into 8 bits (256 gradations) for each R, G, B color information.
Convert to digital data. Shading correction unit 1
In order to eliminate unevenness of the light amount of R, G, B data in the main scanning direction, the data No. 02 has the data read by the white plate 38 for shading correction inside independently for each R, G, B prior to reading the original. Is stored as reference data in a shading memory (not shown), converted into an inverse number, and then multiplied by the read data of the document information to correct the shading. The interline correction unit 104 uses an internal field memory (not shown) according to the scan speed (magnification on the sub-scanning side) in order to match the reading positions of the R, G, and B sensor chips in the scanning direction. Then, the white data is subjected to delay control line by line, and R, G, B data is output. The timing control unit 106 includes the CCD sensor 3
6, A / D conversion unit 100, shading correction unit 102
Also, the timing of the interline correction unit 104 is controlled.

R output from the line correction unit 104,
For the G and B data, the scaling / movement control unit 108
Using two line memories for scaling for each G and B data,
The input / output is alternately performed on one line, and the write timing and the read timing are controlled independently to perform the scaling / movement control in the main scanning direction. In this control, an interpolation process is performed before writing on the reduction side and after reading on the enlargement side according to the scaling ratio to prevent loss or rattling of the image. Also, by this control, image repeat processing, enlarged continuous shooting processing, and mirror processing are performed. The histogram generation unit 110 generates a brightness signal from the R, G, B data after line-correction obtained by preliminarily scanning the document information, and creates a histogram of the document. From the obtained histogram information, automatic color selection judgment to judge the color / monochrome of the original, judgment of the original background level to automatically skip the background level of the original, and original mode of copy operation
Automatically set (standard / photo mode).

The HVC converter 114 temporarily converts the R, G, B data from the scaling / movement controller 108 into a lightness signal (V data) and a color difference signal (Cr, Cb data). Editing processor 1
Upon receiving the V, Cr, and Cb data, 16 performs an editing operation such as color change or coloring by closed loop area detection based on the designation of an optional editor. The bill recognition unit 118 determines whether or not the originals stacked on the original glass 31 are bills or securities, and instructs copy prohibition based on the result. Image interface section 1
20 is V, which is sent via the first image selector 122,
Upon receiving the Cr and Cb data, the image data is transferred to an external device. In order to support various color signal interfaces of image data, in this block, V, Cr, Cb signals to R, G, B signals and X, Y, Z signals and L ^* , a ^* , b which are general color spaces are used. ^{* It} has the function of converting to signals etc. and outputting to an external device, or conversely converting the image data transferred from the outside into V, Cr, Cb signals. Further, the C, M, Y, Bk data to be transferred to the printer unit 20 can be transferred to an external device,
It also has a function of receiving C, M, Y, Bk signals from an external device and transferring them to the printer unit 20 side.

The image synthesizing unit 124 includes the second image selector 1
After selecting any of the V, Cr, and Cb data output from the image interface unit 120 or the edit processing unit 116 via 26, image combination (embedding / character combination) with the document data from the HVC conversion unit 114 is performed. To do. The HVC adjustment unit 128 has a lightness (V: brightness), a hue (H: hue), and a saturation (C: for the V, Cr, and Cb data from the image composition unit 124.
For the purpose of performing image adjustment corresponding to the human sense of "vibrancy", adjustment is independently performed for each of H, V, and C based on the designation of the operation panel. The AE processing unit 130 controls the background level of the document with respect to the lightness component based on the information obtained by the histogram generation unit. Inverse HVC converter 132
Performs data conversion again from V, Cr, Cb data to R, G, B data.

In the color correction unit 134, first, the LOG correction unit 1
36 converts the re-converted R, G, B data into density data (D
While converting to R, DG, and DB), the monochrome data generation unit 138 creates brightness data from the R, G, and B data, and then generates gradation data (DV) for monochrome reproduction. UCR
The BP processing unit 140 uses the difference between the maximum value and the minimum value of R, G, B data (MAX (R, G, B) -MIN (R, G, B)) as the document saturation information, and DR, DG, Minimum value of DB (MIN (DR, DG,
DB)) is used as the original undercolor component of the original and undercolor removal / blackening processing according to those values is performed, and C is determined from the DR, DG, and DB data.
Create O, MO, YO, Bk data. The masking calculation unit 142 performs masking calculation processing for color correction, and
The C, M, Y data (CO, MO, YO) after R processing is converted into CMY data for color reproduction according to the color toner of the printer unit 20. The color data selection unit 144 outputs the monochrome DV data as the monochrome copy mode when the operation panel designation or the ACS determination determines that the color data is monochrome.
In the full color mode, according to the reproduction process signal (CODE), the masking calculation processing data (C, M, Y data) is selected during the C, M, Y reproduction process, and the BP processing data (Bk data) is selected during the Bk reproduction process. Output.

On the other hand, the area discriminating unit 146 determines the minimum value (MIN (R, G, B)) and the difference between the maximum value and the minimum value (MAX (R, G, B) -MIN) from the R, G, B data. (R, G, B)), the discrimination such as the black character discrimination and the halftone dot discrimination is performed, and the result (JD signal)
And the correction data (USM signal) are output. Further, in order to achieve both the reproducibility of the image character area and the graininess of the image, a LIMOS signal for varying the image reproduction period is output to the printer side. The MTF correction unit / sharpness adjustment unit 148
The input C, M, Y, Bk data is controlled optimally for the copied image by controlling edge enhancement, color fringing correction, smoothing processing, etc., based on the area discrimination result. Further, the γ correction / color balance adjustment unit 150 adjusts the γ curve and the color balance of C, M, Y, Bk according to the density level information input from the operation panel. In this way, the variously corrected C, M, Y, Bk data are transferred to the printer side together with the LIMOS signal for switching the gradation reproduction method, and a 400 DPI, 256 gradation full color copy image is obtained. Here, the CPU 152 controls the signal processing unit 10, and the operation panel 154 performs input / output and display of data.

(3) Copy Mode Next, the copy operation mode of this full-color copying machine will be described. FIG. 4 is a basic screen on the operation panel 154, and the user can set various modes. (A) Base processing (AE processing and manual setting) First, is automatic exposure (AE) processing performed for the base processing?
You can choose whether to select one level of manual designation of stages. In the AE processing, five types of originals are selected from the original histogram information by the preliminary scan operation.
(Color standard (background white, with background color) / photo original and black-and-white standard / photo original), color standard (white background) or black-and-white standard original, perform brightness gradation complementation as shown in FIGS. 12 and 13. , For other types (photos), the manual center level is automatically selected. When the manual is specified, the contents are as shown in Table 2.

(B) Original mode An ACS (automatic color mode selection) mode or four types of original modes can be selected. When the ACS mode is selected, one of the four document modes is automatically selected according to the document type determination by the preliminary scan operation. When it is determined that the original is a black-and-white original, either the monochrome standard mode or the photograph mode is automatically selected, and the monochrome mode copy operation is performed by the black one-color reproduction process. For color originals, color standard originals /
Automatically select one of the photo modes and select C, M, Y, Bk 4
Copy operation is performed by a full-color reproduction process using colors.
The same applies to the manual mode, but when the monochrome standard / photo mode is selected, the operation screen changes to the monochrome mode operation screen (not shown), and the R, G, and B data for determining the gradation data for monochrome as the document parameter is set. Select the mixing ratio. (In the ACS mode, the R, G, B average sensitivity distribution is set as the default in the manual operation, and the relative luminous efficiency distribution is set as the default.) Further, the reproduction color can be selected from 16 colors including black. In addition, C, M, Y,
Image separation mode that reproduces Bk data on paper, negative / positive inversion, base color, image erase
Create function for image adjustment, hue (hue) / saturation
(Brightness) / Sharpness / γ correction (contrast brightness / darkness) / Color balance (RC / GM / BY / copy density) are changed at the same time to display multiple monitor images at the same time. There is. In any case, detailed description is omitted.

(4) Preliminary scanning operation In the copying machine of this embodiment, the preliminary scanning operation is performed,
The result is analyzed to determine the original type and automatic exposure
(AE) processing and automatic color selection (ACS) processing are performed. Before copying, the document scanning unit is stopped on the side of the shading correction plate 38 opposite to the document reference position during main scanning. When the copy button is pressed on the operation panel 154,
After the lamp is turned on, the shading correction plate 38 is moved to scan the correction data to scan it, and returns to the document reference position while creating the histogram data of the document. The automatic exposure process and the automatic color selection process are confirmed from the created histogram data, and the main scan operation is started.
This shortens the first copy time.

(5) Histogram Generation Next, the histogram generation in the preliminary scan operation will be described. FIG. 5 is a block diagram of the histogram detection unit 110. The histogram detection unit 110 obtains a histogram of R, G, B data in the original area during the preliminary scanning operation. Since the histogram memories 202 and 204 are initialized in advance before starting the preliminary scan, C
The PU 152 writes “0” in the addresses of all gradation levels (0 to 255) in the histogram memories 202 and 204. From the R, G, B data (8 bits) input from the interline correction unit 104, the brightness creation unit 200
Calculates a lightness signal (VH) based on the following equation, and this is input to the first histogram memory 202 and the second histogram memory 204 as an address.

## EQU1 ## VH = 0.31640625 * R + 0.65625 * G + 0.02734375 * B (1) The lightness signal obtained by this equation is approximate to the human visual acuity (brightness). Here, the target of the histogram creation is not the R, G, B data but the brightness data VH, because the data separated into the brightness / color difference signals is corrected by the automatic exposure process. Will be described in detail.

Based on the sampling interval set value from the CPU 152, the sampling interval determination circuit 206 takes in the intervals (decimation rate) in the histogram memories 202 and 204.
To decide. This is because creating a histogram of all dots of the maximum document size (A3) requires a maximum memory capacity of 32 Mbits, and the sampling interval is appropriately set (main scanning direction: 1/8, sub-scanning direction: 1). / 4) thinning out,
It is set to 1 Mbit. FIG. 6 is a diagram showing an example of a sampling situation in histogram generation. When a document placed on the platen glass 31 (hatched portion) is read, the data at the position of the circle is sampled. Further, the document size is detected before the preliminary scan, and various signals are input to the sampling interval determination circuit 210 from the timing control unit 106. Here, / HD signal (main scanning direction) and / VD signal indicating the document size area
The (sub-scanning direction) is input to the sampling interval determination circuit 210, and the generation of the histogram is permitted only within the effective original area. It should be noted that / TG is a main scanning synchronization signal and has a cycle for each line. (In this specification,
A signal with "/" at the head means a negative logic signal. ) Further, VCLK is a synchronous clock of image data.

When the address ADR is input to the histogram memories 202 and 204, the histogram data of the address is read out, +1 is added to the data by the adders 208 and 210, and the same is written again.
That is, the operation of the histogram is 8 dots per 1
The cycle is a read modify write cycle, the addresses of the histogram memories 202 and 204 indicate gradation levels (brightness), and the data is the frequency (number) of each gradation level.
Is represented. When the preliminary scan is completed, CP
U152 reads the frequency data of each gradation from the histogram memories 202 and 204. As will be described later, the contents of the automatic exposure operation, automatic color selection operation, etc. are determined from the histogram data obtained in the preliminary scan operation.

Two types of histogram memories 202 and 204 are prepared for automatic color selection processing. The first histogram memory 202 simply finds the brightness histogram of the document, and the second histogram memory 204 finds the histogram of the achromatic dots in the document. Therefore, the minimum value circuit 212 and the maximum value circuit 21
Reference numeral 4 detects the MAX value and the MIN value of the input R, G, B data, and the subtraction circuit 216 obtains the difference between them. Then, the comparator 218 determines that the difference is a predetermined level (SRE
When it is determined to be smaller than F), the writing of the brightness VH data to the second histogram memory 204 is permitted.
That the (MAX value-MIN value) of the R, G, B data is small indicates that the document data is achromatic data. Therefore, the second histogram memory 2
04 means that the histogram is calculated only for chromatic data. In the first histogram memory 202, / WE is always at the “L” level, and writing is possible for all pixels.

(6) Automatic Color Selection Processing (ACS) The automatic color selection mode discriminates whether the original placed on the original glass 31 is a monochrome original or a color original and automatically determines the copy mode. Mode. As a result, a black-and-white original can be reproduced in an image in a reproduction process of only Bk, so that the copy speed is increased. In particular, when the automatic document feeder is used, even if a black-and-white document and a color document are mixed, an appropriate copy can be obtained without the operator being aware.

The determination of automatic color selection will be described below. h1 (n) represents frequency data at the brightness level n of the first histogram created in the first histogram memory 202, and h2 (n) represents the second histogram memory 2
The frequency data at the lightness level n of the second histogram created in 04 is represented. The CPU 152 determines the second histogram 2 from the frequencies (h1 (n)) of the first histogram 202.
The third histogram by subtracting each frequency (h2 (n)) of 04
(h3 (n) = h1 (n) -h2 (n)) is created. this is,
The histogram of the chromatic portion of the document is shown. As shown in FIG. 7, two types of histogram memories 202 and 204
The following quantities can be analyzed from the two histograms created in the above. From the first histogram memory 202, W = the number of dots in the background (white) area (n = μ1 to 255) in the original, M = black and white halftone (gray) area (n = μ2 to μ)
1) the number of dots, B = the number of dots in the black region (n = 0 to μ2), and S = the sum of the first histogram total frequencies = the total number of pixels in the original size. Further, the second histogram memory 204
Therefore, C = the number of dots in the color area (n = σ1 to σ2).
That is,

[Equation 2]

In automatic color selection, based on the brightness data,
The document type is discriminated from the ratio of achromatic color to chromatic color. Specifically, using S and C obtained from the histogram, the ratio of chromatic color dots in the document is obtained, and whether or not color copying is performed,
I am deciding whether to make a black and white copy. As described above, C is the number of dots in the color area (n = σ1 to σ2), and Sn is the total number of pixels in the document size. Therefore, C / S corresponds to the ratio of chromatic color to (chromatic color + achromatic color). That is, if the judgment formula (C / S) is less than or equal to the reference value,
Since there are few chromatic colors, the black-and-white copy mode is set, and when it is larger than the reference value, the full-color copy mode is set because there are many chromatic colors. Here, by using S as the denominator, it is possible to ignore the determination of automatic color selection, especially the influence of the document size.

FIG. 8 shows a flow of automatic color mode selection by the CPU 152. First, the histogram creation unit 110
To allow the first and second histogram memories 202, 20 to
A brightness histogram is created in step 4 (step S10).
0). Next, the above C and S are obtained from the histogram (step S102), and the ratio C / S is calculated (step S1).
04). If C / S is larger than a predetermined threshold value (YES in step S106), it is determined to be a color original document (step S108), and if not (NO in step S110), it is determined to be a monochrome original document. (Step S112).

(7) Discrimination of Original Type Further, the CPU 152 first sets the histogram memories 202 and 204 as the first stage of the automatic exposure (AE) process.
The following five types of originals (see Table 1) are determined based on the information (1) and the result of automatic color selection (ACS) (see FIG. 8). (a) Black-and-white photo manuscript (black-and-white photo, black-and-white high-definition halftone printing, etc.) (b) Black-and-white standard manuscript (black-and-white characters, line drawings, etc., relatively white background) (c) Full-color photo manuscript (color silver salt photograph , Color high-definition halftone printing, etc.) (d) Color standard document (white background) (relatively white background including color characters and color line drawings) (e) Color standard document (with background color) (color background) (Documents with a)

The automatic color selection is also obtained from the histogram, and the document type is determined by analyzing the histogram (see FIG. 9). The concept of determining the manuscript type is as follows. For color originals and black-and-white originals, the number of achromatic pixels and the number of chromatic pixels are obtained from the histogram, and the number of chromatic pixels and the total achromatic If the ratio of the number of pixels is larger than a reference value, it is determined that the original is a color original, and if not, it is determined that the original is a monochrome original. Further, the photographic original and the standard original can be determined from the distribution of the histogram. The standard manuscript is a manuscript mainly composed of characters, and the histogram shows a binary distribution as shown in FIGS. Here, the case where the base is not white is also considered. If it shows a binary distribution, it is judged to be a standard manuscript, and if not, it is judged to be a photographic manuscript. Specifically, the number of pixels in the density range (black side) is compared from the histogram with the number of pixels near white, and if the former is small, it is determined that the original document is a binary document and the document is a standard document. In the case of a color standard document, the case where the background is white can be determined by this. In the case of color originals, it is necessary to distinguish between standard originals with a background color and color photo originals, so it is judged that a color photo original is one with a wide distribution in the histogram and an average,
If not, it is determined that the original document is a color standard document with a background color. Specifically, it is determined by the difference between the maximum value and the minimum value in the histogram.

FIG. 9 shows a flow of the document type discrimination by the CPU 152. First, from the data h1 (n) and h2 (n) of the first and second histogram memories 202 and 204, the various sums of frequencies G25, G24, G23, G22, G defined next are given.
21, G20, G35, G34, G33, G32, G31, G
30 is calculated, and further, the background level a (the gradation level indicating the maximum frequency of the output data ID 0.4 or less in the second histogram memory 204) and the character level b (the output data ID 0.6 or more in the second histogram memory 204) are calculated. To obtain the gradation level indicating the maximum frequency (step S
200).

(Equation 3) As shown on the left side of FIG. 10, the brightness VH levels 0 to 25
5 corresponds to the output data ID, but these values are in the six ranges of the output data (0.2 or less, 0.2 to 0.4, 0.4.
.About.0.6, 0.6 to 0.8, 0.8 to 1.1, 1.1 or more), h2 (n) or h2 (n) or h3 (n) (= h1
(n) -h2 (n)). In addition, in FIG. 10, the range indicated by C, M, Y, R, G, and B indicates the existence range of VH in the corresponding color.

Next, photographs (a) and (c) and standard manuscript (b) and
In order to distinguish (d) from the standard document with a background color (e), a photograph document and a document with a background color are determined. First, from the processing result of the automatic color selection (ACS) described above, a black and white original (a)
It is possible to distinguish between (b) and color originals (c), (d), and (e) (step S202). If the determination result of automatic color selection is color (Y in step S202)
ES), the process proceeds to step S204, and the type of color original is determined (here, α2 represents a threshold value). First, output data (ID) achromatic color of 0.4 or more and output data (ID)
If the sum of frequencies with chromatic colors of 0.2 or more (corresponding to a portion other than the white background) accounts for a small portion of the total document frequency (Sn) (YES in step S204), there are many white background portions, and thus the color standard It is determined that the original (white background) (b) (step S206). And for image processing, the background adjustment is
Automatic exposure (AE) processing is set, black character determination processing is set, gradation reproduction switching processing is set, and the original mode is set to the color standard mode (step S208). If output data
If the sum of the frequencies of the achromatic color of (ID) 0.4 or more and the chromatic color of the output data (ID) of 0.2 or more accounts for a large percentage of the total document frequency (S) (NO in step S204), It is determined whether or not the ratio of the sum of frequencies in the frequency block with chromatic color is very high (step S210, where α
3 represents a threshold value). Specifically, the ratio between the difference between the maximum sum and the minimum sum of the chromatic color frequency blocks G30 to G34 and the total manuscript frequency is calculated, and when this ratio is not very high (in step S210). NO), since the image data is not averaged over all brightness gradations, it is determined that the background of the color standard original is colored (a) (step S212). Regarding the image processing, the background adjustment is centered on the standard manual setting, the black character discrimination processing is set, the gradation reproduction switching processing is set, and the original mode is set to the color standard mode (step S21).
4). Otherwise (YES in step S210),
Since the image data is average over all brightness gradations,
It is determined that the original is a color photograph original (c) (step S21
6) Regarding the image processing, the background adjustment is performed at the center of the photo manual setting, the black character determination processing is not set, the gradation reproduction switching processing is not set, and the original mode is the color photographic mode (step S218).

On the other hand, if the discrimination result of the automatic color selection (ACS) is not color (NO in step S202),
The process proceeds to step S220 (where α1 represents a threshold value). If the achromatic color sum of output data (ID) 0.4 or more is small in the total document frequency (S) (YES in step S220), it is determined to be a black and white photograph (e) (step S222). Regarding the image processing, for the background adjustment, the center of the photograph manual is set, the black character discrimination processing is not set, the gradation reproduction switching processing is not set, and the original mode is set to the monochrome standard mode (step S224). Otherwise (NO in step S220), since there are many white background portions, it is determined that the original is a black and white standard document (d) (step S22).
6) Regarding image processing, background adjustment is automatic exposure (AE)
The processing is set, the black character determination processing is not set, the gradation reproduction switching processing is set, and the original mode is set to the monochrome standard mode (step S228).

Finally, the respective document type determination results are displayed on the basic operation screen (FIG. 4) of the operation panel 154 (step S230). Without this display, the user may be uncertain because the determination result of the document type is unknown. Therefore, by displaying the document type on the operation panel 154, the user can immediately understand the determination result. Through the above-described processing, it is possible to determine the document types (a) to (e) and set the image processing corresponding thereto. Table 1 shows the contents of automatic color selection (ACS), image processing mode and document mode for each document type. Also, Table 2
Indicates settings of the background processing in various modes.

[0033]

[Table 1]

[0034]

[Table 2]

(8) HVC conversion and HVC adjustment The copying machine of this embodiment converts the image data into HVC data and performs the processing. The HVC conversion unit 114 includes a matrix calculator that converts R, G, B data into a color space signal composed of a lightness signal (V) and two kinds of color difference signals (Cr, Cb).

[Equation 4] The three attributes of color, which are hue, lightness, and saturation, are obtained as follows using V, Cr, and Cb signals.

## EQU5 ## Lightness (Value) = V Saturation (Chroma) = (Cr ² + Cb ² ) ^1/2 (5) Hue (Hue) = arctan (Cb / Cr) Converted to such signals V, Cr, Cb The reason for doing this is that by performing processing that is similar to the human sense, high image quality is realized and the processing that is performed later (image synthesis, automatic exposure processing, HVC adjustment) becomes easier.

The output of the HVC conversion unit 114 is transferred to the processing units after the image composition unit 124, and also the editing processing unit 11
At 6, edit images such as color changes. On the other hand, the bill recognition unit 118 determines whether the original is a bill or securities, and issues an instruction to prohibit the copy operation. Then, in the image synthesizing unit 124, the V, Cr, Cb signals output from the HVC converting unit 114 are once input to the delay memory 115 and are synchronized with the image signal from the editing processing unit 116.
Then, the image composition unit 124 performs image composition from the output data (V, Cr, Cb) of the delay memory 115 and the output data (V, Cr, Cb) of the image selector 126. Although typical synthesizing methods include watermark synthesizing, embedding synthesizing, and character synthesizing, detailed description thereof will be omitted.

As shown in FIG. 11, the HVC adjusting unit 128
Are provided for the image quality adjustment mode. The HVC adjustment unit 128 includes a matrix calculator 128a that receives the V, Cr, and Cb data and performs the following matrix calculation processing so that image adjustment can be performed independently for each H, V, and C signal. .

(Equation 6) Here, q is a saturation adjustment coefficient, and θ is a hue adjustment coefficient. These coefficients are output from the HVC adjustment control unit 129 and sent from the image quality monitor control unit by Mdata (3
(Bit) is used as a switching signal and selected from eight types of coefficient groups in real time with the image signal. In this way,
Adjustments similar to those of humans are made to facilitate image adjustments according to operator preference.

(9) Automatic exposure process (AE) The background process will be described as an example of the image process according to the document type. Conventionally, in a full-color copying machine, the automatic exposure process may result in a copy having a color balance different from that of the original, so that the automatic exposure process is performed only in the monochrome mode. However, even in full-color mode, when processing such as black character discrimination is introduced and clear mixed black-and-white and originals are reproduced, the background level of the originals is automatically adjusted like automatic exposure processing to prevent show-through. The need for optimal control has arisen. In the present embodiment, a lightness signal (VH) that is similar to human relative luminous efficiency (brightness) is created, and histogram generation and document type determination are performed. As a result, the hue of full-color originals is not changed and black and white /
Automatic exposure processing is performed to automatically copy the original background level without being aware of the color portion. That is,
Once the image signal is converted from R, G, B signals to V, Cr, Cb signals, the data is subjected to automatic exposure processing, and then R, G, B again.
By converting into G and B signals, unique processing is performed in both the full-color mode and the monochrome mode, so that the background level can be optimized. Further, even in the full color mode, no processing is applied to the color component signals Cr and Cb, so that the color balance is not changed by the automatic exposure processing.

More specifically, the background adjustment is
It is performed by automatic automatic exposure processing or manual setting. On the basic operation screen of FIG. 4, the user can select whether to perform the automatic exposure process or to select one of eight levels of manual designation. In the automatic exposure process,
5 from the original histogram information by the prescan operation
Different types of originals (color standard (background white, with background color) / photo original and black-and-white standard / photo original) are performed (see FIG. 9). As shown in FIG. 9, if the color standard original (white background) or the black and white standard original is used, the lightness gradation complementation as shown in FIGS. 12 and 13 is performed, and for other original types, the manual center level is set. Is automatically selected.

The automatic exposure (AE) processing section 130 performs background removal based on the document type information obtained by the histogram generation section 110. Here, the document type (b) and
As for (d), using a look-up table memory (AE table) 131a for the lightness V, the lightness signal (V _in ) before the automatic exposure processing is changed to the lightness signal after the automatic exposure processing.
The (V _{o ut)} determined by the following correction formula, performs the brightness correction.
That is, for monochrome standard manuscripts,

V _out = 256 * (V _in −b−8) / {(a−8) −b} (7) Further, for a color standard document (background white),

V _out = 256 * (V _in −8) / (a−8) (8)

Here, a indicates a background level, and b indicates
It is a character level. In other words, as shown in FIG. 12, with respect to a black and white standard original, the background is removed, and at the same time, light characters such as pencil writing are darkened to make the copy easy to read. Therefore, the brightness between a + 8 and b is expanded to 0 to 255, and the data V _in below a + 8 and above b is discarded. On the other hand, in the color standard document, only the background is removed. For a color standard original, as shown in FIG. 13, the data V _in between 8 and b is expanded to 0 to 255, and the data above b is discarded. In this embodiment, the level for skipping the background is set to 0-8.

In the monochrome / color standard document, the background level a and the character level b are obtained as follows. The following values are obtained from the brightness histogram h1 (n) of the entire original document in the first histogram memory 202. First, n = 136 to 255 (ID 0.
In the range of 4 or less), the gradation level m at which h1 (n) has the maximum frequency is obtained. Then, a = m-8 is set, and the background lightness is set to 255. Similarly, n = 0 to 120 (ID 0.
In the range of 4 or more), the gradation level 1 at which h1 (n) has the maximum frequency is obtained. Then, b = 1 + 8, and the brightness of the character portion = 0. The reason a = m−8 is that the histogram distribution near level m has a normal distribution with some variation, so that the variation is set to ± 8 and gradations near level m are reliably skipped. is there. Similarly,
The reason that b = 1 + 8 is to ensure that the gradation near level 1 is black. Further, the reason why the control is not performed by b in the color original standard mode is that the character is not always black.

Here, since the color components of Cr and Cb are passed through (in the AE tables 131b and 131c, D _in =
D _out ), the color information of the document is not changed, and only the grayscale information (V) is controlled. Therefore, the background level can be automatically adjusted without changing the color information of the color original. Color difference signal C
The r and Cb components are not corrected (V _out =
V), the color balance is not lost.

Further, in the manual setting (release of automatic exposure processing) set on the operation panel 154, it is possible to perform lightness correction for changing the background level value. This mode is different in monochrome / color and photo / standard mode, and the manual setting value is 7 steps. -1 to -4 is the direction to blow the background, and +1, +2 is the direction to apply the fog around ± 0. (See FIG. 4). As for detailed setting contents, in the color standard mode, the monochrome standard mode, and the photograph mode, as shown in Table 2, the levels +2 to -4 of the manual setting are set.

As another image processing corresponding to the document type, there is a black character discrimination processing (color fringing correction) in the MTF correction section 148. As shown in Table 1, this processing is performed on the color standard original document. This is performed in order to optimize the image reproduction of black characters when a color image and a monochrome image are mixed. First, C, M, and Y are detected in the portion determined to be the edge portion of the black character by the area determination unit 146.
The component data is attenuated, and the Bk component data is Bk1.
The data of the lightness V is added to the data of 00% to slightly thicken the character to enhance the edge.

(10) Inverse HVC conversion In the inverse HVC conversion unit 132, the V, Cr, and Cb signals are again converted into
In order to convert to R, G, B signals, the matrix inverse operation described above is performed as follows, and R, G, B are output.

[Equation 9] The above-described scan data processing is performed by converting it to lightness data, but by performing the inverse HVC conversion here, subsequent data processing such as color correction can be performed on the data of the three primary colors.

[0047]

EFFECTS OF THE INVENTION For both color and black and white originals,
Since various document types can be automatically determined, the user does not need to select the document type. Further, even when various originals are mixed and stacked on the automatic original feeder, the original type can be automatically determined and the optimum image processing can be performed for each.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an entire digital color copying machine.

FIG. 2 is a block diagram of a part of a signal processing unit.

FIG. 3 is a block diagram of the remaining part of the signal processing unit.

FIG. 4 is a block diagram of a histogram generation unit.

FIG. 5 is a diagram showing a sampling situation in histogram generation.

FIG. 6 is a diagram showing various amounts obtained from a histogram.

FIG. 7 is a flowchart of automatic color selection.

FIG. 8 is a diagram showing various amounts obtained from a histogram.

FIG. 9 is a flowchart for determining an image type.

FIG. 10 is a diagram for explaining a relationship between a brightness signal and various signals (G25 to G35).

FIG. 11 is a diagram of an HVC adjustment unit, an automatic exposure (AE) processing unit, and an HVC inverse conversion unit.

FIG. 12 is a graph showing a change in document brightness distribution before and after AE processing for a monochrome color standard document.

FIG. 13 is a graph showing changes in the original lightness distribution of a color standard original (white background) before and after AE processing.

[Explanation of symbols]

110 histogram generation unit, 152 CPU, 20
0 brightness creation unit, 202 first histogram memory for all pixels, 204 second histogram memory for chromatic colors, 208, 210 adder for integration, 212 to 218
Chromatic color identification circuit.

Claims (1)

[Claims] 1. A lightness signal generator for converting R, G, B signals of three primary colors obtained by scanning an original by a photoelectric conversion element into a lightness signal, and a histogram generation means for generating a histogram based on the lightness signal. An image processing apparatus comprising: a document type determining unit that determines a document type from a histogram; and a process switching unit that switches subsequent image processing contents based on the determination result of the document type determining unit.