JPH05236267A - Picture reader - Google Patents

Abstract

PURPOSE:To maintain the picture quality in an excellent state by correcting a deviation in the chromaticity due to a temperature change caused by radiation of a light source mainly in such the case that lots of originals are continuously read. CONSTITUTION:A temperature sensor 18 is provided in the vicinity of an image sensor 14. A masking coefficient of a color masking section 24 or a gamma conversion characteristic in a gamma correction section 26 is selected depending on a detected temperature TE by the temperature sensor 18.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus which reads an image by a color image sensor and processes the image.

[0002]

2. Description of the Related Art Conventionally, a still image of a color original is read by an image sensor as image input means of a computer and as an image input means of a digital copying machine, and various processes are performed on the read image data. An image reading device that outputs an image signal is used above.

In a full-color image reading apparatus, a light source with a large amount of light such as a halogen lamp is often used,
The reflected light from the original is dispersed into three primary colors by the R, G, and B transmission filters, and the respective lights are imaged on a monochrome CCD (image sensor). There are various methods such as a filter switching method and an on-chip filter method, depending on the method of splitting light into three primary colors.

An interference film filter is generally inserted in the optical path in order to cut out near-infrared light having a long wavelength of 700 nm or more, which causes noise, among reflected light from the original.

[0005]

As color image processing becomes widespread, many color originals are continuously read, and the light quantity of the light source increases as the original reading speed increases. The temperature of the image sensor and various filters is likely to rise due to the radiant heat of the light source.

When the temperature of the filter rises, the spectral characteristic of the filter fluctuates, and the light amount level of each color light incident on the image sensor fluctuates accordingly. For example, in an interference film filter, moisture in the filter evaporates as the temperature rises, which shifts the transmission region to a shorter wavelength and lowers the transmittance in the red light region, as shown by the curve CL2 in FIG. The light amount level of the red light incident on the CCD is lowered.
Further, when the temperature of the CCD rises, its sensitivity characteristic or output characteristic changes.

As a result, the color reproducibility of the image data output from the image reading device is deteriorated, and in a color copying machine, for example, the chromaticity of the copied image differs from that of the original and the image quality deteriorates. There is. Therefore, for example, the reading of the document image must be temporarily stopped and wait for the temperature to drop, resulting in a significant decrease in work efficiency.

In view of the above problems, the present invention corrects the chromaticity deviation mainly due to the temperature change caused by the irradiation of the light source to improve the image quality, for example, when a large number of originals are continuously read. It is an object of the present invention to provide an image reading device that can be maintained at

[0009]

In order to solve the above-mentioned problems, an apparatus according to the invention of claim 1 is an image reading apparatus which reads an image by a color image sensor and performs processing, and irradiates an original. An irradiation-related amount detection unit for detecting an amount related to the irradiation amount from the light source is provided, and a correction coefficient for color correction is selected according to the value of the amount related to the irradiation amount.

In the apparatus according to the second aspect of the present invention, a temperature sensor provided in the vicinity of the image sensor is used as the irradiation-related amount detecting means, and correction for color correction is performed according to the temperature detected by the temperature sensor. Select a coefficient.

[0011]

The irradiation-related amount detecting means detects the amount related to the irradiation amount from the light source for irradiating the original, and the correction coefficient for color correction such as masking coefficient or gamma conversion characteristic is detected according to the detected value. Is selected, and masking processing, gamma correction, or the like is executed according to the selected correction coefficient.

When a temperature sensor is used as the irradiation-related amount detecting means, the temperature of the image sensor or various filters arranged in the vicinity thereof is detected, and the color correction is performed according to the detected temperature. ..

As the quantity related to the irradiation quantity from the light source,
In addition to the temperature, there are, for example, the total irradiation time or the total number of irradiations of the light source within a certain period of time, the number of times of reading or scanning by the image sensor within a certain period of time, and the like.

[0014]

FIG. 1 is a sectional front view showing a schematic structure of a copying machine 1 having an image reader section IR according to the present invention.

The copying machine 1 produces a color image by electrophotographic method based on the image signal S6 and an image reader section IR which performs signal processing on the read signal obtained by reading the image of the original and outputs it as an image signal S6. And a laser printer unit LP for imaging.

The image reader section IR comprises a scanning system 10 and a signal processing section 20. The scanning system 10 includes a document table glass 16 on which a document is placed, a scanner 15 that scans below the document table glass 16, and a motor 11 that drives the scanner 15.

The scanner 15 includes an exposure lamp 12 for irradiating an original, a SELFOC lens array 13 for collecting reflected light from the original, a color image sensor 14, and an interference film for cutting long-wave near-infrared light. A filter 17 and a temperature sensor 18 arranged near the color image sensor 14 are mounted.

The color image sensor 14 includes R (red) and G on the CCD elements arranged in the main scanning direction.
This is an on-chip filter type contact CCD sensor in which spectral filters that transmit each color of (green) and B (blue) are repeatedly formed in order.

The image of the original is the color image sensor 1
4 reads as color signals of three R, G, and B additive color systems. The photoelectric conversion signal S0, which is the output of the color image sensor 14, is processed by the signal processing unit 20 into four colors of BK (black) in addition to the three subtractive colors of Y (yellow), M (magenta), and C (cyan). It is converted into a signal and sent to the laser printer unit LP as an image signal S6. The signal processor 20 will be described later in detail.

The laser printer section LP comprises a laser optical system 30 which uses a semiconductor laser (not shown) as a light source, and an image forming system 40 which uses an electrophotographic process using a photosensitive drum 41.

The laser optical system 30 includes a polygon mirror 3
1, a Fθ lens 32, a reflection mirror 37, and the like, and emits laser light modulated by an image signal output from the buffer memory 39 for each line to expose the photosensitive drum 41.

In the image forming system 40, a main eraser 42, a charging charger 43, and
Four developing devices 45a to 45d, a transfer drum 51, a cleaner 53, etc. are arranged.

A latent image corresponding to the original is formed on the surface of the photosensitive drum 41 uniformly charged by the charging charger 43 by the above-mentioned exposure. The latent image is the developing device 45.
a, 45d, Y, M, C, B
It is developed as a toner image of K. The toner image is transferred by the transfer charger 46 onto the paper wound around the peripheral surface of the transfer drum 51.

In the case of full-color copying, the transfer drum 5
The toner images of four colors are superposed (multi-transfer) in 1 and then the sheet is transferred to the transfer drum 51 by the separation claw 47.
And is sent to the fixing device 48. The sheet on which the toner image is fixed is discharged to the sheet discharge tray 49.

The sheet is fed from the sheet cassette 50 to the transfer drum 51, electrostatically sucked by the suction charger 54 and wound around the transfer drum 51. FIG. 2 is a block diagram showing the configuration of the signal processing unit 20.

The photoelectric conversion signal S0 from the color image sensor 14 is amplified to a predetermined level by the amplifier 21 and input to the A / D converter 22. A / D converter 22
Converts the photoelectric conversion signal S0 into image data of 128 gradations, for example.

The shading correction unit 23 performs shading correction that compensates for the light distribution of the exposure lamp 12 and the sensitivity difference between each pixel of the color image sensor 14. The color masking unit 24 generates image data D2 corresponding to R, G, and B colors to image data D3 corresponding to Y, M, and C colors. In generating the image data D3, the masking coefficient of the matrix used for density conversion is selected based on the temperature TE detected by the temperature sensor 18.
Details will be described later.

The UCR processing section 25 performs undercolor removal processing to increase the overall contrast and obtain a clear image, and image data D4 corresponding to each color of Y, M, C and BK.
Is output.

The gamma correction unit 26 is composed of a non-volatile RAM that stores a density conversion table for data correction,
In order to correctly reproduce the density of the image of the original, the image data D5 is output by correcting the image data D4 so as to complement the non-linear density reproduction characteristic of the image forming system 40.

The image data D5 is processed by another processor 27 for editing and image quality improvement, and binarization for halftone reproduction by a dither method or the like. Sent to LP.

By the way, the color masking section 24 has the following (1)
~ Masking processing is performed according to the equation (3) to generate image data D3. M = a ₁₁ B−a ₁₂ G + a ₁₃ R (1) C = a ₂₁ B + a ₂₂ G−a ₂₃ R (2) Y = −a ₃₁ B + a ₃₂ G + a ₃₃ R (3) Each of these formulas A plurality of masking coefficients MC, which are the groups of coefficients a _{11 to} a ₃₃ used for the above, are prepared, and are selected according to the temperature TE detected by the temperature sensor 18.

That is, the temperature sensor 18 is arranged in the vicinity of the color image sensor 14 and the interference film filter 17 so as to detect the temperatures thereof, and the temperature TE is detected by the CPU 201 based on the outputs thereof. A selection signal S11 for selecting the masking coefficient MC according to the temperature TE is output from the CPU 201 to the color masking unit 24.

FIG. 3 is a diagram showing the relationship between the temperature TE and the masking coefficient MC. According to FIG. 3, the temperature TE is 30 ° C.
A masking coefficient MC1 is selected if
The masking coefficient MC2 is selected in the case of 30 to 50 ° C, and the masking coefficient MC3 is selected in the case of 50 to 70 ° C. If the temperature exceeds 70 ° C., the copy operation is temporarily stopped because the temperature is abnormally high, and the operation is restarted after the temperature drops.

[0034] In these masking coefficient MC1~3, as the temperature TE increases, coefficient a ₂₃ is set to be gradually increased. As a result, when the temperatures of the color image sensor 14 and the interference film filter 17 increase, the decrease in the red output due to the increase is compensated by the increase of the coefficient a ₂₃ thereof, and the C (cyan) component in the image data D3 is excessive. Is prevented.

That is, for example, when a large number of originals are continuously read, the temperature of the color image sensor 14 and the interference film filter 17 rises due to the radiant heat of the exposure lamp 12, which causes a curve CL2 in FIG. The sensitivity in the red range decreases. Therefore, if the correction of the coefficient a ₂₃ as described above is not performed, the red color of the copy image is faded in comparison with the red color of the original image, and, for example, a flesh-colored skin color becomes a dull skin color. There is a masking coefficient MC1 to MC3 appropriate to the temperature TE.
By performing the selected correction coefficients a _23, and with each other to correct the decrease amount of the red output.

Therefore, the color reproducibility of the copied image in the copying machine 1 is prevented from being deteriorated and the image quality is maintained in good condition. It is not necessary to suspend the copying and wait for the temperature to decrease as in the conventional case. Efficiency does not decrease.

FIG. 4 is a flow chart showing the color correction process by the masking process at the time of copying. When the print SW for starting the copy operation is pressed (step # 11), the temperature TE of the color image sensor 14 and the interference film filter 17 is detected (step # 12),
The masking coefficient MC is selected according to the temperature TE (step # 13).

The processing operation of the color masking section 24 by the selected masking coefficient MC and various other processing operations are performed, whereby the copy operation is executed (step # 14).

The processing from step # 12 onward is repeated until the copy operation for the set number of copies is completed (step # 15). In the above-described embodiment, the color correction associated with the temperature change is performed by the color masking unit 24, but it may be performed by another processing unit, for example, the gamma correction unit 26.

That is, the masking coefficient MC is fixed, the density conversion table for data correction in the gamma correction unit 26 is selected by the selection signal S12 according to the temperature TE, and the gamma conversion characteristic GM is made variable. ..

FIG. 5 is a diagram showing the relationship between the temperature TE and the gamma conversion characteristic GM, and FIG. 6 is a diagram showing the respective gamma conversion characteristics GM for cyan. According to FIG. 5, the temperature TE
Is 30 ° C. or lower, the gamma conversion characteristic GM1 is selected, and when 30 to 50 ° C., the gamma conversion characteristic GM2 is selected.
Is selected and in the case of 50 to 70 ° C., the gamma conversion characteristic G
When M3 is selected and exceeds 70 ° C., the copy operation is stopped.

In FIG. 6, the gamma conversion characteristics GM1 to GM3 are set so that the output value with respect to the cyan input becomes smaller as the temperature TE becomes higher. As a result, similarly to the case of the masking coefficient MC described above, when the temperature of the color image sensor 14 and the interference film filter 17 rises and the sensitivity of red color relatively decreases, the cyan component in the image data D5 increases. It is possible to suppress the occurrence of color loss and maintain color reproducibility. Although not shown, the gamma conversion characteristics GM for magenta and yellow are also selected appropriately according to the temperature TE.

FIG. 7 is a flow chart showing a color correction process by gamma correction during copying. Print SW
When is pressed (step # 21), the temperature TE is detected (step # 22), and the gamma conversion characteristic GM is selected according to the temperature TE (step # 23).

The processing operation of the gamma correction unit 26 based on the selected gamma conversion characteristic GM and other various processing operations are performed, whereby the copy operation is executed (step # 24).

In the above-described embodiment, the case where the correction of the change in chromaticity due to the temperature rise is mainly performed only for red has been described. However, in the color image, the flesh color is the most noticeable and human vision is sensitive. This is because it is enough to correct the red color, which has the greatest effect on the color reproducibility of the skin color. However, depending on the temperature characteristics of the color image sensor 14 and the interference film filter 17, the masking coefficient M for colors other than red or cyan is used.
C or the gamma conversion characteristic GM may be made variable.

In the above embodiment, the temperature sensor 1
The temperature of the color image sensor 14 and the interference film filter 17 was detected by means of 8 for color correction, but the temperature sensor 18 was omitted, and an amount related to the irradiation amount from the exposure lamp 12, for example, exposure within a fixed time. Depending on the total irradiation time or the total number of irradiations of the lamp 12 and the number of scannings by the scanner 15 within a certain time, the masking coefficient M
Color correction may be performed by selecting C or the gamma conversion characteristic GM. This is because these quantities are roughly proportional to the temperature TE of the color image sensor 14 or the interference film filter 17. In addition, these amounts are C
It can be detected by the PU 201.

In the above-described embodiment, the configurations of the signal processing unit 20 and the copying machine 1, the processing contents or the order of the flowcharts, etc. can be variously changed other than those described above. The present invention can be applied to various image reading apparatuses used in addition to the copying machine.

[0048]

According to the present invention, the chromaticity deviation due to the temperature change mainly due to the irradiation of the light source is corrected to maintain a good image quality, for example, when a large number of originals are continuously read. be able to.

[Brief description of drawings]

FIG. 1 is a sectional front view showing a schematic configuration of a copying machine having an image reader unit according to the present invention.

FIG. 2 is a block diagram showing a configuration of a signal processing unit according to the present invention.

FIG. 3 is a diagram showing a relationship between temperature and a masking coefficient.

FIG. 4 is a flowchart showing color correction processing by masking processing during copying.

FIG. 5 is a diagram showing a relationship between temperature and gamma conversion characteristics.

FIG. 6 is a diagram showing respective gamma conversion characteristics for cyan.

FIG. 7 is a flowchart showing color correction processing by gamma correction during copying.

FIG. 8 is a diagram showing a state of sensitivity change in a red region due to a temperature rise of the interference film filter.

[Explanation of symbols]

 IR image reader unit (image reading device) 14 color image sensor (image sensor) 18 temperature sensor (irradiation related amount detecting means) 201 CPU (irradiation related amount detecting means) MC masking coefficient (correction coefficient) GM gamma conversion characteristic (correction coefficient )

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takayoshi Hayashi 2-33 Azuchicho, Chuo-ku, Osaka-shi, Osaka Osaka International Building Minolta Camera Co., Ltd.

Claims (2)

[Claims] 1. An image reading apparatus for reading an image by a color image sensor for processing, comprising an irradiation-related amount detecting means for detecting an amount related to an irradiation amount from a light source for irradiating a document. Every other time, an image reading device is characterized in that a correction coefficient for color correction is selected according to a value of an amount related to an irradiation amount. 2. The irradiation-related amount detecting means is a temperature sensor provided in the vicinity of the image sensor, and selects a correction coefficient for color correction according to the temperature detected by the temperature sensor. The image reading device according to claim 1.