Source: https://patents.google.com/patent/JP5011814B2/en
Timestamp: 2019-10-17 14:11:20
Document Index: 196227184

Matched Legal Cases: ['Application No. 2006', 'art 15', 'art 16', 'art 20', 'art 22', 'art 111', 'art 151', 'art 210', 'art 214']

JP5011814B2 - Imaging apparatus, image processing method, and computer program - Google Patents
Imaging apparatus, image processing method, and computer program Download PDF
JP5011814B2
JP5011814B2 JP2006134700A JP2006134700A JP5011814B2 JP 5011814 B2 JP5011814 B2 JP 5011814B2 JP 2006134700 A JP2006134700 A JP 2006134700A JP 2006134700 A JP2006134700 A JP 2006134700A JP 5011814 B2 JP5011814 B2 JP 5011814B2
sensitivity pixel
JP2006134700A
JP2007306447A (en
JP2007306447A5 (en
2006-05-15 Application filed by ソニー株式会社 filed Critical ソニー株式会社
2006-05-15 Priority to JP2006134700A priority Critical patent/JP5011814B2/en
2007-11-22 Publication of JP2007306447A publication Critical patent/JP2007306447A/en
2009-06-25 Publication of JP2007306447A5 publication Critical patent/JP2007306447A5/ja
2012-08-29 Publication of JP5011814B2 publication Critical patent/JP5011814B2/en
The present invention relates to an imaging apparatus, an image processing method, and a computer program. In particular, the present invention relates to an imaging apparatus, an image processing method, and a computer program that perform signal processing of imaging data by a solid-state imaging device.
A general single-plate color solid-state image sensor has a color filter that allows only a specific wavelength component to pass through each pixel on the surface of the image sensor. To restore. At this time, the color arrangement used in the color filter is, for example, as shown in FIG. 1A, a color arrangement expressing red (R), green (G), and blue (B), or FIG. As shown in FIG. 5, an arrangement in which white (Y) and red (R), green (G), and blue (B) as luminance signals are combined is used. In a single-plate color solid-state image sensor, each pixel only has information on a single color component as described above. Therefore, by performing interpolation using the color information of surrounding pixels, the necessary color in each pixel is obtained. A demosaic process is performed to restore the components.
FIG. 2 shows a configuration of an imaging apparatus including a single-plate color type solid-state imaging device. The single-plate color type solid-state imaging device 13 receives light that passes through the color filter 12 among light incident through the optical lens 11. An image signal that is photoelectrically converted by the solid-state imaging device 13 and output as an electrical signal is converted into a digital signal by an A / D converter (not shown), and then the camera signal processing unit 14 performs clipping processing, gamma correction, and white balance. Correction, demosaic processing, and the like are performed and sent to the image compression unit 15. The image compression unit 15 reduces the data amount of the image signal, converts it into a predetermined recording image format, and outputs it. The recording unit 16 records the converted image data on a recording medium. Here, image compression processing does not necessarily have to be performed. However, in recent years, image compression is usually performed because the number of pixels of the image sensor has increased and the device itself has been required to be downsized. .
With reference to FIG. 3, the demosaic processing of an image acquired by a single-plate color type solid-state imaging device will be described. A single-plate color type solid-state imaging device is configured to perform imaging through a color filter having a color array such as a primary color Bayer array (see FIG. 1). Only color component data of a specific wavelength is acquired. When a single-plate color solid-state image sensor with a Bayer arrangement is used, the output image 20 of the solid-state image sensor is a color mosaic image having only R, G, or B information in each pixel.
The demosaic processing unit 21 performs a process of restoring all information of each color component data, that is, R, G, and B, by performing a color interpolation process for each pixel.
First, the restoration of the G signal executed by the demosaic processing unit 21 will be described. In the Bayer array shown in FIG. 1A, the G signal is acquired in a checkered pattern. In the pixel in which G signal is not present in the output image 20 of the solid-state imaging device (take G 11 as an example), by interpolation processing based on the G signal in the periphery, G signals are generated. Specifically, the G signal (G 11 ) is restored by the following equation.
G11 = (1/4) (G 01 + G 21 + G 10 + G 12)
Next, restoration of the R signal and the B signal will be described. In the Bayer array shown in FIG. 1A, both R and B have data every other pixel line. For example, the R signal exists but the B signal does not exist in the uppermost pixel line of the output image 20 of the solid-state imaging device shown in FIG. In the second pixel line, the B signal exists but the R signal does not exist.
Data is acquired every other pixel in each pixel line where data R or B exists. When an R signal (B signal) does not exist in the output image 20 of the solid-state imaging device and an R signal (B signal) exists on the same line (R 01 and B 12 are taken as an example), the pixel on the pixel line The interpolated pixel value in the pixel without the R and B signals is calculated by the following formula, and the R signal (B signal) of each pixel is restored.
R 01 = (1/2) (R 00 + R 02 )
B 12 = (1/2) (B 11 + B 13 )
Similarly, when an R signal (B signal) is present in the same column (R 10 and B 21 are taken as an example), an interpolated pixel value in a pixel without the R and B signals is calculated by the following formula, The R signal (B signal) of the pixel is restored.
R 10 = (1/2) (R 00 + R 20 )
B 21 = (1/2) (B 11 + B 31 )
Further, when there is no R signal (B signal) in the same line or the same column (R 11 and B 22 are taken as an example), the interpolated pixel value in the pixel without the R and B signals is calculated by the following formula: Then, the R signal (B signal) of each pixel is restored.
R 11 = (1/4) (R 00 + R 02 + R 20 + R 22 )
B 22 = (1/4) (B 11 + B 13 + B 31 + B 33 )
The demosaic processing unit 21 performs the color interpolation processing as described above, and outputs an R signal 22r, a G signal 22g, and a B signal 22b for all pixels. Note that the interpolation processing is an example, and color interpolation processing using correlation with other color signals may be performed.
In recent years, in digital still cameras and movie cameras, improving the quality of images taken under low illumination is an important issue. When shooting an image under low illumination, it is common to slow down the shutter speed, use a lens with a bright aperture value, or use a visible light source such as a flash.
In this case, if the shutter speed is decreased, camera shake and subject blur will be caused. Also, the aperture value of the lens usually has a limit, and it cannot be brightened beyond a certain level. Furthermore, when an external light source of visible light is used, there is a problem that the atmosphere due to the illumination on the spot is impaired.
For example, in Patent Document 1 and Patent Document 2, the color arrangement described above with reference to FIG. 1B, that is, white (Y) and red (R), green (G), and blue (B as luminance signals) are described. ) Is used for signal processing to obtain a high-resolution image using an imaging device to which a Bayer array is combined. Japanese Patent Application Laid-Open No. H10-228707 describes signal processing for obtaining a high resolution using white pixels of checkered pixels by applying a color filter array in which white pixels shown in FIG. 1B are arranged in a checkered pattern.
That is, according to the arrangement shown in FIG. 1 (b), the Y pixels in the checkered arrangement have sensitivity to almost the entire visible light, so that the green (G) pixels are arranged in the checkered arrangement as shown in FIG. 1 (a). A larger signal is obtained. For this reason, an image with a good S / N ratio can be obtained.
However, in the arrangement as shown in FIG. 1B, the exposure period of the light receiving element corresponding to white (Y) and the light receiving element corresponding to each pixel of red (R), green (G), and blue (B) is set. If they are the same, the amount of light received by the element corresponding to white (Y) receives a larger amount of light than the elements corresponding to red (R), green (G), and blue (B). In such a combination arrangement, there is a problem that when the light amount is adjusted according to one element, the appropriate light amount corresponding to the other element is not obtained.
In such a case, if the exposure time is suitable for one of the elements, the exposure time is not suitable for the other element. For example, when the exposure time is set so that one element does not saturate, there is a problem in that a sufficient signal charge cannot be obtained with the other element and the S / N deteriorates. On the other hand, when the exposure time is set so that a sufficient signal charge can be obtained in any case, there is a problem that saturation occurs in one element.
JP-A-4-88784 USP 5323233
The present invention provides an image pickup apparatus that can adjust sensitivity imbalance and obtain high-quality image data in a configuration in which an image pickup element having a combination array of light receiving elements that receive different light components is applied, and An object is to provide an image processing method and a computer program.
An imaging device composed of a plurality of elements arranged on an array, and composed of a high-sensitivity pixel-compatible device that receives a relatively large amount of light and a low-sensitivity pixel-compatible device that receives a relatively small amount of light Elements,
An exposure control unit that independently controls an exposure period of the high-sensitivity pixel corresponding element and the low-sensitivity pixel corresponding element in the imaging element;
An image generation unit that executes an image generation process based on an output signal of the image sensor;
A comparison process between the high sensitivity pixel evaluation image based on the output data of the high sensitivity pixel corresponding element and the low sensitivity pixel evaluation image based on the output data of the low sensitivity pixel corresponding element is executed, and the corresponding pixels in the two evaluation images A configuration in which a pixel area determined to have a small difference between corresponding pixels based on a pixel value difference or a pixel value ratio is separated from a pixel area determined to have a large difference, and different image processing is executed in each pixel area The imaging apparatus is characterized by the above.
Furthermore, in one embodiment of the imaging device of the present invention, the image generation unit outputs the output data of the high-sensitivity pixel-corresponding element for a pixel region that is determined to have a small difference between corresponding pixels in the two evaluation images. Image processing using both output data of the low-sensitivity pixel corresponding element and output data of the high-sensitivity pixel corresponding element or the output of the low-sensitivity pixel corresponding element for the pixel region determined to have a large difference. The present invention is characterized in that image processing based on only one of the data is executed to generate an image.
Furthermore, in an embodiment of the imaging apparatus of the present invention, the imaging element includes a low-sensitivity pixel corresponding element that receives light in each specific wavelength region of RGB, and a high-sensitivity pixel corresponding element that receives light in the visible light region. The image generation unit is configured to generate a low-sensitivity pixel evaluation image generated based on output data of RGB-compatible low-sensitivity pixel-compatible elements based on output data of WL and visible light-compatible high-sensitivity pixel-compatible elements. When the high-sensitivity pixel evaluation image to be performed is WH, a calculation formula using parameters a, b, and c as coefficients,
WL = aR + bG + cB,
The low-sensitivity pixel evaluation image WL is generated based on the above, and the process of determining the parameters a, b, and c according to the characteristics of the image sensor is performed.
Furthermore, in an embodiment of the imaging apparatus of the present invention, the image generation unit is configured to apply different values to the parameters according to light sources.
Furthermore, in an embodiment of the imaging apparatus of the present invention, the image generation unit includes a difference absolute value | E | between the high-sensitivity pixel evaluation image, a corresponding pixel of the low-sensitivity pixel evaluation image, and a predetermined threshold value. The comparison processing is executed, and different image processing is executed between a pixel region having a difference exceeding a threshold value and a pixel region having a threshold value or less.
Furthermore, in an embodiment of the imaging apparatus of the present invention, the image generation unit includes a plurality of predetermined thresholds and absolute difference values | E | of the corresponding pixels of the high-sensitivity pixel evaluation image and the low-sensitivity pixel evaluation image. And a different image process according to the difference amount defined by the plurality of threshold values.
Furthermore, in an embodiment of the imaging apparatus of the present invention, the image generation unit performs output processing of the high-sensitivity pixel corresponding element and low-sensitivity pixels as different image processing according to the difference amount defined by the plurality of threshold values. The present invention is characterized in that the image processing is performed by changing the utilization ratio with the output data of the corresponding element.
Furthermore, in an embodiment of the imaging apparatus of the present invention, the image generation unit generates an evaluation image from which a high-frequency component is cut and compares in the comparison process between the high-sensitivity pixel evaluation image and the low-sensitivity pixel evaluation image. It is the structure which performs this.
Furthermore, in an embodiment of the imaging device of the present invention, the image generation unit outputs the high-sensitivity pixel corresponding element for a pixel having a large difference between corresponding pixels in the two evaluation images and a surrounding pixel region of the pixel. The present invention is characterized in that the image processing based on only one of the data or the output data of the low sensitivity pixel corresponding element is executed to generate an image.
Furthermore, in an embodiment of the imaging apparatus of the present invention, the image generation unit compares the data before executing the interpolation process in the comparison process between the high-sensitivity pixel evaluation image and the low-sensitivity pixel evaluation image. It is the structure which performs a process.
Furthermore, in an embodiment of the imaging apparatus of the present invention, the high-sensitivity pixel corresponding element constituting the imaging element is an element that receives invisible light such as a visible light region and infrared light.
An image processing method for executing image processing in an imaging apparatus,
Applying an image sensor consisting of a high-sensitivity pixel-compatible element that receives a relatively large amount of light and a low-sensitivity pixel-compatible element that receives a relatively small amount of light, a high-sensitivity pixel-compatible element and a low-sensitivity pixel A step of inputting an output signal of an image sensor, which is taken by independently controlling an exposure period with a corresponding element, to an image generation unit;
In the image generation unit, an evaluation image comparison for performing a comparison process between a high sensitivity pixel evaluation image based on output data of the high sensitivity pixel corresponding element and a low sensitivity pixel evaluation image based on output data of the low sensitivity pixel corresponding element Steps,
In the image generation unit, a pixel area determined to have a small difference between corresponding pixels based on a pixel value difference or a pixel value ratio of the corresponding pixels in the two evaluation images is distinguished from a pixel area determined to have a large difference. An image processing step for generating an image by performing different image processing in each pixel region;
A computer program for executing image processing in an imaging apparatus;
Under the control of the control unit, an image sensor composed of a high-sensitivity pixel-compatible element that receives a relatively large amount of light and a low-sensitivity pixel-compatible element that receives a relatively small amount of light is applied. Inputting an output signal of an imaging element, which is captured by independently controlling the exposure period of the corresponding element and the low-sensitivity pixel corresponding element, to the image generation unit;
Evaluation image comparison for causing the image generation unit to perform a comparison process between a high sensitivity pixel evaluation image based on output data of the high sensitivity pixel corresponding element and a low sensitivity pixel evaluation image based on output data of the low sensitivity pixel corresponding element. Steps,
In the image generation unit, a pixel area determined to have a small difference between corresponding pixels based on a pixel value difference or a pixel value ratio of the corresponding pixels in the two evaluation images is distinguished from a pixel area determined to have a large difference. An image processing step of generating an image by executing different image processing in each pixel region;
According to the configuration of the present invention, an image sensor such as RGBW, that is, an image sensor having a low sensitivity pixel corresponding element (RGB) and a high sensitivity pixel corresponding element (W) is applied, and the exposure time of the low sensitivity pixel corresponding element is increased. In a configuration in which shooting is performed with the exposure time of the high-sensitivity pixel corresponding element set to be short, an evaluation image composed of data of only the low-sensitivity pixel corresponding element (RGB) and data of only the high-sensitivity pixel corresponding element (W) The pixel value comparison with the evaluation image consisting of is executed, the image generation processing consisting of only one image is executed for the pixel portion having a large difference, and the image based on the two images is executed for the pixel portion having a small difference. Since it is configured to generate, it is possible to generate a high-quality image that does not cause an error due to the difference in the moving subject area image due to the difference in the exposure period.
Hereinafter, an imaging apparatus, an image processing method, and a computer program according to the present invention will be described with reference to the drawings. The description will be given in the following order.
1. 1. Processing example and problem of imaging data using RGBW imaging device 2. Image processing configuration according to the present invention (2.1) Overall configuration (2.2) Details of evaluation image generation processing (2.3) Details of evaluation image comparison processing Other Embodiments (3.1) Evaluation Image Control (3.2) Image Processing Unit Control (3.3) Evaluation Image Comparison Processing Range Control (3.4) Optimal Control According to Pixel Value Difference
[1. Processing of imaging data using RGBW imaging device and problems]
First, an example of image data processing using the RGBW image sensor and problems will be described. The image sensor applied in the image pickup apparatus of the present invention has, for example, the color arrangement shown in FIG. That is,
Red (R) that transmits wavelengths near red,
Green (G) that transmits wavelengths in the vicinity of green,
Blue (B) that transmits wavelengths near blue,
W that transmits all of RGB,
These four types of filters have spectral characteristics. The four types of spectroscopy consist of an R channel, a G channel, a B channel, and a W channel that transmits all of RGB, and a mosaic image consisting of the four types of spectroscopy is obtained by this imaging device.
The spectral characteristics of the four types of filters will be described with reference to FIG. FIG. 5 shows the wavelength on the horizontal axis and the intensity received by each RGBW light receiving element on the vertical axis. The intensity corresponds to the transmittance of the filter corresponding to each light receiving element. The B element includes a filter having a high transmittance of an optical signal having a wavelength near 450 nm corresponding to blue, and the intensity distribution of the light received by the B element has an intensity of an optical signal having a wavelength near 450 nm corresponding to blue. highest. The filter corresponding to the G element is a filter having a high transmittance of an optical signal having a wavelength near 550 nm corresponding to green, and the intensity distribution of light received by the G element is an optical signal having a wavelength near 550 nm corresponding to green. Has the highest strength. The filter corresponding to the R element is a filter having a high transmittance of an optical signal having a wavelength near 600 nm corresponding to red, and the intensity distribution of the light received by the R element is an optical signal having a wavelength near 600 nm corresponding to red. Has the highest strength. The filter corresponding to the W element has a property of transmitting all signals of the RGB components, and the W element receives all visible light in each of the RGB wavelength regions.
As described above, the imaging element applied in the imaging apparatus of the present invention includes a specific wavelength region signal acquisition element (RGB element) that acquires a visible light signal corresponding to a specific light wavelength region such as RGB, and visible light such as RGB. This is a single plate type image pickup device having an element arrangement constituted by a wide wavelength region signal acquisition element (W element) for acquiring an optical signal including all components.
The image pickup device applied in the image pickup apparatus of the present invention is an image pickup device having such four types of RGBW-compatible transmission filters. As shown in FIG. 4, the RGB device and RGB color for individually acquiring RGB color signals. It is composed of W elements that acquire all signal components. Note that the RGBW arrangement can be set to other arrangements shown in FIG. 4, for example, the arrangement shown in FIG. 6. The optical filter array shown in FIG. 6 corresponds to a configuration obtained by rotating the array shown in FIG. 4 by 45 degrees.
4 and 6, the W signal acquisition elements are arranged in a checkered pattern. In the imaging apparatus of the present invention, signal processing is executed based on image data captured by applying the imaging device shown in FIGS.
Next, a general signal processing example based on image data captured by applying the image sensor shown in FIG. 4 or 6 will be described with reference to FIG. FIG. 7 shows a luminance signal (W), two color difference signals (RW), and (B-W) by signal processing of an image taken by the image sensor having the RGBW arrangement shown in FIG. 4 or FIG. It is a figure which shows the signal processing structure for acquiring. Note that, for example, processing such as white balance adjustment is performed on the data acquired by the image sensor, but these processing are the same as conventional processing and are not shown in FIG. .
The configuration shown in FIG. 7 acquires a mosaic image that is an acquisition signal of a W element from a signal acquired by the image sensor (CCD) 101 having the RGBW arrangement shown in FIG. 4 or FIG. A luminance signal generation unit that generates a W demosaic image as a luminance signal, an RGB mosaic image that is an acquisition signal of an RGB element is acquired, an RGB demosaic image corresponding to a visible light region signal is generated, and a color difference based on the RGB demosaic image And a color difference signal generation unit for generating a signal. In FIG. 7, the low-pass filter 111 corresponds to a luminance signal generation unit, and the low-pass filters 112 to 117 and the matrix calculation unit 117 correspond to a color difference signal generation unit.
Signal processing to which the configuration of FIG. 7 is applied will be described. First, a signal photographed by the image sensor (CCD) 101 having the RGBW arrangement shown in FIG. 4 or 6 is converted into digital data by the AD converter 102. Here, the generated signals are four mosaic images corresponding to each of RGBW.
For example, when the image sensor having the color arrangement described with reference to FIG. 4 is applied, mosaic images of four RGBWs as shown in FIG. 8A are acquired. These four mosaic images are respectively input to low-pass filters 111 to 116 that execute an interpolation process for setting the pixel values of all the pixels by a process of interpolating a pixel portion having no pixel value with surrounding pixel values. Demosaic processing is executed.
As described above with reference to FIG. 3, the demosaic process is performed by a process of setting the pixel values of all the pixels by executing interpolation based on the surrounding pixel values for the pixels having no pixel value. . For example, a method similar to the known Vargra algorithm can be applied. The Vargra algorithm is an algorithm that performs demosaicing by obtaining eight-direction gradients of pixel values and averaging pixel values having similar gradients.
This demosaic process is a process of determining the pixel value of a pixel portion where no pixel value exists based on the pixel values of surrounding pixels. This process is performed by a so-called two-dimensional FIR filter. That is, a filter having a coefficient corresponding to the pixel position is applied. For R and B, a two-stage low-pass filter is applied, and after processing by the low-pass filters 113 and 114 as interpolation filters corresponding to offset sub-sampling, low-pass filters 115 and 116 similar to the low-pass filter 112 are used. The pixel values of all the pixels are set.
By this interpolation processing, for example, a demosaic image as shown in FIG. The demosaic image 151 is an R channel demosaic image generated by the interpolation processing in the low-pass filter 113, 115 shown in FIG. 7, and the demosaic image 152 is the G channel generated by the interpolation processing in the low-pass filter 112 shown in FIG. , The demosaic image 153 is a B-channel demosaic image generated by the interpolation processing in the low-pass filter 114, 116 shown in FIG. 7, and the demosaic image 154 is the interpolation processing in the low-pass filter 111 shown in FIG. It is a demosaic image of the W channel generated by.
RGBW in the four demosaic images shown in FIG. 8 (2) is a pixel value obtained by the mosaic image, and rgbw indicates an interpolation pixel value obtained by the demosaic process.
In the demosaic image 154 shown in FIG. 8 generated by the interpolation processing in the low-pass filter 111 shown in FIG. 7, the pixel values corresponding to the intensity of the light including the W channel, that is, the entire wavelength region of the visible light region of RGB, are It will be set to the pixel. This demosaic image is obtained as an output from the low-pass filter 111 as shown in FIG.
On the other hand, the RGB demosaic images generated by the low-pass filters 112 to 116, that is, the demosaic images 151 to 153 shown in FIG. 8B are input to the matrix calculation unit 117 shown in FIG. Color difference signals [R−W] and [B−W] are generated and output by the matrix calculation based on the matrix calculation.
However, in an imaging device having a light receiving element having such an RGBW arrangement, if the exposure period is the same, the amount of light received by a W-compatible element that receives light of all visible light wavelengths is red (R), Compared to green (G) and blue (B) compatible elements, a large amount of light is received. In such a combination arrangement, there is a problem that when the light amount is adjusted according to one element, the appropriate light amount corresponding to the other element is not obtained. In such an arrangement, as described above, there is a problem that when the light amount is adjusted according to the sensitivity of one element, the light amount is not appropriate for the other element. In the imaging apparatus of the present invention, it is possible to adjust the sensitivity imbalance and obtain high-quality image data in a configuration in which an imaging element having a combination array of light receiving elements having different sensitivities is applied.
The applicant of the present invention, in the previous patent application: Japanese Patent Application No. 2006-31932, is a configuration in which an image sensor having a combination arrangement of light receiving elements having different sensitivities is applied. A device having a control configuration for receiving a light amount adapted to each element by independently controlling a sensitivity pixel corresponding element and a low sensitivity pixel corresponding element to make each exposure time different has been proposed. Specifically, for low-sensitivity pixel-compatible elements, the exposure time is increased, and for high-sensitivity pixel-compatible elements, the exposure process is shortened to perform shooting processing. A typical image is generated.
However, with such a control configuration, there is no problem when shooting a stationary subject, but a problem occurs when shooting a moving subject. This problem will be described with reference to FIG. FIG. 9A shows the state transition of the subject to be photographed over time. During the period from time t1 to time t5, the ball included in the subject is moving from left to right.
By controlling the high-sensitivity pixel-corresponding element (W) and the low-sensitivity pixel-corresponding element (RGB) independently for this subject, and by varying the exposure time, it is possible to receive the amount of light adapted to each element. Assume that shooting is performed. In this case, the exposure time of the low-sensitivity pixel corresponding element (RGB) is a period T1 shown in FIG. 9A, and the exposure time of the high-sensitivity pixel corresponding element (W) is a period T2 shown in FIG. Here, T1> T2.
As a result, the acquired image of the low-sensitivity pixel corresponding element (RGB) is an image at time t1 to t5, that is, the low-sensitivity pixel-corresponding element captured image shown in FIG. The acquired image of W) is an image of time t4 to t5 , that is, a high-sensitivity pixel-corresponding element captured image shown in FIG. 9 (b2). A composite image is generated from these images, but the subject is clearly different between the low-sensitivity pixel-corresponding element captured image shown in FIG. 9B1 and the high-sensitivity pixel-corresponding element captured image shown in FIG. 9B2. Are included.
That is, the low-sensitivity pixel-corresponding element captured image shown in FIG. 9 (b1) includes the moving part of the ball during the period of time t1 to t3, but the high-sensitivity pixel-corresponding element captured image shown in FIG. 9 (b2). Does not include the moving part of the ball during the period from time t1 to t3, and a background image is taken in this part. Accordingly, in this image portion, the color difference signals [R−W] and [B−W] in the signal processing circuit having the configuration of FIG. 7 are generated only from the image information of the ball, but the luminance signal (W) is An image that is a background image and is an image obtained by synthesizing both is output.
[2. Image processing configuration according to the present invention]
The image processing configuration of the present invention will be described below. In the image processing according to the present invention, in the configuration in which shooting is performed by performing exposure time control according to the sensitivity of the RGBW imaging device composed of elements having different sensitivities, the moving object is moved to the subject. Even when the image is included, a more accurate image can be output.
(2.1) Overall Configuration FIG. 10 shows the configuration of the imaging apparatus of the present invention. The imaging apparatus 200 includes an imaging element 201 having a combined configuration of the low-sensitivity pixel corresponding element 202 and the high-sensitivity pixel corresponding element 203, and exposure periods of the low-sensitivity pixel corresponding element 202 and the high-sensitivity pixel corresponding element 203 in the imaging element 201. It has an exposure control unit 205 and an image generation unit 210 that are controlled independently. The image generation unit 210 includes a low sensitivity pixel evaluation image generation unit 214, a high sensitivity pixel evaluation image generation unit 215, an evaluation image comparison unit 216, an image processing mode determination unit 217, and an image processing unit 218.
The image sensor 201 is an image sensor composed of a plurality of elements arranged on the array, and includes a high sensitivity pixel corresponding element that receives a relatively large amount of light, and a low sensitivity pixel corresponding element that receives a relatively small amount of light. It is an imaging device comprised from these. For example, the red (R) that transmits the wavelength in the vicinity of the red color described above with reference to FIGS.
This is an image pickup element composed of these four types of RGBW light receiving elements. The low sensitivity pixel corresponding element 202 corresponds to an RGB element, and the high sensitivity pixel corresponding element 203 corresponds to a W element. The high-sensitivity pixel corresponding element 203 may be an element that receives all wavelengths of visible light, but may be configured as an element that receives invisible light regions such as visible light and infrared light.
The exposure control unit 205 controls the exposure periods of the low sensitivity pixel corresponding element 202 and the high sensitivity pixel corresponding element 203 in the image sensor 201 independently. That is, by controlling the high-sensitivity pixel corresponding element (W) and the low-sensitivity pixel corresponding element (RGB) independently and by varying the exposure time of each, the control to receive the light amount adapted to each element, Perform shooting. Specifically, as described above with reference to FIG. 9, the exposure time of the low sensitivity pixel corresponding element (RGB) is the period T1 shown in FIG. 9A, and the exposure of the high sensitivity pixel corresponding element (W). As for the time, as shown in a period T2 shown in FIG. 9A, control is performed to increase the exposure time for the low-sensitivity pixel corresponding element and shorten the exposure time for the high-sensitivity pixel corresponding element.
The image generation unit 210 receives an output signal of the image sensor 201 under the control of the control unit, and executes image generation processing based on the input signal. The low sensitivity pixel evaluation image generation unit 214 generates a low sensitivity pixel evaluation image WL as a first evaluation image from only the light reception data of the low sensitivity pixel corresponding element 202. The low-sensitivity pixel evaluation image WL is image data generated based on only the R, G, and B signals acquired by the RGB elements without applying the W signal acquired by the W elements. This image data is generated by interpolation processing based only on RGB signals. The interpolation process is a process to which the demosaic process described above with reference to FIG. 8 is applied.
On the other hand, the high-sensitivity pixel evaluation image generation unit 215 generates a high-sensitivity pixel evaluation image WH as a second evaluation image from only the light reception data of the high-sensitivity pixel corresponding element 203. The high sensitivity pixel evaluation image WH is image data generated based only on the W signal acquired by the W element. This image data is generated by interpolation processing based only on the W signal. The interpolation process is a process to which the demosaic process described above with reference to FIG. 8 is applied.
The evaluation image comparison unit 216 applies only the low sensitivity pixel evaluation image WL based only on the R, G, and B signals generated by the low sensitivity pixel evaluation image generation unit 214 and only the W signal generated by the high sensitivity pixel evaluation image generation unit 215. The comparison with the high sensitivity pixel evaluation image WH based is performed. The evaluation image comparison unit 216 performs pixel value comparison of corresponding pixels of each image. For example, a pixel region having a pixel value difference larger than a predetermined threshold is specified.
An area having a pixel value difference larger than a predetermined threshold corresponds to, for example, a pixel portion where the presence or absence of a moving subject described above with reference to FIG. 9 occurs between two images. The evaluation image comparison unit 216 specifies a pixel region having a pixel value difference larger than a predetermined threshold based on the two evaluation images, and outputs pixel region specification information to the image processing mode determination unit 217.
The image processing mode determination unit 217 determines an image processing mode in units of pixels based on the pixel area specifying information input from the evaluation image comparison unit 216, and controls the image processing unit 218 to optimize the pixel units. Perform image processing. Specifically, the image processing mode determination unit 217 has a low sensitivity without applying the signal (W) of the high sensitivity pixel corresponding element (W element) for a pixel region having a pixel value difference larger than a predetermined threshold. The image processing unit 218 generates an image based only on the acquisition signal (RGB) of the pixel corresponding element (RGB element). On the other hand, for a pixel region having a pixel value difference equal to or less than a predetermined threshold, both the signal (W) of the high sensitivity pixel corresponding element (W element) and the acquisition signal (RGB) of the low sensitivity pixel corresponding element (RGB element) The image processing unit 218 generates an image based on the above.
The image processing unit 218 generates an image based on both the signal (W) of the high sensitivity pixel corresponding element (W element) and the acquisition signal (RGB) of the low sensitivity pixel corresponding element (RGB element). In the signal processing described above with reference to FIG. 7, the RGBW signal is input and the luminance signal (W) and the color difference signals (RW) and (BW) are generated. On the other hand, the image processing unit 218 generates an image based only on the acquisition signal (RGB) of the low sensitivity pixel corresponding element (RGB element) without applying the signal (W) of the high sensitivity pixel corresponding element (W element). 7 is executed as a process in which only RGB is input and a signal (R + G + B) is applied instead of W in the configuration described with reference to FIG. That is, the luminance signal (W ′) and the color difference signals (R−W ′) and (B−W ′) are generated using R + G + B as the pseudo luminance signal W ′.
(2.2) Details of Evaluation Image Generation Processing A low-sensitivity pixel evaluation image WL based only on R, G, and B signals generated by the low-sensitivity pixel evaluation image generation unit 214 and a high-sensitivity pixel evaluation image generation unit 215 generate In order to enable accurate pixel value comparison with the high-sensitivity pixel evaluation image WH based only on the W signal, it is preferable to perform control according to the characteristics of the image sensor.
A specific evaluation image generation process will be described with reference to FIG. As described above, only the low-sensitivity pixel evaluation image WL based on only the R, G, and B signals generated by the low-sensitivity pixel evaluation image generation unit 214 and the W signal generated by the high-sensitivity pixel evaluation image generation unit 215 only. The comparison with the high-sensitivity pixel evaluation image WH based on is performed as a pixel value comparison process of each corresponding pixel. In this case, the pixel value of each pixel of the high-sensitivity pixel evaluation image WH is determined by the amount of incident light in the entire wavelength region of the visible light region.
FIG. 11A shows the spectral characteristics of the filter of the image sensor similar to that described above with reference to FIG. The characteristic of the filter corresponding to each element of RGBW is shown. W transmits the entire visible light region including the RGB wavelength region, and each of RGB transmits and receives the red, green, and blue wavelengths.
In order to accurately compare the evaluation image generated from only the W signal obtained by the light receiving element having such characteristics with the evaluation image including only the RGB signal, the evaluation image is adjusted. That is, a characteristic curve as shown in FIG. 11B: aR + bG + cB = WL is obtained, and an evaluation image consisting only of RGB is calculated based on this characteristic curve. a, b, and c are parameters as coefficients, which are determined according to the spectral characteristics of the image sensor. Specifically, parameters a, b, and c are calculated so that the difference between the WL line and the W line calculated by aR + bG + cB = WL is minimized. For this parameter calculation, for example, the least square method is applied.
A specific example of calculation processing of the parameters a, b, and c as coefficients will be described. Parameters: a, b, and c can be calculated by the following procedure. First, based on the spectral characteristics of R, G, and B, the intensity WL (λ) corresponding to each wavelength in the low-sensitivity pixel evaluation image is calculated by the following equation.
In the above formula, λ is a wavelength, and each of R (λ), G (λ), and B (λ) indicates the received light intensity of each RGB element at each wavelength (λ). here,
Error = W (λ) −WL (λ)
The coefficients a, b, and c are calculated so that the error is minimized.
It should be noted that the parameters: a, b, and c as coefficients differ in optimum values depending on the shooting environment, and it is preferable to apply different parameters depending on the shooting environment. That is, when the light source to be irradiated is different, such as sunlight, a fluorescent lamp, or an incandescent lamp, the optimal parameter changes because the wavelength component contained in the light source is different. Therefore, it is preferable to calculate or select a parameter according to such a light source.
FIG. 12 shows the configuration of the low sensitivity pixel evaluation image generation unit 214 that executes the selection of the parameters (a, b, c) based on the light source and generates the low sensitivity pixel evaluation image WL. FIG. 12 is a block diagram illustrating a detailed configuration example of the low-sensitivity pixel evaluation image generation unit 214 in the imaging apparatus described with reference to FIG. The low-sensitivity pixel evaluation image generation unit 214 includes a light source information input unit 251, a parameter selection unit 252, a parameter table 253, and an evaluation image generation unit 254.
The light source information input unit 251 inputs light source information of the shooting environment. Specifically, it is configured as an input unit by the user and inputs light source information such as sunlight, fluorescent light, incandescent light, and the like. Or it is good also as a structure which inputs light analysis information by a sensor and inputs light source analysis information, such as sunlight, a fluorescent lamp, and an incandescent lamp.
The parameter selection unit 252 selects parameters (a, b, c) as application coefficients for generating a low-sensitivity pixel evaluation image based on the light source information input from the light source information input unit 251. The parameter table 253 stored in the storage unit stores parameters corresponding to light sources such as sunlight, fluorescent light, and incandescent light. The parameter selection unit 252 receives light source information input from the light source information input unit 251. Are selected and input to the evaluation image generation unit 254.
The evaluation image generation unit 254 inputs an image based on the low-sensitivity pixel corresponding element (RGB element) and applies the parameter input from the parameter selection unit 252 to generate the evaluation image WL = aR + bG + cB. This generated evaluation image WL is input to the evaluation image comparison unit 216 in the imaging apparatus illustrated in FIG. 10, and the high sensitivity pixel evaluation image WH generated from the light reception data of the W element input from the high sensitivity pixel evaluation image generation unit 215. The comparison process is executed.
(2.3) Details of Evaluation Image Comparison Processing Next, details of evaluation image comparison processing in the evaluation image comparison unit 216 in the imaging apparatus shown in FIG. 10 will be described. As described above, the evaluation image comparison unit 216 generates the low sensitivity pixel evaluation image WL based only on the R, G, and B signals generated by the low sensitivity pixel evaluation image generation unit 214 and the high sensitivity pixel evaluation image generation unit 215. Comparison with the high-sensitivity pixel evaluation image WH based only on the W signal is performed.
The evaluation image comparison unit 216 performs a pixel value comparison of corresponding pixels of each image, and identifies a pixel region having a pixel value difference equal to or greater than a predetermined threshold. The evaluation image comparison unit 216 compares the two images of the low-sensitivity pixel evaluation image WL and the high-sensitivity pixel evaluation image WH, and performs processing using the two images based on the comparison result, It is determined whether or not to execute processing using only an image (low-sensitivity pixel-compatible element (RGB) -compatible image).
The pixel value comparison is executed as a pixel value comparison calculation process for the corresponding pixel of each evaluation image. The comparison calculation is executed by calculating a difference or a ratio between the corresponding pixels of the two images. Hereinafter, an example of the comparison calculation process using the difference will be described.
The evaluation image comparison unit 216 calculates the difference E of the corresponding pixels of each evaluation image based on the following formula.
E = X WL -X WH
X WL : Pixel value of the low-sensitivity pixel evaluation image WL X WH : Pixel value of the high-sensitivity pixel evaluation image WH
The evaluation image comparison unit 216 compares the absolute value | E | of the difference E calculated based on the above formula with a predetermined threshold TH.
｜ E ｜ ＞ TH
When the above formula is satisfied, that is, the pixel area whose absolute difference value is larger than the threshold value TH corresponds to, for example, a pixel portion in which the presence or absence of the moving subject described above with reference to FIG. 9 occurs between the two images. To do.
As described above, the evaluation image comparison unit 216 specifies a pixel region having a pixel value difference larger than a predetermined threshold based on the two evaluation images, and outputs the pixel region specification information to the image processing mode determination unit 217. . The image processing mode determination unit 217 determines an image processing mode in units of pixels based on the pixel area specifying information input from the evaluation image comparison unit 216, and controls the image processing unit 218 to optimize the pixel units. Perform image processing. Specifically, the image processing mode determination unit 217 has a low sensitivity without applying the signal (W) of the high sensitivity pixel corresponding element (W element) for a pixel region having a pixel value difference larger than a predetermined threshold. The image processing unit 218 generates an image based only on the acquisition signal (RGB) of the pixel corresponding element (RGB element). On the other hand, for a pixel region having a pixel value difference equal to or less than a predetermined threshold, both the signal (W) of the high sensitivity pixel corresponding element (W element) and the acquisition signal (RGB) of the low sensitivity pixel corresponding element (RGB element) The image processing unit 218 generates an image based on the above.
As a specific example of the threshold value TH applied in the evaluation image comparison unit 216, for example, assuming that each pixel value is 8 bits (256 gradations), TH = 10 gradations. That is, it is determined whether or not the difference between the pixel value [X WL ] of the low sensitivity pixel evaluation image WL and the pixel value [X WH ] of the corresponding pixel of the high sensitivity pixel evaluation image WH exceeds 10 gradations. When the difference exceeds 10 gradations, the pixel area is an area having a different image in each evaluation image, that is, a pixel in which the presence or absence of the moving subject described with reference to FIG. 9 occurs between the two images. Judged to correspond to the part (failure area).
However, in practice, since it is difficult to make the spectral characteristics of the low-sensitivity pixel evaluation image WL and the high-sensitivity pixel evaluation image WH exactly the same, the determination value needs to have a certain value. It is desirable to adjust the spectral characteristics so that they match. The image processing mode determination unit 217 determines an image processing mode in units of pixels based on the determination information input from the evaluation image comparison unit 216, and controls the image processing unit 218 to perform optimal image processing in units of pixels. Is executed. That is, it is determined for each pixel whether image generation is performed using information of both high-sensitivity pixels and low-sensitivity pixels, or image generation is performed using only one of the information. In the case of the present embodiment, since the low-sensitivity pixels have color information, image generation is executed using only the low-sensitivity pixels in the image area where the difference E is larger than the threshold value.
The pixel portion (failure area) in which the presence or absence of the moving subject described with reference to FIG. 9 occurs between two images is a pixel area having a pixel value difference larger than a predetermined threshold value, and corresponds to a high-sensitivity pixel. The image processing unit 218 generates an image based only on the acquisition signal (RGB) of the low-sensitivity pixel-compatible element (RGB element) without applying the element (W element) signal (W). On the other hand, the other image region, that is, a portion where a subject in which both images are common is photographed is a pixel region having a pixel value difference equal to or smaller than a predetermined threshold, and a signal (W element) signal ( The image processing unit 218 generates an image based on both the W) and the acquired signal (RGB) of the low-sensitivity pixel corresponding element (RGB element). Note that since the RGB sampling frequency seen from the filter array is lower than W, the resolution of the image based only on the acquisition signal (RGB) of the low-sensitivity pixel-compatible element (RGB element) is reduced. This is an area where the subject is originally moving, and resolution degradation is not noticeable.
The image processing unit 218 executes image generation processing corresponding to each pixel value difference in each pixel area, and synthesizes the finally generated generation data for each pixel to generate one image as an output image To do.
As described above, in the image processing unit 218, an image is obtained based on both the signal (W) of the high sensitivity pixel corresponding element (W element) and the acquisition signal (RGB) of the low sensitivity pixel corresponding element (RGB element). The processing to be generated is the signal processing described above with reference to FIG. 7, and the RGBW signal is input to generate a luminance signal (W) and color difference signals (RW) and (BW). On the other hand, the image processing unit 218 generates an image based only on the acquisition signal (RGB) of the low sensitivity pixel corresponding element (RGB element) without applying the signal (W) of the high sensitivity pixel corresponding element (W element). 7 is executed as a process in which only RGB is input and a signal (R + G + B) is applied instead of W in the configuration described with reference to FIG. That is, the luminance signal (W ′) and the color difference signals (R−W ′) and (B−W ′) are generated using R + G + B as the pseudo luminance signal W ′.
Thus, in the imaging apparatus of the present invention, an imaging element such as RGBW, that is, an imaging element having a low-sensitivity pixel corresponding element (RGB) and a high-sensitivity pixel corresponding element (W) is applied, and exposure of the low-sensitivity pixel corresponding element is performed. In a configuration in which shooting is performed with a long time set and a short exposure time set for a high sensitivity pixel-compatible element, an evaluation image composed of data of only a low-sensitivity pixel-compatible element (RGB) and a high-sensitivity pixel-compatible element (W) The pixel value comparison with the evaluation image consisting only of the data is executed, the image generation processing consisting of only one image is executed for the pixel portion having a large difference, and the two image is applied to the pixel portion having a small difference. Since the image is generated based on the above, a high-quality image that does not cause an error due to the difference in the moving subject region image due to the difference in exposure period as described above with reference to FIG. 9 is obtained. Door can be.
In the above-described embodiment, the high-sensitivity pixel corresponding element 203 is described as an element that receives all wavelengths of visible light. However, as described above, the element that receives invisible light regions such as visible light and infrared light. You may comprise as.
[3. Other Examples]
Next, a plurality of embodiments to which some changes are added will be described with the above-described imaging apparatus configuration of the present invention as a basic configuration.
(3.1) Control of Evaluation Image In the above-described imaging device configuration, a low-sensitivity pixel evaluation image WL based on only the R, G, and B signals generated by the low-sensitivity pixel evaluation image generation unit 214 and high-sensitivity pixel evaluation image generation In order to enable accurate pixel value comparison with the high-sensitivity pixel evaluation image WH based only on the W signal generated by the unit 215, it is preferable to perform control according to the characteristics of the image sensor. In the above-described embodiment, the processing example of determining the parameters a, b, and c as coefficients and generating the low-sensitivity pixel evaluation image WL = aR + bG + cB has been described.
However, the resolution of the high sensitivity pixel evaluation image WH based only on the W signal generated by the high sensitivity pixel evaluation image generation unit 215 and the low sensitivity based only on the R, G, and B signals generated by the low sensitivity pixel evaluation image generation unit 214. When compared with the resolution of the pixel evaluation image WL, the resolution of the high-sensitivity pixel evaluation image WH is higher. For this reason, the difference value tends to increase in the high frequency region of the image. That is, a large difference tends to occur between the two evaluation images at the edge portion of the subject.
This problem can be solved by generating an evaluation image from which high-frequency components are cut and performing comparison. An embodiment in which such high-frequency component cut processing is executed will be described. FIG. 13 is a diagram illustrating a configuration example of the imaging apparatus according to the present embodiment. An imaging device 280 illustrated in FIG. 13 includes, as a configuration unit similar to the imaging device 200 illustrated in FIG. 10 described above, an imaging device 201 having a combination configuration of a low-sensitivity pixel correspondence element 202 and a high-sensitivity pixel correspondence element 203, The image generation unit 281 includes a low-sensitivity pixel evaluation image generation unit 214, a high-sensitivity pixel evaluation image generation unit 215, an evaluation image comparison unit 216, an image processing mode determination unit 217, and an image processing unit 218. Furthermore, in the configuration of the present embodiment, the low-pass filter (LPF) 282 that performs high-frequency component cut of the evaluation image generated by the low-sensitivity pixel evaluation image generation unit 214 and the evaluation generated by the high-sensitivity pixel evaluation image generation unit 215. A low-pass filter (LPF) 283 that performs high-frequency component cutting of the image is included.
The evaluation image comparison unit 216 has a low-pass filter (LPF) 282 cut the high-frequency component for the low-sensitivity pixel evaluation image based only on the R, G, and B signals generated by the low-sensitivity pixel evaluation image generation unit 214. An evaluation image WH ′ in which a high-frequency component is cut by a low-pass filter (LPF) 283 with respect to the evaluation image WL ′ and the high-sensitivity pixel evaluation image based only on the W signal generated by the high-sensitivity pixel evaluation image generation unit 215 To perform image comparison. By this processing, it is possible to eliminate the tendency for a large difference between the two evaluation images at the edge portion of the subject, and it is possible to perform accurate image comparison. Note that, for example, a Gaussian filter can be applied as the low-pass filter, and the size (the number of taps) and the shape of the filter are optimized so that each frequency band is closer.
(3.2) Control of Image Processing Unit As described above, the evaluation image comparison unit 216 is a low-sensitivity pixel evaluation image WL based only on the R, G, and B signals generated by the low-sensitivity pixel evaluation image generation unit 214. And the high-sensitivity pixel evaluation image WH based only on the W signal generated by the high-sensitivity pixel evaluation image generation unit 215 is executed as a pixel value comparison of corresponding pixels of each image, and the image processing mode determination unit 217 Based on the pixel area specifying information input from the evaluation image comparison unit 216, an image processing mode for each pixel is determined, and the image processing unit 218 is controlled to perform optimal image processing for each pixel. Specifically, the image processing mode determination unit 217 has a low sensitivity without applying the signal (W) of the high sensitivity pixel corresponding element (W element) for a pixel region having a pixel value difference larger than a predetermined threshold. The image processing unit 218 generates an image based only on the acquisition signal (RGB) of the pixel corresponding element (RGB element). On the other hand, for a pixel region having a pixel value difference equal to or less than a predetermined threshold, both the signal (W) of the high sensitivity pixel corresponding element (W element) and the acquisition signal (RGB) of the low sensitivity pixel corresponding element (RGB element) The image processing unit 218 generates an image based on the above.
However, when such an evaluation is performed on a pixel-by-pixel basis and the image processing mode is determined and image processing is performed, depending on the situation of the moving subject, originally there are different subject portions in the two evaluation images. Despite the fact that the image is being taken, it may happen that the pixel value has no difference. In such a case, there is a possibility that a pixel area where correct image processing is not performed may occur. In order to prevent such an error, it is effective to use an area including a plurality of pixels as an image processing unit, instead of setting an image processing unit as a single pixel unit. As described above, the image processing mode determination unit 217 determines a processing mode using an area including a plurality of pixels as an image processing unit, and causes the image processing unit 218 to execute the processing mode.
An example of image processing mode determination in the image processing mode determination unit 217 will be described with reference to FIG. For example, as illustrated in FIG. 14, when a certain broken pixel 291, that is, a broken pixel 291 in which the difference between the low-sensitivity pixel evaluation image WL and the high-sensitivity pixel evaluation image WH is larger than a threshold value, the broken pixel is detected. A plurality of pixel regions 292 centering on 291 are set as regions for performing image processing in one image processing mode. That is, the image processing unit 218 generates an image based only on the acquisition signal (RGB) of the low sensitivity pixel corresponding element (RGB element) without applying the signal (W) of the high sensitivity pixel corresponding element (W element). To do. In the example shown in the figure, a 5 × 5 pixel area 292 centered on the broken pixel 291 is used as one image processing unit. By this process, it is possible to reduce the failure of the failed area.
(3.3) Evaluation Image Comparison Processing Range Control As described above, the evaluation image comparison unit 216 performs low sensitivity pixel evaluation based only on the R, G, and B signals generated by the low sensitivity pixel evaluation image generation unit 214. The comparison between the image WL and the high-sensitivity pixel evaluation image WH based only on the W signal generated by the high-sensitivity pixel evaluation image generation unit 215 is executed as a pixel value comparison of the corresponding pixels of the images.
In the processing example described above, the low-sensitivity pixel evaluation image WL is generated based on the interpolation image generated by executing the demosaic processing described above with reference to FIG. 8, that is, the interpolation processing using the output data of the low-sensitivity pixel corresponding element. Similarly, the high-sensitivity pixel evaluation image WH is generated based on the interpolation image, and the evaluation between these images is executed. Hereinafter, a comparison processing configuration based on an image before executing such interpolation processing will be described.
An example of image comparison processing by the evaluation image comparison unit 216 will be described with reference to FIG. FIG. 15 is an output of an image sensor having an RGBW element configuration, and is data before interpolation processing corresponding to each RGBW signal, that is, data before demosaic processing. The evaluation image comparison unit 216 inputs the data before the interpolation processing from the image sensor, and sets a pixel area including all RGBW signals, for example, a 4 × 4 pixel area as the evaluation unit area 293 as shown in the figure. Perform the comparison.
The evaluation image comparison unit 216 selects a 4 × 4 pixel region,
Average value of R,
Average value of G,
Average value of B,
Each of these average values is calculated, and based on these average values, an average value of WL in a 4 × 4 pixel region is calculated. Further, an average value of W in the 4 × 4 pixel region is calculated. A difference is calculated from the calculated average value WL and the average value W, and a comparison with a predetermined threshold (TH) is performed. The comparison process is performed in this unit, but thereafter, the target area may be moved at a pitch of one pixel, and various processing modes such as comparison is performed by moving at a pitch of this area (vertical and horizontal pixels). Is possible.
For an area having a pixel value difference larger than a predetermined threshold, only the acquisition signal (RGB) of the low sensitivity pixel corresponding element (RGB element) is applied without applying the signal (W) of the high sensitivity pixel corresponding element (W element). The image processing unit 218 generates an image based on the above. On the other hand, for a pixel region having a pixel value difference equal to or less than a predetermined threshold, both the signal (W) of the high sensitivity pixel corresponding element (W element) and the acquisition signal (RGB) of the low sensitivity pixel corresponding element (RGB element) The image processing unit 218 generates an image based on the above. In this process, the image processing unit is not divided into one pixel unit, but is divided into a plurality of pixel areas such as 4 × 4 pixels.
(3.4) Optimal control according to pixel value difference In the above-described processing example, the pixel value difference between one threshold value (TH) and two evaluation images is compared, and a pixel value difference larger than a predetermined threshold value is determined. For the pixel region having, an image based only on the acquisition signal (RGB) of the low sensitivity pixel corresponding element (RGB element) is generated without applying the signal (W) of the high sensitivity pixel corresponding element (W element), The pixel region having a pixel value difference equal to or less than a predetermined threshold is based on both the signal (W) of the high sensitivity pixel corresponding element (W element) and the acquisition signal (RGB) of the low sensitivity pixel corresponding element (RGB element). An image is generated, and two image processing modes are selectively applied.
Hereinafter, the processing example to be described does not select such two image processing modes, but executes three or more stages of different image processing according to the value of the pixel value difference between the two evaluation images. It is an example.
X WL : Pixel value of the low-sensitivity pixel evaluation image WL X WH : Pixel value of the high-sensitivity pixel evaluation image WH This process is the same as the process example described above.
The evaluation image comparison unit 216 compares the absolute value | E | of the difference E calculated based on the above formula with a plurality of predetermined thresholds TH1 to THn. Based on the absolute value | E | Thus, a plurality of processing modes are determined.
0 ≦ | E | <TH1: Low sensitivity: High sensitivity = 0: 10
TH1 ≦ | E | <TH2: Low sensitivity: High sensitivity = 3: 7
TH2 ≦ | E | <TH3: Low sensitivity: High sensitivity = 5: 5
TH3 ≦ | E | <TH4: Low sensitivity: High sensitivity = 7: 3
TH4 ≦ | E |: Low sensitivity: High sensitivity = 10: 0
That is, in the region where the absolute value | E | of the difference E between the two evaluation images is 0 or more and less than TH1, an image consisting only of the data of the high sensitivity pixel corresponding element is generated, and the absolute value | E | is TH1 or more and less than TH2. Is generated with the use ratio of the data of the low-sensitivity pixel corresponding element and the data of the high-sensitivity pixel corresponding element being 3: 7, and the area where the absolute value | E | is less than TH2 is less than TH2 An image is generated with the use ratio of the data of the sensitive pixel corresponding element and the data of the highly sensitive pixel corresponding element being 5: 5, and the region where the absolute value | E | is between TH3 and less than TH4 is the data of the low sensitivity pixel corresponding element. Is set to 7: 3, and an area where the absolute value | E | is equal to or greater than TH4 is to generate an image only from the data of the low-sensitivity pixel corresponding element. It is.
As a specific example of the threshold value TH applied in the evaluation image comparison unit 216, for example, assuming that each pixel value is 8 bits (256 gradations), TH1 = 10 gradations, TH 2 = 20 gradations, TH 3 = 30 gradations, TH 4 = 40 gradations.
For this region, the W signal utilization ratio in the configuration described with reference to FIG. 7 is obtained, the signal (W) of the high sensitivity pixel corresponding element (W element) is 7, and the low sensitivity pixel corresponding element (RGB element) is acquired. The process is executed with a distribution in which the pseudo signal luminance signal W ′ = R + G + B generated from the signal (RGB) is set to 3.
In this way, instead of the choice of whether or not to use either pixel information, as an intermediate between them, by defining what percentage (weight) to use and generating an image, The boundary of the still area can be a natural image.
The series of processing described in the specification can be executed by hardware, software, or a combined configuration of both. When executing processing by software, the program recording the processing sequence is installed in a memory in a computer incorporated in dedicated hardware and executed, or the program is executed on a general-purpose computer capable of executing various processing. It can be installed and run.
As described above, according to the configuration of the present invention, an image sensor such as RGBW, that is, an image sensor having a low-sensitivity pixel corresponding element (RGB) and a high-sensitivity pixel corresponding element (W) is applied, and a low-sensitivity pixel is applied. In a configuration that executes shooting with a long exposure time for the corresponding element and a short exposure time for the high-sensitivity pixel-compatible element, the evaluation image consists of only data for the low-sensitivity pixel-compatible element (RGB) and high-sensitivity pixel support. The pixel value comparison with the evaluation image consisting of data of only the element (W) is executed, the image generation processing consisting of only one image is executed for the pixel portion having a large difference, and the pixel portion having a small difference is calculated. Since an image based on the two images is generated, a high-quality image can be generated in which no error due to the difference between the moving subject region images due to the difference in exposure period occurs.
It is a figure explaining the example of the Bayer arrangement as a color arrangement used with a general color filter. It is a figure which shows the structure of the imaging device which comprises the solid-state image sensor of a single plate color system. It is a figure explaining a demosaic process. It is a figure explaining the example of arrangement composition of the image sensor applied in the present invention. It is a figure explaining the spectral characteristic of the image sensor applied in this invention. It is a figure explaining the example of arrangement composition of the image sensor applied in the present invention. It is a figure explaining the example of an image signal processing structure. It is a figure explaining the mosaic image and demosaic image produced | generated in the process of this invention. It is a figure explaining the phenomenon based on the difference in an exposure period. It is a figure explaining the structural example of the imaging device which concerns on one Example of this invention. It is a figure explaining the production | generation process of the evaluation image applied in this invention. It is a figure explaining the structural example of the low sensitivity pixel corresponding | compatible element body Europe and Asia evaluation image generation part of the imaging device which concerns on one Example of this invention. It is a figure explaining the structural example of the imaging device which concerns on one Example of this invention. It is a figure explaining the image processing execution aspect in the imaging device which concerns on one Example of this invention. It is a figure explaining the example of an image comparison process structure in the imaging device which concerns on one Example of this invention.
DESCRIPTION OF SYMBOLS 11 Optical lens 12 Color filter 13 Solid-state image sensor 14 Camera signal processing part 15 Image compression part 16 Recording part 20 Output image of a solid-state image sensor 21 Demosaic processing part 22 R, G, B signal which a demosaic processing part outputs 101 Imaging element ( CCD)
DESCRIPTION OF SYMBOLS 102 AD conversion part 111-116 Low pass filter 117 Matrix calculating part 151-154 Demosaic image 200 Imaging device 201 Imaging element 202 Low sensitivity pixel corresponding element 203 High sensitivity pixel corresponding element 205 Exposure control part 210 Image generation part 214 Low sensitivity pixel evaluation image Generation unit 215 High sensitivity pixel evaluation image generation unit 216 Evaluation image comparison unit 217 Image processing mode determination unit 218 Image processing unit 251 Light source information input unit 252 Parameter selection unit 253 Parameter table 254 Evaluation image generation unit 280 Imaging device 281 Image generation unit 282 , 283 Low-pass filter 291 Broken pixel 292 Pixel area 293 Pixel area
An exposure control unit that independently controls an exposure period of the high-sensitivity pixel-compatible element and the low-sensitivity pixel-compatible element in the image sensor in the imaging process of one image frame ;
A comparison process between a high-sensitivity pixel evaluation image based on output data of the high-sensitivity pixel corresponding element and a low-sensitivity pixel evaluation image based on output data of the low-sensitivity pixel corresponding element is executed, and corresponding pixels of the two evaluation images A configuration in which a pixel area determined to have a small difference between corresponding pixels based on a pixel value difference or a pixel value ratio is separated from a pixel area determined to have a large difference, and different image processing is executed in each pixel area An imaging device characterized by being:
For a pixel region that is determined to have a small difference between corresponding pixels in the two evaluation images, image processing is performed using both the output data of the high sensitivity pixel corresponding element and the output data of the low sensitivity pixel corresponding element. For pixel regions determined to have a large difference, a process of generating an image by executing image processing based on only one of the output data of the high-sensitivity pixel corresponding element or the output data of the low-sensitivity pixel corresponding element. The imaging apparatus according to claim 1, wherein the imaging apparatus is configured to execute the following.
It consists of a low-sensitivity pixel corresponding element that receives light in each specific wavelength region of RGB and a high-sensitivity pixel corresponding element that receives light in the visible light region,
The low-sensitivity pixel evaluation image generated based on the output data of the RGB-compatible low-sensitivity pixel-compatible element is WL, and the high-sensitivity pixel evaluation image generated based on the output data of the high-sensitivity pixel-compatible element compatible with visible light is WH. A calculation formula applying parameters a, b, and c as coefficients,
2. A configuration in which a low-sensitivity pixel evaluation image WL is generated based on the configuration, and a process of executing the process of determining the parameters a, b, and c according to characteristics of an image sensor. The imaging device described in 1.
The imaging apparatus according to claim 3, wherein different values are applied to the parameters according to light sources.
Comparing the absolute difference value | E | between the high-sensitivity pixel evaluation image and the corresponding pixel of the low-sensitivity pixel evaluation image with a predetermined threshold value, and a pixel area having a difference exceeding the threshold value and pixels below the threshold value The imaging apparatus according to claim 1, wherein the imaging apparatus is configured to execute different image processing for each region.
The difference absolute value | E | between the high-sensitivity pixel evaluation image and the corresponding pixel of the low-sensitivity pixel evaluation image is compared with a plurality of predetermined threshold values, and a difference amount defined by the plurality of threshold values is obtained. The image pickup apparatus according to claim 1, wherein the image pickup apparatus is configured to execute different image processing according to the response.
As different image processing according to the difference amount defined by the plurality of threshold values,
The imaging apparatus according to claim 6, wherein the imaging apparatus is configured to execute image processing in which a utilization ratio between output data of the high sensitivity pixel corresponding element and output data of the low sensitivity pixel corresponding element is changed.
The imaging apparatus according to claim 1, wherein in the comparison process between the high-sensitivity pixel evaluation image and the low-sensitivity pixel evaluation image, an evaluation image in which a high-frequency component is cut is generated and compared.
Image processing based on only one of the output data of the high-sensitivity pixel corresponding element or the output data of the low-sensitivity pixel corresponding element for the pixel having a large difference between the corresponding pixels in the two evaluation images and the surrounding pixel region of the pixel The imaging apparatus according to claim 1, wherein the processing for generating an image by executing is executed.
2. The imaging according to claim 1, wherein in the comparison process between the high-sensitivity pixel evaluation image and the low-sensitivity pixel evaluation image, a comparison process to which data before an interpolation process is applied is executed. apparatus.
The imaging device according to any one of claims 1 to 10, wherein the high-sensitivity pixel corresponding element constituting the imaging element is an element that receives invisible light such as a visible light region and infrared light.
And high-sensitivity pixels corresponding element for receiving a relatively large amount of light, a relatively small amount of light applied to the image pickup element composed of a low-sensitivity pixels corresponding device for receiving, in the photographing processing of one image frame, high sensitivity Inputting an output signal of an image sensor, which is captured by independently controlling the exposure period of the pixel-corresponding element and the low-sensitivity pixel-corresponding element, to the image generation unit;
Under the control of the control unit, to apply the high-sensitivity pixel corresponding element for receiving a relatively large amount of light, the image pickup element composed of a low-sensitivity pixels corresponding element for receiving relatively small amount of light, one image frame In the imaging process, the step of causing the image generation unit to input an output signal of the imaging element that is captured by independently controlling the exposure period of the high sensitivity pixel corresponding element and the low sensitivity pixel corresponding element;
JP2006134700A 2006-05-15 2006-05-15 Imaging apparatus, image processing method, and computer program Expired - Fee Related JP5011814B2 (en)
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US11/747,129 US7839437B2 (en) 2006-05-15 2007-05-10 Image pickup apparatus, image processing method, and computer program capable of obtaining high-quality image data by controlling imbalance among sensitivities of light-receiving devices
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