JPH01280967A - Initial setting mode operating method for digital color copying machine - Google Patents

Abstract

PURPOSE:To reproduce a smooth picture by applying twice scanning prior to the scanning of an actual original picture, applying first the shading correction of a read element of a digital scanner and using a signal after shading correction in the 2nd scanning so as to take white balance. CONSTITUTION:Prior to the scanning of the actual original picture, at first the first scanning for shading correction for a digital scanner is applied. Then the 2nd scanning is applied. The signal read from a white board is subjected to picture processing by the scanning and the CCD is subjected to shading correction already by the 1st scanning and the picture signal is corrected based on the shading correction coefficient and used for gamma correction and the result is stored in a frame memory 30. Thus, the data is used as the white balance data at actual original picture read picture processing and white balance is taken by an image processor 19. Then smooth picture reproduction is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD The present invention relates to a method of operating a digital color copier in an initial setting mode.

PRIOR ART In general, in a color copying machine, a good color image is:
It is possible to reproduce colors that are faithful to the original. Here,
Since digital color copying machines handle digital signals sampled by a digital scanner, quantization errors, ie, noise, occurring in each processing step pose a problem. If the quantization level is given by, for example, about 12 to 16 bits, the level difference between one quantization level is small, so the total amount of noise is also small. but,
From a practical level, it is common to process at 6 to 8 bits due to cost considerations. Therefore, quantization noise appears on the image in the form of roughness of color dots, that is, color noise. This additional noise is one of the major factors that impairs image quality.

Correction of sensitivity unevenness of a reading sensor (COD) in a digital scanner, which causes such noise, is generally performed in the form of shading correction.

That is, conventionally, gray scale white balance is performed in the form of shading correction in a scanner. This is to balance the white light (such as the white light of the document pressing plate) by correcting errors caused by uneven sensitivity of the R, G, and B reading signals of the scanner.

However, the output signal of the scanner is then processed by a processing unit such as an image processor, but when the quantization level of the scanner unit and processing unit is 6 to 8 bits, the quantization error after processing occurs at each step. As a result, the error increases. Therefore, even if white shading correction is performed, even if the original is gray scale, the signal after UCR processing will be
The three-channel Y, M, and C color signals remain as noise. Here, OCR processing refers to the signal amount common to three of Y, M, and C signals, that is, the amount of black.
This is a process in which the signal is multiplied by K and extracted, and the remainder is used as a color signal. Therefore, the grayscale read signal is inherently UC
Y, M after R processing.

All C components must be O, but in reality, noise remains as described above. Such noise appears on the image as roughness in color.

In other words, in the case of the conventional method, although the scanner's white balance (low-frequency sensitivity unevenness) is corrected, high-frequency noise remains in some areas.

Furthermore, the current situation is that no countermeasures have been taken at all for calculation errors and quantization errors that occur in the image processing section.

That is, at present, smoothing processing that attempts to flatten noise by averaging adjacent images is common. but,
This also smoothes the image signal, causing thin lines to become blurred and character reproducibility to deteriorate. In other words, noise and blur amount have an antinomic relationship, and the reality is that compromises are made where appropriate.

Purpose The present invention has been made in view of the above points, and provides a digital color copying machine that can remove noise generated in a digital scanner and an image processing section and improve image reproducibility. The purpose is to provide an initial setting mode operating method.

Structure In order to achieve the above-mentioned object, the present invention has the following features: After powering on the main body,
Prior to the actual scanning of the original document image, the first scanning operation for shading correction of the digital scanner is performed, and then the light intensity of the original illumination light source is set to a light intensity different from the normal original illumination light intensity, and the white plate on the back side of the original pressure plate is set. While illuminating the white plate, the reflected light from the white plate is read by the digital scanner after shading correction, and color correction, gamma correction, masking processing and U
Perform processing such as CR correction processing, store the three-channel Y, M, and C signals after the UCR correction processing in memory, and perform a second scanning operation to set the initial value of white balance after image processing. Features.

That is, prior to scanning the actual document image, two scanning operations are performed, the first scanning is for shading correction and the shading of the reading element of the digital scanner is corrected, and the second scanning is for correcting the shading of the reading element after the shading correction. By performing image processing on the read signal and adjusting the white balance of the R, G, and B color noise after the image processing, the noise is removed near the output of the image processing section, and the correction noise that occurs is removed. This cancels the noise and reproduces the image quality without blurring it.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

The digital color copying machine to which this embodiment is applied can be roughly divided into a digital scanner section, an image processor section (image processing section), and a plotter section (laser color printer section). These are controlled by the system controller, but roughly speaking, first, the scanner section scans the document at a scanning speed that matches the magnification specified by the start signal from the system controller, and converts the document image into a photoelectric device such as a CCD. The R, G, and B components are read as 8-bit image data and sent to the image processor in synchronization with a synchronization signal from the image processor.

This image processor uses R, G, and B from the scanner.
Image processing such as γ correction and UCR one-color correction is performed on each 8-bit image data, and the image data is converted into 3-bit image data each of Y, M, C, and BK, and sent to the printer at a predetermined timing. In the laser color printer section, the laser diode is modulated according to each 3-bit image data Y, M, C, BK sent from the image processor in synchronization with the synchronization signal, and a color copy image is printed on transfer paper using an electrophotographic process. get.

Here, the configuration of the digital scanner used in this embodiment will be explained with reference to FIGS. 3 and 4. FIG. 3 shows a cross-sectional configuration of a digital scanner 1 that photoelectrically converts and reads a document image, including a contact glass 3 on which a document 2 is placed, a document illumination light source 4, first and second scanning mirrors 5 and 6, and an imaging lens 7. Also provided is an optical system of a photoelectric conversion unit 8 that electrically reads reflected light from the original. Further, a lighting circuit 9 for driving the document illumination light source 4 and a D for mechanical scanning (sub-scanning) are also provided.
A C motor 10, a video processing circuit 11, etc. are also built-in.

Since such a digital scanner 1 uses a fixed original scanning method to accommodate the versatility of originals, the original illumination light source 4 and the original illumination light source 4 are used so that the optical path length of the original reflected light 12 is always constant during sub-scanning. The first carriage 13 carrying the first scanning mirror 5 and the second carriage 14 carrying the second scanning mirror 6 are maintained at a speed ratio of 2:1, and the DC
It is driven in sub-scan by a motor 10.

Here, as shown in FIG. 4, the photoelectric conversion unit 8 includes three CCDs 15a, L5b, and 15c (which reads an image on the same main scanning line by dividing it into three parts) and an amplifier 16a that amplifies each photoelectric conversion output. .

It consists of 16 b and 16 c. These CCD1
The electrical signals detected on the light receiving surfaces of 5a, 15b, and 15c (
The image density information) is processed by the A/D converter 17 and the shading correction circuit 18, and then becomes Y.

The M and C signals are transmitted to an image processor 19 as shown in FIG.

When the main scanning of one sub-scanning line by these CCDs 15 is completed, the first and second carriages 13 and 14 are driven in the sub-scanning direction by the DC motor 1o, and the reading of the next sub-scanning line is started. In FIG. 4, when the scanning is completed to the right edge of the document, the DC motor 10
2 carriages 13,14 are return driven.

Here, the rotational angular velocity of the DC motor 10 is determined by a rotary encoder 20 provided on the motor shaft and a speed signal generation circuit 21.
is fed back, and the sub-scanning speed control circuit 22 performs constant speed control and speed control during startup/stopping and the like.

The document reading process of the digital scanner 1 is sequentially controlled by the scanner control circuit 23. For this reason, the scanner control circuit 23 receives a signal from a position sensor 24 such as a home position sensor. Further, the reading timings of the CCDs 15a to 15c and the like are controlled in synchronization with clock pulses generated by a timing generator 26 based on ○5C25 under the control of a scanner control circuit 23.

The A/D converter 17 converts the analog signals (image density information) read by the CCDs 15a to 15c into 8-bit digital signals. Here, the read signal of the CCD 15 includes distortion caused by optical illuminance unevenness, sensitivity variations of each reading pixel of the COD, and the like. Therefore, the shading correction circuit 18 corrects the data after A/D conversion to remove such distortion.

The configuration of the image processor 19 will now be explained with reference to FIG. First, a γ correction circuit 27 is provided to which Y, M, and C signals that have been color corrected via the A/D converter 17 and the shading correction circuit 18 are input. This γ correction circuit 27 corrects the gradation of data (gamma correction), and then inputs the data to a masking processing circuit 28.

This masking processing circuit 28 performs color correction for Y and M.

C resolution wavelength range and laser color printer section (not shown)
This circuit corrects the deviation from the coloring wavelength of the toner pigment to obtain a good color balance.

The masked Y, M, and C signals are input to the UCR processing circuit 29 and subjected to UCR correction processing.

That is, a process is performed in which equal amounts of the three Y, M, and C signals are extracted as a black BK signal. This process prevents excessive consumption of color toner.

In this embodiment, processing is performed using 8 bits, but a frame memory 30 is provided for storing color noise generated after UCR correction processing. This frame memory 30 is provided with memories corresponding to the number of pixels of the read image. Then, when the correction mode is activated, the residual Y after the UCR correction process after capturing the achromatic color signal (obtained by scanning the white plate provided on the back side of the document pressure plate in the digital scanner 1).

The M and C signals are stored in a frame memory 30. Here, the amount of exposure light from the document illumination light source 4 during scanning to capture the achromatic signal is set to a different amount of light than the amount of light during normal reading, for example, about half the normal amount of light. By reducing the amount of light to about half of the normal amount,
Halftone white light (equivalent to gray on the entire surface) is obtained for the white background on the back side of the document pressure plate, and this can be used as a chart for noise detection by the image processor 19.

Furthermore, when creating an image, the Y
, M, C signals and Y stored in the frame memory 3o.
, M, and C signals are performed by the difference calculation circuit 31.

That is, let the noise Y, M, C signals be YN+M)(,CN, and let the Y, M, C signals of the image be YS+MS, cs,
If the image range is x'y, then f (Ys'(x-y)] = f (Ys(x-y))-f [YN(x-y)]
f (Ms'(x-y)) = f[Ms(x-y))-f(Ms(x-y))f
[Cs'(x-y)) = f (Cs(x-y))-f (CN(x-y))
A correction calculation is performed.

The data after such correction calculation is sent to the density pattern circuit 3.
2, density pattern processing is performed, and furthermore, the lighting time for each dot of the laser color printer is determined by the multi-value processing circuit 33, and is output to the printer side. That is, Y and M after multivalue processing.

The C and BK data control on/off of laser light for each color in a laser color printer.

It should be noted that overall control of the image processor 19 is performed by a main body control circuit 34, and timing control is performed by a synchronous control circuit 35.

Therefore, in this embodiment, as shown in FIG. 1, after turning on the power of the main body and before actually scanning the original image,
A first scanning operation for shading correction of the digital scanner 1 is performed.

In this scanning, the shading correction circuit 18
Shading correction of the CCD 15 is performed by this. Next, a second scanning operation is performed. This is to read the white plate (gray scale) on the back side of the document pressure plate, but the amount of light from the document illumination light source 4 at this time is about half of the normal amount as described above. The signal read from the white plate by this scanning operation is image-processed by the circuit shown in Fig. 1, but the first scanning (from this point onwards, the CCD 15 has already undergone shading correction, and the image signal is corrected based on this shading correction coefficient. This data is subjected to γ correction, etc., and is stored in the frame memory 3o, thereby becoming white balance data during actual document image reading and image processing.As a result, the P,
The G and B color noises, that is, the white balance in the image processor 19 section is taken.

Effects As described above, the present invention performs two scanning operations before scanning an actual document image, in the first scanning operation, shading correction of the reading element of the digital scanner is performed, and in the second scanning operation, the shading correction is performed after the shading correction. Since normal image processing is performed on the signal and color noise after UCR correction processing, that is, white balance is taken, it is possible to reduce the quantized color noise that is basically associated with digital color copying machines, and improve the resolution of character image areas. Smooth image reproducibility can be achieved without any damage.

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention, and FIG. 1 is a flowchart showing processing, FIG. 2 is a block diagram of an image processor, FIG. 3 is a longitudinal side view of a digital scanner, and FIG. 4 is a block diagram thereof. . 1... Digital scanner, 4... Original illumination light source, 3
0...Memory! c::

Claims (1)

[Claims] After turning on the power of the main unit, and before actually scanning the original image, perform the first scanning operation for shading correction of the digital scanner, and then set the light intensity of the original illumination light source to a light intensity different from the normal original illumination light intensity and scan the original. While illuminating the white plate on the back side of the pressure plate, the reflected light from this white plate is read by the digital scanner after shading correction, and processing such as color correction, gamma correction, masking processing, and UCR correction processing is performed by normal image processing means, Said U
Initial settings of a digital color copying machine characterized by performing a second scanning operation to store three-channel Y, M, and C signals after CR correction processing in a memory and to set an initial value of white balance after image processing. How the mode works.