JP2006060476A - Method for correcting signal outputted from image pickup element and image processor using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide images of high image quality by suppressing excessive correction of image signals and preventing occurrence of black vertical stripes on images. <P>SOLUTION: An image processor comprises: an imaging device having optically shielded pixels and optically non-shielded pixels; a setting means for setting a correction amount upper limit value corresponding to image pickup conditions, respectively; an arithmetic means for computing a correction amount on the basis of signals from the optically shielded pixels; a comparison means for comparing the correction upper limit value and the correction amount; and a correction means for correcting the signals from the optically non-shielded pixels by using the correction amount in the case of deciding that the correction amount is smaller than the correction upper limit value by the comparison means and correcting the signals from the optically non-shielded pixels by using the correction upper limit value in the case of deciding that the correction amount is larger than the correction upper limit value by the comparison means. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image processing apparatus such as a video camera or a digital camera, and more particularly to a defect correction method for an image sensor.

As a conventional defect pixel and vertical transfer path defect correction method, a defect address of an image sensor is detected by a detection unit, and the detected address is stored in a storage unit such as a ROM or a RAM, and the peripheral pixels of the defect portion at the time of photographing There is a method of performing interpolation based on information. (For example, reference 1)
As a method for correcting pixels in the vertical direction, there is a method of detecting the signal amount of the OB column or dummy pixel column of the photographed image and subtracting the detected signal amount from the column of the effective pixel portion. This technique is also used in a method for correcting a defective pixel column in the vertical direction due to a defect in the vertical transfer path, that is, a vertical line defect.
JP-A-5-68209

  However, in the method disclosed in Document 1, since the detected address is stored in a storage unit such as a ROM or a RAM, the capacity of the ROM or the RAM is limited in an image pickup device in which a lot of continuous defects such as a vertical line scratch exists. There is a problem of pressure. Further, when there is an adjacent flaw in the vertical line flaw, there is a problem that interpolation cannot be performed from either the vertical direction or the horizontal direction. In addition, since vertical line scratches are often lower in level than normal point scratches, there is also a problem that they are difficult to detect when scratches are detected.

  On the other hand, as a method of correcting pixels in the vertical direction, correction is performed by detecting the signal amount of the OB column or dummy pixel column of the photographed image and subtracting the detected signal amount from the column of the effective pixel portion. There is a technique, and vertical line scratches can be corrected. However, the smear phenomenon caused by the light entering the vertical transfer path is the same as the vertical flaw as an appearing phenomenon. Therefore, the above method only corrects the smear by one color. For this reason, when smear occurs at the time of shooting a high-luminance subject, a delay occurs in the correction processing, and the column to be originally corrected cannot be accurately corrected, and the image quality may be deteriorated. In particular, if a high-luminance subject moves or an image processing device moves when smear occurs, an overcorrection (on the image) that corrects a column other than the column where the original smear correction is to be made with a large correction amount. As a phenomenon that appears, black vertical streaks) occur, and there has been a problem that image quality deterioration becomes significant.

  In order to achieve the above object, an image processing apparatus according to the present invention includes an image sensor having pixels that are optically shielded, pixels that are not optically shielded, and a correction amount upper limit value corresponding to each imaging condition. Setting means for setting; calculation means for calculating a correction amount based on a signal from the optically shielded pixel; comparison means for comparing the correction upper limit value with the correction amount; and the comparison means When it is determined that the correction amount is smaller than the correction upper limit value, the correction amount is used to correct a signal from the optically unshielded pixel, and the comparison means And a correction unit that corrects a signal from the optically unshielded pixel using the correction upper limit value when it is determined that the correction amount is larger than the correction upper limit value.

  The image processing method of the present invention is an image processing method of an image processing apparatus having an image sensor having pixels that are optically shielded and pixels that are not optically shielded, and each corresponds to an imaging condition. A setting step for setting a correction amount upper limit value, a calculation step for calculating a correction amount based on a signal from the optically shielded pixel, and a comparison step for comparing the correction upper limit value with the correction amount When the comparison step determines that the correction amount is smaller than the correction upper limit value, the correction amount is used to correct a signal from the optically unshielded pixel, When the comparison step determines that the correction amount is larger than the correction upper limit value, a correction step of correcting a signal from the optically unshielded pixel using the correction upper limit value; Have .

  Even when a defect exists in the image sensor, an appropriate correction process can be performed, and a high-quality image can be obtained.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(Embodiment)
FIG. 1 is a block diagram showing a configuration of an image processing apparatus, here a digital camera, according to an embodiment of the present invention.

  First, the function of each part in FIG. 1 will be described. Reference numeral 10 denotes an image processing apparatus (a digital camera in the present embodiment), and the internal functions are described in detail. Reference numeral 12 denotes an image sensor (CCD in the present embodiment) that converts light into an electrical signal, and 11 denotes light from a subject. Is a lens for condensing the image on the CCD 12, and 13 is an image processing circuit for converting an analog video signal output from the CCD 12 into an image signal (including an A / D converter for converting an analog signal into a digital signal in the image processing circuit). , 14 is a timing generator for generating pulses for driving the CCD 12, 15 is a storage means (here, RAM) for storing photographing data and image data, and 16 is a photographing image recording medium (here, removable from the digital camera 10). Then, the image data temporarily recorded in the RAM 15 is finally recorded with a compact flash (registered trademark) card).Reference numeral 17 denotes a control means (here, a CPU) that controls all functions of the digital camera, and 18 denotes a thermistor that measures the ambient temperature of the CCD 12. The image sensor 12 includes an OB portion that is a pixel portion that is optically shielded and an effective pixel portion that is a pixel portion that is not optically shielded.

  Next, the flow of the embodiment of the present invention will be described using the flowchart of FIG. In the present embodiment, an example of moving image shooting will be described. In the live view mode, the same effect can be obtained with the same configuration.

  First, video shooting is started (S101). At the start of shooting, moving image shooting conditions are recorded in shooting data in the RAM 15, and shooting sensitivity information is acquired from the shooting data in the RAM 15 (S102). Further, the CCD ambient temperature is acquired from the thermistor 18 under the control of the CPU 17 (S103). The thermistor is preferably located closer to the pixel portion of the CCD.

  Next, for each frame of a moving image, an OB portion or a dummy pixel portion (a signal generated when reading is performed in a state where there is no accumulated signal in the image sensor 12 is called a dummy signal. By measuring the signal of the dummy pixel portion), the vertical line scratch level and smear level are measured (S104). When the smear phenomenon due to the high brightness subject does not occur, the correction value of the vertical line scratch can be obtained by calculating the addition average value L by measuring this level. FIG. 3 is a diagram showing a method of measuring the OB portion or the dummy pixel portion, and shows a case where only a vertical line scratch has occurred. The vertical line scratch is a phenomenon caused by a defect in the vertical transfer portion, and the same level of floating occurs in the same row as shown in FIG. This floating amount also occurs in the OB part [2] and the dummy pixel part [3]. In the present embodiment, the vertical line defect correction is performed by obtaining the addition average value L of each column of the OB portion for each frame of the moving image and subtracting the addition average value L from the column of the effective pixel portion.

  On the other hand, there are cases in which smear occurs when moving images of high-luminance subjects are taken. The smear generation principle is a phenomenon that occurs when light enters the vertical transfer path, so the phenomenon that appears is the same as a vertical line scratch. Therefore, in the method of performing vertical line scratch correction by subtracting the addition average value L from the column of effective pixels as described above, vertical line scratches and smears cannot be separated, and when vertical line scratch correction is performed, Smear correction is performed at the same time as vertical line flaw correction. In this case, since the level of the vertical line scratch is very small and the smear level may be very large, when the smear occurs, the addition average L of each column of the OB column or the dummy pixel column is obtained, and the effective pixel portion If the average value is subtracted from this column, a shift due to a time difference occurs in the column to be corrected, and there is a possibility that black vertical stripes due to oversubtraction occur in the image. In particular, when a high-luminance subject moves or when the digital camera shakes and moves, this black vertical stripe appears prominently.

  Therefore, in the present embodiment, in order to reduce the level of the black vertical stripe, the vertical line scratch level upper limit value is calculated, and an upper limit is set for the vertical line scratch correction amount. That is, when there is a high-luminance subject that causes smear, the level of black vertical stripes can be reduced by performing correction with the correction amount of the upper limit value.

The vertical line scratch is a phenomenon caused by a defect in the vertical transfer path, for example, a vertical transfer path scratch. Therefore, the vertical line scratch level also increases as the temperature rises. Further, as shown in FIG. 4, the vertical line scratch level also increases in proportion to the photographing sensitivity. Therefore, assuming that the ambient temperature (° C.) of the CCD 12 is x, the photographing sensitivity is ISO y, and the vertical line scratch level at ISO 100 and 0 ° C. is z LSB, the vertical line scratch level K can be approximately calculated by the following equation (S105). ).
K≈z × (y / 100) × 2 ^{(1 + x / 8)}
However, x ≧ 0 ° C.

  FIG. 5 is a graph obtained by graphing the above formula, and represents the correction upper limit value corresponding to the photographing sensitivity and the image sensor temperature. In the present embodiment, K calculated by the above equation is used as the vertical line scratch correction upper limit value and compared with the addition average value L calculated in S104 (S106).

  When the comparison result is K <L, the correction upper limit value K is subtracted from each column of the entire effective pixel area (S107).

  When the comparison result is K ≧ L, the vertical average defect correction is performed by subtracting the addition average value L corresponding to that column from each column of the entire effective pixel region (S108).

  In the present embodiment, the above operation is performed every frame during moving image shooting. However, S102, S103, and S105 may be performed not at every frame but at a fixed period. In the present embodiment, the line scratch correction upper limit value is calculated based on two types of the CCD ambient temperature and the imaging sensitivity. However, the upper limit value may be calculated using only one of them.

  As described above, according to the present embodiment, high brightness subject shooting is performed by calculating a correction amount upper limit value for line scratch correction from the temperature of the image sensor and shooting sensitivity information during live view or movie shooting. Even when smear occurs due to the above, the correction upper limit value is limited, so that a good live view image and moving image can be taken. In particular, black vertical streaks that occur when a high-luminance subject moves or when the digital camera shakes or moves can be reduced, and a high-quality image can be obtained.

It is a functional block diagram of the digital camera which concerns on embodiment of this invention. It is a flowchart which shows operation | movement of embodiment of this invention. It is an image sensor block diagram showing the example of vertical line flaw generation of an embodiment of the invention. It is a graph showing the correction | amendment upper limit according to the imaging sensitivity of embodiment of this invention. It is a graph showing the correction | amendment upper limit according to the imaging sensitivity of embodiment of this invention, and image pick-up element temperature.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Digital camera which is an imaging device 11 Lens 12 CCD which is an imaging device
13 Image processing circuit 14 Timing generator 15 RAM as storage means
16 Compact Flash (registered trademark) card as a recording medium 17 CPU as control means
18 Thermistor as temperature detection means

Claims (5)

An image sensor having pixels that are optically shielded and pixels that are not optically shielded;
Setting means for setting a correction amount upper limit value corresponding to each imaging condition;
A calculation means for calculating a correction amount based on a signal from the optically shielded pixel;
Comparison means for comparing the correction upper limit value with the correction amount;
If the comparison unit determines that the correction amount is smaller than the correction upper limit value, the correction unit is used to correct a signal from the pixel that is not optically shielded, and the comparison unit. When the correction amount is determined to be larger than the correction upper limit value, the correction means corrects the signal from the optically unshielded pixel using the correction upper limit value. An image processing apparatus.   The image processing apparatus according to claim 1, wherein the imaging condition includes at least one of a temperature condition and a sensitivity condition. It further has temperature detection means for measuring either the temperature of the imaged image element or the ambient temperature of the image sensor,
The image processing apparatus according to claim 1, wherein the setting unit sets a correction amount upper limit value according to an image sensor obtained by the temperature detection unit or a temperature around the image sensor. A lens that forms an image on the image sensor;
An A / D converter for A / D converting a signal from the image sensor;
An image processing apparatus comprising: a storage control unit that controls to store a signal from the correction unit in a storage unit. An image processing method of an image processing apparatus having an image sensor having a pixel that is optically shielded and a pixel that is not optically shielded,
A setting step for setting a correction amount upper limit value corresponding to each imaging condition;
A calculation step of calculating a correction amount based on a signal from the optically shielded pixel;
A comparison step of comparing the correction upper limit value and the correction amount;
When the comparison step determines that the correction amount is smaller than the correction upper limit value, the correction amount is used to correct a signal from the pixel that is not optically shielded, and the comparison step When the correction amount is determined to be larger than the correction upper limit value, the correction step of correcting a signal from the optically unshielded pixel using the correction upper limit value is included. An image processing method.

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