JP4150599B2 - Digital camera with exposure compensation - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a digital camera equipped with a solid-state imaging device having both low-sensitivity pixels and high-sensitivity pixels, and more particularly to a digital camera with an exposure correction function that allows a user to manually perform exposure correction.
[0002]
[Prior art]
In digital cameras such as digital still cameras and digital video cameras, the saturation amount of charge accumulated in the photodiodes that make up each pixel of the solid-state image sensor decreases as the number of pixels increases, that is, the photodiodes become smaller. Has a drawback that the dynamic range becomes narrow.
[0003]
In order to overcome this drawback, for example, in the prior art described in Japanese Patent Application Laid-Open No. 2001-8104, a high-sensitivity pixel obtained from a high-sensitivity pixel by providing two types of pixels, a high-sensitivity pixel and a low-sensitivity pixel, in a solid-state imaging device. The dynamic range of the subject image is expanded by combining image data and low-sensitivity image data obtained from low-sensitivity pixels.
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 2001-8104
[Problems to be solved by the invention]
The silver halide film camera is generally equipped with an exposure correction function, and the user can manually set an exposure correction value when shooting a subject. For this reason, it has become common for digital cameras to be equipped with an exposure correction function.
[0006]
However, a solid-state image sensor of a digital camera that is currently popular in the market does not have two types of pixels, a low-sensitivity pixel and a high-sensitivity pixel, and has only the same sensitivity. For this reason, the conventional exposure correction function installed in the digital camera is not premised on combining high-sensitivity image data and low-sensitivity image data, and the above-described conventional technique also uses the exposure correction value set by the user. It is not taken into consideration how to be reflected on the composite image.
[0007]
An object of the present invention is to reflect an exposure correction value set by a user on a synthesized image when synthesizing high-sensitivity image data obtained from high-sensitivity pixels and low-sensitivity image data obtained from low-sensitivity pixels. An object is to provide a digital camera with an exposure compensation function.
[0008]
[Means for Solving the Problems]
A digital camera with an exposure correction function that achieves the above object includes a solid-state imaging device having high-sensitivity pixels and low-sensitivity pixels, an exposure correction value input unit, and an exposure amount based on the exposure correction value input by the input unit With an exposure correction function comprising: image combining means for generating combined image data by combining high-sensitivity image data captured by the high-sensitivity pixel and low-sensitivity image data captured by the low-sensitivity pixel In digital cameras,
The image composition means obtains the composite image data (data) as a value obtained by multiplying the first value by the second value,
When the high-sensitivity image data (high) exceeds a threshold (th) , a value obtained by adding the low-sensitivity image data (low) to the high-sensitivity image data (high) as it is is the first value,
When the high-sensitivity image data (high) does not reach the threshold (th) , a value obtained by multiplying the ratio of the high-sensitivity image data (high) to the threshold (th) by the low-sensitivity image data (low) And the value obtained by adding the high-sensitivity image data (high) as the first value,
The second value is a value (-k × high / th) obtained by multiplying the high-sensitivity image data (high) by a coefficient (−k) and dividing by the threshold (th) according to the scene ( a value obtained by adding α) (-k × high / th + α), either larger of the gain value (p) for the entire composite image,
The exposure correction is performed by changing the gain value (p) and the threshold value (th) , thereby changing the dynamic range of the composite image.
[0009]
With this configuration, exposure correction intended by the user can be reflected in the composite image.
[0010]
The image synthesizing means of the digital camera with an exposure correction function according to the present invention has a wide dynamic range of the synthesized image when the exposure correction value is an overexposure correction, and the synthesis when the exposure correction value is an underexposure correction. It is characterized by narrowing the dynamic range of the image.
[0011]
With this configuration, when the user sets overexposure, it is possible to obtain an overall bright image while maintaining the highlight details, and when the user sets underexposure, the overall image is darkened. It is possible to use gradation effectively.
[0014]
When the exposure correction value is an overexposure correction, the image synthesizing unit of the digital camera with an exposure correction function according to the present invention reduces the ratio of the high-sensitivity image data and increases the ratio of the low-sensitivity image data. When the dynamic range of the composite image is widened and the exposure correction value is under-exposure correction, the dynamic range of the composite image is narrowed by increasing the ratio of the high-sensitivity image data and decreasing the ratio of the low-sensitivity image data. It is characterized by doing.
[0015]
With this configuration, it is possible to easily and reliably reflect the exposure correction intended by the user in the composite image.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[0017]
FIG. 1 is a configuration diagram of a digital still camera according to an embodiment of the present invention. In this embodiment, a digital still camera will be described as an example. However, the present invention can also be applied to other types of digital cameras such as a camera mounted on a small electronic device such as a digital video camera or a mobile phone.
[0018]
The digital still camera shown in FIG. 1 includes a photographic lens 10, a solid-state image sensor 11, a diaphragm 12 provided between them, an infrared cut filter 13, and an optical low-pass filter 14. The CPU 15 that controls the entire digital still camera controls the light emitting unit 16 and the light receiving unit 17 for flash, controls the lens driving unit 18 to adjust the position of the photographing lens 10 to the focus position, and stops the aperture driving unit. The opening amount of the diaphragm 12 is controlled via 19 to adjust the exposure amount to an appropriate exposure amount.
[0019]
Further, the CPU 15 drives the solid-state image sensor 11 via the image sensor driving unit 20 and outputs the subject image captured through the photographing lens 10 as a color signal. In addition, a user instruction signal is input to the CPU 15 through the operation unit 21 serving as an input unit, and the CPU 15 performs various controls according to the instruction.
[0020]
The electric control system of the digital still camera includes an analog signal processing unit 22 connected to the output of the solid-state imaging device 11, and an A / D conversion that converts RGB color signals output from the analog signal processing unit 22 into digital signals. The circuit 23 is provided and these are controlled by the CPU 15.
[0021]
Further, the electric control system of this digital still camera includes a memory control unit 25 connected to the main memory 24, a digital signal processing unit 26 described later in detail, and compresses the captured image into a JPEG image and decompresses the compressed image. Mounted on the back side of the camera, the compression / decompression processing unit 27, the integration unit 28 for integrating the photometric data and adjusting the white balance gain, the external memory control unit 30 to which the removable recording medium 29 is connected. And a display control unit 32 to which the liquid crystal display unit 31 is connected. These are connected to each other by a control bus 33 and a data bus 34, and are controlled by a command from the CPU 15.
[0022]
In such a digital still camera, when the user performs exposure correction when shooting a subject image, the operation unit 21 is operated to call up an exposure correction menu and display it on the liquid crystal display unit 31. A predetermined exposure correction value, for example, +0.3 EV, +0.6 EV,..., −0.3 EV, −0.6 EV,.
[0023]
The digital signal processing unit 26, the analog signal processing unit 22, the A / D conversion circuit 23, and the like shown in FIG. 1 can be mounted on a digital still camera as separate circuits. 11 is manufactured on the same semiconductor substrate using LSI manufacturing technology, and it is preferable to form one solid-state imaging device.
[0024]
FIG. 2 is a pixel arrangement diagram of the solid-state imaging device 11 used in the present embodiment. The pixel 1 in the CCD portion that captures an image with a wide dynamic range has a pixel arrangement described in, for example, Japanese Patent Laid-Open No. 10-136391, and each pixel in the odd row is horizontally aligned with each pixel in the even row. A vertical transfer path (not shown) that is arranged with a ½ pitch shift and transfers signal charges read from each pixel in the vertical direction is meandered so as to avoid each pixel in the vertical direction. ing.
[0025]
In the illustrated example, each pixel 1 according to the present embodiment includes a low-sensitivity pixel (sub-pixel) 2 that occupies about 1/5 of the area of the pixel 1 and a high-sensitivity pixel (subpixel) that occupies the remaining about 4/5. Main signal) 3 so that the signal charge of each low-sensitivity pixel 2 and the signal charge of each high-sensitivity pixel 3 can be distinguished and transferred to the vertical transfer path. . It should be noted that the ratio and the position at which the pixel 1 is divided are determined by design, and FIG. 2 is merely an example.
[0026]
The solid-state imaging device 11 has been described by taking a CCD having a honeycomb pixel arrangement as shown in FIG. 2 as an example, but may be a Bayer CCD or a CMOS sensor.
[0027]
FIG. 3 is a processing configuration diagram of the digital signal processing unit 26. The digital signal processing unit 26 employs a logarithmic addition method in which high-sensitivity image data and low-sensitivity image data are each subjected to gamma correction and then subjected to addition processing, and the high-sensitivity image output from the A / D conversion circuit 23 is used. An offset correction circuit 41a that takes an RGB color signal that is a digital signal and performs an offset process, a gain correction circuit 42a that white balances an output signal of the offset correction circuit 41a, and a gamma correction for the color signal after gain correction. A gamma correction circuit 43a for performing, an offset correction circuit 41b for performing an offset process by taking in RGB color signals which are digital signals of low-sensitivity images output from the A / D conversion circuit 23 shown in FIG. 1, and an offset correction circuit 41b The gain correction circuit 42b for white balance of the output signal and the color signal after gain correction And a gamma correction circuit 43b for performing gamma correction. When linear matrix processing or the like is performed on the signal after offset correction, it is performed between the gain correction circuits 42a and 42b and the gamma correction circuits 43a and 43b.
[0028]
The digital signal processing unit 26 further interpolates the RGB color signal after the image composition by performing an image composition process by taking both output signals of each of the gamma correction circuits 43a and 43b and performing image composition processing. Reduces noise from the RGB interpolation calculation unit 45 for obtaining RGB three-color signals, the RGB / YC conversion circuit 46 for obtaining the luminance signal Y and the color difference signals Cr and Cb from the RGB signal, and the luminance signal Y and the color difference signals Cr and Cb. A noise filter 47, a contour correction circuit 48 that performs contour correction on the luminance signal Y after noise reduction, and a color difference matrix circuit 49 that performs color correction by multiplying the color difference signals Cr and Cb by the color difference matrix. Prepare.
[0029]
The above-described image composition processing circuit 44 synthesizes the high-sensitivity image data output from the gamma correction circuit 43a and the low-sensitivity image data output from the gamma correction circuit 43b in units of pixels based on the following equation 1. Output.
[0030]
[Expression 1]
data = [high + MIN (high / th, 1) × low] × MAX [(− k × high / th) + α, p]
Where: high: Data after gamma correction of high sensitivity (high output) image signal
low: Data after gamma correction of low sensitivity (low output) image signal p: total gain
k: coefficient
th: threshold α: value determined by the scene (≈1)
It is. Note that α = 1 may be fixed.
[0031]
If the data after gamma correction is 8-bit data (256 gradations), the threshold value th is designated by, for example, “219” from the value 0 to 255 and the user of the digital still camera or the designer of the digital still camera. The value to be
[0032]
FIG. 4 is a graph showing how the MIN (high / th, 1) in Equation 1 changes. As shown in FIG. 4, the first term of the equation 1 adds the low-sensitivity image data low as it is to the high-sensitivity image data high when the high-sensitivity image data high exceeds the threshold th, When high does not reach the threshold th, it indicates that a value obtained by multiplying the ratio of the high sensitivity image data high to the threshold th by the low sensitivity image data low is added to the high sensitivity image data high.
[0033]
In the present embodiment, the added data obtained in the first term is not used as composite image data as it is, but the second term (MAX [(− k × high / th) + α, p]) is added to the first term. A value obtained by multiplying is used as composite image data. FIG. 5 is a diagram showing the change when MAX = (− k × high / th) + α, p] and k = 0.2.
[0034]
In the second term, the coefficient “k” is preferably a value “0.2” in the solid-state imaging device 11 of the embodiment shown in FIG. When the signal charge saturation ratios of the high-sensitivity pixel 3 and the low-sensitivity pixel 2 are different as in the solid-state imaging device 11 shown in FIG. 2, the coefficient k can be obtained conveniently by the following equation (2).
[0035]
[Expression 2]
Coefficient k = 1−Sh / (Sh + Sl)
Here, Sh: signal charge saturation amount of high sensitivity pixel Sl: signal charge saturation amount of low sensitivity pixel
In the example shown in FIG. 2, the area ratio of the photodiode does not become the saturation ratio as it is, but it can be regarded as an area ratio for convenience, and when the above example is applied,
k = 1-4 / (4 + 1) = 1-0.8
= 0.2
It becomes.
[0037]
The solid-state imaging device having both high-sensitivity pixels and low-sensitivity pixels is not limited to that illustrated in FIG. 2, and for example, as shown in FIG. 6, a large number of photodiodes (not shown) formed in the same size and shape. It is conceivable to change the aperture area of the microlens provided on top of the above and provide the high sensitivity pixel 3 and the low sensitivity pixel 2. In this case, the saturation amount of the signal charge of the high-sensitivity pixel and the low-sensitivity pixel is the same, and thus Equation 2 cannot be applied. Equation 1 can be applied by obtaining the coefficient value. The value of the coefficient k is a value that is determined by the configuration of the solid-state imaging device, and is not arbitrarily changed by the user, but is set to a fixed value when the imaging apparatus is shipped.
[0038]
In Equation 1, an experimentally determined value is used as the value of the total gain p in this embodiment. p is a gain for the entire composite image data, and the dynamic range of the image can be controlled by controlling the value of p.
[0039]
The parameter value of p is variable, but the lower limit value pmin is also determined by the following equation (3).
[0040]
[Equation 3]
pmin = Sh / (Sh + Sl)
[0041]
For digital cameras that have a maximum final output when the high-sensitivity image data is output at the maximum value, the high-sensitivity image data is set so that the combined value of the high-sensitivity image data and the low-sensitivity image data becomes the maximum value. And gain operation is required for low-sensitivity image data. That is, when high-sensitivity image data and low-sensitivity image data corresponding to the saturation amount are output from the solid-state imaging device, the output value is multiplied by a gain corresponding to pmin (<1), and the final output value becomes the maximum value. Therefore, it is necessary to convert the image data.
[0042]
For example, when the saturation ratio of the high sensitivity pixel and the low sensitivity pixel is 4: 1, pmin = 4 / (4 + 1) = 0.8
Therefore, p = pmin may be set for a high-contrast shooting scene, and the total gain p is set to a value larger than pmin for a shooting scene with low contrast.
[0043]
The smaller the total gain p value, the wider the dynamic range, and the larger the value, the narrower the dynamic range. Specifically, in a high-contrast shooting scene (such as midsummer clear sky), p = 0.8, p = 0.86 in cloudy or shaded, p = 0.9 under indoor fluorescent lamp, and so on. The value of p is changed according to. Thereby, when the data after gamma correction is 8-bit data, the 8-bit gradation value can be used more effectively.
[0044]
Even if the user sets the value of p by specifying the type of scene using the operation unit 21 shown in FIG. 1, the digital still camera itself can change the scene of the captured image based on the detection values of various sensors. Automatic determination and automatic setting may be used. For example, the white balance gain amount is obtained from the integrated value of the photometric data obtained by the integrating unit 28. Since the scene can be automatically determined from the white balance value, the value of p can be automatically set. .
[0045]
FIG. 7 is a diagram showing how the dynamic range changes when the value of p is changed. When the total gain p is increased, the characteristic line a has a small dynamic range, and when the total gain p is decreased, the characteristic line a changes to a characteristic line B having a large dynamic range.
[0046]
As described above, in this embodiment, since the high-sensitivity image data and the low-sensitivity image data are added and then multiplied by the total gain according to the shooting scene, it is possible to generate an image with a wide dynamic range with white balance. . In addition, since the logarithmic addition method is employed to combine the images after reducing the number of bits of the high-sensitivity image data and the low-sensitivity image data, the circuit scale can be reduced and the cost can be reduced.
[0047]
Next, a case where the user designates an exposure correction value from the operation unit 21 when photographing a subject image will be described. For example, when the user corrects the exposure amount plus and sets it to overexposure, high-sensitivity pixels that originally hit the bright part of the image are likely to be saturated. Therefore, when synthesizing processing, spread dynamic range, while maintaining highlight detail, brighter overall.
[0048]
Further, when the user corrects the exposure amount minus and sets the underexposure, the image becomes dark overall and the contrast is lowered. In this case, it is possible to effectively use the gradation of the output image by reducing the dynamic range during the synthesis process.
[0049]
As described above, it is possible to reflect the exposure correction intended by the user in the composite image by controlling the width of the dynamic range in accordance with the exposure correction of the user. In the present embodiment, the control is performed by changing the value of the total gain p, which is the above-described parameter of Equation 1, and the value of the threshold value th. Specifically, these values are determined by the following equation (4).
[0050]
[Expression 4]
p = p0−kp × ΔEV
th = th0−kth × ΔEV
Here, p0, th0: values used at the proper exposure determined by the camera kp, kth: coefficient (both> 0)
ΔEV: Exposure compensation value
As can be seen from Equation 4, when the user corrects the exposure value to +0.3 EV, for example, to overexposure and ΔEV = + 0.3 EV, both the p value and the th value become small. For this reason, in the calculation of Equation 1 in the synthesis process, the ratio of high-sensitivity image data is small, the ratio of low-sensitivity image data is large, and the dynamic range is expanded.
[0052]
Further, when the user corrects the exposure value to minus 0.6 EV, for example, and underexposure, ΔEV = −0.6 EV, and the p value and the th value become large. For this reason, in the composition process, the ratio of high-sensitivity image data is large, the ratio of low-sensitivity image data is small, and the dynamic range of the composite image is narrowed.
[0053]
As described above, according to the present embodiment, when the user manually corrects exposure, the ratio of the image composition is changed according to the exposure correction value to change the width of the dynamic range of the composite image. The exposure correction intended by the user can be realized on the composite image.
[0054]
【The invention's effect】
According to the present invention, since the dynamic range of the composite image is controlled according to the exposure correction value of the user, the exposure correction intended by the user can be reflected in the composite image.
[Brief description of the drawings]
FIG. 1 is a block diagram of a digital still camera according to an embodiment of the present invention.
FIG. 2 is a schematic surface view of the solid-state imaging device shown in FIG.
FIG. 3 is a processing configuration diagram of a digital signal processing unit shown in FIG. 1;
FIG. 4 is an explanatory diagram of mathematical expressions that are arithmetically processed in a composite image output mode according to an embodiment of the present invention.
FIG. 5 is an explanatory diagram of mathematical expressions that are arithmetically processed in a composite image output mode according to an embodiment of the present invention.
FIG. 6 is a pixel arrangement diagram according to another embodiment of the solid-state imaging device.
FIG. 7 is a diagram illustrating how a dynamic range changes.
[Explanation of symbols]
1 pixel 2 low sensitivity pixel (sub pixel)
3 High sensitivity pixels (main pixels)
10 Lens 11 Solid-state imaging device 15 CPU
21 Operation unit 23 A / D converter 26 Digital signal processing unit 29 Recording medium 44 Image composition processing circuit

Claims (3)

A solid-state image pickup device having a high-sensitivity pixel and a low-sensitivity pixel, an exposure correction value input unit, and a high image captured by the high-sensitivity pixel under an exposure amount based on the exposure correction value input by the input unit In a digital camera with an exposure correction function, comprising image combining means for combining the sensitivity image data and the low sensitivity image data captured by the low sensitivity pixels to generate composite image data,
When the image composition means obtains the composite image data (data) as a value obtained by multiplying the first value by the second value,
When the high-sensitivity image data (high) exceeds a threshold (th) , a value obtained by adding the low-sensitivity image data (low) to the high-sensitivity image data (high) as it is is the first value,
When the high-sensitivity image data (high) does not reach the threshold (th) , a value obtained by multiplying the ratio of the high-sensitivity image data (high) to the threshold (th) by the low-sensitivity image data (low) And the value obtained by adding the high-sensitivity image data (high) as the first value,
The second value is a value (-k × high / th) obtained by multiplying the high-sensitivity image data (high) by a coefficient (−k) and dividing by the threshold (th) according to the scene ( a value obtained by adding α) (-k × high / th + α), either larger of the gain value (p) for the entire composite image,
A digital camera with an exposure correction function , wherein the exposure correction is performed by changing the gain value (p) and the threshold value (th) to change the dynamic range of the composite image.   The image composition means widens the dynamic range of the composite image when the exposure correction value is overexposure correction, and narrows the dynamic range of the composite image when the exposure correction value is underexposure correction. The digital camera with an exposure correction function according to claim 1.   When the exposure correction value is overexposure correction, the image composition means widens the dynamic range of the composite image by reducing the ratio of the high-sensitivity image data and increasing the ratio of the low-sensitivity image data. 3. The dynamic range of the composite image is narrowed by increasing the ratio of the high-sensitivity image data and decreasing the ratio of the low-sensitivity image data when the correction value is underexposure correction. Digital camera with exposure compensation function as described.

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