JP2000270173A - Image processing unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately perform correction of a phase shift among element arrays as accurately as possible and to enhance the reproducibility of black thin lines. SOLUTION: This image processing unit performs correction processing to each color of image data obtained from an image sensor having a structure where a plurality of element arrays that are elongated in the main scanning direction are arranged in parallel at a prescribed pitch in a subscanning direction. The unit is provided with a plurality of inter-line correction means 15R, 15G, 15B so as to correct a misalignment among the element arrays in the sub scanning direction of the image sensor where reference colors for the correction are different from each other, and with a correction output means 15A that outputs image data ROUT, GOUT and BOUT corrected on the basis of image data outputted from a plurality of the inter-line correction means.

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 mounted on a digital color copying machine or the like, and more particularly, to a position between R, G and B in a sub-scanning direction in a reduction type color CCD sensor or the like. The present invention relates to an inter-line correction process for correcting a shift.

[0002]

2. Description of the Related Art An image reading section of a color copier or the like
For example, as described in Japanese Patent Application Laid-Open No. 9-261492, a method in which information obtained by reducing and projecting a document image via an optical system is read by a reduced color CCD sensor is generally used from the viewpoint of cost. . As shown in FIG. 12, the reduced-type color CCD sensor has element arrays of R (red), G (green), and B (blue) in which pixels are arranged in the main scanning direction, and has a predetermined interval in the sub-scanning direction. It has a structure arranged in parallel with each other with a distance d.

When an image is read using the above-described color CCD sensor, R, R in the sub-scanning direction, which is the direction in which the original and the CCD sensor move relative to each other mechanically, are used.
Due to the G and B positional shifts (interval d), a temporal shift, that is, a phase shift occurs between the R, G, and B color image signals obtained from the CCD sensor.

In order to correct a phase shift between R, G, and B (hereinafter, also referred to as a "position shift"), R output image data that occurs first is delayed by a time corresponding to an interval 2d (for example, eight lines). By delaying the next G output image data by a time corresponding to the interval d (for example, four lines), a correction process for adjusting the phase to the last R output image data is performed.

[0005] Further, when the magnification at which the original image is reduced and projected changes, such as when the scanning speed in the sub-scanning direction changes in a color copier having a reduction / enlargement function, the phase between R, G and B is changed. In some cases, the deviation does not become an integral multiple of one line and a fraction (decimal part) occurs. In such a case, it is necessary to correct the phase shift between R, G, and B as accurately as possible by interpolation. That is, when the corrected position is a certain position between the lines, the density value of each color at that position is obtained by a weighted average of the values on the lines on both sides.

[0006]

However, in the correction of the phase shift between R, G, and B when the above-described color CCD sensor is used, when the decimal part is corrected by the interpolation processing, the black fine line is not corrected. Reproducibility may deteriorate. This is because when the above-described interpolation process is performed when the reduced projection of the black thin line is close to, for example, one dot width, R, G,
It is considered that the cause is that the balance of the reading characteristics of each of the B colors is largely lost.

Therefore, the density level of the color other than the color used as the reference for the correction becomes low. As a result, the thin black line becomes greenish or reddish, and the reproducibility is reduced.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and provides an image processing apparatus capable of correcting a phase shift between element rows as accurately as possible and improving the reproducibility of a fine black line. With the goal.

[0009]

As shown in FIG. 2, in the image processing apparatus according to the present invention, a plurality of element rows long in the main scanning direction are arranged parallel to each other at a predetermined pitch in the sub-scanning direction. An image processing device that performs a correction process of image data of each color obtained from an image sensor having a structured
A plurality of line-to-line correction units 15R, 15G, and 15 that use different reference colors for correction for correcting positional deviation between element rows in the sub-scanning direction of the image sensor.
B and image data ROUT, GO corrected based on the image data output from the plurality of inter-line correction means.
Correction output means 15A for outputting UT and BOUT. Correction of less than one line is usually performed by interpolation processing.

[0010] In the image processing apparatus according to the second aspect of the present invention, the image signal of each color of R, G, B is output from each element row of the image sensor, and the inter-line correction means 15R, 1
5G and 15B perform the line correction process using the R, G, and B colors as reference colors in the correction. Correction output means 15A
Calculates and outputs an average value of image data for each color.

[0011]

FIG. 1 is a block diagram showing an overall configuration of an image processing apparatus M1 according to the present invention, and FIG. 2 is a block diagram showing a configuration of an inter-line correction unit 15.

In FIG. 1, information obtained by reducing and projecting an original image via an optical system is used as a reduction type color CCD sensor 1.
2 is read. The obtained image signals of each color of R, G, and B are input to the A / D converter 13. The A / D converter 13 converts R, G, and B image signals that are analog signals into R, G, and B image data that is 8-bit digital data (256-gradation density data). The obtained R, G, B image data is supplied to the shading correction unit 1.
After the shading correction for correcting the light amount unevenness in the main scanning direction is performed by 4, it is input to the line-to-line correction unit 15.

The line-to-line correction unit 15 includes a CCD sensor 12
Is a circuit for correcting a phase shift of an image signal (image data) due to a positional shift between the R, G, and B lines. As shown in FIG. 2, R, G, B
Of three line-to-line correction circuits 15 each using
R, 15G, and 15B, and a correction output unit 15A that outputs corrected image data by obtaining an average value for each color for image data output from the R, 15G, and 15B.
Each of the inter-line correction circuits 15R, 15G, 15B performs correction by delaying image data other than the reference color using a field memory. A specific circuit configuration will be described later.

Returning to FIG. 1, the R, G, and B image data output from the line-to-line correction unit 15 is
Corrects the color shift caused by the chromatic aberration of the lens system.
Further, a scaling / movement processing unit 1 including a scaling line memory
At 7, an enlargement / reduction process in the main scanning direction according to the magnification is performed.

The image data output from the scaling / movement processing unit 17 is input to a color conversion unit 18, where adjustment between R, G, and B is performed, and an RGB system (addition) is performed by a color correction unit 19. Color system)
CMY-based (color-reduced) image data C
(Cyan), M (magenta), Y (yellow), Bk
(Black). The C, M, Y, and Bk image data are subjected to processes such as edge enhancement and smoothing by an MTF correction unit 20 and then provided to a printer unit via a printer interface 21.

The R, R output from the color conversion unit 18
The G and B image data are also provided to the area determination unit 22.
The determination of whether the read image is a halftone image, a character image, or a photographic image is performed by the area determination unit 22.
When the determination result is given to the MTF correction unit 20, the MTF correction unit 20 switches whether or not to perform correction processing such as edge enhancement and smoothing according to the type of image in the area.

The area determining section 22 outputs a signal indicating a black character area, an inner edge, an outer edge, a black edge correction amount, and the like, in addition to the signal indicating the determination result described above.
Although not shown, the image processing apparatus M1 is provided with a reference drive pulse generator, a line buffer, a histogram generator, an ACS determiner, and the like. The reference drive pulse generation unit generates a clock signal necessary for processing of each unit including the CCD sensor 12. The line buffer stores one line of image data of each color of R, G, and B read by the CCD sensor 12. The histogram generation unit generates lightness data from the image data of each color of R, G, and B obtained by the preliminary scan, and generates the histogram on a memory. The ACS determination unit determines whether or not each dot is a color dot based on the saturation data, counts the number of color dots in each block area of 512 dots on the document, and determines whether the pixel is a color area or a monochrome area. Is determined.

In addition, a one-dot-wide black fine line detection unit for detecting whether or not the image currently being read is a substantially one-dot-wide black fine line may be provided. Such a one-dot-wide black fine line detection unit includes B image data output from the shading correction unit 14, R image delay data RMD and G image delay data GMD output from the line-to-line correction unit 15.
Then, it is determined whether or not the currently processed image portion in the image information projected on the CCD sensor 12 is a one-dot-width black fine line. The result of this determination is, for example, the area determination unit 22
Is output to

Note that, in the image processing apparatus M1, the order of arrangement of each unit, that is, the order of processing image data, can be variously changed in addition to the above. FIG.
Is a block diagram of the inter-line correction circuit 15G, FIG. 4 is a block diagram showing an example of the configuration of the interpolation calculation unit 38, and FIG. 5 is a diagram showing an example of the timing of the reset signal RES and each output image data.

The line-to-line correction circuit 1 described here
5G is a correction circuit using G (green) as a reference color. R
Line-to-line correction circuits 15R and B using (red) as a reference color
The basic configuration and operation of the line-to-line correction circuit 15B using (blue) as a reference color
Since it is the same as G, detailed description here is omitted.

In FIG. 3, signals RIN, BIN, GI
N is R (red), B (blue), and G (green) image data inputs, respectively. These image data inputs RIN, BI
N and GIN are subjected to delay correction for an integer number of lines by the first correction unit 30 and are subjected to interpolation processing for fractions (decimal numbers) by the second correction unit 31 to become image data outputs R1, B1, and G1. .

The first correction unit 30 includes a field memory 33
35, the image data inputs RIN and GIN are delayed with respect to the image data input BIN. That is, as described in the description of the related art, the image data input RIN is set to C
The delay between the R element row and the B element row in the sub-scanning direction of the CD sensor 12 (element row interval) is 2d, and the image data input GIN is delayed in the sub-scanning direction of the CCD sensor 12. It is delayed by a time corresponding to the element row interval d between the G element row and the B element row. Element row spacing d
Is represented by the number of lines shifted between the two element rows. In the present embodiment, the element row interval d between the G element row and the B element row is “4”, and the element row interval 2d between the R element row and the B element row is 2d.
Is “8”.

The field memories 33 to 35 are used for delaying image data in units of a plurality of lines. For example, each of the field memories 33 to 35 has 256K.
Assuming a storage capacity of Byte and an image data capacity of each color of 5 KByte (5,000 pixels) per line, 51 lines of image data can be delayed per field memory.

As shown in FIG. 3, the image data input RIN
Are two serially connected field memories 33,
34 can delay up to 102 lines,
The image data input GIN is stored in one field memory 35.
Can be delayed up to 51 lines.

In this case, the actual delay amount is determined by controlling the timing of the reset signal applied to the read reset terminal RRES and the write reset terminal WRES of each of the field memories 33 to 35. In addition,
“−” Added to the head of each signal sign indicates a negative logic signal, and “−” is omitted in this description.
The same applies to the other drawings and their descriptions.

When a reset signal is applied to the write reset terminal WRES, each of the field memories 33 to 35
When writing of input data is started and a reset signal is given to the read reset terminal RRES, output of accumulated data is started. Therefore, after the reset signal is applied to the write reset terminal WRES, the read reset terminal RR
The period until the reset signal is supplied to the ES is the delay amount.

A reset signal RES0 is applied to the write reset terminals WRES of the field memories 33 and 35, and a reset signal RE is applied to the read reset terminals RRES.
S1 is provided. The reset signal RES1 is applied to the write reset terminal WRES of the field memory 34, and the reset signal RES2 is applied to the read reset terminal RRES. Therefore, the image data input R
INR indicates two serially connected field memories 3
3, 34, the image data input GI is delayed by the period from the reset signal RES0 to the reset signal RES2.
NR is the reset signal RE by the field memory 35.
It is delayed by a period from S0 to the reset signal RES1. The image data input BINR is passed to the second correction unit 31 without delay.

FIG. 5 shows a state in which G image delay data GMD is obtained with an n-line delay from B image data, and R image delay data RMD is obtained with an n-line delay. The value of n, that is, the number of lines corresponding to the delay time from the reset signal RES0 to the reset signal RES1, is an integer part (in) of a value obtained by multiplying the element column interval by a scaling factor.
t). In the case of the same magnification, the element column interval itself is, for example, 4 lines.
× 0.6 = 2.4, which is the integer part 2. Actually, a value obtained by adding 1 to this value is set as a final delay amount (number of lines). This is for facilitating the interpolation processing in the second correction unit 31 described later. Similarly, with respect to the number of lines corresponding to the delay time from the reset signal RES0 to the reset signal RES2, a value obtained by adding 1 to twice the integer part (int) of the value obtained by multiplying the element column interval by the scaling factor is finally obtained. The delay amount (number of lines) is used.

As described above, the obtained R-delayed image data and G-delayed image data are supplied to the second correction section 31 together with the undelayed B image data. Second correction unit 31
Outputs the G-delayed image data as image data output G1 without performing the correction process, and performs the interpolation process on the R-delayed image data and the B-image data based on the G-delayed image data.

The second correction unit 31 includes FIFO memories (also referred to as field memories) 36 and 37 for delaying the image data by one line, and interpolation calculation units 38 and 39 for each of the R-delayed image data and the B image data. Having. The R delay image data R _n is input to the A input terminal of the interpolation operation unit 38, and the R delay image data R _n−1 further delayed by one line in the FIFO memory 36 is input to the B terminal. An interpolation coefficient α is input to the K terminal from a CPU or the like. The interpolation calculation unit 38 calculates the interpolation data R _n ′ between the data R _n and the data R _n−1 using the interpolation coefficient α according to a formula described later.

On the other hand, the A input terminal of the
B image data B delayed by one line in IFO memory 37
_n-1 is input, and B image data B _n before delay is input to the B terminal.
Is entered. Further, an interpolation coefficient α is input to the K terminal. Interpolation operation unit 39, the interpolation data B with data B _n and the data B _n-1 according to the equation below using the interpolation coefficient α
_{Operate n} '.

The interpolation coefficient α is a fraction (decimal part) when the scaling factor is multiplied by the element row interval. In the above-described example, the value 2 obtained by multiplying the element row interval “4” by 0.6 is used. .4 is the decimal part 0.4. Therefore, the interpolation coefficient α is obtained from the following equation.

[0033]

Α = element row interval × magnification rate−int (element row interval × magnification rate) where int () is an operator for extracting the integer part of the numerical value of ().

Using this interpolation coefficient α, R
And B, that is, the interpolation data R _n 'and B
_n 'is obtained from the following equation.

[0035]

(Equation 2)

[0036]

(Equation 3)

In the above equations (Equations 2 and 3), the coefficient α or (α-1) multiplied by the data of the (n-1) th line and the data of the nth line is represented by the R image data and the B image The opposite is true for the data. In this connection, as shown in FIG. 3, the relationship between the image data input to the A and B terminals of the interpolation calculation units 38 and 39 and the delay data for one line is determined by the interpolation calculation for the R image data. The reverse is true in the section 38 and the interpolation operation section 39 for B image data. this is,
This is because, as described above, the CCD sensor 12 has a structure in which the R element row and the B element row are arranged before and after the G element row. That is, the relationship between the equations (Equation 2 and Equation 3) is schematically shown in FIG.

In FIG. 6, R_n, R_n-1, B_n, B
_n-1Is fixed, the value of the interpolation coefficient α is 0 to 1
Changes to G_nIs position B_n-1(R_n) From side B
_n(R _n-1) Side. As described above, the first correction
In the unit 30, the R image data is compared with the B image data.
The second correction unit 3 delays one extra line.
The interpolation operation at 1 compensates for that one line,
The phases of the R, G, and B image data are aligned.
You.

As described above, by performing the interpolation processing of the decimal part by the second correction unit 31 in addition to the position deviation correction of the integer line by the first correction unit 30, more detailed color deviation correction can be performed. It can be carried out.

However, since the interpolation processing of the decimal part is performed by taking a weighted average of the densities of the preceding and succeeding lines, for example, in the case of a one-dot-width thin line, the density is greatly reduced by this interpolation processing. For this reason, in the case of a thin black line, the balance of the densities of the R, G, and B colors may be lost, and the reproducibility may deteriorate. This will be described with reference to FIG.

FIG. 7 shows R, G,
FIG. 6 is a diagram schematically showing the phase and density of each B image data. FIG. 7A shows a state before correction by the line-to-line correction circuit 15G. (B) shows the position (phase) and density of each of the corrected R, G, and B image data when the magnification is equal, that is, when the correction coefficient α is 0. In this case, since the interpolation processing of the decimal part in the second correction unit 31 is not actually performed, there is no reduction in the density of each image data, and the first correction unit 30 performs only the positional deviation correction for the integer lines. Will be.

FIG. 7C shows that the correction by both the first correction unit 30 and the second correction unit 31 of the line-to-line correction unit 15 is performed when the magnification is not the same and the correction coefficient α does not become 0. 9 shows the phases and densities of the R, G, and B image data at the time of the execution. In this case, while the density of the G image data serving as a reference, ie, the interpolation processing is not performed, does not change, the density of the R and B image data is greatly reduced by the interpolation processing. As a result, the balance of the densities of the respective colors is greatly disrupted as it is, and the reproducibility of the fine black line is deteriorated.

FIG. 10 is a diagram showing a state of a change in density value by correction in the case of a thin line, and FIG. 11 is a diagram showing a state of change of a density value by correction in the case of a thin line. As can be seen from these figures, it is understood that the density value of image data shifted from the reference color is reduced by performing the correction.

Therefore, in the present embodiment, as shown in FIG. 2, three line-to-line correction circuits 15R, 15G, and 15 using R (red), B (blue), and G (green) as reference colors.
B to perform interpolation processing, and output the corrected output
Thus, the average value for each color of the image data output from them is obtained.

In FIG. 2, a correction output unit 15A calculates an average value for each color of the image data output from the line-to-line correction circuits 15R, 15G, and 15B, and outputs image data ROUT, GOUT, and BOUT. That is, ROUT = (R0 + R1 + R2) / 3 GOUT = (G0 + G1 + G2) / 3 BOUT = (B0 + B1 + B2) / 3 FIG. 8 is a block diagram showing an example of the configuration of the correction output unit 15A.
FIG. 9 is a diagram for explaining the operation of the correction output unit 15A.

As shown in FIG. 8, the correction output unit 15A
It can be constituted by three adders 151 to 153 and three dividers (multipliers) 154 to 156. In FIG. 9, when the density values of the R, G, and B colors are completely equal,
That is, image data when an achromatic color is ideally read is shown. 9A shows image data R0, G0, and B0 corrected using R as a reference color.
(B) shows image data R corrected using G as a reference color.
9, G1 and B1, FIG. 9C shows image data R2, G2 and B2 corrected using B as a reference color, and FIG. 9D shows image data ROUT, GOUT and B of their average values.
OUT is shown. In this example, 3
The two image data ROUT, GOUT, and BOUT are identical to each other.

As described above, the three line-to-line correction circuits 15R, 15G, and 15 using R, G, and B as reference colors, respectively.
With respect to the image data output from B, an average value is obtained for each color, and the image data subjected to the line-to-line correction is obtained. Thus, the phase shift between the element rows of the CCD sensor 12 is accurately corrected. And R, G,
The balance of the density of each color of B is maintained. As a result, the reproducibility of the black fine line can be improved.

In the above embodiment, the element row interval d is set to "4" and the element row interval 2d is set to "8". For example, the element row interval d is set to "8" and the element row interval 2d is set to "16".
For example, a numerical value other than these, or a numerical value other than an integer may be used. Three line-to-line correction circuits 15R, 15
Although the average value of the image data output from G and 15B has been obtained, a weighting coefficient may be used or a root-mean-square may be performed. Further, image data corrected based on image data from two line-to-line correction circuits may be obtained.

In the above-described embodiment, the line-to-line correction unit 15 and the line-to-line correction circuits 15R, 15G, 15B, etc. are implemented by hardware by hardware circuits, by executing programs by a CPU, or by software. Each can be realized by a combination. In addition, the line-to-line correction unit 15 or the image processing device M
The configuration of each part or the whole of 1, the processing contents, the processing order, etc.
It can be changed appropriately according to the spirit of the present invention.

[0050]

According to the present invention, the phase shift between the element rows can be corrected as accurately as possible, and the reproducibility of the fine black line can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an overall configuration of an image processing apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of an interline correction unit.

FIG. 3 is a block diagram of an inter-line correction circuit.

FIG. 4 is a block diagram illustrating an example of a configuration of an interpolation operation unit.

FIG. 5 is a diagram illustrating an example of a timing of a reset signal and each output image data.

FIG. 6 is a schematic diagram for explaining decimal part interpolation processing by a second correction unit of the line-to-line correction circuit.

FIG. 7 is a diagram schematically showing the phase and density of image data of each color in the case of a black thin line of one dot width.

FIG. 8 is a block diagram illustrating an example of a configuration of a correction output unit.

FIG. 9 is a diagram for explaining the operation of a correction output unit.

FIG. 10 is a diagram showing how a density value changes due to correction in the case of a thin line.

FIG. 11 is a diagram illustrating a state of a change in density value due to correction when the line is not a thin line.

FIG. 12 is a schematic diagram showing a structure of a reduction type color CCD sensor.

[Explanation of symbols]

M1 image processing device 12 CCD sensor (image sensor) 15 line-to-line correction unit 15R, 15G, 15B line-to-line correction circuit (line-to-line correction unit) 15A correction output unit (correction-output unit)

Claims (2)

[Claims] An image processing apparatus for correcting image data of each color obtained from an image sensor having a structure in which a plurality of element rows long in a main scanning direction are arranged in parallel in a sub-scanning direction at a predetermined pitch. A plurality of inter-line correction means for correcting a positional shift between element rows in the sub-scanning direction of the image sensor, the reference colors being different from each other, and a plurality of inter-line correction means output from the plurality of inter-line correction means. An image processing apparatus comprising: a correction output unit that outputs image data corrected based on image data. 2. An image sensor of each color of R, G, and B obtained from an image sensor in which element rows for R, G, and B that are long in the main scanning direction are arranged in parallel with each other at a predetermined pitch in the sub-scanning direction. An image processing apparatus for performing a correction process, wherein each of R, G, and B is used to correct a positional shift between each of R, G, and B element rows in a sub-scanning direction of the image sensor. A plurality of line-to-line correction units, and a correction output unit that outputs, as image data corrected for an average value for each color, of image data output from the plurality of line-to-line correction units. An image processing apparatus characterized by the following.