JPH02268075A - Picture processing device - Google Patents

Abstract

PURPOSE:To attain picture reproduction with excellent resolution and gradation even in the case of a picture mixed with a character and a photograph and to obtain gradation of an intermediate tone picture such as a photograph with simple constitution by converting a brightness data into a density data and applying the density correction in response to the selected mode. CONSTITUTION:An original picture is read in a facsimile equipment and a brightness signal via an A/D converter 201 is corrected by a picture signal correction circuit 202 in response to the deviation of the characteristic of a CCD element or fluctuation of distribution of a light of a light source or the like and converted into a density signal by a brightness-density conversion circuit 203. The signal is subjected to density correction from a conversion table drawn in a ROM of a density correction circuit 204 selected in response to the mode from the CPU and outputted via a binarizing processing section 205. Through the simple constitution above, the picture reproduction with excellent resolution and gradation for a picture in mixture of an intermediate tone picture, character such as a photograph is attained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an image processing device that performs quantization processing on image data, and in particular to an image processing device that can reproduce images containing text and photographs in a pseudo manner. It relates to a processing device.

[Conventional technology]

2. Description of the Related Art Conventionally, digital copying machines, digital facsimiles, and the like are known to read image information from a document, quantize the resulting image data into, for example, binary data, and print or transmit the data to a partner device.

Here, as a binarization processing method for quantizing image data into binary data, simple binarization processing using a fixed threshold is generally used when the original is text or line drawings, and dithering is generally used when the original is a photograph. It is used.

In addition, when text and photos are mixed in a document, the resolution of the text area can be improved by performing simple binarization processing on the text areas of the document and binarization processing using the dither method on the photo areas of the document. and improves the gradation of photographic areas.

[Problem that the invention is trying to solve]

However, in the conventional example described above, when a single document contains both text and photographs, it is necessary to switch between simple binarization processing and dithering binarization processing within the document, resulting in a complicated configuration. .

Therefore, as a binarization method that can achieve both resolution and gradation for originals containing a mixture of text and photographs, a density-preserving binary
Valuation methods have been attracting attention in recent years.

The density-preserving binarization method corrects error data that occurs when image data is binarized, and includes the error diffusion method, the minimum average error method, or the average density-preserving method applied by the applicant. There is.

However, with this type of density-preserving binarization processing method, such as the error diffusion method, it is possible to reproduce good gradation in the halftone areas of the original, but grainy noise occurs in the reproduced image in the highlight areas of the original. However, there have been disadvantages in that the reproduced image may have some white spots in dark areas of the original. Particularly in facsimile machines, the generation of this noise also reduces encoding efficiency.

In addition, even when processing the text portion of a document, the dither method has some drawbacks, such as missing edges and poor line connections.

The present invention aims to eliminate the above-mentioned drawbacks of the prior art. An object of the present invention is to provide an image processing device capable of reproducing images with excellent resolution and gradation with a simple configuration.

(Means and Effects for Solving the Problems) According to the present invention, there is an input means for inputting luminance data, a data conversion means for converting the luminance data into density data, and a photo mode or text/photo mode is selected. mode selection means; correction means for correcting the density data based on the mode selected by the selection means; and processing means for quantizing the density data corrected by the correction means using a density-preserving quantization method. By providing this, the density data is corrected based on the photo mode or text/photo mode selected by the selection means, and the corrected density data is quantized by the quantization means using a density-preserving quantization method. This is what I did.

〔Example〕

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings. Figure 's1 is a block diagram of a facsimile machine to which the present invention is applied.

In FIG. 1, 102 is a reading unit that reads a document, and the reading unit 102 quantizes the signal read by the CCD (solid-state image sensor) line sensor 101 into binary data of white and black. . Note that the reading section will be explained in detail later.

Reference numeral 103 denotes a recording unit for recording images, and the recording unit 103 is constituted by a thermal transfer printer, a laser beam printer, an inkjet printer, etc., which are normally used in facsimile machines.

Reference numeral 104 denotes an operation display section for operating the facsimile machine, and is composed of a plurality of manual key switches, a key scanning circuit, a display such as a liquid crystal display for displaying various information, and a display drive circuit.

Reference numeral 105 is an encoding/decoding unit that encodes transmission data and decodes received data.

106 is a CPU that controls the entire system via the system bus 1oO, 108 is a read-on memory (ROM) that stores a control program for the CPU 106, and 107 is a random access memory (RAM) that performs image processing and controls the CPU 106. Use it as a work area.

109 is a modem that modulates transmitted data and demodulates received data; 110 is an NCU (network controller) that switches the telephone line 110a to the modem 109 side or the telephone 111 side;
control unit).

FIG. 2 is a block diagram showing details of the reading section 102 shown in FIG. 1.

201 is an AD converter, which converts analog image data read by the input centimeter unit 101 into digital image data with a quantization number of 6 bits. Note that this digital image data is luminance data. There are 64 levels of gradation, and the lowest luminance data (000000) is the darkest black (000000).
total black), and the data with the highest brightness (111111)
indicates the brightest white (complete white).

Luminance data from the AD converter 201 is sent to an image signal correction circuit 202. Here, the CC of the input sensor section 101 is
The sensitivity unevenness of D and the shading distortion, which is distortion of the light distribution characteristics of the light source, are corrected.

203 is a brightness/density conversion circuit that converts the brightness data from the image correction circuit 202 into density data. An example of using a ROM in the degree/concentration conversion circuit 203 is shown in FIG.
The luminance signal from the image correction circuit 202 is input to addresses AO to A5 of the ROM, and density data based on the input/output correspondence table shown in FIG. 4 is output to the output terminals DO to D5 of the ROM. The input/output correspondence table in Figure 4 shows the relationship between brightness and density (?
R degree=-γ log (luminance) is satisfied.

A density correction table 204 corrects the density data from the brightness/density conversion table 203.

An example of using a ROM for the density correction table is shown in FIG.
The density data from the brightness/density conversion table 203 is stored in addresses AO to A5 of the ROM, and the CPU 10 is stored in address A6 of the ROM.
The data conversion table written in the ROM is selected by inputting the control signal CNT from 6 manually. Corrected density data based on the input/output correspondence table shown in FIG. 6 is output from the output terminals Do to D5 of the ROM.

The table in the ROM can be selected by the control signal CNT, and the table CNT can be selected according to the key operation on the operation display section 104 in FIG.
is output from CPLI. FIG. 7 is a diagram showing the operation panel of the operation display section 104 for switching the control signal CNT, and 701 is a switch 702 for selecting halftone mode (photo mode) and auto mode (photo/text mode).
703 is an LED which indicates the selected mode by lighting the LED. In this embodiment, when the photo mode is selected with the switch 701, CNT=O, and the table 601 in FIG. 6 is selected. When the photo/text mode is selected with the switch 701, CNT=1 and the table 602 in FIG. 6 is selected.

FIG. 8 is a graph showing the table of FIG. 6.

In other words, when CNT=O, the photo mode table 601 in FIG. 6 is selected and correction of the density data is not substantially performed.Therefore, when processing a photo original, this photo mode is selected. By doing so, it is possible to reproduce a good halftone image.

If CNT=1, the photo/text mode table 602 in FIG. 6 is selected, and the density data is corrected.

As a result, by selecting this photo/text mode for originals that contain both photos and text, the resolution of the text area can be significantly improved, although the gradation of the photo area will be slightly sacrificed. Accordingly, encoding efficiency can also be improved.

FIG. 9 is a flowchart showing the operation of selecting a density correction table and executing image processing according to the input key.

In step S02, it is determined whether or not the photo mode has been selected by the mode selection key 701. If the photo mode has been selected, the process proceeds to SO3, turns on the photo LED 703, and outputs "rcNT=o" to SO4.Density correction circuit 2
In step 04, CNT=O sent from cpuios is received, and the density correction table 601 shown in FIG. 6 is selected.

If it is not photo mode in step SO2, proceed to SO5,
Determine whether the mode is text/photo mode. If it is the text/photo mode, the process advances to SO6, the text/photo LED 702 is turned on, and CNT-1 is output at SO7. In the density correction circuit 204, the CNT sent from the CPU 106
=1, and the density correction table 602 in FIG. 6 is selected.

Next, the process proceeds to step S08, and it is determined whether or not the start key 704 has been pressed. If it has been pressed, the process proceeds to step S09, and the image processing density correction circuit 204 and the binarization processing section 205 are instructed to start. In step SIO, it is determined whether or not the end of the image processing has been notified from the binarization processing unit 205, and if it is the end, the image processing is ended in Sll.

In this way, in this embodiment, in the case of an image containing a mixture of text and photographs, correction is performed on the density data that has been converted to brightness and density.
The corrected density data is binarized using the error diffusion method.

As a result, when the density data is less than or equal to the predetermined value (5), the density data is corrected to be completely white (0), so that it is possible to prevent grainy noise from occurring in the highlight portion of the image.

Further, when the density data is equal to or greater than a predetermined value (35), the density data is corrected to full black (63), so that it is possible to prevent black spots in dark areas or edges from being cut off in character areas.

In addition, when encoding binary data that has been binarized by the encoding/decoding 105, the encoding efficiency can be improved, and images with excellent resolution and gradation can be produced at high speed. It becomes possible to send a message to the other party's facsimile machine.

FIG. 10 is a block diagram showing details of the binarization processing section 205 of FIG. 2.

Data X1. sent from the density correction circuit 204. (density data) is the error data E1. from the adder 1015 that occurred when the binarization process was already performed. J and adder 10
01 is added.

This error-corrected data D1. J is the following formula % Formula % This Dl, J is the threshold value T (
T=32). In other words, the binary output Y11.
is expressed as follows.

D,,,>T...Y,,j=63 DI,JET...Y,,j=0 On the other hand, D3. , is sent to the error calculator 1007. The error calculator 1007 outputs Dl, J and the binarized output Y1. Error E1.j distributed to surrounding pixels based on j. Calculate j. That is, El and J can be expressed as follows.

El, "=D+" Yl, J This El, j is sent to the error distribution value calculation circuit 100B,
The error distribution value calculation circuit 1008 calculates the value of the error to be distributed to the four surrounding pixels of the pixel of interest.

FIG. 11 is a diagram showing a weighting matrix, and this matrix is composed of the error E1. The position and ratio of pixels to which j is allocated are shown.

In the error distribution value calculation circuit 1008, A1. , and B1. J is determined as follows.

However, this error distribution value calculation circuit 1008 has a configuration in which the decimal places are rounded down. In other words, only integer operations can be performed. Note that Int represents rounding down to the decimal point. Then, the error E1. generated at the pixel of interest by rounding down the decimal point. J and A1.J distributed to the surrounding four pixels calculated by the error distribution value calculation circuit 1008.
” said B1. A remainder R1, J is generated between R1 and j. This can be expressed as the following formula.

R4, "Leak E+j-2X (A1.J +B1.J)
This remainder R1,'' is sent to the latch 1009, delayed by a pixel, and added to the input data X1*14 of the next pixel.

On the other hand, A5 is sent to the adder 1013 for allocation to pixel (i+1.j) and to the adder 1004 for allocation to pixel (i, j+1). Also, B1. J is pixel (i+1.j
+1), the latch 1003 and the pixel (i-1,
j+1) to an adder 1006 for distribution.

The memory 1011 is a memory that stores errors distributed to the j+1th line, and can store error data of pixels for at least one line.

Timing generation circuit 1010 includes latch circuits 1009.
Latch signals to 1003, 1005, 1012, 1014, address signals to memory 1011, etc. each f! Tl
Generate a signal.

Next, the aforementioned error distribution method will be explained in more detail using FIG. 13.

FIG. 12 is a diagram showing the flow of binarization processing using the error diffusion method. First, let P+, Q+, R+, St be the weighted errors generated at the pixel of interest
As shown in Figure (a), the image is distributed to four surrounding pixels. Here, 21 goes to adder 1013 in FIG. 10, and Q goes to adder 1.
006, R1 to adder 1004, S, to latch 10
Sent to 03. Ql is then written to address 1 in memory 1011.

Next, when the pixel of interest moves to X2, the error P2+Q2+R2+s2 is dispersed to the surrounding four pixels as shown in FIG. 12(b). Here, 22 is sent to adder 1013. Also, Q2 is aFt2 which is added to R3 generated at X by the adder 1006 and written to address 2 of the memory 1ott.
is added with Sl generated in XI and m in adder 1004.
s2 is sent to latch 1003.

Next, when the pixel of interest moves to X, as shown in FIG. 12(C), an error P5. Qs, Fts, and S3 are distributed to four surrounding pixels. Here, R3 is sent to adder 1013.

Further, Q3 is added to Sl generated at XI and R2 generated at x2 in an adder 1006, and is written to address 3 in the memory 1011. R5 is S generated at x2, and adder 10o
4 is added.

S, is sent to latch 1003.

When the above processing is performed for one line, the following values will be written to the memory 101.

Memory address 1...M+=Q+ Memory address 2...M2 =R1+Q2 Memory address 3...M, =S, +R2+Q3 Memory address 4...
M4=S, +R, +Q4 Memory address 1...M, ms
, -2+R, -, +Q.

When the processing for one line is completed and the processing moves to the next line, the error that occurred in the previous line is read out from the memory.

The error read from the memory is added to the error that occurred one pixel before in an adder 1013 and output from a latch 1014.

Reading of the error from the memory 1011 is controlled by a timing generation circuit 1010 so as to correspond to the previous line. If the pixel of interest is X1, the timing generation circuit 101O controls to read the address of M1-3 in the memory 1011.

By performing the above-described processing on all human data, it is possible to perform binarization using the error diffusion method.

As explained above, the processing of the embodiment of the present invention can be performed in photo (halftone) mode, text/
Photo (auto) mode can be selected, and text/
When the photo mode is selected, the brightness data is converted to density data, and after the density data is corrected, it is
It is a value processing.

That is, in the text/photo mode, density data below a predetermined value can be converted to all-white density data. As a result, it is possible to prevent granular noise from occurring in highlight portions of an image due to the accumulation of positive error data.

Also, when the light intensity of the fluorescent tube is small, such as at low temperatures, the video signal from the COD becomes small compared to the dynamic range of the AD converter, so even if all self-portraits are read,
A certain number of numerical values are output from the AD converter, which may cause granular noise.

In this case as well, as described above, by converting density data below a predetermined value into all-white density data, it is possible to prevent the occurrence of grainy noise. Thereby, when encoding binary data, encoding efficiency can be improved and data transmission time can be significantly reduced.

Further, according to this embodiment, in the text/photo mode, density data exceeding a predetermined value is converted to all-black density data. This can prevent dark areas of the image from appearing white due to accumulation of negative error data.

Furthermore, by converting density data of a predetermined value or higher into all-black density data, even characters with light density can be reproduced as clear black in the same way as when simple binarization processing is performed.

Furthermore, since this embodiment is configured to perform density correction, it is also possible to perform binarization processing in accordance with the characteristics of the recording system.

In this way, in this embodiment, when performing binarization processing using the error diffusion method, the luminance data is converted into density data as a preprocessing, and then the density data is corrected to improve the resolution of the text part and the gradation of the photograph part. Images with excellent quality and quality can be reproduced.

In this embodiment, there are two processing modes: photo mode and text/photo mode, and an example in which binarization processing is performed using the error diffusion method has been explained. It is also possible to provide one.

In addition, in this embodiment, the error diffusion method was explained as an example of a density-preserving binarization method, but the present invention uses density-preserving binarization methods such as the average error minimum method and the average density preservation method. However, it can be realized.

In addition, in this embodiment, in the density correction table 602 of FIG.
The function in the interval w (6)<B≦B, (34) is 100=B 100: Corrected density (output) B: Document density (manual power) It is not limited to this, and B=αB α>0 may be used.

In the above-described embodiment, an example has been described in which the photo mode and the text/photo mode are switched by manual selection by the operator, but it is also possible to switch between the photo mode and the text/photo mode by automatically recognizing the document.

Examples are shown below.

A second embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 13 is a block diagram of an image processing apparatus to which a second embodiment of the present invention is applied.

In FIG. 13, reference numeral 1301 indicates analog image data from a scanner 1301a that reads a document.

1302 is a preprocessing unit that performs preprocessing on the analog image data 1301a, and 1302a is digital image data quantized to 6 bits. Note that this digital image data is luminance data.

A selector 1303 controls the flow of image signals.

1305 is a brightness/density conversion table for converting brightness data into density data.

Reference numeral 1306 denotes a density correction table for correcting density data.

Reference numeral 1307 denotes an error diffusion processing unit that converts the density data sent from the density correction table 1306 into binary data using the error diffusion method. .

A printer 1308 records the data binarized by the error diffusion processing unit 1307.

1304 determines whether the original read by the scanner 101 is a text/photo original or a photo original, and creates the density correction table 1.
This is a document determining unit that sends a determination signal to 306 .

FIG. 14 is an internal configuration diagram of the preprocessing section 1302.

First, a video signal 1301a from a scanner 1301 is quantized into 6 btt by an AD converter 1401. Here, there are 64 levels of gradation, and the data with the lowest brightness (0
00000) 2 indicates the darkest black (all black), and the highest brightness data (111111) z indicates the lightest white (all white)
shows.

The luminance data from the AD converter 1401 is processed by the image signal correction circuit 1402 to correct unevenness in CCD sensitivity of the scanner A101.
and shading distortion, which is distortion of the light distribution characteristics of the light source, is corrected.

FIG. 15 is a diagram showing the flow of the image processing method in the second embodiment.

First, in step S20, the original is read, and in S21, it is determined whether the original is a photo original or a photo/text original.

Next, in S22, a density correction table is selected based on the determination result in S21.

In step S23, the original is read again, and in step S24, the read original is binarized.

FIG. 16 is a flowchart showing the processing flow of the document determining unit 1304.

In step S31, parameters used by the document determining section 1304 are initialized.

In step S32, f=max (a, b, c, d, x
)-min (a, b, c, d, x).

(a, b, c, d, x) indicate the luminance values of pixels located at the positions shown in FIG. Operators max() and m1n() are pixel values a, b, c.

The maximum and minimum values of d and x are shown.

Next, in step S33, compare f obtained in step 332 with the parameters, and if f≧, it is set as a text/photo area and step 540
Proceed to step 4 and add 1 to the value of variable M.

If f<k, it is set as a photo area, and the process advances to step S35, where 1 is added to the value of variable P.

In step S36, it is checked whether or not all pixels of the document have been judged. If all pixels have been judged, the process proceeds to S37, and if not, the process proceeds to S32.

In step 337, it is determined whether the manuscript is a text or photo manuscript.
Or determine whether it is a photographic manuscript.

Using M and P obtained through the above processing, P-αM is calculated at 337.
≧h h: The determination parameter is calculated, and if (P-αM) is greater than or equal to h, the process proceeds to S38 as a photographic original, and the control signal CNT=O is sent to the density correction table 1306.

If (P-αM) is less than h, S3 is considered a text/photo manuscript.
9, the control signal CNT=O is sent to the density correction table 130.
Send on 6.

Through the above processing, it is determined whether the document is a text/photo document or a photo document, and the density correction table 130 is created according to the determination result.
Select table 6.

Brightness/density conversion table 1305, density correction table 1
306 and error diffusion processing section 1307 correspond to the luminance density correction circuit 203, density correction circuit 204, and binarization processing section 205 in FIG. 2, respectively, and perform the same processing, so a description thereof will be omitted here.

In this way, according to the second embodiment, in addition to the first embodiment, it is possible to automatically identify the photo mode and the text/photo mode, and select the density correction table according to each mode. There is no need for the operator to select the mode accordingly.

In addition, in FIG. 13, an example was explained in which the data binarized by the error diffusion processing unit 1307 is recorded by the printer 1308, but as in the first embodiment, the encoding unit, modem, N
By providing a communication function such as a CU, the second embodiment can also be applied to a facsimile machine.

(Effects of the Invention) As explained above, according to the present invention, halftone images such as photographs can be reproduced with good gradation, and even images containing text and photographs can be reproduced with high resolution and high resolution with a simple configuration. Images with excellent gradation can be reproduced.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a facsimile machine that is an embodiment of the present invention. FIG. 2 is a block diagram showing details of the reading section of FIG. 1. Figure 3 shows the ROM that performs the luminance/density data conversion, Figure 4 shows the input/output correspondence table of the luminance/density data conversion circuit, and Figure 5 shows the ROM that performs the density correction circuit. Figure 6 is a diagram showing the input/output correspondence table of the density correction circuit, Figure 7 is a diagram showing the operation panel, Figure 8 is a graph showing the input/output correspondence table for density correction, and Figure 9 is a diagram showing the input/output correspondence table of the density correction circuit. Figure 10 shows a flowchart of image processing, Figure 10 is a block diagram of the binarization processing section, Figure 11 shows an error diffusion matrix, and Figure 12 shows the flow of binarization processing using the error diffusion method. 13 is a block diagram of an image processing device according to a second embodiment of the present invention, FIG. 14 is a block diagram showing details of the preprocessing section of FIG. 13, and FIG. 15 is a block diagram of an image processing device according to a second embodiment of the present invention FIG. 16 is a flowchart showing the flow of document discrimination processing, and FIG. 17 is a diagram showing the positional relationship of pixels used for document discrimination. In the figure! 00...System bus 101...Input sensor 102...Reading section 103...Recording section 104...Operation display section 105...Code, decoding section 106...CPU 107...RAM 108...ROM 109...Modem 110...NCU (Network Control IIll...Telephone 203...Brightness/density conversion circuit 204...Density correction circuit 205...Binarization processing section There is.Unit) Figure 5 also 10

Claims (1)

[Scope of Claims] Input means for inputting luminance data; data conversion means for converting the luminance data into density data; mode selection means for selecting photo mode or text/photo mode; an image processing apparatus comprising: a correction means for correcting the density data based on a mode determined by the correction means; and a processing means for quantizing the density data corrected by the correction means using a density-preserving quantization method. .