JPS62262848A - Illuminating method having shading correction function - Google Patents

Abstract

PURPOSE:To realize a shading correction without executing the electrical processing and adjustment of each LED chip, by varying a distance to the original of each part of a light source, bringing the end part separated from the illumination center of the light source closest to the original, and executing the shading correction. CONSTITUTION:A light source 5 is placed stepwise so that its distance to an original 1 becomes the longest l1 in the center part of the light source 5, and becomes shorter l1>l2>l3... as said distance goes to both sides therefrom. By setting the light source 5 in this way, an illuminance distribution on the upper face of the original 1 becomes the lowest in the center of a sensor, and becomes higher as it goes to both sides. In such way, the illuminance distribution on an image sensor can be made uniform, and a shading correction is executed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an illumination method having a shading correction function.

[Background of the invention]

The image reading optical system of an electrophotographic copying machine or hand scanner (portable image reader) irradiates a document with light from a line-shaped illumination light source, and uses an image sensor such as a CCD to capture the reflected light. It is configured to read images such as characters and images of a document by reading the document.

FIG. 8 shows an example of this, and is an example of a reading optical system of a hand scanner. In this example, the original 1 is irradiated from diagonally above the original 1 with a linear light source 2 made of an LED array, and the reflected light from the original 1 is incident on an image sensor 4 made of a CCD through an imaging lens 3. It is configured as follows. Here, the light a2 is arranged so that its longitudinal axis is parallel to the document 1. FIG. 9 is a front view of this optical system.

However, since the luminance of such a line light source 1 is uniform in the axial direction, the image sensor 4 suffers from shading in which the illuminance is highest at the center of the sensor and decreases toward both sides, as shown in FIG. appears.

Therefore, when using such a light source, shading correction has conventionally been performed electrically after the fact. Another method has been to adjust the current supplied to each LED chip of the LED array or to adjust the mutual spacing between the LED chips to change the axial brightness characteristics of the light source.

However, the method of electrically performing shading correction is quite complicated and is not suitable for hand scanners or small copying machines. In addition, to adjust the current that does not flow through each LED chip in the LED array, or to adjust the mutual spacing between the LED chips, each LED chip must be adjusted individually, which is time-consuming and costly to manufacture. There was the problem of high prices.

[Purpose of the invention]

An object of the present invention is to provide an illumination method in which shading correction can be realized without electrical processing or individual adjustment of LED chips, and in which the optical system can be easily manufactured.

[Structure of the invention]

To this end, the present invention is configured such that the distance of each part of the light source to the original is made different, and the end part of the light source that is far from the center of illumination is brought closest to the original for shading correction.

〔Example〕

Examples of the present invention will be described below. FIG. 1 is a diagram showing an embodiment thereof. In this embodiment, the distance between the light source 5 and the original l is 11, which is the longest at the center of the light source 5, and becomes shorter toward both sides, such that I! , >7!
They were arranged in a stepwise manner so that 2>p, . . . . By setting the light source 5 in this manner, the illuminance distribution on the upper surface of the document 1 is lowest at the center of the sensor, as shown in FIG. 2, and increases toward both sides. Therefore, the illuminance distribution on the image sensor can be made uniform as shown in FIG. 3, and shading correction can be performed.

However, arranging the light sources in a stairway like this tends to complicate the configuration somewhat.

In consideration of this point, FIG. 4 shows an embodiment in which a linear light source 6.7 having uniform brightness in the axial direction is used and arranged at an angle with respect to the original 1.

This direction of inclination is set so that the adjacent ends of both light sources 6 , 7 are furthest from the surface of the original 1 . In other words, the setting is such that the end portion away from the center of illumination is closest to the document.

When the light sources 6.7 arranged in this manner are used, the illuminance on the document surface, as shown in FIG. 5, has a distribution characteristic almost similar to that shown in FIG. 2 described above, and is highest at the center of the sensor. Then, as shown in FIG. 6, the illuminance on the sensor is approximately the same in each part 4, and shading is corrected.

Since the above-mentioned shading follows the fourth power law, the illuminance at both sides is extremely reduced compared to the center.

FIG. 7 is a diagram showing an embodiment that takes this point into account. Light sources 8 are placed on both sides of the central linear light source 8, which is arranged parallel to the surface of the document 1, so that the end portions are closer to the surface of the document 1. Similar light sources 9 and 10 are arranged at an angle so that the portions of the document corresponding to both sides of the sensor 4 are illuminated more intensely.

〔Effect of the invention〕

From the above, according to the illumination method of the present invention, not only can shading correction be realized, but the configuration is simple,
It has the characteristic of being easy to manufacture.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the light source of the image reading optical system and a document according to an embodiment of the present invention, FIG. 2 is a diagram showing the illuminance distribution on the document surface with the configuration shown in FIG. 1, and FIG. 3 is a diagram showing the sensor 4 is a front view of the optical system of another embodiment. FIG. 5 is a diagram showing the illuminance distribution on the document surface with the configuration shown in FIG. 4.
The figure shows the illuminance distribution on the sensor, Figure 7 is a front view of the optical system of yet another embodiment, Figure 8 is a side view of the conventional optical system, and Figure 9 is the optical system of Figure 8. The front view, FIG. 10, is a diagram showing the illuminance distribution of the optical system shown in FIG. ■... Original, 2... Line light source, 3... Imaging lens, 4... Image sensor, 5... Light source, [i~
10... Line light source. Agent Patent Attorney Tsuneaki Nagao Figure 1 Figure 2 ■ Figure 8 = -, q+tt'''''aq'c Hiro-π body l Figure 7

Claims (3)

[Claims] (1) In an image reading optical system configured to illuminate an original with one or more linear light sources with a uniform luminance distribution and read an image of the original using light reflected from the original, An illumination method characterized in that distances of each part of the light source to the document are made different, and shading correction is performed by bringing the end portion of the light source farthest from the center of illumination closest to the document. (2) Claim 1 characterized in that the light source is arranged at different distances from the document in a stepped manner.
Lighting method described in section. (3) The illumination method according to claim 1, wherein the light source is arranged at an angle with respect to the document.