JP3569352B2 - White balance adjustment device - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to an electronic still camera, and more particularly to an improvement in a device for performing white balance adjustment.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in an electronic still camera, white balance adjustment is performed so that a white subject is photographed white regardless of the color temperature of illumination light. For example, when the color temperature of the illuminating light is high, the coefficient multiplied by the color difference signal Cb including the B signal is determined to be smaller than the coefficient multiplied by the color difference signal Cr including the R signal. The sensitivity is suppressed, and the subject image is prevented from becoming bluish.
[0003]
[Problems to be solved by the invention]
When performing flash photography, since the flash light travels at a limited distance, the color temperature of the subject relatively close to the camera body is close to that of the flash light, and the color temperature of the subject relatively far from the camera body is the external temperature. Close to that. Therefore, if white balance adjustment is performed based on the color temperature of the strobe light, white balance adjustment cannot be performed for a distant subject. Conversely, if white balance adjustment is performed based on the color temperature of external light, a white balance adjustment can be performed for a short-distance subject. There is a problem that the white balance cannot be adjusted.
[0004]
In view of the above problems, the present invention provides an apparatus capable of performing white balance adjustment with high accuracy regardless of the subject distance in flash photography, and performing the adjustment processing in a short time. It is intended to provide.
[0005]
[Means for Solving the Problems]
A white balance adjusting device according to the present invention includes: a means for determining an exposure condition in a state where a strobe is fired; a first memory for storing image data obtained without firing the strobe in the exposure condition; A second memory for storing image data obtained by emitting a strobe under an exposure condition and each image data stored in the first and second memories are read, and according to a result of comparing the luminance of the same pixel. And white balance adjustment means for performing white balance adjustment on the image data read from the second memory.
[0006]
【Example】
Hereinafter, the present invention will be described based on illustrated embodiments.
FIG. 1 is a block diagram of an electronic still camera provided with a white balance adjusting device according to one embodiment of the present invention.
[0007]
Light rays passing through the lens 11 and the aperture 12 are irradiated on a light receiving surface of a CCD (solid-state imaging device) 13, and a subject image is formed on the CCD 13. A large number of photoelectric conversion elements are provided on the light receiving surface of the CCD 12, and a color filter including, for example, R, G, and B color filter elements is provided on the upper surface of the photoelectric conversion element. Each photoelectric conversion element corresponds to one pixel data. The subject image is converted into an electric signal corresponding to a predetermined color by each photoelectric conversion element, and subjected to predetermined processing in a signal processing circuit 14 to generate image data including a luminance signal Y and color difference signals Cb and Cr. .
[0008]
Further, in the signal processing circuit 14, a photometric value is calculated based on the pixel data output from the CCD 13 before the photographing operation, and is input to the exposure strobe control circuit 15. The exposure strobe control circuit 15 determines the opening degree (aperture value) of the aperture 12 and the shutter speed, that is, the exposure condition, based on the photometric value, and controls the exposure control (charge accumulation control) and the light emission operation of the strobe 16. Done. In the present embodiment, under this exposure condition, the first exposure operation without the flash light emission operation and the second exposure operation with the flash light emission operation are performed.
[0009]
The image data output from the signal processing circuit 14 is converted into a digital signal in the A / D converter 17 and input to the first image memory 21 or the second image memory 22. The first image memory 21 stores image data (first luminance signal Y ₁ ) obtained by the first exposure operation in which the strobe 16 does not emit light, and the second image memory 22 stores the strobe 16. The image data (second luminance signal Y ₂ , color difference signals Cb ₂ , Cr ₂ ) obtained by the second exposure operation for emitting light is stored. For the second image memory 22 stores each luminance signal Y ₂ and the color difference signals Cb _2, Cr ₂ a, is divided into separate memory areas mutually, each memory area have a storage capacity of one image are doing.
[0010]
First luminance signal Y ₁ read out from the first image memory 21, the raster / in block conversion circuit 23 is a raster / block conversion, one image pixel data into blocks of N 8 × 8 pixels Divided. That is, when the number of pixels of one image is about 400,000, N is about 6,200. First luminance signal BY ₁ which is divided into blocks is input to the luminance comparison circuit 24.
[0011]
The second luminance signal Y ₂ and the color difference signals Cb ₂ and Cr ₂ read from the second image memory 22 are subjected to raster / block conversion in a raster / block conversion circuit 25. Second luminance signals BY ₂ that is divided into blocks is inputted to the luminance comparing circuit 24, the color difference signals are divided into blocks BCb _2, BCr ₂ is inputted to the white balance adjustment circuit 26, respectively. Although only one raster / block conversion circuit 25 is shown in the figure, it is actually provided for each signal.
[0012]
FIG. 2 shows a block of 8 × 8 pixels. The parameter x indicates the horizontal position of the pixel, and the parameter y indicates the vertical position of the pixel. Each of the parameters x and y takes a value in the range of 0 to 7. For example, the luminance signal of the pixel at the fourth position from the left end and at the fifth position from the upper end is represented by BY _n (3, 4). The coordinates (x, y) are relative coordinates defined for each block.
[0013]
In the luminance comparison circuit 24, the first and second luminance signals BY ₁ and BY ₂ are compared, and a luminance comparison function L (x, y) is obtained according to the following equation (1).
L (x, y) = BY ₂ (x, y) −BY ₁ (x, y) (1)
That is, the luminance comparison function L (x, y) is the difference between the luminance signals BY ₁ and BY ₂ of the same pixel, and is obtained for the representative pixel (for example, (3, 4) pixel) for each block. Note that this representative pixel is assumed to be a pixel indicating the average luminance value of the block, but need not be located near the center of the block.
[0014]
In the CCD light receiving pixel in the pixel which receives the reflected light of the flash light by the object having a substantially larger value than the luminance signal BY ₁ towards the first second luminance signals BY _2, strobe light There the pixel of the subject is not irradiated, the second luminance signal bY ₂ has a first substantially the same value as the luminance signal bY ₁ in. Therefore, in this embodiment, when the value of the luminance comparison function L (x, y) is larger than a predetermined reference level, the white balance is adjusted based on the strobe light, and the value of the luminance comparison function L (x, y) is set to the reference value. When the level is lower than the level, the white balance is adjusted based on external light. This reference level has a value in a predetermined range, and when the value of the luminance comparison function L (x, y) is within the range, white balance adjustment is performed based on light intermediate between strobe light and external light. Done.
[0015]
In the luminance comparison circuit 24, the value of the luminance comparison function L (x, y) of the representative pixel is obtained in all the blocks. In the white balance adjustment circuit 26, each block is calculated based on the luminance comparison function L (x, y). White balance adjustment is performed every time. That is, the coefficients Ab and Ar according to the luminance comparison function L (x, y) are multiplied by the color difference signals BCb ₂ and BCr ₂ , respectively, to obtain the color difference signals BCb ₃ and BCr ₃ whose white balance has been adjusted.
[0016]
Since the color temperature of the strobe light is constant, the coefficient of the white balance adjustment based on the strobe light is a constant and is stored in the white balance adjustment circuit 26 in advance. On the other hand, since the color temperature of the external light changes according to the shooting conditions, the coefficient of the white balance adjustment based on the external light is based on the signal obtained from the white balance sensor 27 provided on the outer surface of the camera body. Thus, it is generated in the white balance adjustment circuit 26.
[0017]
The color difference signals BCb ₃ and BCr ₃ output from the white balance adjustment circuit 26 and the second luminance signal BY ₂ output from the luminance comparison circuit 24 are output from the data compression processing circuit 28 in accordance with, for example, the JPEG algorithm. Processing such as discrete cosine transform, quantization, and Huffman coding is performed, and compression processing is performed. The compressed image signals (D _Y , D _Cb , D _Cr ) are recorded on an IC memory card (recording medium) M.
[0018]
FIG. 3 is a flowchart showing a processing routine for white balance adjustment in the present embodiment.
In step 101, white balance information of external light is obtained based on a signal obtained by the white balance sensor 27. In step 102, the exposure strobe control circuit 15 determines an appropriate aperture value and shutter speed when the strobe 16 is used, that is, exposure conditions, based on the photometric value input from the signal processing circuit 14. Next, when it is determined in step 103 that the release switch (not shown) is not set to the ON state, the process returns to step 101. However, when the release switch is switched to the ON state, the photographing operation is performed in step 104 and subsequent steps. , The compressed data of the image is recorded on the recording medium M.
[0019]
In step 104, shooting (first exposure operation) is performed with the strobe 16 not emitting light under the above-described exposure conditions. The electric signal generated in the CCD 13 by this photographing is converted into a _first luminance signal Y ₁ (image data) in the signal processing circuit 14, and the first luminance signal Y ₁ is stored in the first image memory 21 in step 105. Is done. In step 106, shooting (first exposure operation) is performed with the strobe 16 emitting light, and a second luminance signal Y ₂ , color difference signals Cb ₂ , and Cr ₂ (image data) are obtained. These image data are stored in the second image memory 22 in step 107.
[0020]
In step 108, the first luminance signal Y ₁ is read from the first image memory 21 and subjected to raster / block conversion in the raster / block conversion circuit 23. Similarly, the second luminance signal Y ₂ and the color difference signals Cb ₂ and Cr ₂ are read from the second image memory 22 and are raster / block converted by the raster / block conversion circuit 25. In step 109, the block number N is set to 1. In step 110, the luminance signals BY ₁ (x, y) and BY ₂ (x, y) of the representative pixel (x, y) of the block with the block number N are read from the first and second image memories 21 and 22. . In step 111, the first and second luminance signals BY ₁ (x, y) are output from the luminance comparing circuit 24. , BY ₂ (x, y), that is, the luminance comparison function L (x, y) is calculated according to the above equation (1).
[0021]
In steps 112 to 117, a coefficient for white balance adjustment is set according to the value of the luminance comparison function L (x, y). FIG. 4 shows the relationship between the value of the luminance comparison function L (x, y) and light used as a reference in white balance adjustment. As understood from this figure, the white balance adjustment coefficient is set based on the strobe light when the brightness comparison function L (x, y) is larger than the first reference value S1. When the brightness comparison function L (x, y) is between the first reference value S1 and the second reference value S2, the white balance adjustment coefficient is set based on the intermediate light between the strobe light and the external light. When the brightness comparison function L (x, y) is smaller than the second reference value S2, the brightness comparison function is set based on external light.
[0022]
As shown by a solid line C in FIG. 5, the amount of strobe light (the amount of reflected strobe light) applied to the subject increases as the subject distance decreases, and the first reference value S1 is a predetermined value greater than the second reference value. Only have larger values. That is, for example, when a subject located at a distance h is considered, the amount of strobe light Ch applied to the subject is larger than the first reference value S1, so that the white balance adjustment of the pixel corresponding to the subject is performed based on the strobe light. Is On the other hand, the pixel corresponding to the background portion (∞) has a strobe light amount equal to 0 and smaller than S2, so that the white balance adjustment is performed based on external light.
[0023]
In step 112, it is determined whether the brightness comparison function L (x, y) is larger than the first reference value S1. When the brightness comparison function L (x, y) is larger than the first reference value S1, in step 113, a white balance adjustment coefficient is set based on the strobe light. When it is determined in step 112 that the brightness comparison function L (x, y) is smaller than the first reference value S1, in step 114, the brightness comparison function L (x, y) is smaller than the second reference value S2. It is determined whether or not. When the brightness comparison function L (x, y) is smaller than the second reference value S2, in step 115, a white balance adjustment coefficient is set based on external light. When the brightness comparison function L (x, y) is between the first reference value S1 and the second reference value S2, in step 116, the coefficient of white balance adjustment is performed based on light intermediate between strobe light and external light. Is set.
[0024]
In step 117, the white balance adjustment is performed for the block with the block number N using the white balance adjustment coefficient obtained in step 113, 115 or 116, and the color difference signals BCb ₃ and BCr ₃ are generated. In step 118, the second luminance signal BY ₂ and the color difference signals BCb ₃ and BCr ₃ are output to the data compression processing circuit 28. In step 119, the signals BY ₂ , BCb ₃ , and BCr ₃ are subjected to compression processing and recorded on the recording medium M.
[0025]
In step 120, it is determined whether or not the block number N has reached the number n of blocks of one image (for example, 6200). If the block number has not reached the block number n, the block number N is incremented by 1 in step 121, and the process returns to step 110 and the above-described operation is repeated. On the other hand, if it is determined in step 120 that the block number N has reached the number of blocks n, a recording operation completion process such as a write prohibition process on the recording medium M is performed in step 122, and this processing routine ends. I do.
[0026]
As described above, in this embodiment, for each block, a comparison is made between the case where the strobe light is irradiated and the case where the strobe light is not irradiated, and the white balance adjustment based on the strobe light is performed for the block where the influence of the strobe light is large. The white balance adjustment is performed based on the external light for the blocks that are less affected by the strobe light. Therefore, even when flash photography is performed on one image in which a long-distance subject and a short-distance subject are mixed, white balance adjustment can be performed for each block in a short time by simple processing. it can.
[0027]
Further, in this embodiment, the number of pixels of the unit block in the white balance adjustment is equal to the number of pixels of the unit block of the image compression in the data compression processing circuit 28, so that the efficiency of the data processing is high.
[0028]
In the above embodiment, the white balance adjustment is performed for each block. However, one white balance adjustment may be performed for some blocks.
[0029]
Further, in the above-described embodiment, the white balance adjustment is performed in three steps, but may be performed in two steps with one reference value, or may be performed in three or more steps.
[0030]
【The invention's effect】
As described above, according to the present invention, in flash photography, white balance adjustment can be performed with high accuracy regardless of the subject distance, and the adjustment processing can be performed in a short time.
[Brief description of the drawings]
FIG. 1 is a block diagram of an electronic still camera including a white balance adjustment device according to an embodiment of the present invention.
FIG. 2 shows a block of 8 × 8 pixels.
FIG. 3 is a flowchart illustrating white balance adjustment.
FIG. 4 is a diagram illustrating a relationship between a value of a luminance comparison function and light used as a reference in white balance adjustment.
FIG. 5 is a diagram showing the relationship between the amount of strobe light applied to a subject and the subject distance.
[Explanation of symbols]
13 CCD
16 Strobe 21 First image memory 22 Second image memory 26 White balance adjustment circuit 27 White balance sensor

Claims (5)

Means for determining an exposure condition in a state in which the strobe is fired, a first memory for storing image data obtained without the strobe being fired in the exposure condition; A second memory for storing the read image data and each image data stored in the first and second memories, and reading out the second memory according to the result of comparing the luminance of the same pixel. A white balance adjustment unit for performing white balance adjustment on the image data obtained. The white balance adjusting means adjusts white balance based on strobe light when a difference between the luminance read from the first memory and the luminance read from the second memory is larger than a reference level, The white balance adjustment device according to claim 1, wherein when the difference in luminance is smaller than a reference level, white balance adjustment is performed based on external light. The reference level has a value within a predetermined range, and the white balance adjustment means adjusts white balance based on light intermediate between strobe light and external light when the difference in luminance is within the predetermined range. 3. The white balance adjusting device according to claim 2, wherein: The white balance adjustment unit reads out each image data stored in the first and second memories for each unit block having a predetermined number of pixels, and compares the luminance of pixels at corresponding positions for each block. The white balance adjustment device according to claim 1, wherein white balance adjustment is performed on the image data read from the second memory according to a result. The white balance adjusting device according to claim 4, further comprising an image compression processing circuit, wherein the number of pixels of the unit block is equal to the number of pixels of the unit block of the image compression processing performed by the image compression processing circuit. .

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