JP3184286B2 - Image signal correction method and image reading device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image signal correcting method and an image reading apparatus, and more particularly, to an image signal correcting method and an image reading apparatus in an image reading apparatus using a CCD line sensor. For example, the present invention is applied to an image input device such as a scanner, a copying machine, and a facsimile.

[0002]

2. Description of the Related Art In an image reading apparatus using a CCD line sensor or the like, an output of a line sensor in a dark state is stored in a memory and subtracted from data obtained by reading an image as means for correcting an output in a dark state. There is a way. For non-linearity of a line sensor at an exposure level close to darkness which cannot be corrected by the correction method described above, for example, in Japanese Patent Laid-Open No. 2-94962, the minimum value of an exposure range necessary for image reading The correction is performed by setting a correction criterion for the output value at a slightly smaller exposure amount and subtracting the output value of the line sensor at the exposure amount from the data obtained by reading the image.

The dark output correction by the method of subtracting the dark data from data obtained by reading an image has the following disadvantages. That is, the photoelectric output characteristics of an image sensor such as a line sensor are not linear at an exposure level close to a dark state as shown in A and C in FIG. 4 and tend to vary. Therefore, when the correction is performed by the above-described correction method, the correction is performed as illustrated in FIG. 5, and the correct correction is not always performed. Also, the above-mentioned Japanese Patent Application Laid-Open No. 2-949
According to the correction according to JP-A-62-62, the correction is as shown in FIG. 6, and the photoelectric output characteristics of each pixel become uniform in a required exposure range, and correct correction can be performed.
It has the following disadvantages. That is, the correction amount in the correction method is a very small value because the sensor output is the minimum value of the exposure range necessary for image reading or an exposure amount slightly smaller than the minimum value. For this reason, the S / N of this correction signal is deteriorated, so that highly accurate correction cannot be performed.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has been made in consideration of the above circumstances, and has been made in consideration of the above, and has been made in consideration of the above-described circumstances. It is made for the purpose of providing a method and an image reading device.

[0005]

To achieve the above object, the present invention provides (1)
When reading the image by the photoelectric conversion elements, the difference value of the output value of the photoelectric conversion element at the maximum value of the required exposure range to the image reading, the output value of the photoelectric conversion element in a substantially intermediate value of the required exposure range to an image reading In the intermediate value
That generate an output value of the photoelectric conversion element at the minimum value of the exposure range required to read images by subtracting from the output value of the photoelectric conversion elements, the photoelectric by subtracting the output value from the output values obtained by reading the image (2) In an image reading apparatus that obtains an electric signal corresponding to the density of a document by a photoelectric conversion element, an output obtained by reading a white reference plate is used for image reading. It is stored in a white reference memory that is stored as an output value of the photoelectric conversion element corresponding to the maximum value of the exposure range, and the output value stored in the white reference memory and the photoelectric conversion at almost the intermediate value of the exposure range required for image reading. First subtraction for obtaining a difference value between output values of elements
An output value of the photoelectric conversion element at the intermediate value,
A second subtractor for obtaining a difference value from the difference value, a correction value memory for storing an output of the second subtractor, and an output value stored in the correction value memory from an output value obtained by reading an image. And a third subtractor for subtracting
In the above (2), as a means for obtaining an exposure amount substantially at an intermediate value of an exposure range required for image reading, reading the white reference plate after controlling the intensity of the light source,
(4) In the above (2), as a means for obtaining an exposure amount substantially in the middle of an exposure range required for image reading, a reference reflection plate or transmission plate is provided, and the reflection plate or transmission plate is read and obtained. It is characterized by. Less than,
A description will be given based on an embodiment of the present invention.

FIG. 1 is a block diagram for explaining an embodiment of an image signal correcting method and an apparatus in an image reading apparatus according to the present invention. In FIG. 1, reference numeral 1 denotes a CCD line sensor, and 2 denotes an A / D converter. Reference numeral 3 is a white reference memory, reference numerals 4, 5, and 7 are subtractors, and reference numeral 6 is a correction value memory. First, the white reference of one line is stored. That not shown main scanning direction of the white reference plate (exposure amount corresponding to e ₁₎ CCD line sensor 1
, And A / D converted by the A / D converter 2, and stored in the white reference memory 3. The output of each pixel at this time is V ₁ as shown in FIG. Next, the output of the CCD line sensor with respect to the exposure value (e ₂ ) of the intermediate value of the required exposure range is controlled by, for example, controlling the intensity of a light source, or using a reflection plate or a transmission plate having a density corresponding to the exposure amount. It is obtained by reading, A / D converted by the A / D converter 2, and guided to the subtractor 4 and the subtractor 5. At this time, the white reference memory 3 inputs the stored value to the subtractor 4. The value output from the A / D converter 2, the values output from the subtracter 5 because it is V ₂ in FIG. 2 V ₂ - a (V ₁ -V _2), which is V ₃ in FIG. 2 Is equivalent to This output is input to the correction value memory 6 and stored.

Next, an image is read. At the time of image reading, the signal that has been A / D converted by the A / D converter 2 is input to the subtractor 7 and is subtracted and corrected by the value read from the correction value memory 6. When the correction is performed in this manner, as shown in FIG.
The non-linearity in the dark output of each pixel of the line sensor 1 and the exposure amount which is very close in the dark is not affected.

As described above, when an image is read by the photoelectric conversion element, the maximum value of the exposure range (e
The output value of the photoelectric conversion elements in ₁₎ (V _1), substantially from the intermediate value (e ₂₎ the output value of the photoelectric conversion elements in the (V _2), the necessary exposure to the image reading of the required exposure range to an image reading The output value (V ₃ ) of the photoelectric conversion element at the minimum value (e ₃ ) of the range is obtained. By subtracting the output value (V ₃ ) from the output values (V ₁ , V ₂ ) obtained by reading the image, the variation between the pixels of the photoelectric conversion element can be corrected as shown in FIG. . In addition, to obtain an exposure amount at an intermediate value of the exposure range, the white light reference plate is read after controlling the intensity of the light source, or a reference reflection plate or a transparent plate is read.

[0009]

As apparent from the above description, the present invention has the following effects. (1) An image signal correction method according to claim 1, wherein the output value of the photoelectric conversion element at the maximum value of the exposure range required for image reading and the output value of the photoelectric conversion element at a substantially intermediate value of the exposure range required for image reading. The output value of the photoelectric conversion element at the minimum value of the exposure range required for image reading is created from this value, and subtracted from the output of reading the image. It is possible to accurately correct characteristics, variations, and the like. (2) The image reading device according to the second aspect corrects the image signal by using the image signal correction method according to the first aspect. Therefore, the non-linearity of the sensor at the dark output and the exposure amount very close to the dark is obtained. And variations can be accurately corrected. (3) In the image reading apparatus according to the third aspect, in addition to the effect of the image reading apparatus according to the second aspect, the intensity of the light source is controlled as a means for obtaining an exposure amount substantially in the middle of the exposure range required for image reading. Therefore, the image signal can be corrected with a simple configuration. (4) In the image reading apparatus according to the fourth aspect, a reference reflection plate or a transmission plate is provided as a means for obtaining an exposure amount substantially in the middle of the exposure range required for image reading. Compared with the image reading apparatus, a control circuit for the light source is not required, and the configuration is further simplified.

[Brief description of the drawings]

FIG. 1 is a configuration diagram for explaining an embodiment of an image signal correction method and an image reading device according to the present invention.

FIG. 2 is a diagram illustrating an output of each pixel.

FIG. 3 is a diagram showing a subtractor output.

FIG. 4 is a diagram showing the photoelectric output characteristics of a CCD line sensor.

FIG. 5 is a diagram showing the corrected photoelectric output characteristics of the CCD line sensor.

FIG. 6 is a diagram showing corrected photoelectric output characteristics of the CCD line sensor.

[Explanation of symbols]

1 CCD line sensor, 2 A / D converter, 3 white reference memory, 4, 5, 7 subtractor, 6 correction value memory.

Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H04N 1/40-1/409 H04N 1/46 H04N 1/60

Claims (4)

(57) [Claims] When an image is read by a photoelectric conversion element, an output value of the photoelectric conversion element at a maximum value of an exposure range required for image reading and an output value of the photoelectric conversion element at a substantially intermediate value of an exposure range required for image reading. The difference value with the value
Subtract from the output value of the photoelectric conversion element at the intermediate value
It obtain the output value of the photoelectric conversion element at the minimum value of the exposure range required to read images in, for correcting variations between pixels of the photoelectric conversion element by subtracting the output value from the output values obtained by reading the image An image signal correction method characterized by the above-mentioned. 2. An image reading apparatus which obtains an electric signal corresponding to the density of a document by a photoelectric conversion element, wherein an output obtained by reading a white reference plate is output by a photoelectric conversion element corresponding to a maximum value of an exposure range required for image reading. The first value is stored in a white reference memory that is stored as an output value, and a difference value between the output value stored in the white reference memory and the output value of the photoelectric conversion element at a substantially intermediate value of the exposure range necessary for image reading is obtained. A subtractor,
The output value of the photoelectric conversion element at the intermediate value and the difference value
A second subtractor for obtaining a difference value between the second subtractor, a correction value memory for storing an output of the second subtractor, and an output value stored in the correction value memory from an output value obtained by reading an image. An image reading apparatus, comprising: a third subtractor. 3. An image according to claim 2, wherein the means for obtaining an exposure amount substantially at an intermediate value of an exposure range required for image reading is obtained by reading a white reference plate after controlling the intensity of a light source. Reader. 4. A means for obtaining an exposure amount substantially at an intermediate value of an exposure range required for image reading, comprising a reference reflection plate or transmission plate, and reading the reflection plate or transmission plate. The image reading device according to claim 2.