JPS60254876A - Shading correcting device - Google Patents

Abstract

PURPOSE:To obtain easily and precisely a multi-valued image signal by reading a correcting image signal out of a read-only memory. CONSTITUTION:For example, an analog-level image signal is inputted, a scan start signal 54 is generated, and the writing of shading correcting data 61 is completed to put a RAM48 in a readable state. In such a case, the RAM48 is read repeatedly on the basis of address information from an address counter 58 to obtain low-order digit address information 62 of a RAM49. A selector 44, on the other hand, supplied the input image signal as high-order digit address information to a ROM49. The ROM49 is stored with a corrected image signal 65 after shading correction in respective memory areas selected with pieces of address information 62 and 63, and the image signal is read out and sent.

Description

DETAILED DESCRIPTION OF THE INVENTION "Industrial Application Field" The present invention is a flat-scanning reader equipped with a solid-state image sensor such as a CCD, in which shape ink of an image signal read by the solid-state image sensor is corrected. The present invention relates to a shape ink correction device.

``Prior Art'' Solid-state image sensors are widely used as photoelectric conversion elements in reading devices, such as facsimile machines or some types of copying machines, that convert image information on a document into electrical signals and read them.

FIG. 8 shows an example of such a device. A document 12 is placed on the platen 11 with its reading surface facing downward. Immediately below the platen 11, a single fluorescent lamp 13 for illuminating the original 12 is arranged in the main scanning direction of the original 12.

The light reflected from the original 12 by the fluorescent lamp 13 is incident on the lens 14, and an optical image is formed on the solid-state image sensor 15. The solid-state image sensor 15 is a one-dimensional image sensor using, for example, a CCD, and is configured to scan the original 12 in a plane by moving it in the sub-scanning direction, thereby reading image information.

In such a reading device, even when the density is uniform over one line, such as in the case of a blank document, the photoelectric conversion output of the solid-state image sensor 15 is usually non-uniform. One of the causes of this is variation in the luminance distribution of the light source.

FIG. 9 is only useful for explaining this. Fluorescent light 13
When used as a light source, the light rays 16 are most concentrated at the center of the reading line of the original 12. The illuminance is highest at the center of the document 12, and decreases toward the edges, which causes the photoelectric conversion output to become thicker (changed).Other causes of nonuniform photoelectric conversion output include:
Examples include a decrease in the amount of light around the lens 14 due to the cosine fourth power law, and non-uniform sensitivity of the elements of the solid-state image sensor 15.

If the photoelectric conversion output of the solid-state image sensor 15 becomes non-uniform in this way, it will adversely affect the signal processing process at the stage of converting an analog image signal into a digital signal, causing deterioration of image quality. FIG. 10 is for explaining the deterioration in image quality when an image signal is binarized. Assume that image information 17 (black and white information) as shown in FIG. On the other hand, from a solid-state image sensor, for example, a non-uniform photoelectric conversion output 18 as shown in the figure is obtained. Suppose that this is binarized at a certain Threnjord level. In this case, there is a possibility that the signal level corresponding to black image information (hereinafter referred to as black level) in the center of one line will be erroneously binarized as white image information; There is a possibility that a signal level corresponding to image information (hereinafter referred to as white level) may be erroneously binarized as black image information. Therefore, for example, the threshold level I! , i, a digital image signal 19 is obtained which is considerably degraded compared to the original image information, as shown in FIG.

FIG. 11 shows a conventional shading correction device proposed to eliminate such drawbacks.

The A/D converter 21 of this device receives a photoelectric change detection power (shading waveform) 22 over one line as shown in FIG. 12a as a result of reading a white background line with a solid-state image sensor. The A/D converter 21 converts this into a digital quantity and stores it in the memory 23. After this, at the stage when the image signal is actually read, the D/
These digital quantities are sequentially converted into analog quantities using the A converter 24. This shading correction signal 25 obtained from the D/A converter 24 has a threshold level f
12 is manually input to the comparator 26, and the image signal 27 obtained by photoelectrically converting the original is binarized (FIG. 12b). As a result, the white level and black level of the image information are binarized without error, and a high-quality digital image signal 28 (FIG. 12C) is obtained.

However, such a conventional shading correction device requires a D/Δ converter for converting a digital signal after A/D conversion into an analog signal for shading correction, making the device expensive. There was a drawback.

"Problems to be Solved by the Invention" In view of the above circumstances, the present invention provides a method for easily and accurately realizing aging correction.111. - The object of the present invention is to provide a ding correction device.

"Means for Solving the Problems" In the present invention, as shown in principle in FIG. A random access memory (hereinafter referred to as RA) stores shading correction data 31 in which the signal level of the image signal obtained by
It's called M. )32. The stored shading correction data 31 is read out by the shading correction data reading means 33 while being associated with each main scanning position of the image signal when reading the original. The image signal 34 obtained from the solid-state image sensor and the read shading correction data 35 are input to a read-only memory (hereinafter referred to as ROM) 37 as address information 36. From this R, OM 37, a corrected image signal 38 is read out in which the image signal 34 has been corrected for naging using the shading correction data 35.

Note that the part to be read used in this shading correction device does not need to be a special paper or the like, and may be a ground color part or a white printed part existing at the leading edge of the document to be actually read. Further, the ROM 37 may be an element in which a corrected image signal is written in advance in such a manner that the image signal obtained by i etc. by the solid-state image sensor is divided by the shape ink correction data.

"Example" The present invention will be described in detail with reference to Examples below.

FIG. 2 shows the shape ink correction device of this embodiment. An analog-level image signal 42 is manually input to the A/D converter 41 of this device from an image sensor (solid-state image sensor) not shown. The A/D converter 41 creates an image signal for each pixel that is quantized in 256 steps from "0" (black) to "255" (white) according to the signal level, and converts it into parallel 8-bit signals. It is supplied to the selector 44 as an image signal 43. Selector 44
converts this input image signal 43 to multi-by-break 4
Depending on the signal content of the shading correction control signal 47 supplied from 5, the shading correction control signal 47 is selectively output to the RAM 48 or the ROM 49.

By the way, FIG. 3 shows a document used in a reading device in which this aging correction device is used. The original 51 is composed of a band-shaped white reference area 52 provided at its leading edge, and a manuscript writing area 53 in which characters, figures, etc. are written. The white reference area 52 is a ground color area where nothing is printed, and data for ink correction is created using this area as a reference.

The background color of the document 51 is usually white or something similar to this, but in the case of so-called color paper, a thick white line may be printed across the entire width of the area 52. Of course, even if the background color is other than white, if the density is uniform in the main scanning direction, it can be used as it is as the white reference area 52.

Now, when the reading device starts reading the document 51, a scanning start signal 54 (FIG. 4a) is generated at the start of reading scanning for each line. The scanning start signal 54 is input to a counter 55 in the shading correction device, and the number of signals is counted.

The counter 55 is a counter that counts a numerical value N, and is a scanning start signal 54 . The carry signal 56 of H (high) level (Fig. 4b)
) occurs. The integer N is set to a value such that the main scanning line is approximately at the center of the white reference area 52 at this time.

When the H level carry signal 56 is generated, the multi-by-break 45 sets the shading correction control signal 47 to the H level during this Nth line scanning period. Only during this period, the selector 44 transfers the manually input image signal 43 to the RAM.
48.

The RAM 48 is set to a writing state in this state where the shading correction control signal 47 is at H level, and the image signal 43 is written.

This writing is performed while corresponding to each main scanning position using the address information 59 output from the address counter 58.

In this way, the image signal obtained by scanning the white reference area 52, that is, the shading correction data 1 is written in the RAM 48 before scanning of the document text writing area 53 is started. Figure 5 shows this siniding correction data 61.
This is an example.

When the writing of the shading correction data 1 is completed and the shading correction control signal 47 returns to the L (low) level, the RAM 48 enters the read state. In this state, the read operation of the RAM 48 is repeated using the address information 59 output from the address counter 58 in synchronization with the operation start signal 54. The shading correction data read out in this manner becomes lower address information 62 of the ROM 49. On the other hand, from the time when the shading correction control signal 47 changes to L level, the selector 44 outputs the manually inputted image signal 43 as upper address information 63.
Supply to M49.

In the ROM 49, a corrected image signal 65 after shading correction is written in each memory area selected by the address information 62, 63. Address information 62
The signal level of the shading correction data shown in
, and the signal level of the image signal of the document indicated by the address information 63 is 3, then the signal level 2c of the corrected image signal 65 written in the ROM 49 can be determined by the following equation.

The Vc-Vs/V corrected image signal 65 is read out pixel by pixel in synchronization with a video clock (not shown), and is sent as 8-bit (256 steps) data to a subsequent recording device or display device. FIG. 6 shows the signal level (2) of the image signal 43 when a gray portion of the same gradation of a document is read over one line. In this way, even if the image signal is high in level at the center of the line and decreases in level toward both sides, the shading correction data 61 shown in FIG.
By taking the ratio, a corrected image signal 65 whose shading has been corrected can be obtained as shown in FIG.

"Effects of the Invention" As explained above, according to the present invention, since the corrected image signal is read out from the ROM, it is possible to easily obtain a highly accurate multivalued image signal. Furthermore, by appropriately modifying the contents of the ROM in advance, it is possible to impart desired characteristics to the gradation expression in a recording device or a display device, for example, it is possible to easily emphasize a highlighted portion.

[Brief explanation of the drawing]

FIG. 1 is a diagram of the principle of the present invention, and FIGS. 2 to 7 are for explaining an embodiment of the present invention. Of these, FIG. 2 is a block diagram showing the configuration of a shading correction device, and FIG. 4 is a diagram of various waveforms for explaining the operation of the shading correction device, FIG. 5 is a waveform diagram showing changes in the signal level of shading correction data over one line, and FIG. 6 is a diagram of the original. Waveform diagram showing an example of a change in signal level of an image signal for one line during reading, No. 7
The figure is a waveform diagram showing the signal level of the corrected image signal after shading correction of the image signal shown in Figure 6, Figure 8 is a schematic configuration diagram of the reading device, and Figure 9 is the unevenness of illuminance on the document surface. 10 is an explanatory diagram showing the cause of
FIG. 1 is a block diagram of a conventionally proposed shading correction device, and FIG. 12 is various waveform diagrams showing the process of binarizing an image signal in this conventional device. 31.35...Shading correction data, 3
2.48...RAM. 33...Shading correction data reading means, 37.49...ROM. 38.65...Corrected image signal, 43...Picture signal, 62.63...Address information. Applicant Fuji Xerox Co., Ltd. Agent Patent Attorney Umeo Yamauchi Figure 8 Figure 12 Figure 10 Figure 11 Figure 12

Claims (1)

[Claims] 1. The signal level or a random access memory that stores the density level of the portion to be read as shading correction data that corresponds to each main scanning position; and a random access memory that stores this shading correction data at each main scanning position of an image signal when reading the original. A shading correction data reading means that reads the data in correspondence with each other, and an image signal obtained from a solid-state image sensor while reading a document, and shading correction data read out in synchronization with the image signal from the shading correction data reading means as address information, and shading is corrected. A shading correction device comprising: a read-only memory for reading out a corrected image signal. 2. The random access memory stores the image signal read from the uniform ground color part in the main scanning direction provided at the leading edge of the original as shading correction data, and the read-only memory The shape ink correction device according to claim 1, wherein the shape ink correction device performs shading correction by dividing the signal level of an image signal of a document portion to be read later by shading correction data, and outputs this as a corrected image signal. .