JP2002044442A - Shading correction method and image processor employing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a shading correction method, in which the unevenness of output can be corrected accurately, regardless of the input level to an image input device. SOLUTION: A first correction coefficient for substantially equalizing the output values from all pixel parts is calculated at each specified pixel parts of an image input device; a second correction coefficient corresponding to the input value at each pixel part at the time of image input is calculated by interpolating the first correction coefficient; and the output value from each pixel part of the image input device is then corrected by the second correction coefficient.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shading correction method for correcting output unevenness of a digital image read by an image input device such as a line sensor used in a digital photo printer, and a shading correction process using the method. The present invention relates to an image processing apparatus for performing the processing.

[0002]

2. Description of the Related Art Conventionally, for example, a CCD device (Charge Cou
When processing a digital image photoelectrically read by an image reading device equipped with a solid-state imaging device such as a pled device, uneven output from the light source and uneven output (shading) due to variations in the optical input system are corrected. Various methods are known.

[0003] The occurrence of shading is a serious problem that degrades the quality of an input image.
In the sub-scanning direction of the read image, a one-dimensional band-like unevenness that is easily perceived by human eyes is generated, so that the image quality is significantly deteriorated.

As a method of correcting output unevenness, a transmission image (or reflection image) obtained by irradiating a predetermined amount of light to a filter or film having a uniform light transmission level is generally used. There is a shading correction method in which a CCD is read as a reference image and a correction is made so as to have a constant output level for each read pixel portion. Specifically, a correction coefficient (multiplier) for correcting to a luminance level such as an average value or a maximum value obtained from the output value of each pixel portion so that a constant luminance level is obtained for the entire region of the image.
Is determined in advance for each read pixel unit or for each predetermined small area, and the output value of each pixel unit of the input image is corrected by multiplying the output value by the corresponding correction coefficient.

[0005]

However, CCDs
In an image input device using a solid-state imaging device such as a device,
Generally, the input-output characteristics, that is, the relationship between the input value (the amount of accumulated light) and the output value in the image input device does not show perfect linearity.

FIG. 5 shows a case where light of a constant intensity is incident on a photosensitive surface of a line sensor in which a pixel portion is constituted by a CCD element, and the position of the CCD element constituting each pixel portion (each pixel portion along the main scanning direction). The position of the output value corresponding to () is shown. In the figure, the CCD is obtained by changing the charge accumulation time in the CCD element while light of a constant intensity is incident.
The input value of the element is changed from the reference value to an eight-fold value. It can be seen that the variation state of the output value for each CCD element changes depending on the input value of the CCD element.

FIG. 6 is a diagram showing a case where a correction output value at each pixel portion position, that is, an output value of each pixel portion, is multiplied by a corresponding correction coefficient when a correction process is performed by a conventionally used shading correction method. 6 is a graph showing the calculated values for each accumulation time. In this shading correction method,
A correction coefficient is created at four times the accumulation time, and the correction coefficient is also used for correcting an output value read at another different accumulation time. As shown in the figure, with respect to the correction result of the output value read at the accumulation time four times the reference value, the variation of the corrected output value among the respective pixel portions is eliminated, As for the correction result of the output value read during the accumulation time, it can be seen that the variation in the corrected output value is not sufficiently eliminated.

As described above, the above-described conventional shading correction method has a problem that output unevenness cannot be accurately corrected for image data read with a light amount different from that at the time of obtaining the correction coefficient.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a shading correction method and a shading correction method capable of accurately correcting output unevenness regardless of an input level at the time of image reading. An object of the present invention is to provide an image processing apparatus using a correction method.

[0010]

According to a first aspect of the present invention, there is provided a shading correction method comprising the steps of: outputting, for each predetermined pixel portion of an image input device, output values from all pixel portions for each set input value; By calculating a first correction coefficient to make approximately the same, by interpolation calculation of the first correction coefficient,
Calculating a second correction coefficient corresponding to the input value of each pixel unit at the time of image input; and correcting the output value from each pixel unit at the time of image input by the second correction coefficient. It is characterized by including.

According to the above configuration, the first correction coefficient corresponding to a plurality of set input values is calculated for each predetermined pixel portion of the image input device, and the first correction coefficient is calculated by interpolation. A second correction coefficient corresponding to the input value of the actual input image is calculated. The output value from each pixel unit is corrected by the second correction coefficient.

Thus, even in an image input device in which the pixel portion has a non-linear input-output characteristic, regardless of the input level to each pixel portion at the time of image input, the image output from each pixel portion is Shading correction can be performed with high accuracy.

According to a second aspect of the present invention, there is provided a shading correction method according to the first aspect.
The image input device is characterized in that the pixel portion is a line sensor extending in the main scanning direction.

According to the above arrangement, even when an image input by a scanning method is performed by using a line sensor including a pixel portion having a non-linear input-output characteristic as an image input device, shading of an input image is performed. Correction can be performed effectively.

According to this, in addition to the effect of the first aspect, the shading correction of the output image can be accurately performed regardless of the input level to each pixel portion of the line sensor, and the image quality in the sub-scanning direction is greatly deteriorated. Unevenness can be suppressed.

According to a third aspect of the present invention, there is provided an image processing apparatus including a shading correction unit for performing shading correction of an image by the shading correction method according to the first or second aspect. .

According to the above configuration, even when an image input device including a pixel unit having a non-linear input-output characteristic is used, shading correction of an output image is performed regardless of the input level to the pixel unit. It can be performed with high accuracy.

Thus, in addition to the effects of the first and second aspects, various image processing, exposure processing, and the like can be performed using highly reproducible image data on which shading correction has been performed with high accuracy.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS.

FIG. 3 is a schematic diagram showing the overall configuration of a digital photographic printer including an image processing unit 17 (image processing device) using the shading correction method according to the present embodiment. This digital photographic printer prints an original image on a photosensitive material by printing, developing and drying the photosensitive material based on the image data of the original image.

As shown in FIG. 1, the digital photographic printer captures images in accordance with instructions from a scanner 11 which captures an image of a photographed film or the like and captures it as image data, and a mouse 15 or a keyboard 16 as an instruction input member. The image processing unit 17 that performs various processes on image data, and the monitor 1 that displays various information being processed on a screen
3 and a printer 14 for performing print output based on the processing result.

The scanner 11 irradiates light from the upper surface of the film 100 with a light source 101 and captures the transmitted light from the lower surface of the film 100 with a CCD 102 (image input device), thereby capturing the image of the film 100 as image data. Things.

The printer 14 transports the paper 141 by the transport roller 142, performs a baking process in the exposure unit 143, performs a developing process in the developing unit 144, and performs a drying process in the drying unit 145, and then outputs the photo as an external photograph. To discharge.

The image processing section 17 reads out the main memory 1 for storing image data taken in from the scanner 11 or digital image data taken in from a recording medium such as a flexible disk, and reads out image data stored in the main memory 1. A parameter input unit 12 for displaying parameters on a monitor 13 and setting parameters for correcting the displayed image as needed, an image processing block 2 (shading correcting means) for correcting the image using the parameters, The buffer memory 3a of the buffer block 3 for temporarily storing the image data that has passed through the processing block 2 before outputting it to the printer 14, and the image data stored in the buffer memory 3a are read out and sequentially output to the printer 14, and Buffer the new corrected image data according to And a dedicated CPU (not shown) to the write control to the memory 3a.

The main memory 1 is a memory having a capacity to store the image data (raw data) for a plurality of images.
Image data of 80 frames). With such a large capacity, the above-described image processing and the like can be performed during image capture from the scanner 11.

FIG. 2 is a schematic diagram of the scanner 11 and the image processing unit 17 for explaining how an image is read by the scanner 11 and the read image data is sent to the image processing unit 17. As shown in the figure, a scanner 11 includes a light source 101, a diffuser 111, a film transport device 112 for transporting a film on which an image to be read is captured, and a captured image of the film in a main scanning direction. CCD 102 which is a line sensor along
A slit 113, a zoom lens 114, a stop 115, and a CCD 102 for reading the image are arranged in this order on the optical axis. The CCD 102 is a line sensor in which a CCD element as a pixel unit extends in the main scanning direction.

The CCD 102 has an amplifier 1 for amplifying image data read by the CCD 102.
16 are connected. The image data signal amplified by the amplifier 116 is sent to an image processing block 2, a main memory 1, and a buffer block 3 as appropriate via an A / D (analog / digital) converter 117.

Next, an image reading operation according to the configuration shown in FIG. 2 will be described. The light emitted from the light source 101 is diffused by the diffuser 111, and then enters the light incident surface of the film transported by the film transport device 112. The slit 113 is located on the light emission surface side of the film, and has a slit along the main scanning direction. Thereby, the image photographed on the film is two-dimensionally slit-scanned by the slit 113 extending along the main scanning direction. That is, the photographed image on the film is transferred to the film transport device 112 and the slit 11
3, by the CCD 102 which is a line sensor,
It is read line by line. The configuration for sequentially scanning the film is not limited to this. Moving optical means such as a rotating mirror is provided between the film transport device 112 and the slit 113, and the film transport device 112 is fixed by the movable optical device while the film is fixed. May be changed by changing the area of the light transmitted through the slit 113 incident on the slit 113 to sequentially scan and read the film.

The light from the light source transmitted through the film passes through the slit 113, and then forms an image on the light receiving surface of the CCD 102 by the zoom lens 114 and the stop 115. Then, the image is separated into each color component of RGB by the CCD 102, read photoelectrically, amplified by the amplifier 116, and
After being converted into a digital signal by the converter 117, it is sent to the image processing unit 17.

In the following, image data sent from the CCD 102 as digital signals is processed by the image processing unit 1
The content of the shading correction process (shading correction method) performed in Step 7 will be described.

The shading correction processing in the present embodiment is performed by correcting the image signal value of the image data output from the scanner 11 using a shading correction table created in advance.

FIG. 1A shows, as a first stage of the shading correction processing according to the present embodiment, that the output values from all the pixel portions for each set input value are substantially equal for each predetermined pixel portion of the CCD 102. 9 is a flowchart showing a procedure for calculating a first correction coefficient to be performed and completing a shading correction table.

As shown in the figure, first, in S1, the creation of a correction coefficient is started, and in S2, the accumulation time for capturing a CCD is set. By setting the accumulation time of image capture by the CCD 102 while the intensity of light from the light source 101 is temporally constant, the amount of light incident on the CCD 102, that is, the input value, can be accurately controlled.

In S 3, a filter having a uniform light transmittance is installed in the optical path in the diffuser 111 in order to make the intensity distribution of the light from the light source 101 uniform. At this time, the film of the film transport device 112 is removed from the optical path. The light transmitted through the filter is repeatedly accumulated by the CCD 102 for the accumulation time set in S2.

As a filter having a uniform light transmittance,
For example, a film obtained by photographing a reference plate having a predetermined density, or an ND (Neutral) which has uniform transmittance in visible light in all wavelength ranges and can obtain transmitted light of the same intensity for each color component.
Density) filter or the like can be used.

In S4, a shading correction coefficient is created for each CCD element of the CCD 102. In particular,
The output values from each CCD element accumulated in S3 are transferred to all CCDs.
A first correction coefficient is created for each CCD element so that the elements are substantially equal. For example, a first correction coefficient can be calculated for each CCD element by calculating an average of output values from all CCD elements and dividing the average by an output value from each CCD element. The calculated first correction coefficients are sequentially stored in the main memory 1.

In S5, it is determined whether or not the number of times the CCD 102 has captured the light transmitted through the filter has reached a desired number of times. If not, the procedure of S2 to S4 is repeated. For example, when photometry is performed using eight types of set input values, the storage time in S2 is changed while S2 to S4
Is repeated eight times. In S6, the creation of the correction coefficient ends.

As described above, by executing the steps from S1 to S6, the first correction coefficient for making the output values from all the pixel portions substantially equal to the respective set input values is calculated, and the respective set input values are calculated. Is completed.

In the present embodiment, the first correction coefficient is obtained for each pixel portion. However, the present invention is not limited to this. For example, the first correction coefficient may be obtained for each fixed region composed of a predetermined pixel portion. The required configuration may be adopted.

FIG. 1B is a flowchart for explaining a procedure for performing a correction process on an output value from the CCD 102 as a second stage of the shading correction process according to the present embodiment. The image data read by the CCD 102 and temporarily stored in the main memory 1 is subjected to a correction process for each pixel unit or for each fixed region including a predetermined pixel unit using the shading correction table.

First, as shown in S7, when the correction process is started, an image photographed on a film is read by the CCD 102 of the scanner 11 (S8). Then
In S9, interpolation calculation of a correction coefficient corresponding to the input level (input value) at the time of image input in S8 is performed.

In the interpolation calculation, first, of the first correction coefficients respectively corresponding to the plurality of setting input values stored at the time of creating the shading correction table, two large and small setting values closest to the input value to the pixel of interest are set. The first correction coefficient corresponding to the input value is read from the main memory 1. By performing interpolation calculation using these two types of first correction coefficients, it is possible to calculate a second correction coefficient corresponding to the input value of each pixel unit. The input value to the pixel unit of interest is
Based on the data accumulated in step 3, the output value of the pixel unit of interest may be back calculated.

The input value of the pixel of interest to be actually subjected to the shading correction processing is Ai, and the set input value in which the first correction coefficient is stored in the shading correction table is A
, A2,..., The first correction coefficient corresponding to
1, B2,..., The input value Ai (A1 <A
i <A2), the second correction coefficient Ci is Ci =
(B2-B1) (Ai-A1) / (A2-A1) + B1
It can be calculated by linear interpolation represented by

For example, in the shading correction table, as a set input value, the accumulation time is set to 1 time, 2 times as large as the reference value.
It is assumed that the first correction coefficient is written for each pixel portion in the case of double, quadruple, and eight times. Then, it is assumed that the input value of the pixel of interest to be actually subjected to the shading correction processing corresponds to the value when the accumulation time is six times the reference value. In this case, the second correction coefficient Cp used for the shading correction processing for a certain pixel unit p is the first correction value for the pixel unit p corresponding to the case where the accumulation time is four times and eight times the reference value as the set input value. Correction coefficients B3 and B
4 and Cp = (B3 + B4) / 2.

In S10, the second correction coefficient is used to calculate
Output value correction processing from each pixel unit is performed. That is,
A correction output value is calculated by multiplying the output value from each pixel unit by the corresponding second correction coefficient, and the shading correction processing is completed.

FIG. 4B is a graph showing a variation in the correction output value after performing the shading correction processing in the present embodiment. In the figure, the horizontal (x)
The axis indicates the pixel unit position, and the vertical (y) axis indicates the corrected output value, that is, the value obtained by multiplying the output value of each pixel unit by the corresponding second correction coefficient. The standard deviation was 1.116265.

On the other hand, FIG. 4A shows a conventional shading correction process, that is, an input image read at a storage time six times the reference value by a shading correction coefficient obtained at a storage time four times the reference value. 9 is a graph showing a result of performing a shading correction process. In FIG. 14A, the standard deviation of the corrected output value was 2.131285.

As is clear from the comparison between the standard deviations of FIGS. 4A and 4B and the standard deviation of the two, it is understood that the shading correction according to the present embodiment can perform more accurate shading correction. . That is, CCD
Irrespective of the input level at the time of image reading by 102, output unevenness can be accurately corrected.

In this embodiment, the interpolation calculation is performed by linear interpolation. However, the present invention is not limited to this, and another interpolation calculation generally used may be used.

In this embodiment, the shading correction table is created in advance.
The shading correction table may be configured to be appropriately created as needed. Further, in order to obtain a reference image at the time of creating the shading correction table, a reflecting member or the like that reflects a certain amount of light may be used instead of a transmissive film or the like.

[0051]

According to the first aspect of the present invention, there is provided a shading correction method.
As described above, for each predetermined pixel portion of the image input device,
Calculating a first correction coefficient for making the output values from all the pixel portions substantially equal to each set input value, and performing an interpolation calculation of the first correction coefficient to obtain an input value of each of the pixel portions at the time of image input. Calculating a corresponding second correction coefficient;
Correcting the output value from each of the pixel units at the time of image input using the second correction coefficient.

Therefore, the first correction coefficient corresponding to a plurality of set input values is calculated for each predetermined pixel portion of the image input device, and the first correction coefficient is calculated by interpolation of the first correction coefficient.
A second correction coefficient corresponding to the input value of the actual input image is calculated. The output value from each pixel unit is corrected by the second correction coefficient.

Thus, even in an image input device in which the pixel portion has a non-linear input-output characteristic, regardless of the input level to each pixel portion at the time of image input, the image output from each pixel portion is There is an effect that shading correction can be performed with high accuracy.

According to a second aspect of the invention, as described above, in the configuration of the first aspect, the image input device is a line sensor having a pixel portion extending in the main scanning direction.

Therefore, the shading correction of the input image can be effectively performed even when the image input by the scanning method is performed by using the line sensor including the pixel unit having the non-linear input-output characteristics as the image input device. Can be performed.

Thus, in addition to the effect of the first aspect, the shading correction of the output image can be accurately performed regardless of the input level to each pixel unit of the line sensor, and the image quality in the sub-scanning direction is greatly deteriorated. This has the effect of suppressing the occurrence of unevenness.

According to a third aspect of the present invention, as described above, the image processing apparatus is provided with the shading correction means for performing the shading correction of the image by the shading correction method according to the first or second aspect.

Therefore, even when an image input device including a pixel unit having nonlinear input-output characteristics is used, shading correction of an output image can be accurately performed regardless of the input level to the pixel unit. Can be.

Thus, in addition to the effects of the first and second aspects, various image processing, exposure processing, and the like can be performed using highly reproducible image data that has been subjected to accurate shading correction. Play.

[Brief description of the drawings]

FIG. 1A is a flowchart showing a procedure for creating a shading correction coefficient for each exposure amount and completing a shading correction table as a first stage of the shading correction process according to the present embodiment. (B)
9 is a flowchart illustrating a procedure for performing a correction process on an output value from a CCD as a second stage of the shading correction process according to the present embodiment.

FIG. 2 is a schematic diagram of a scanner and an image processing unit according to the embodiment.

FIG. 3 is a schematic diagram illustrating an overall configuration of a photographic processing apparatus including an image processing unit that performs shading correction processing according to the present embodiment.

FIG. 4A is a graph showing a result of performing an input image correction process using a conventional shading correction process. (B) is a graph showing a result of performing an input image correction process using the shading correction process according to the present embodiment.

FIG. 5 is a graph showing how an output value state of an image input device corresponding to each pixel portion position changes according to an input level at the time of reading.

FIG. 6 is a graph showing a correction output value at each pixel portion position for each input level when image processing is performed by a conventionally used shading correction method.

[Explanation of symbols]

 2 Image processing block (shading correction means) 17 Image processing unit (image processing device) 102 CCD (image input device)

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Keiji Sakai 579-1 Umehara Umehara, Wakayama-shi, Wakayama Noritsu Koki Co., Ltd. F-term (reference) 5B047 AA05 AB04 BA01 BB02 BC05 BC07 BC11 DA04 5C077 LL04 MM03 MM27 MP08 PP06 PP46 PQ08 PQ12 PQ20 PQ23 RR19 TT09

Claims (3)

[Claims] A step of calculating, for each predetermined pixel unit of the image input device, a first correction coefficient for making output values from all pixel units substantially equal to each set input value; Calculating the second correction coefficient according to the input value of each pixel unit at the time of image input by interpolation calculation, and calculating the output value from each pixel unit at the time of image input by the second correction coefficient. Correcting the shading. 2. The shading correction method according to claim 1, wherein the image input device is a line sensor whose pixel section extends in the main scanning direction. 3. An image processing apparatus comprising a shading correction unit for performing shading correction of an image by the shading correction method according to claim 1.