JPS59223060A - Original reader - Google Patents

Abstract

PURPOSE:To eliminate unevenness in reading of an original picture with a simple constitution by removing the unevenness in a light source with an optical member and further electrically correcting the data by means of the corrected light. CONSTITUTION:Since the quantity of shading is large like the characteristic shown by the dotted line (a) even in the effective reading area (l) of an one- dimensional image pickup element (CCD) 1 in the case of a parallel type aperture, reverse correction is performed by changing the shape of the aperture in accordance with the luminance distribution on an original and the luminance distribution is made flat like the other characteristic shown by the soild line (b). Since the shading of a lens can be measured in advance, correction coefficients to each picture element of the CCD 1 are written in a multiplying ROM 11 in advance. Therefore, a value which is obtained by multiplying image data converted by an AD converter 3 by a correction coefficient corresponding to the picture element, is outputted. In this case, it can be managed without using a large number of bits for the correction coefficient, because it is the correction coefficient of the lens only that is required to be written in the ROM 11. That is to say, no RAM is required and, at the same time, even the capacity of the multiplying ROM 11 can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a document reading device that exposes a document to light using a light source and reads an image using light reflected from the document.

In this type of image reading device, in the optical system that transmits original information to the image sensor, the light source, especially the fluorescent lamp or halogen lamp, exhibits uneven brightness distribution due to structural problems, and the image sensor It has been pointed out that the amount of light at the periphery of the lens used to image the original information decreases due to an essential problem of the optical system (COS θ law). in this case,
For example, even if the density of the background of a document is completely uniform, the intensity of the reflected light will be uneven, causing fluctuations in the read signal level. This is especially true when a fluorescent lamp is used as a light source. is lower than the central portion, the peripheral portion of the document is read darkly and accurate document information cannot be transmitted.

FIG. 1 shows an example of the configuration of a document reading device.

A document table GD made of glass or the like is formed above the reading section R, and a user places a document to be read on this document table GD. At the bottom of the document table GD, there is a bar-shaped light source L1゜L2 such as a fluorescent light that illuminates the document and scans the document (sub-scanning).
A one-dimensional image sensor CCD that passes through the first plane mirror PM1 shown in FIG. 2, the plane mirror PM2 shown in FIG.
(Change Coupled Device) An image sensor is provided.

Light source L1. L2 and the first plane mirror PM1 are integrated by a support ST1 and are fixed to the carriage CAi. The carriage CA1 moves forward on the guide rail GL from left to right (direction F) in the figure and back from right to left by a well-known drive means.

The second plane mirror 2M2ti is moved on the guide rail GL by the carriage CA2 in the same direction as the first plane mirror PM1 at a speed 1/2 of the moving speed of the first plane mirror PM1.

Incidentally, at the end of the forward movement, the plane mirrors PM1 and PM2 are at the position PM1' indicated by the dotted line in the figure.

Move to P M 2'. At this time, the optical path length from the document table GD to the lens OPL through the plane mirrors PM1 and PM2 is always kept constant.

The main scanning direction of the image sensor CCDI is perpendicular to the drawing. If the signals from the light-receiving elements of the image sensor CCD I are read out in an orderly manner during the forward movement of the Senkukyo PMi and PM2, sequential signals obtained by raster scanning the document surface can be obtained.

In this device, in order to prevent reading errors caused by uneven ups and downs in the optical system, a conventional method has been used in which a correction circuit as shown in Fig. 2 is used to correct the unevenness of the electrically read image signal. was. That is, for each copy, when the reading position of the one-dimensional image sensor CCDI is at a predetermined reading start position, that is, the home position HP, the following sequence is performed. First, a light source L1 (not shown). L2 is turned on and a standard white or gray plate EF having a uniform density is irradiated over the entire surface of the imaging device CCD provided on the home position HP during reading, and the reflected light is input to the CCDI.

At this time, in the second illustrated circuit, the switch 4 is set to the 1 side, and the photoelectrically converted signal from the CCD 1 passes through the AMP 2, and is then converted to analog/digital ()=/D by a further converter 3.
) converted. The NΦ-converted image data is then sampled every few pixels and written into the memory RAM5. The reason why sampling is not performed for all pixels but every few pixels is to save the memory capacity of the AM5.

Based on the shading data of one captured pixel, several adjacent pixels (including white pixels) are corrected.

Next, when scanning the original, switch 4 is set to the 2 side, and C0D
The N converted image data of i is stored in a sequential multiplication memory ROM.
6 as an address signal, the contents of the RAM 5 are also read out in correspondence with the signal number bits of the CCD 1, and are similarly input as an address signal to the multiplication ROM B.

Multiplying ROM6 [is R, the input value from AM5 is, for example, V4
If the value is R, 0M6, the content obtained by multiplying the input value from CCD 1 by a value of 4/6 is written in advance as a correction value. As a result, in the multiplication ROM 6, R, AM 5
Based on the input value from the CCD 1, the image data from the CCD 1 is corrected pixel by pixel and output to the comparator. However, such a configuration requires R and AM to store data obtained by reading the reference plate, and also requires, for example, a CCD.
Even if the number of pixels of 1 is sampled every few bits, if the non-uniformity due to the optical system is large and the correction amount is large, the memory R
AM requires a very large capacity, making the entire device expensive. Furthermore, if sampling is performed by thinning out several bits, there is a drawback that if there is local unevenness in the amount of light in that area, it will not be possible to correct it.

The present invention has been made in view of the above points, and it is an object of the present invention to eliminate non-uniformity of image reading signals caused by various causes, and to achieve even better image reading.

Hereinafter, the present invention will be explained in more detail 1311j using the drawings.

FIGS. 3 and 4 show embodiments to which the present invention is applied. Third
The figure uses a fluorescent lamp as the light source for exposure, similar to the configuration in Figure 1.
The shape of the aperture of the fluorescent lamp (a) and the luminance distribution on the document surface (b) are shown. That is, with the parallel aperture, the amount of shading is large even within the effective reading area I of the one-dimensional image sensor cc:c+i, as shown by the characteristic shown by the dotted line (A). Therefore, we performed reverse correction by changing the shape of the aperture according to the brightness distribution on the document surface.
As shown in FIG. 6(b) (b), the brightness distribution is extremely uniform and has a 7-rat distribution.

The shading of the arrow by the lens OPL is electrically corrected using a circuit as shown in FIG. In other words, since the shading of the lens OPL can be measured in advance, the CCD
A correction coefficient corresponding to each pixel of 1 is written in the multiplication ROM 11 in advance.

When Φ-converted image data is input to the NΦ converter 6 of the CCD 1, a value obtained by multiplying the image data by a correction coefficient corresponding to that pixel is output.

As a result, the read signal of the CCD 1 is corrected and outputted to the comparator 12. In this case, the amount of light from the light source is made uniform by the shape of the aperture, so there is no need to consider the amount of shading correction for the light source, and only the correction coefficient of the lens needs to be written into the ROM 11. The number of bits of the correction coefficient can be reduced.

That is, compared to the conventional example, R and AM are not required, and the capacity of the multiplication ROM 1i can be reduced.

As explained above, an aperture-shaped fluorescent lamp is provided in the illumination system to improve the non-uniformity of the brightness distribution on the document surface, and the shading of the lens OPL is corrected by multiplying E in advance.
By performing correction using the correction coefficients written in the OM 11, it is possible to provide a shading correction device that is simpler and cheaper than the conventional example.

In this example, the light amount correction on the light source side was performed using the 7-percha shape of the fluorescent lamp, but as shown in FIG. It is also possible to provide a correction plate 15 shaped according to the luminance distribution of the lamp 16, and use this to correct the light and focus it on the lens OPL.Incidentally, reference numeral 14 is a reflecting mirror for changing the optical path.In this case, Since the correction plate 15 can be realized using a very inexpensive sheet metal, it can be achieved at a lower cost than the embodiment shown in the second figure, that is, the method of changing the shape of the aperture of the fluorescent lamp.

Further, if the correction circuit shown in FIG. 4 is replaced with the conventional correction circuit shown in FIG. 2, the accuracy of correction can be further improved.

Further, in this embodiment, a fluorescent lamp was used as the light source, but it goes without saying that other light sources such as a halogen lamp or an incandescent lamp may be used.

As described above, according to the present invention, the non-uniformity of the light source is removed by an optical member, and the read data from the original exposed by this corrected source is further electrically corrected. Non-uniformity in image reading can be more completely removed with a simple configuration.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a configuration example of a document reading device, FIG. 2 is a conventional image data correction circuit diagram, FIG. 6 is a diagram explaining optical correction according to the present invention, and FIG. 4 is a correction circuit according to the present invention. figure,
FIG. 5 is a diagram illustrating another optical correction of the present invention.
1 is CCD, OPL is lens, 6 and 11 are multiplication "OMs"
7 and 12 are comparators, and 15 is a correction plate.

Claims (1)

[Claims] A light source for exposing an original; a means for optically correcting non-uniformity of the light amount of the light source; a means for photoelectrically reading an original image using reflected light from the original; and a reading signal from the reading means. A document reading device comprising means for electrically correcting level non-uniformity.