JP2003101884A - Shading correcting device and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten processing time of shading correction. SOLUTION: The shading correction is performed for luminance data equivalent to parts 11 at both ends of an object image for one frame and the shading correction is not performed for the luminance data equivalent to a center part 12. Since influence of shading due to an aberration of an image pickup lens appears on the periphery of the object image, shading is inconspicuous even when the shading correction is not performed for the center part. Since the shading correction is performed for the luminance data of a part of the object image, the processing time is shortened.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an apparatus and method for shading correction of a video signal.

[0002]

BACKGROUND OF THE INVENTION Due to the characteristics of a solid-state electronic image pickup device, the lens aberration of an image pickup lens, and the like, density unevenness (shading) may occur in an image obtained by image pickup. Shading correction is performed by multiplying the video signal output from the solid-state electronic image sensor by a shading correction coefficient.

However, the shading correction requires a relatively long processing time.

[0004]

DISCLOSURE OF THE INVENTION An object of the present invention is to end shading correction in a relatively short time.

The shading correction apparatus according to the present invention is a video signal input means for inputting a video signal representing an image for one frame, and a part of the image for one frame among the video signals input from the video signal input means. Shading correction means for shading-correcting a video signal representing the image of 1 is included.

The present invention also provides a method suitable for the above shading correction apparatus. That is, this method
A video signal representing an image of one frame is input, and a video signal representing a part of the image of the one frame of the input video signal is subjected to shading correction.

According to the present invention, a video signal representing an image for one frame (including an analog video signal and digital image data) is input, and a video signal representing a part of the image for one frame is subjected to shading correction. It Since the shading correction is not performed on all the video signals representing the image for one frame, but the shading correction is performed on the video signal representing a part of the image for one frame, the processing time can be shortened.

The shading correction means is, for example, for shading correction of a video signal representing a part of the image except the central portion of the image for one frame.

The aberration of the image pickup lens is larger in the peripheral portion than in the center. Therefore, the shading caused by the aberration of the imaging lens is larger in the peripheral portion than in the central portion of the image. Since the shading correction is performed on the video signal representing a part of the image excluding the central portion of the image, it is possible to obtain an image from which shading has been removed while shortening the time required for shading correction.

The shading correction means may perform shading correction on a video signal representing an image in a range separated by a predetermined distance or more from the center or center line of the image for one frame. The range outside the range of a circle or rectangle having the same center as the center of the image is the shading correction range.

When the video signal input from the video input means is digital image data, a storage means for storing the digital image data after shading correction of the digital image data input to the video signal input means is further provided. In this case, the shading correction means replaces the digital image data representing the partial image of the digital image data input from the video signal input means with the digital image data stored in the storage means and outputs the digital image data. It will be a thing.

Since the digital image data after the shading correction is stored and the image data after the shading correction is replaced and output, the shading correction is required as compared with the case where the shading correction calculation is performed on the input digital image data each time. You can save time.

A solid-state electronic image pickup device for outputting a video signal representing the image of one frame, an image pickup lens for forming a subject image on a light-receiving surface of the solid-state electronic image pickup device, and a combination of the solid-state electronic image pickup device and the image pickup lens. It may further be provided with a detection means for detecting. In this case, the storage means may store a plurality of digital image data after the shading correction corresponding to the combination of the solid-state electronic image pickup device and the image pickup lens. The shading correction means replaces the digital image data representing the partial image of the digital image data stored in the storage means with digital image data corresponding to the combination detected by the detection means. Will be output.

Image data after shading correction corresponding to the combination of the solid-state electronic image pickup device and the image pickup lens can be output.

The shading correction means has a primary differential coefficient of 0 at the boundary between the shading correction range corrected by the shading correction means and the range excluding the shading correction range in the image for one frame.
It is preferable to perform shading correction based on a correction curve that When the shading correction is performed, the boundary between the shading correction range and the range excluding the shading correction range is smoothly switched without a feeling of strangeness.

The shading correction means uses a shading correction curve obtained by using a shading correction curve that gives the same shading correction value for the video signals representing the pixels in the same column or the same row to different values for each row or column. It is preferable to make adjustment using adjustment data having

If adjustment is not performed using different adjustment data for each row or column, a line may appear in the horizontal or vertical direction of the image after shading correction due to the level change in the same row or column. Since adjustment is performed using different adjustment data for each row or column, it is possible to prevent lines from occurring in the image after shading correction.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of the present invention and is a block diagram showing a part of the electrical construction of a digital still camera.

The digital still camera has a function of correcting shading caused by the aberration of the image pickup lens 1, the characteristics of the CCD 2, and the like. For this,
The digital still camera includes a corrected luminance data storage circuit 7. The corrected brightness data storage circuit 7 stores the brightness data that is shading-corrected for each coordinate of the input data in correspondence with the input brightness data. Assuming that the level of the input brightness data is 0 to 255, 256 kinds of brightness data after shading correction are stored in the corrected brightness data storage circuit 7 for each coordinate corresponding to the combination of the imaging lens 1 and the CCD 2. It will be.

By the image pickup lens 1, the subject image is CCD
An image is formed on the light receiving surface of 2. CCD2 is RGB on the light receiving surface
Color filters are formed, and RGB video signals representing one frame of the subject image are output. RGB
The video signal is converted into RGB digital image data in the analog / digital conversion circuit 3 and input to the gamma correction circuit 4. The gamma-corrected RGB digital image data is input to the Y / C processing circuit 5, and luminance data Y and color difference data C (RY and BY) are generated.

The generated brightness data is input to the switching circuit 6, the corrected brightness data storage circuit 7 and the CPU 8.
The shading corrected luminance data output from the corrected luminance data storage circuit 7 is also input to the switching circuit 6. The switching circuit 6 is provided with a switching control signal from the CPU 8, and based on this switching control signal, the Y / C processing circuit 5
Either the brightness data output from or the brightness data output from the corrected brightness data storage circuit 7 is selected and output.

In this embodiment, the shading correction is not performed for all the luminance data for one frame, but the shading correction is performed for the luminance data corresponding to a partial range of one frame, and the shading correction is performed for the other range. Shading correction is not performed on the corresponding luminance data. Therefore, when the brightness data corresponding to the shading correction range is input to the CPU 8, the switching circuit 6 is switch-controlled so that the brightness data output from the corrected brightness data storage circuit 7 is selected. Luminance data corresponding to a range other than the shading correction range is stored in the CPU.
8 is input, the switching circuit 6 is switched and controlled so that the luminance data output from the Y / C processing circuit 5 is selected.

A range of shading correction and a range of non-shading correction of an image for one frame are determined according to the combination of the imaging lens 1 and the CCD 2. For the shading correction range, the brightness data obtained by imaging is replaced with the shading-corrected brightness data stored in advance for each coordinate. Since the shading correction is not performed on all the brightness data of the image for one frame, but the shading correction is performed on the brightness data of a part of the image, the processing time can be shortened. Further, since the brightness data obtained by the image pickup is replaced with the brightness data which has been stored in advance for each coordinate and has been subjected to the shading correction, the processing time can be further shortened as compared with the case where the shading correction calculation is performed each time. The shading correction will be described in more detail later.

The luminance data output from the switching circuit 6 and Y
The color difference data C output from the / C processing circuit 5 is compressed by a compression circuit (not shown) and recorded on a memory card (not shown) or the like.

In the above-described embodiment, the shading correction is performed on the luminance data, but the shading correction may be similarly performed on the color difference data.

FIG. 2A shows (a frame of) one subject image obtained by imaging. (B) is a graph showing a correction coefficient used in a conversion formula for obtaining the shading-corrected luminance data, and (C) is a luminance data level before shading correction for one line and luminance data after shading correction. -It is a graph which shows a level.

The number of pixels in the horizontal direction of one frame of the subject image is H,
The origin 0 of the X coordinate (horizontal direction) is the center of the subject image in the horizontal direction. In absolute value in the horizontal direction | H
/ 4 | or more | H / 2 | or less range (hatched)
11 is the range in which shading correction is performed as described above, and range 12 that is 0 or less and less than | H / 4 | is the range in which shading correction is not performed. Horizontally | H / 4
| Is the boundary between the range where shading correction is performed and the range where shading correction is not performed. That is, both ends in the horizontal direction are the range 11 in which the shading correction is performed, and the center part is the range 12 in which the shading correction is not performed.

The aberration of the image pickup lens 1 largely occurs in the peripheral portion of the image pickup lens 1. Therefore, larger shading occurs in the peripheral portion than in the central portion of the subject image. Since both ends of the subject image are shading-corrected, shading correction can be efficiently performed. It goes without saying that shading correction may be performed not only on both ends in the horizontal direction but also on image parts at both ends in the vertical direction (both ends in the vertical direction).

Shading correction is performed according to conversion formula 1.

Yout = [1 + a * {(| X | -H / 4) / (H / 4)} ² ] * Yin + r ... Conversion Formula 1 Here, Yout is the luminance data after shading correction (described above). With a level from 0 to 255), a
Is a predetermined coefficient, X is the position of the X coordinate of the pixel corresponding to the brightness data to be shading corrected, and Yin is Y / C
Luminance data (having levels from 0 to 255 as described above) generated by the generation circuit 5, r is -0.5 to +0.5
Is a random number.

[1 + a × {(| X | −H /
4) / (H / 4)} ² ] is the correction coefficient shown in (B) above. This correction coefficient has a primary differential coefficient of 0 at the boundary of | X | = H / 4. Therefore, the brightness data without shading correction is continuously and smoothly connected to the brightness data with shading correction. When a subject image is displayed by using the shading-corrected luminance data, it is possible to prevent a sense of discomfort from occurring at the boundary.

In the conversion formula 1, a random number r is added to the input brightness data Yin. Therefore, the brightness level after shading correction changes even for pixels in the same column. When the pixels in the same column are aligned and the brightness level changes, it may appear as if a line is drawn in that column, but since the random number r is added, the pixels in the same column are aligned and the brightness level is changed. Can be prevented from changing.

By performing the shading correction on the brightness data using the conversion formula 1, the brightness levels at both ends of the subject image in the horizontal direction are improved as shown in (C). Moreover, as described above, in the image after shading correction, the boundary between the shading corrected range and the non-shading corrected range becomes inconspicuous.

In the above embodiment, the conversion formula 1 may be used for n consecutive X coordinates. The amount of data stored in the corrected luminance data storage circuit 7 becomes 1 / n.

Further, in the above-described embodiment, the shading correction is performed at both ends of the subject image in the horizontal direction, but as shown by the broken line circle 13 in FIG.
The outside of is the range for shading correction, and the broken circle 13
The inside may be set as a range in which shading correction is not performed.
In this case, the following conversion formula 2 will be used instead of the conversion formula 1 described above.

Yout = [1 + a × {(| R | −D / 4) / (D / 4)} ² ] × Yin + r ... Conversion Formula 2 In conversion formula 2, R is the same center as the center of the subject image. The radius of the circle indicated by the broken line, and D is the length of the diagonal line of the subject image.

FIG. 3 shows another embodiment, and is a block diagram showing a part of the electrical construction of the digital still camera. In this figure, the same parts as those shown in FIG.

The digital still camera shown in FIG. 3 is provided with a corrected luminance data storage circuit 7 for storing the corrected luminance data corresponding to the image pickup lens 1 and the CCD 2, but the corrected luminance data storage circuit 7 shown in FIG. The brightness data storage circuit 23 has not only corrected brightness data corresponding to the combination of the imaging lens 1 and the CCD provided in the digital still camera, but also various types corresponding to various combinations of the imaging lens and the CCD. The corrected luminance data, or the calculation formula and the coefficient for generating the corrected luminance data are stored.

The digital still camera includes a detection circuit 21 for detecting the type of the imaging lens 1 and a detection circuit 22 for detecting the type of the CCD 2. A signal indicating each detection result is input to the CPU 24. A selection signal is given from the CPU 24 to the corrected luminance data storage circuit 23,
The corrected luminance data corresponding to the imaging lens 1 and the CCD 2 specified by the input detection signal is read from the corrected luminance data storage circuit 23. When the calculation formula and the coefficient corresponding to the combination of the photographing lens and the CCD are stored, the corrected luminance data is generated by the calculation formula according to the detection result. The luminance data output from the Y / C processing circuit 5 and the luminance data output from the corrected luminance data storage circuit 23 are switched according to the shading correction range and output from the switching circuit 6 in the above-described embodiment. Is the same as.

FIG. 4 is a flow chart showing a processing procedure for storing the corrected luminance data in the corrected luminance data storage circuit 23.

A reference subject having a substantially constant brightness such as a white diffuser is prepared, and the reference subject is photographed by using an image pickup lens so that an image of the reference subject is formed on the light receiving surface of the CCD (step 31). .

The brightness represented by the brightness data obtained since the reference subject was photographed should be substantially constant. If the brightness data is reduced, it is considered to be caused by shading. In consideration of the decrease, the coefficient a is determined so that the brightness data is allowed to be almost constant, and the correction is performed according to the conversion formula 1. Luminance data is generated (step 32).

The generated luminance data is stored in the corrected luminance data storage circuit 23 corresponding to the type of the image pickup lens and the type of CCD used (step 33).

The combination of the image pickup lens and the CCD is changed, and the above-mentioned steps 31 to 33 are repeated.

In this way, the corrected luminance data corresponding to many combinations of the image pickup lens and the CCD are stored in the corrected luminance data storage circuit 23, so that the digital still camera is provided. The corrected luminance data corresponding to the combination of the image pickup lens 1 and the CCD 2 can be selected.

FIG. 5 is a flow chart showing the procedure of shading correction.

As described above, the detection circuits 21 and 22 detect the combination of the image pickup lens 1 and the CCD 2 provided in the digital still camera (step 41).

Corrected luminance data corresponding to the detected combination of the imaging lens 1 and the CCD 2 is selected from the corrected luminance data stored in the corrected luminance data storage circuit 23 (step 23).

The switching circuit 6 is switched and controlled so that the selected corrected luminance data is replaced with the luminance data corresponding to the shading correction range (step 43).

Even if the image pickup lens 1 and the like can be replaced, shading correction can be performed using the corrected luminance data corresponding to the replaced image pickup lens 1.

It goes without saying that not only is it possible to select the corrected luminance data having a level corresponding to the combination of the image pickup lens and the CCD, but the shading correction range may be changed according to the combination. Absent. The range of shading correction can be changed by changing the denominator of H / 4 or D / 4 in the above conversion formula 1 or conversion formula 2.

FIG. 6 shows still another embodiment,
It is a block diagram which shows a part of electric constitution of a digital still camera. In this figure, the same parts as those shown in FIG.

In the above-described embodiment, the shading correction is performed on the luminance data, but the one shown in FIG. 6 is the shading correction performed on each of the RGB digital image data.

The corrected image data stores the corrected image data for each of RGB.

The RGB digital image data output from the analog / digital conversion circuit 3 is input to the switching circuit 51 and the corrected image data storage circuit 52. When the RGB digital image data corresponding to the correction range is input to the corrected image data storage circuit 52, the corrected RGB digital image data stored in the corrected image data storage circuit 52 is output from the switching circuit 51. The switching circuit 51 is controlled by the CPU 53.

Thus, not only the luminance data but also the RGB
Shading correction may be performed on color image data such as image data.

[Brief description of drawings]

FIG. 1 is a block diagram showing a part of an electrical configuration of a digital still camera.

FIG. 2A is a subject image obtained by imaging,
(B) is a graph showing a correction coefficient, and (C) is a graph showing a luminance data level before correction and a luminance data level after correction.

FIG. 3 is a block diagram showing an electrical configuration of a digital still camera.

FIG. 4 is a flowchart showing a corrected luminance data storage processing procedure.

FIG. 5 is a flowchart showing a shading correction processing procedure.

FIG. 6 is a block diagram showing an electrical configuration of a digital still camera.

[Explanation of symbols]

1 Imaging lens 2 CCD 6 switching circuit 7,23,52 Corrected luminance data storage circuit 8,24,53 CPU 11 Correction range 21, 22 detection circuit

Continued front page    F term (reference) 5B047 AB04 BA03 BB04 BC05 DA04                       DB01                 5C021 PA02 PA17 PA92 XA03 XA67                       YC00                 5C024 AX01 BX01 CX35 GY01                 5C077 LL18 MM03 MP08 PP06 PP32                       PP58 SS03 TT09

Claims (8)

[Claims] 1. A video signal inputting means for inputting a video signal representing an image for one frame, and a video signal representing a part of the image for one frame among the video signals input from the video signal inputting means. A shading correction device having a shading correction means for performing shading correction. 2. The shading correction device according to claim 1, wherein the shading correction means performs shading correction on a video signal representing a part of the image except the central portion of the image for one frame. 3. The shading correction means is for shading correction of a video signal representing an image in a range separated by a predetermined distance or more from the center or center line of the image for one frame. Shading correction device. 4. A video signal input from the video input means is digital image data, and a storage means for storing the digital image data after shading correction of the digital image data input to the video signal input means is further provided. The shading correction means replaces the digital image data representing the partial image of the digital image data input from the video signal input means with the digital image data stored in the storage means and outputs the digital image data. The shading correction device according to claim 1. 5. A solid-state electronic image pickup device for outputting a video signal representing the image of one frame, an image pickup lens for forming a subject image on a light receiving surface of the solid-state electronic image pickup device, the solid-state electronic image pickup device and the image pickup lens. Further comprising detection means for detecting the combination of the above, and the storage means stores a plurality of digital image data after the shading correction corresponding to the combination of the solid-state electronic image pickup device and the image pickup lens. The shading correction means replaces the digital image data representing the partial image of the digital image data stored in the storage means with digital image data corresponding to the combination detected by the detection means, and outputs the digital image data. The shading correction apparatus according to claim 4, which is configured to: 6. The correction in which the first-order differential coefficient is 0 at the boundary between the shading correction range corrected by the shading correction unit and the range excluding the shading correction range in the image for one frame by the shading correction unit. The shading correction apparatus according to claim 1, wherein shading correction is performed based on a curve. 7. A shading correction video signal obtained by the shading correction means using a shading correction curve that gives the same shading correction value for video signals representing pixels in the same column or in the same row, for each row or column. The shading correction apparatus according to claim 1, wherein adjustment is performed using adjustment data having different values. 8. A video signal representing an image for one frame is input,
A shading correction method for shading-correcting a video signal representing a part of the image of one frame among the input video signals.