JP4500146B2 - Image correction apparatus and image correction method - Google Patents

Description

  The present invention relates to correction processing for defective pixels in an image photographed by a digital camera or the like.

  FIG. 3 is a diagram showing a configuration of a conventional digital camera. As shown in FIG. 3, the digital camera includes an image sensor 101, a CDS unit 102, an AGC unit 103, an AD conversion unit 104, a scratch correction processing unit 105, a video signal processing unit 107, and each of these processes. And a microcomputer 108 for controlling the unit.

  The signal photoelectrically converted by the image sensor 101 is input to the video signal processing unit 107 via the CDS unit 102, the AGC unit 103, the AD conversion unit 104, and the defect correction processing unit 105. The color filter array of the image sensor 101 is the primary color Bayer array shown in FIGS. 4 (a) to 4 (c).

  Here, the operation of the scratch correction processing unit 105 provided in the digital camera will be described with reference to FIGS. The defect correction processing unit 105 determines whether or not correction processing is necessary for all the pixels of the output signal, and performs correction processing as necessary. The necessity of the correction process is determined based on the difference between the value of the pixel to be corrected and the value calculated from the surrounding pixels. That is, as shown in FIGS. 4A to 4C, it is determined whether or not correction is necessary for the correction target pixel 200 using the calculated values calculated from the values of the eight neighboring pixels 202. To do. 4A shows an example in which the correction target pixel is an R signal, FIG. 4B shows an example in which the correction target pixel is a G signal, and FIG. 4C shows an example in which the correction target pixel is a B signal. .

  FIG. 5A is a diagram illustrating a state of signals in the target pixel 200 and the peripheral pixels 202. When the difference between the correction target pixel 200 and the calculated value calculated from the surrounding pixels 202 is larger than the correction determination threshold, the value of the correction target pixel is replaced with the calculated value. As the calculated value, for example, the maximum value, minimum value, average value, or weighted average value of the surrounding eight pixels can be used.

  FIG. 6 is a flowchart showing a defect correction process in a conventional digital camera. As a flow of defect correction processing, first, a correction determination threshold value is read (S201), and then correction data for performing correction processing based on the correction determination threshold value for all pixels is calculated (S202).

  By the way, in a digital camera using an image sensor, in order to obtain a highly sensitive signal, the exposure time may be lengthened or the gain of the AGC unit may be increased. If the exposure time or the gain of the AGC portion is different from the normal exposure state, the scratch correction performance is not sufficiently satisfied for the following reason, and scratches on the screen become conspicuous.

  That is, if the exposure time is lengthened or the gain of the AGC unit is increased, the amount of accumulated charge increases, and the output level approaches the upper limit value (for example, 255LSB) that the pixel can take. As a result, as shown in FIG. 5B, even when the pixel to be corrected has a scratch, the difference from the values of the surrounding pixels decreases, and if the difference falls below the correction determination threshold, the scratch correction processing is not performed. Pixel defects will remain on the screen. On the other hand, if the correction determination threshold is set small, unnecessary correction is performed and the image quality deteriorates.

In order to solve this problem, Patent Document 1 or Patent Document 2 discloses a method of providing an appropriate correction determination threshold value for each exposure time or for each gain of the AGC unit. FIG. 7 is a diagram illustrating an example in which the correction determination threshold is changed for each exposure time. When the exposure time is 1T, the correction determination threshold is set to 100 LSB, and correction processing is performed when the difference between the values calculated by the target pixel and the surrounding pixels is larger than 100 LSB. When the exposure time is 2T, the correction determination threshold is 50LSB, and when the exposure time is 4T, the correction determination threshold is 25LSB. Whether or not correction is necessary is determined in consideration of a decrease in the difference from the surrounding pixels accompanying the increase. As described above, the correction determination threshold value for the defect correction processing is provided for each of the normal exposure and the long-time exposure so that appropriate correction can be performed according to the exposure time.
JP 2003-333435 A JP 2001-128068 A

  However, in the conventional defect correction processing method described above, it is necessary to provide a correction determination threshold finely for each exposure time or for each gain of the AGC unit in order to obtain a high-quality signal. Therefore, there is a problem in that the storage capacity for storing these values is increased and the adjustment work for determining the correction determination threshold is complicated.

  In view of the above background, the present invention provides an image correction apparatus that can reduce the storage capacity, avoid complicated adjustment work, and perform appropriate correction regardless of the AGC gain setting, exposure time, and the like. Objective.

  An image correction apparatus according to the present invention includes a correction processing unit that performs image correction processing by correcting pixels detected using a correction determination threshold, and a defect that detects a defective pixel of an image corrected by the correction processing unit. Pixel detection means, and determination means for determining whether or not the total number of defective pixels detected by the defective pixel detection means exceeds a preset reference value, the total number of defective pixels being the reference value The correction processing unit changes the correction determination threshold value and corrects the image in response to the determination by the determination unit that the value exceeds.

  With this configuration, it is determined whether or not the number of defective pixels in the image corrected by the correction processing unit exceeds the reference value, and if it exceeds the reference value, correction is performed again, so that the defect in the corrected image Correction is performed until the number of pixels becomes less than the reference value. Thus, appropriate correction can be performed regardless of the exposure amount, the gain of the AGC unit, and the like.

  In the image correction apparatus, the correction processing unit may calculate the value of the pixel to be corrected as the calculated value when a difference between the value of the pixel to be corrected and a calculated value calculated from surrounding pixels is larger than the correction determination threshold. May be replaced.

  With this configuration, appropriate correction can be performed based on the values of the surrounding pixels.

  In the image correction apparatus, the correction processing unit may obtain an average value of the peripheral pixels as the calculated value.

  With this configuration, the correction value of the pixel can be appropriately determined using the continuity of the image.

  In the image correction apparatus, the defective pixel detection unit may detect the pixel to be inspected when a difference between a value of the pixel to be inspected and a calculated value calculated from surrounding pixels exceeds a preset defective pixel determination threshold value. You may detect as a defective pixel.

  With this configuration, it is possible to detect a pixel having a greatly different value from the calculated value calculated from the surrounding pixels as a defective pixel.

  The digital camera of the present invention has a configuration including the above-described image correction apparatus.

  With this configuration, appropriate correction can be performed on an image captured by a digital camera regardless of the exposure amount, the gain of the AGC unit, or the like.

  The mobile phone of the present invention has a configuration including the above-described image correction device.

  With this configuration, appropriate correction can be performed on an image input to the mobile phone regardless of the exposure amount, the gain of the AGC unit, or the like. For inputting an image to the mobile phone, the image may be taken by a camera included in the mobile phone, or image data may be received from another mobile phone or other communication terminal.

  An image correction method according to the present invention includes a correction processing step for correcting an image by correcting a pixel detected using a correction determination threshold, and a defective pixel for detecting a defective pixel of the image corrected in the correction processing step. A detection step and a determination step of determining whether or not the total number of defective pixels detected in the defective pixel detection step exceeds a preset reference value, and the total number of defective pixels exceeds the reference value In accordance with the determination in the determination step, the correction processing threshold is changed and the correction processing step is performed again.

  With this configuration, it is determined whether or not the number of defective pixels in the image corrected in the correction processing step exceeds the reference value, and if it exceeds the reference value, correction is performed again, so that the defective pixel in the corrected image The correction is performed until the number of is less than the reference value. Thus, appropriate correction can be performed regardless of the exposure amount, the gain of the AGC unit, and the like. Various configurations of the image correction apparatus of the present invention can be applied to the image correction method of the present invention.

  According to the present invention, it is determined whether or not the number of defective pixels in the image corrected by the correction processing means exceeds a reference value, and correction is performed until the number of defective pixels in the corrected image is less than the reference value. Therefore, it is possible to perform an appropriate correction regardless of the exposure amount, the gain of the AGC unit, and the like.

  Hereinafter, a digital camera provided with an image correction apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows the configuration of a digital camera according to an embodiment of the present invention. As shown in FIG. 1, the digital camera according to the embodiment includes an image sensor 101, a CDS unit 102, an AGC unit 103, an AD conversion unit 104, a flaw correction processing unit 105, a flaw detection unit 106, and an image. A signal processing unit 107 and a microcomputer 108 for controlling each of these processing units are provided. The configuration other than the scratch detection unit 106 has the same function as the digital camera described with reference to FIG.

  The scratch detection unit 106 has a function of detecting defective pixels (scratches) in an image using a preset defective pixel determination threshold. Specifically, when the difference between the pixel to be inspected and the calculated value calculated from the surrounding pixels exceeds the defective pixel determination threshold, the pixel to be inspected is detected as a defective pixel. The flaw detection unit 106 performs this flaw detection processing on all pixels of the image.

  FIG. 2 is a flowchart illustrating a flaw correction process of the digital camera according to the embodiment. As a flow of defect correction processing, a defective pixel determination threshold value, a defective pixel total number reference value, an initial value of a correction determination threshold value, and a lower limit value of a correction determination threshold value are read in advance (S101).

  Next, the scratch correction processing unit 105 of the digital camera performs correction processing (S102) on the captured image. After executing the correction process (S102), the scratch detection unit 106 of the digital camera executes defective pixel detection (S103) for detecting defective pixels in the corrected image.

  Subsequently, the microcomputer 108 determines whether or not the total number of defective pixels detected in the defective pixel detection step exceeds the defective pixel total reference value. When the total number of defective pixels exceeds the defective pixel total number reference value (yes in S104), the process proceeds to the correction determination threshold determination (S105), and when the total number of defective pixels does not exceed the defective pixel total number reference value ( No in S104) and the scratch correction process is terminated.

  When the total number of defective pixels exceeds the defective pixel total reference value (Yes in S104), the correction determination threshold value is compared with a predetermined lower limit value of the correction determination threshold value (S105). When the correction determination threshold value is larger than the lower limit value of the correction determination threshold value (yes in S105), the correction determination threshold value is updated (S106), and when the correction determination threshold value is not larger than the lower limit value (no in S105). The scratch correction process ends. Here, the reason why the correction determination threshold value is compared with the lower limit value is to prevent the digital camera flaw correction process in the embodiment of the present invention from entering an infinite loop and to appropriately end the correction process. .

  When the correction determination threshold value is larger than the lower limit value of the correction determination threshold value (yes in S105), the correction determination threshold value is rewritten to a smaller value (S106), and the correction process (S102) is executed again. The image correction process in the digital camera of the embodiment has been described above.

  In the image correction apparatus of the present embodiment, the scratch detection unit 106 detects defective pixels (scratches) from the image after correction corrected by the scratch correction processing unit 105, and the total number of detected scratches is based on the total number of defective pixels. Determine whether the value is exceeded. If the scratch exceeds the defective pixel total reference value, the scratch correction processing unit 105 performs correction again, so that the correction is performed until the number of defective pixels in the corrected image becomes smaller than the reference value. Become. Thus, even if the correction determination threshold value is not set in advance according to the exposure amount and the gain of the AGC unit, appropriate correction can be performed regardless of the exposure amount and the gain of the AGC unit.

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

  In the above-described embodiment, an example in which the image correction apparatus is applied to a digital camera has been described. However, the image correction apparatus can also be applied to a mobile phone.

  As described above, as an image correction apparatus or the like that has an excellent effect that appropriate correction can be performed regardless of the exposure amount, the gain of the AGC unit, and the like, and that corrects an image captured by a digital camera or the like. Useful.

The figure which shows the structure of the digital camera of embodiment Flowchart showing scratch correction processing of the digital camera of the embodiment Diagram showing the configuration of a conventional digital camera (A) A diagram showing an example of a peripheral pixel used for correcting a pixel of an R signal (b) A diagram showing an example of a peripheral pixel used for correcting a pixel of a G signal (c) A diagram of peripheral pixels used for correcting a pixel of a B signal Figure showing an example (A) The figure which shows the mode of the signal level in the attention pixel and peripheral pixel at the time of normal exposure (b) The figure which shows the state of the signal level in the attention pixel and peripheral pixel at the time of long exposure Flow chart showing scratch correction processing in a conventional digital camera The figure which shows an example which changed the correction determination threshold value for every exposure time

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Image pick-up element 102 CDS part 103 AGC part 104 AD conversion part 105 Scratch correction process part 106 Scratch detection part 107 Video signal process part 108 Microcomputer

Claims (7)

Correction processing means for performing image correction processing by correcting pixels detected using a correction determination threshold;
Defective pixel detection means for detecting defective pixels in the image corrected by the correction processing means;
Determination means for determining whether the total number of defective pixels detected by the defective pixel detection means exceeds a preset reference value;
With
The image correction apparatus, wherein the correction processing unit changes the correction determination threshold and corrects an image in response to determination by the determination unit that the total number of defective pixels exceeds the reference value.   The correction processing unit replaces the value of the pixel to be corrected with the calculated value when a difference between the value of the pixel to be corrected and a calculated value calculated from surrounding pixels is larger than the correction determination threshold value. The image correction apparatus according to claim 1.   The image correction apparatus according to claim 2, wherein the correction processing unit obtains an average value of the peripheral pixels as the calculated value.   The defective pixel detection means detects the pixel to be inspected as a defective pixel when a difference between a value of the pixel to be inspected and a calculated value calculated from surrounding pixels exceeds a preset defective pixel determination threshold value. The image correction apparatus according to claim 1, wherein:   A digital camera comprising the image correction apparatus according to claim 1.   A mobile phone comprising the image correction apparatus according to claim 1. A correction processing step for correcting the image by correcting the detected pixel using the correction determination threshold;
A defective pixel detection step of detecting defective pixels of the image corrected in the correction processing step;
A determination step for determining whether or not the total number of defective pixels detected in the defective pixel detection step exceeds a preset reference value;
With
In accordance with the determination in the determination step that the total number of defective pixels exceeds the reference value, the correction processing step is performed again while changing the correction determination threshold.

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