JPH0879519A - Image reader - Google Patents

Abstract

PURPOSE: To measure a shading correction coefficient by excluding the influence of a flaw or dust on a white chart to be received as far as possible. CONSTITUTION: This reader is equipped with a light source 21 which illiminates an original, a line sensor 1 which detects reflected light from the original by moving in a sub-scanning direction, the white chart 25 being the reference of exposure condition for reading, and a control means 5 which performs the moving control of the line sensor and processes image data read by the line sensor. The control means fetches data at plural places on the white chart for plural times, respectively, and compares the data at plural places at every pixel, and sets large data and a ratio of data to the maximum value in the data as the shading correction coefficient.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading device.

[0002]

2. Description of the Related Art In a conventional image reading device, when measuring a shading (uneven amount of light) correction coefficient, if white reference data is simply used as a reference, shading is caused by dust or scratches on a white reference plate. An error may occur in the correction data. In addition, the influence of noise of the CCD and the circuit system also causes an error in the shading correction data.

For example, as shown in FIG. 6A, when an error occurs in the shading correction data due to the influence of dust, if the input value is corrected by the shading correction coefficient created from this shading correction data, it is obtained. The correction values obtained are as shown in FIG. That is, the error of the shading correction data becomes the error of the image as it is, and the same error occurs in all lines, so that it appears in the image as unsightly and noticeable vertical stripes.

[0004]

In order to remove vertical stripes due to errors in shading correction data, a method is used in which a white chart has a width and a plurality of lines of data are taken and averaged while moving a carriage on the white chart. Can also be considered. According to this method, the influence of scratches and dust existing at the position where the carriage is moved is certainly received, if not 100%. Further, there is a problem that the control becomes complicated because the carriage has to be moved during the reading of the white chart.

The present invention has been made in view of the above problems, and it is an object of the present invention to measure a shading correction coefficient while avoiding the influence of scratches and dust on the white chart as much as possible.

[0006]

In order to achieve this object, an image reading apparatus of the present invention comprises a light source (2) for illuminating a document.
1), a line sensor (1) that moves in the sub-scanning direction to detect reflected light from a document, a white chart (25) that serves as a reference of exposure conditions for reading, and movement control of the line sensor. And a control means (5) for processing the image data read by the line sensor, wherein the control means fetches data at a plurality of points on the white chart a plurality of times and compares the data at a plurality of points for each pixel. , The larger data and the ratio to the maximum value in the data are used as the shading correction coefficient.

[0007]

In the image reading apparatus having the above structure, the shading correction coefficient is measured by capturing the line data at a plurality of points on the white chart, so that the influence of scratches and dust on the white chart is reduced. The shading correction coefficient can be measured with the least possible reception.

[0008]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block connection diagram showing an embodiment of an image reading apparatus according to the present invention. 2 is a front view showing an embodiment of the image reading device according to the present invention, and FIG. 3 is a perspective view showing an embodiment of the image reading device according to the present invention.

The reading light is emitted from the light source 21 and the original 20 is read.
(FIGS. 2 and 3). The input image light beam reflected by the document 20 is supplied to the CCD line sensor 1 via the lens 23. The input image light beam is photoelectrically converted into an electric signal (analog signal) by the CCD line sensor 1. The analog signal is digitally encoded by the A / D converter 2, and the CPU 5 captures it in the RAM 10 via the image processing circuit 3 and the FiFo buffer 4.

When the reading of one line is completed, the stepping motor 7 is controlled by the CPU 5 to move the CCD line sensor 1 in the sub-scanning direction (direction of arrow a in FIGS. 2 and 3).
Move to the next capture position of. The CPU 5 controls the stepping motor 7 via the stepping motor drive circuit 8.
Drive control. The stepping motor 7 includes a timing gear 28, a timing pulley 29, and a timing belt 3.
The carriage 24 is driven in the sub-scanning direction via 0 and the coupling member 31. The CCD line sensor 1 is mounted on the carriage 24, guided by the guide plate 25 and the guide shaft 26, and moves in the sub-scanning direction (direction of arrow a in FIGS. 2 and 3).

The CCD line sensor 1 is 1 in the main scanning direction.
The line is read, and the stepping motor 7 moves to the next position. Repeat this for one original 20
Read the whole.

In the image reading apparatus, the shading correction coefficient is measured in order to correct the shading (uneven amount of light) by the light source 21. When measuring the shading correction coefficient, dust on the white chart and noise included in the measurement data are problems. Next, a method for solving these problems will be described. The white chart is shown in Figure 2.
Lower side of the platen glass 22 of the bottom, that is, the carriage 24
It is generally provided near the initial position of the.

The noise component contained in the measurement data can be solved by capturing the same line a plurality of times and taking an average. For dust on the white chart, data is captured at two locations (SD_POS1 and SD_POS2) on the white chart 25 (FIG. 4) multiple times and averaged. The data of the same position (main scanning direction) of the CCD line sensor 1 is compared, and the larger one is selected. As a result,
The influence of dust existing at different positions in the main scanning direction, such as the dust 1a to 3a, can be eliminated. However, the influence of dust existing at the same position in the main scanning direction such as dust 4a cannot be removed. However, dust such as dust 4a is considered to be difficult to attach because the white chart 25 is attached downward. In addition, SD_POS
The distance between 1 and SD_POS2 is, for example, 3 mm.

The maximum value of the 1-line data thus formed is detected to obtain the shading correction coefficient of each pixel. The maximum value is SDNmax and each pixel data is SD_DAT
Let [n] be the shading correction coefficient SD of each pixel.
[N] is

SD [n] = SDNmax / SD_DAT [n].

Further, the measurement time and the image quality can be adjusted by changing the number of times of capturing. For example, when a test image such as a preview is captured, time is prioritized over image quality. Therefore, the number of captures can be suppressed to about 4 to shorten the measurement time, and as a result, the reading time can be shortened. Further, when the image quality is prioritized as in the case of the final scan, the number of captures is set to about 64 to reduce the influence of noise and improve the image quality.

In this way, by capturing the line data at two points on the white chart 25, the influence of dust and scratches on the white chart 25 can be effectively and almost certainly removed at a required level with a simple structure. The shading correction data can be calculated at a processing speed suitable for the purpose. Hereinafter, the shading correction coefficient measurement sequence will be described with reference to the flowchart of FIG.

In FIG. 5, when the program starts, first, in step S1, if the reading mode is preview, the number N of times of capture is set to four. In addition, if the final scan is 64 times. Next, the carriage 24
Is moved to the position SD_POS1 on the white chart 25 (step S2). Position SD of white chart 25
The data SD_DAT1 [n] at the location of _POS1 is fetched N times (step S3). The carriage 24 is moved to the position SD_POS2 on the white chart 25 (step S4). Position of white chart 25 SD_POS2
The data SD_DAT2 [n] at the location is fetched n times (step S5).

Next, for all n,

SD_DAT [n] = max (SD_DA
T1 [n], SD_DAT2 [n]) is calculated. However, max (a, b) is an operation for comparing a and b and selecting the larger one (step S6). SD
Detect the maximum value of _DAT [n] and set it to SDNmax
(Step S7). Shading correction coefficient SD
[N]

SD [n] = SDNmax / SD_DAT [n] is calculated (step S8), and the program ends.

[0023]

As described above, according to the image reading apparatus of the present invention, the shading correction coefficient is measured by capturing the line data at a plurality of points on the white chart. It is possible to measure the shading correction coefficient while minimizing the influence of scratches and dust on the surface.

[Brief description of drawings]

FIG. 1 is a block connection diagram showing an embodiment of an image reading apparatus according to the present invention.

FIG. 2 is a front view showing an embodiment of the image reading apparatus according to the present invention.

FIG. 3 is a perspective view showing an embodiment of an image reading apparatus according to the present invention.

FIG. 4 is a front view showing an embodiment of an image reading apparatus according to the present invention.

FIG. 5 is a flowchart showing an embodiment of the image reading device according to the present invention.

FIG. 6 is a characteristic diagram showing an example of a conventional image reading apparatus.

[Explanation of Codes] 1 CCD line sensor 1a Dust 2 A / D converter 2a Dust 3 Image processing circuit 3a Dust 4 FiFo buffer 4a Dust 5 CPU 7 Stepping motor 8 Stepping motor drive circuit 20 Original 21 Light source 22 Platen glass 24 Carriage 25 White chart

Claims (4)

[Claims] 1. A light source for illuminating a document, a line sensor that moves in a sub-scanning direction to detect reflected light from the document, a white chart that serves as a reference of exposure conditions for reading, and the line sensor. Movement control and a control means for processing the image data read by the line sensor, wherein the control means fetches data at a plurality of points of the white chart and compares the data at a plurality of points for each pixel. Then, the image reading device is characterized in that the larger data and the ratio to the maximum value in the data are used as the shading correction coefficient. 2. The image reading apparatus according to claim 1, wherein the control unit captures data at a plurality of points of the white chart a plurality of times. 3. The image reading apparatus according to claim 1, wherein the control unit captures data at two locations on the white chart a plurality of times. 4. The image reading device according to claim 1, wherein the white chart is built in the device.