JPS63209275A - Picture signal processor - Google Patents

Abstract

PURPOSE:To suppress the generation of unevenness in density or stripes due to a variable power processing by changing the strength of an edge emphasis according to a variable power ratio. CONSTITUTION:The secondary differentiating signal 312 of a main scanning direction and the secondary differentiating signal 317 of a sub-scanning direction independently increased and decreased according to a main scanning magnification and a sub-scanning magnification respectively by multipliers 801 and 802 are added to the picture element signal 307 of a noticed picture element by an adder 318, thereby, an edge emphasized picture signal 219 is obtained. This picture signal 219 is inputted to a double buffer memory 214 to execute the variable power processing relating to the main scanning direction according to the variable power ratio. Since the variable power processed picture signal is subjected to the edge emphasis processing considering the variable power ratio, the unevenness in the density or the stripes is prevented from being generated in the picture according to the variable power processing.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an image signal processing device that processes an image signal obtained by reading an original image using an image sensor such as a CCD.

[Prior art]

Conventionally, digital copying machines have been configured using a known laser beam printer using electrophotographic technology as an image recording output section, and a scanner that performs main scanning photoelectric conversion reading using a line sensor such as a CCD as an image reading section. ing. Reading in the sub-scanning direction of this scanner is performed by mechanically relatively moving the document in a direction perpendicular to the reading direction of the photoelectric conversion element.

When scaling an output image with this device configuration, it is necessary to stably change the scanning speed of both the main laser scan in the axial direction of the photoreceptor of the laser beam printer and the rotation of the sub-scan drum in the vertical direction. Because it is extremely difficult, the scaling operation is mostly performed on the scanner side.

That is, magnification in the sub-scanning direction is reduced by increasing the document scanning speed of the scanner relative to the rotational speed of the drum, and enlarged by slowing it down. In addition, magnification in the main scanning direction is reduced by thinning out the image signals for main scanning lines read by the line sensor for each predetermined pixel, and by duplicating the image signals for the - lines for each predetermined pixel. Enlargement is performed by recording.

On the other hand, a process called edge enhancement processing is performed to enhance the contours of the read image and obtain a sharp image. As an example of this edge enhancement processing, it is known to perform second-order differentiation in the main scanning direction and sub-scanning direction using a Laplacian filter, and correct the pixel of interest based on the result of this second-order differentiation.

FIG. 8 shows an example of an edge emphasis processing circuit.

■The digital image signal 801 input for each line is stored in each line memory 802 of the delay buffer memory 802 for 3 lines.
0. 821. 822, and from this buffer memory 802, the current line image signal 803. ] Image signal before line 804. Image signal for three lines, including image signal 805 before two lines, is output. These image signals are
The latch 806 delays each pixel.

Here, the pixel of interest is a signal 807 obtained by delaying the image signal 804 of one line by two pixels, and in the multiplier 810, this pixel of interest 807 is multiplied by 2 times the pixel 807 before and after the image signal 804 in the main scanning direction.
The result of multiplying 8,809 by (-1) is added by adder 8]1, and the result is a secondary differential signal 312 in the main scanning direction for the pixel of interest.
get.

Furthermore, a multiplier 815 multiplies the pixel signals 813 and 814 of the lines before and after the same main scanning positional relationship as the pixel of interest by (-1), and the result of doubling the pixel signal of interest 807 is added to an adder 816.
A second differential signal 817 in the sub-scanning direction for the pixel of interest is obtained.

By adding these second-order differential signals 812 and 817 to the pixel of interest in an adder 818, an edge-enhanced image signal 8 is obtained.
Get 19.

It has become clear that the scaling method and edge enhancement processing described above have various negative effects on the output image.

First, even if an original with uniform density is read, the digital image signal will not be uniform. This is partly due to the internal configuration of the CCD line sensor, as shown in FIG.

That is, each pixel output of the light receiving cell 601 is an even numbered pixel.

The charges are transferred by separate charge transfer units 602 and 603 for each odd-numbered pixel, passed through separate amplifiers 604 and 605, and outputted by a multiplexer 606 as one line of image signal.

Therefore, variations in sensitivity among each light-receiving cell, variations in DC offset amount due to differences in transfer parts, and even nonlinear amplification due to minute signals in the amplifier are causes of variations in digital image signals from pixel to pixel. There is.

In order to correct this variation, various correction means such as DC drift removal and shading correction have been proposed, but all of them use the property that the output of the CCD line sensor is linear with respect to the photofluorescence, and the amount of light is small. If there is non-linearity of the light-receiving element or non-linearity of the amplifier, it will not be possible to correct it completely.

This correction error is mostly contained in black information, which is a small amount of light,
Due to the configuration of the above-mentioned CCT, there is variation from pixel to pixel, as shown in FIG. 10(a).

This variation in the main scanning direction is emphasized by the edge emphasis circuit shown in FIG. 8 as shown in FIG. 1O (1)).

This variation is further emphasized as shown in FIG. 1O(c) by the image reduction process using the image magnification described above. In other words, a part where a high density part is scattered like part C-1 has a series of bright pixels, and it stands out as a sharp white line in the copy output. In addition, in the part where the light density part is scattered, such as (, -2 part), dark pixels are continuous, and it stands out as a sharp black line in the copy output.

On the other hand, in the case of enlargement, the image information subjected to edge enhancement processing is watered down in the main scanning direction as shown in Figure 10(d), so density variations are emphasized and output by the increased output area per pixel. be done.

As described above, the conventional technique has a disadvantage in that the CCD unevenness emphasized by edge enhancement is further emphasized by main scanning magnification processing.

Further, in the sub-scanning, there was a similar problem due to a mismatch between magnification change and edge enhancement.

As shown in FIG. 11(a), one pixel of the CCD line sensor has a certain aperture length in both the main scanning direction and the sub-scanning direction. In the figure, both are shown as length a. When this CCD line sensor having an aperture length a in the sub-scanning direction moves and scans the document by a distance b in the sub-scanning direction and reads one pixel of the document, the document will be read as shown in FIG. 11(b).
The area of ax(a+b) is read as one pixel.

Here, if the reading movement i1b in the sub-scanning direction is the scan length when reading at the same magnification, an image read in a document area of 81 on a certain scanning line as shown in FIG. 11(C) will be recorded by the printer as a pixel of Pl. , the image read in the document area S2 by the same pixel in the next scanning line is recorded by the printer at the pixel P2, and each pixel Pl and P2 has an aperture area corresponding to the CCD line sensor's opening area shown with diagonal lines. The portion is commonly included as a blur.

Here, the recorded image is the blur ratio per pixel.
As shown in Figure 1(d), if the document reading movement amount in the sub-scanning direction per pixel is 1--b and the recording magnification in the sub-scanning direction is set to 400%, the same result will occur as the magnification increases. , it can be seen that as the sub-scanning length decreases, the denominator of the blur ratio equation decreases, and the blur increases.

As described above, in the conventional method, the use of fixed-strength edge enhancement in the sub-scanning direction has the disadvantage that as the magnification increases, the number of blurred lights included in the image increases.

〔the purpose〕

The present invention has been made in view of the above-mentioned drawbacks of the conventional configuration, and aims to reduce uneven streaks in main scanning due to variable magnification, and to eliminate increase in blur in sub-scanning due to increase in magnification.

〔Example〕

Below, the present invention will be explained using preferred embodiments.

FIG. 1 is a diagram showing an example of a document reading device (hereinafter referred to as a scanner) to which the present invention is applied. A CCD line sensor 103 in which a plurality of light receiving elements are arranged on one line is used to read the image information of the original 102 held by the original cover 100 and placed on the original platen glass 101. The illumination light is reflected on the surface of the original 102 and passes through the mirrors 105, 106 and 107 to the lens 1.
8 to form an image on the CCDCC line sensor 103.

Light source】04. Optical unit 113 consisting of mirror 105
and mirror 106. Optical unit 114 consisting of 107
is designed to move at a relative speed of 2.1. This optical unit is operated by a DC servo motor 109.
Move from left to right at a constant speed while applying L control.

This moving speed is variable according to the magnification on the outward journey, and is 180 mm/sec when the image is at the same magnification, 22.5 mm/sec when it is enlarged by 800%, and 360 m when it is reduced by 50%.
m/sec. CCD line sensor] 03
While reading at a resolution of 400 dots/inch, the optical unit is moved from the Baume Bongeon at the left end to the right position to a predetermined position, and then moved back to the home position to complete one scan. The home position is detected by the light shielding plate 111 crossing a home position sensor 110 made of a photointerrupter. Standard density plate 1
12 is used for shading correction and light intensity control of the light source 104, and a home position sensor 110 is used for shading correction and light intensity control of the light source 104.
The position where 11 is detected is the standard density plate 112
This is a position that can be read by the line sensor 103.

FIG. 2 is a block diagram of signal processing from image reading to recording. 201 is a laser emitting unit, and the laser light emitted from this unit is sent to a drum 2 that rotates at a constant speed by a polygon scanner 202 that rotates at a high speed at a constant speed.
03 is scanned in the axial direction. At this time, a photodiode 2 is placed close to the tram on the extension line of the scanning line.
04, the passage of the laser beam is detected, and a main scanning synchronization signal 205 is generated.

In synchronization with this synchronization signal 205, the reference clock generator 2
The image signal for one line read out from the CCD line memory 103 using the two-phase clocks 207 and 208 from 06 is amplified by the amplifier 209, and then sent to the A/D converter 21.
8b per pixel synchronized to pixel clock 211 at 0
After being converted into an it digital image signal 212, it is input to an edge enhancement circuit 213.

This edge emphasizing circuit 213 is composed of a Laplacian filter using a three-line delay buffer, and performs edge emphasizing processing by performing quadratic differentiation independently in the main scanning direction and the sub-scanning direction.

The image signal edge-enhanced by the edge-enhancing circuit 2]3 is transferred to the line memory 2 of the double buffer memory 214.
27 and 228 for each line, and read out again to perform magnification processing in the main scanning direction.

A write address counter (hereinafter referred to as W-address counter) 215 and a read address counter (hereinafter referred to as R-address counter) 216 for performing this scaling process are as follows.
Each operates in synchronization with the main scanning synchronization signal 205.

The scaling process is performed by changing the ratio of operating speeds of the W-address counter and the R-address counter. In order to change the operating speed of this counter, first and second clock control circuits 217. 218 is used.

The first clock control circuit 217 for the W-address counter 215 uses, for example, two TTLs with model number 74167 connected in cascade, and operates according to a magnification signal MM from a row encoder SW that sets the main scanning magnification, which will be described later. , controls the number of passing clocks among the 100 input clocks.

Further, the second clock control circuit for the R-address counter 216 is constructed by connecting two TTLs of model number 7497 in cascade, for example, and the first clock control circuit 216
Similarly to 7, the number of passing clocks among the input 4096 clocks is controlled according to the magnification signal MM.

Below, the case of reduction and enlargement are shown at magnification of 50% and 200%.
Let me explain using an example.

In the case of reduction to 50%, as shown in FIG. 3, the first clock control circuit 217 controls the pixel clock 211 to be thinned out at a ratio of 2 clocks to 1 clock, thereby forming the write clock 220. The W-address 221 generated by the W-address counter 216 according to the write clock 220 changes by one address every two pixels of the edge-enhanced write image signal, and the memory 214 stores the write image signal 219. Only even-numbered pixels of are written. The R-address 223 is generated by the R-address counter 216 in accordance with the readout clock 222 formed by outputting the image signal written in this memory 214 as it is without decimating the pixel clock 211 by the second clock control circuit 218. Read it with . The image signal 224 read out from the memory 214 in this way is 50% of the write image signal 219 in the main scanning direction.
It will be magnified.

As explained above, the reduction rate M (%) is determined by the number of clocks P out of 100 clocks set in the first clock control circuit 217 as shown in the following equation.

M (%) P In other words, the same value as the reduction rate M (%) is set to the number of clock passes P
It will be set as .

On the other hand, when enlarging to 200%, as shown in FIG.
W-address counter 2 as is without thinning processing.
15.

When reading out the image signal written in this memory 214, the second clock control circuit 218 controls the pixel clock 211.
A read clock 222 is created by passing the clock at a rate of one clock every two clocks. According to this read clock 222, the image signal 224 read out by the R-address 223 generated by the R-address counter 216 has a period of one pixel that is twice that of the write image signal 219, and is scaled by 200% in the main scanning direction. Become something.

As explained above, the enlargement rate M (%) is determined by the number Q of passing clocks among 4096 clocks set in the second clock control circuit 218 as shown in the following equation.

100 Q The image signal scaled in the main scanning direction in this way is modulated into an analog signal by the D/A converter 225, and then sent to the amplifier 2.
26 and is amplified by the laser driver 201.
Controls the amount of laser light emitted corresponding to a pixel. The amount of charge on the drum 203 is controlled by the laser light whose emission amount is controlled, and an electrostatic latent image corresponding to the image signal is formed line by line on the drum 203. This latent image is formed by an electrophotographic process (not shown). It is output as a toner developed image whose density is modulated for each pixel.

2304 is a DC servo motor that generates a driving force for reciprocating the optical unit, and 231 is a motor 2.
This is an encoder that generates a clock signal 239 synchronized with the rotation of 30.

236 is a reference clock generation unit that generates a reference clock for rotation control of the motor 230, and the reference clock generation unit 2
The reference clock from 36 is divided into a clock signal 237 of a predetermined frequency by a frequency dividing circuit 235, and then the clock signal is divided by a third clock control circuit 234 according to a magnification signal SM from a rotary encoder SW that sets a magnification in the sub-scanning direction. Controls the number of passing clocks.

Clock signal 238 from third clock control circuit 234
is input to the PLL control circuit 233, and the PLL control circuit 233 outputs a drive signal to the driver 232 so that the clock signal 238 and the clock signal 239 match,
Thereby, the rotation of the motor 230 is controlled to move the optical unit forward at a speed corresponding to the magnification ratio.

FIG. 5 shows a detailed configuration of the edge enhancement circuit shown in FIG.

The image signal input from the A/D converter (21O in FIG. 2) is delayed in a delay buffer 302 having line memories 810 to 812 for three lines.

In other words, the delay buffer memory 302 for three lines, which is addressed by the output of the address counter 301 that identifies the pixels for the line, processes the image signal of the current line 303, the image signal of one line before 304, the image signal of two lines before Image signals for three lines of 305 are output. Further, these image signals are delayed in units of pixels by a latch 306.

Here, the pixel of interest is a pixel signal 307 obtained by delaying the image signal 304 of one line by two pixels, and the multiplier 310 doubles this pixel of interest 307 and converts the previous and subsequent pixel signals 308 and 309 in the main scanning direction to ( -1) Adder 3 multiplies the result
11 to obtain a second-order differential signal 312 in the main scanning direction for the pixel of interest.

Furthermore, the pixel signals 313 and 314 of the lines before and after the pixel of interest in the same main scanning positional relationship are multiplied by (=1) in the multiplier 315, and the result of doubling the pixel signal of interest 307 is added to the adder 316.
, to obtain a second-order differential signal 317 in the sub-scanning direction for the pixel of interest.

801 is a multiplier for increasing or decreasing the main scanning edge emphasis signal 312, and 803 inputs the output of the rotary encoder 5W805, which sets the main scanning magnification in percentage units, as an address, and calculates the corresponding main scanning edge emphasis signal multiplication coefficient. This is a ROM that outputs 807. 802 is a multiplier for increasing/decreasing the sub-scanning edge emphasis signal 317, and 804 inputs the output of the rotary encoder 5W806 for setting the sub-scanning magnification in percentage units as an address, and calculates the corresponding sub-scanning edge emphasis signal multiplication coefficient. This is a ROM that outputs 808.

The coefficient ROM 803 is configured as shown in FIG. 6 in order to prevent white streaks and black streaks caused by reduction in the main scanning direction and pixel density unevenness caused by enlargement from becoming even stronger in area.

In Figure 6, the horizontal axis is the main scanning magnification set by the rotary encoder 5W805, and the vertical axis is the output multiplication coefficient 8.
07 value is shown.

As you can see in this figure, when the magnification is 100%, the multiplication coefficient is 1
As the magnification decreases, the multiplication coefficient decreases and the multiplication coefficient becomes 0 as the magnification decreases and the black streaks increase.
．． It is set at 5. At a magnification of 50% or less, information loss is prevented (meaning the multiplication coefficient is not reduced).

In addition, in the case of enlargement at a magnification of 100% or higher, the unevenness of density in the output becomes noticeable from about 200%, so the multiplication coefficient is gradually decreased. Even the density unevenness that occurs becomes more noticeable as the area increases, so the multiplication coefficient is set to O to prevent edge enhancement in the main scanning direction.

In this way, in this embodiment, in order to prevent the density unevenness of each pixel from becoming noticeable due to variable magnification image processing, the coefficient ROM 803 controls the main scanning edge enhancement amount according to the main scanning magnification to adjust the unevenness amount. There is.

On the other hand, a ROM that outputs the sub-scanning edge emphasis signal multiplication coefficient
804 is configured as shown in FIG. 7 in response to an increase in the amount of blur included in one pixel due to an increase in magnification in the sub-scanning direction.

In other words, if the multiplication coefficient at 100% magnification is 1 and the coefficient 2 at 800% magnification is connected with a straight line, 100% to 80
The coefficients up to 0% are determined. The reason why the multiplication coefficient is not increased at a magnification of 800% or more is to prevent the contours of the dark and light edges of the output image from being emphasized and output due to excessive edge emphasis.

Also, not reducing the multiplication coefficient when the magnification is below 100% is
This is to remove a certain amount of blur included in an optical system such as a lens even if the sub-scanning speed increases and the blur included in pixels decreases.

In this way, the second-order differential signal 312 in the main-scanning direction and the second-order differential signal 317 in the sub-scanning direction, which have been independently increased or decreased by the multipliers 801 and 802 according to the main-scanning magnification and the sub-scanning magnification, respectively, are sent to the adder 318. Pixel signal 307 of the pixel of interest
The edge-enhanced image signal 21
Get 9.

This image signal 219 is transmitted to the double buffer memory 2 described above.
14, and magnification processing in the main scanning direction according to the magnification ratio is executed.

It should be noted that since the image signal to be subjected to the scaling process is subjected to edge enhancement processing that takes into account the scaling factor, the occurrence of density unevenness and streaks in the image due to the scaling process can be prevented as much as possible.

In this embodiment, a multiplier is used to increase or decrease the second-order differential signal according to the scaling factor, but the number of delay lines in the line buffer memory 302 is increased so that the line from which the second-order differential is taken is the line of interest. It is also effective to increase or decrease the physical size of the Laplacian filter according to the magnification ratio, such as not only the front and rear lines but also the front and rear lines and the rear and rear lines.

As explained above, in this embodiment, the main scanning direction is used.

The strength of edge enhancement can be set independently for each sub-scanning direction, and the best output can be obtained by applying optimal processing to the blurring factors unique to the main scanning and sub-scanning.

Furthermore, even if it is necessary to suppress the amount of correction for only one of the image processing methods such as scaling processing, the control becomes simple because there is no effect on the correction of the other image processing.

In addition, by varying the amount of edge enhancement depending on the magnification ratio, scaling in the main scanning direction suppresses image deterioration caused by scaling, such as density unevenness and blurring in the sub-scanning direction, and produces a uniform output image that is not affected by the magnification. can get.

〔effect〕

As explained above, according to the present invention, by changing the strength of edge enhancement according to the magnification ratio, 1. It is possible to suppress density unevenness and streaks caused by magnification processing.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of the image reading device, Fig. 2 is a block diagram of the image processing circuit, Fig. 3 is a timing chart of main scanning reduction processing, and Fig. 4 is a cross-sectional view of the image reading device.
The figure is a timing chart of main scanning enlargement processing, Figure 5 is a diagram showing a configuration example of an edge emphasis circuit, Figure 6 is a diagram showing a main scanning edge emphasis multiplication coefficient table, and Figure 7 is a diagram showing a sub-scanning edge emphasis multiplication coefficient. Figure 8 is a diagram showing a conventional example of an edge emphasis circuit, Figure 9 is a diagram showing the configuration of an image reading line sensor, and Figure 1.0 is a diagram showing main scanning pixel unevenness due to edge emphasis and scaling. , FIG. 11 is a diagram showing scanning blur in the sub-scanning direction, and 10
3 is a CCD line sensor, 213 is an edge emphasis circuit, 2
14 is a double buffer memory, 301 is an address counter, 302 is a delay buffer memory, 803 and 804 are ROMs, 805 and 806 are rotary encoders SW
It is.

Claims (2)

[Claims] (1) It has a reading means that electrically reads the original image using a photoelectric conversion element, and a processing means that performs edge enhancement processing on the image signal from the reading means, and the strength of edge enhancement is adjusted to the reading magnification of the image. An image signal processing device characterized by changing the image signal based on the signal. (2) An image signal processing device according to claim (1), characterized in that the strength of edge enhancement in each of the main scanning direction and the sub-scanning direction is determined based on the image magnification ratio in each direction. .