JP3915404B2 - Imaging apparatus and white balance adjustment method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an imaging apparatus particularly suitable for a digital camera and a white balance adjustment method thereof.
[0002]
[Prior art]
In recent years, with the spread of personal computers, digital cameras using electronic image sensors such as CCDs and CMOS area sensors have become widespread. This main digital camera is largely different from a so-called silver salt camera using a silver salt film in that the white balance must be adjusted in order to make the color temperature of the image appropriate.
[0003]
Therefore, in this white balance adjustment, white pixel data is generally detected from image data in the entire area of the shooting screen, and a white balance that is considered appropriate is obtained from the detected white pixel data. (Incidentally, here, the white pixel data indicates data of pixels distributed in an area regarded as white when white extraction is performed from the primary color RGB signal by color process processing.)
[0004]
[Problems to be solved by the invention]
However, since white pixel data is detected from the image data of the entire screen, white balance is automatically adjusted based on the average color temperature of the entire screen regardless of the position and composition of the subject on the screen. Therefore, there are many cases where accurate white balance adjustment cannot be performed on the subject itself that the user wants to photograph.
[0005]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an imaging apparatus capable of performing accurate white balance adjustment according to the position of a subject and a white balance adjustment method thereof. There is to do.
[0006]
[Means for Solving the Problems]
According to the first aspect of the present invention, a dividing unit that divides color image data obtained from an image sensor into a plurality of screen areas, and an extraction that extracts white pixel data from the image data for each screen area divided by the dividing unit. Means for comparing the white pixel data of the specific screen area obtained by the extraction means with a preset reference value, and the image data of the specific screen area based on the comparison result of the comparison means It is characterized by comprising white balance adjustment means for adjusting white balance by changing the image data of the screen area and weighting.
[0007]
With such a configuration, accurate white balance adjustment can be performed according to the position of the subject.
[0008]
The invention described in claim 2 is characterized in that in the invention described in claim 1, further comprising a specifying means for arbitrarily specifying the specific screen area from a plurality of screen areas divided by the dividing means.
[0009]
With such a configuration, in addition to the operation of the invention described in claim 1, the user arbitrarily designates a specific screen region in accordance with the position on the screen of the subject to be imaged at that time. Therefore, it is possible to always perform accurate white balance adjustment according to the subject regardless of the composition of the image.
[0010]
According to a third aspect of the present invention, in the first aspect of the present invention, the specific image region includes a screen center portion.
[0011]
With such a configuration, in addition to the operation of the invention described in claim 1 above, the white balance adjustment is performed in consideration of the screen area including the central portion of the screen, so that the influence of the peripheral portion of the screen is suppressed. In addition, accurate white balance adjustment with emphasis on the center can be performed.
[0012]
According to a fourth aspect of the present invention, in the first aspect of the invention, the dividing unit divides the image data into a plurality of screen areas so that the areas are not equal, and the specific image area is divided into the divided areas. The screen area having the largest area divided by the means is used.
[0013]
With such a configuration, in addition to the operation of the invention described in claim 1, the white balance adjustment is performed in consideration of the largest area of the screen area divided in an uneven area. For this reason, if the area in the screen that is considered to have a relatively large number of patterns in which the subject is positioned as the composition has the largest area, accurate white balance adjustment can be performed with higher probability.
[0014]
The invention described in claim 5 is characterized in that, in the invention described in claim 1, the image area from which most white pixel data is extracted is defined as the specific image area.
[0015]
With such a configuration, in addition to the operation of the first aspect of the invention, white balance adjustment is performed with emphasis on an area where there are the most white pixels, and thus more accurate white balance is necessary. Therefore, the white balance can be made more natural and uncomfortable even on the entire screen.
[0016]
According to a sixth aspect of the invention, a division step for dividing color image data obtained from an image sensor into a plurality of screen regions, and extraction for extracting white pixel data from the image data for each screen region divided in the division step A comparison step for comparing the white pixel data of the specific screen area obtained in the extraction step with a preset reference value, and the image data of the specific screen area based on the comparison result of the comparison step And a white balance adjustment step of adjusting white balance by changing the weight of the image data of the screen area.
[0017]
With such a method, it is possible to perform accurate white balance adjustment according to the position of the subject.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment in which the present invention is applied to a digital still camera will be described with reference to the drawings.
[0019]
FIG. 1 shows the circuit configuration, and 10 is a digital camera. The digital camera 10 can set a recording mode and a reproduction mode. In the recording mode, the CCD 12 disposed behind the lens 11 is scan-driven by a timing generator (TG) 13 and a vertical driver 14. Then, the photoelectric conversion output for one screen is output at every fixed period.
[0020]
The photoelectric conversion output is appropriately gain-adjusted for each primary color component of RGB in the state of an analog value signal, then sampled and held by a sample hold circuit (S / H) 15, and digital data by an A / D converter 16. The color process circuit 17 including the pixel interpolation process is performed in the color process circuit 17 to generate the luminance signal Y and the color difference signals Cb and Cr as digital values, and DMA (Direct Memory).
Access) controller 18.
[0021]
The DMA controller 18 once uses the luminance signal Y and the color difference signals Cb and Cr output from the color process circuit 17 by using the synchronization signal, memory write enable signal, and clock signal from the color process circuit 17 once. Writing to the buffer and DMA transfer to the DRAM 20 via the DRAM interface (I / F) 19 are performed.
[0022]
After completing the DMA transfer of the luminance and color difference signals to the DRAM 20, the CPU 21 reads the luminance and color difference signals from the DRAM 20 via the DRAM interface 19 and writes them into the VRAM 23 via the VRAM controller 22.
[0023]
A digital video encoder (hereinafter abbreviated as “video encoder”) 24 periodically reads the luminance and color difference signals from the VRAM 23 via the VRAM controller 22, generates a video signal based on these data, and generates a display unit 25. Output to.
[0024]
The display unit 25 is composed of, for example, a backlit color liquid crystal display panel and its drive circuit, and is disposed on the back side of the camera body, and functions as an EVF (Electronic View Finder) in the recording mode. Therefore, by performing display based on the video signal from the video encoder 24, an image based on the image information fetched from the VRAM controller 22 at that time is displayed.
[0025]
Then, with the image at that time being displayed as a monitor image in real time on the display unit 25 as described above, the shutter keys in the plurality of keys constituting the key input unit 26 are operated at the timing when recording and storage are desired. Then, a trigger signal is generated.
[0026]
In response to this trigger signal, the CPU 21 stops the path from the CCD 12 to the DRAM 20 immediately after the completion of the DMA transfer of the luminance and color difference signals for one screen currently captured from the CCD 12 to the DRAM 20, and records and saves them. Transition to the state.
[0027]
In this recording and storage state, the CPU 21 transmits the luminance and color difference signals for one frame written in the DRAM 20 through the DRAM interface 19 to each of the Y, Cb, and Cr components of 8 × 8 pixels. A unit called a block is read and written to the JPEG circuit 27, and the JPEG circuit 27 compresses data by processing such as ADCT (Adaptive Discrete Cosine Transform), Huffman coding which is an entropy coding system, The obtained code data is read out from the JPEG circuit 27 as a data file of one image, and written into a flash memory 28 which is a non-volatile memory that is detachably mounted as a storage medium of the digital camera 10.
[0028]
Then, the CPU 21 activates the path from the CCD 12 to the DRAM 20 again as the luminance and color difference signals for one frame are compressed and the writing of all the compressed data to the flash memory 28 is completed.
[0029]
At this time, the CPU 21 also creates image data in which the number of constituent pixels of the original image data is greatly thinned out, and stores this in the flash memory 28 in association with the original image data as a preview image also called a thumbnail image. Let
[0030]
In addition to the shutter key described above, the key input unit 26 includes a recording / re-mode switching key for switching between a recording (REC) mode and a reproducing (PLAY) mode, a mode key for selecting various shooting modes, and an image. Consists of cursor keys that specify each of the up / down / left / right directions and the “Enter” key for determining the selection contents for selection and designation of the focus adjustment position on the white balance screen. The signal is sent directly to the CPU 21.
[0031]
Further, in the playback mode, the CPU 21 stops the path from the CCD 12 to the DRAM 20, and the CPU 21 reads the code data for a specific frame from the flash memory 28 according to the operation of the image selection key or the like of the key input unit 26, and JPEG. The luminance and color-difference signals for one frame are expanded and stored in the VRAM 23 via the VRAM controller 22 in units of basic blocks of 8 vertical pixels × 8 horizontal pixels obtained by writing to the circuit 27 and performing the decompression process by the JPEG circuit 27. . Then, the video encoder 24 generates a video signal based on the luminance and color difference signals for one frame expanded and stored in the VRAM 23 and causes the display unit 25 to display the video signal.
[0032]
Next, the operation of the above embodiment will be described.
[0033]
First, a conceptual configuration of a circuit for performing white balance adjustment in the color process circuit 17 is shown in FIG. Here, the CCD 12 will be described as having a primary color (RGB) color filter.
[0034]
In the figure, the image data output from the CCD 12 and digitized via the sample hold circuit 15 and the A / D converter 16 is input to the decomposer 31.
[0035]
This decomposer 31 decomposes the input image data for each color component and outputs it together. The G signal closest to the luminance signal is sent directly to the matrix circuit 32 and the white extraction circuit 33, while R The signal is directly sent to the matrix circuit 32 via the amplifier 34a and directly to the white extraction circuit 33. Similarly, the B signal is sent directly to the matrix circuit 32 via the amplifier 34b and directly to the white extraction circuit 33.
[0036]
A white extraction circuit 33 to which RGB signals are directly input from the decomposer 31 extracts a signal in a position range that is considered to be a white pixel (hereinafter referred to as “white pixel”) in the image from the input content, The integrated values of these pixels are calculated and output to the color temperature detection circuit 35.
[0037]
The color temperature detection circuit 35 adjusts the gains of the amplifiers 34a and 34b based on the integration value given from the white extraction circuit 33, and the RGB signal input to the matrix circuit 32 is GR = GB at the white pixel portion. = 0.
[0038]
The color temperature detection circuit 35 calculates matrix difference signals Cb and Cr from the RGB signals whose white balance is adjusted in accordance with the white pixel portion in this way, and outputs them to the next stage.
[0039]
Next, the automatic tracking operation for white balance adjustment in the color process circuit 17 will be mainly described.
[0040]
FIG. 3 shows a series of processing contents related to white balance adjustment executed by the color process circuit 17 every time image data is obtained by driving the CCD 12. As shown in FIG. 4, after dividing into three block areas (1) to (3) (step A01), the white extraction circuit 33 extracts white pixels for each block area, and the number of white pixels And the integral value are calculated and output to the color temperature detection circuit 35 (step A02).
[0041]
The color temperature detection circuit 35 determines whether or not to perform white balance adjustment based on whether or not the number of white pixels in the block area (1) at the center of the screen is greater than a preset reference value n (step A03).
[0042]
Here, only when it is determined that the number of white pixels is larger than the reference value n, the block area (1) in the center of the screen is weighted as compared with the other peripheral block areas, and an amplifier for white balance adjustment Gain control of 34a and 34b is performed (step A04).
[0043]
As one of the weighting methods, the number of white pixels per unit area and the integrated value are calculated in accordance with the ratio of the areas of the block regions (1) to (3), and those values are calculated in the block region (1 ) To (3) are calculated so that the center of the screen is weighted so that the ratio is 4: 1: 1, for example, values for changing the R and B signals are calculated from the number of white pixels and the integrated value, and based on the values. Thus, it is conceivable to perform gain control with the amplifiers 34a and 34b.
[0044]
Thus, by performing the white balance adjustment as described above every time the CCD 12 is driven to obtain image data, the digital camera 10 can be made to follow up so that a correct white balance is always obtained.
[0045]
In the above description, as shown in FIG. 4, the data for one frame is divided into a plurality of block areas (1) to (3) having different areas, and the white balance is focused on the block area (1) at the center of the screen. Since the adjustment is performed, particularly when the center-weighted exposure is set as the AE (automatic exposure) function of the digital camera 10 and the center spot AF is set as the AF (automatic focus) function, these are used together. This makes it possible to perform accurate white balance adjustment suitable for the subject image.
[0046]
Also, one frame of image data is divided into block areas with a total area of, for example, a total of 9 vertical 3 x horizontal 3 areas or a total of 25 vertical 5 x 5 area areas, and the cursor key is set in the manual mode setting for white balance adjustment. The user may be able to arbitrarily select a block area for which the white balance adjustment is focused on depending on the positional relationship between the subject and the composition at the time of shooting. It is possible to perform shooting with white balance that accurately reflects the user's intention.
[0047]
In addition, by devising the division pattern of the screen area, the area of the part where the subject is supposed to be located in common in more composition is set so that the area is larger than the other block areas, the most area It is also possible to perform white balance adjustment by weighting white pixels assuming that a region having a large weight is weighted over other regions, so that accurate white balance adjustment can be performed with higher probability.
[0048]
In addition, the area of the divided screen area is not taken into consideration, and white areas are adjusted by weighting the white pixels as if the area with the largest number of extracted white pixels is weighted over other areas. It is good.
[0049]
FIG. 5 shows other processing contents of the embodiment of the present invention. At first, after dividing image data for one frame into preset areas (step B01), white data is displayed. The extraction circuit 33 extracts white pixels for each region, calculates the number of white pixels and the integral value, and outputs them to the color temperature detection circuit 35 (step B02).
[0050]
First, the color temperature detection circuit 35 selects a region that is the largest among the number of white pixels for each region (step B03), and the maximum value of the number of white pixels in the selected region is a preset reference value n. It is determined whether or not the white balance adjustment is performed based on whether or not it is larger (step B04).
[0051]
Here, only when it is determined that the number of white pixels is larger than the reference value n, the selected area is weighted in comparison with other peripheral block areas, and the amplifiers 34a and 34b for white balance adjustment are used. Gain control is performed (step B05).
[0052]
As one of the weighting methods, the number of white pixels per unit area and the integrated value are calculated in accordance with the ratio of the areas of the block regions (1) to (3), and those values are calculated in the block region (1 ) To (3) are calculated so that the center of the screen is weighted so that the ratio is 4: 1: 1, for example, values for changing the R and B signals are calculated from the number of white pixels and the integrated value, and based on the values. Thus, it is conceivable to perform gain control with the amplifiers 34a and 34b.
[0053]
Thus, by performing the white balance adjustment as described above every time the CCD 12 is driven to obtain image data, the digital camera 10 can be made to follow up so that a correct white balance is always obtained.
[0054]
In this way, without considering the area of the divided area, white balance adjustment is performed with emphasis on the area where there are the most white pixels and therefore more accurate white balance is necessary. Even the entire screen can be made more natural and uncomfortable white balance.
[0055]
Although the present invention has been described as being applied to a digital still camera using a CCD as an image pickup device as an embodiment, the present invention can be applied to an image pickup device or a still camera / video as long as the digital camera requires white balance adjustment. Of course, the present invention can be applied without distinguishing between cameras.
[0056]
In addition, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention.
[0057]
Further, the above embodiments include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. For example, even if some constituent elements are deleted from all the constituent elements shown in the embodiment, at least one of the problems described in the column of the problem to be solved by the invention can be solved, and described in the column of the effect of the invention. In a case where at least one of the obtained effects can be obtained, a configuration in which this configuration requirement is deleted can be extracted as an invention.
[0058]
【The invention's effect】
According to the first aspect of the present invention, it is possible to perform accurate white balance adjustment in accordance with the position of the subject.
[0059]
According to the second aspect of the invention, in addition to the effect of the first aspect of the invention, the user arbitrarily designates a specific screen area according to the position on the screen of the subject to be imaged at that time. By doing so, it is possible to always perform an accurate white balance adjustment in accordance with the subject regardless of the composition.
[0060]
According to the third aspect of the invention, in addition to the effect of the first aspect of the invention, the white balance adjustment is performed in consideration of the screen area including the central portion of the screen. Can be controlled and accurate white balance adjustment can be performed with emphasis on the center.
[0061]
According to the invention described in claim 4, in addition to the effect of the invention described in claim 1, the white balance adjustment is performed in consideration of a portion having the largest area in the screen area that is divided unevenly. Therefore, if the area in the screen that is considered to have a relatively large number of patterns in which the subject is positioned as the composition has the largest area, accurate white balance adjustment can be performed with higher probability.
[0062]
According to the fifth aspect of the invention, in addition to the effect of the first aspect of the invention, white balance adjustment is performed with emphasis on an area where there are the most white pixels and thus more accurate white balance is necessary. Therefore, the white balance can be made more natural and uncomfortable even on the entire screen.
[0063]
According to the sixth aspect of the present invention, it is possible to perform accurate white balance adjustment in accordance with the position of the subject.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an electronic circuit configuration of a digital camera according to an embodiment of the present invention.
2 is a block diagram showing a conceptual configuration of a circuit that performs white balance adjustment in the color process circuit of FIG. 1;
FIG. 3 is a flowchart showing processing details of white balance adjustment in the color process circuit according to the embodiment;
FIG. 4 is a view illustrating division of image data for one frame into a plurality of block areas according to the embodiment;
FIG. 5 is a flowchart showing another processing content of white balance adjustment in the color process circuit according to the embodiment;
[Explanation of symbols]
10 ... Digital camera 11 ... Lens 12 ... CCD
13 ... Timing generator (TG)
14 ... Vertical driver 15 ... Sample hold circuit (S / H)
16 ... A / D converter (A / D)
17 ... Color process circuit 18 ... DMA controller 19 ... DRAM interface (I / F)
20 ... DRAM
21 ... CPU
22 ... VRAM controller 23 ... VRAM
24 ... Video encoder 25 ... Display unit 26 ... Key input unit 27 ... JPEG circuit 28 ... Flash memory 31 ... Decomposer 32 ... Matrix circuit 33 ... White extraction circuits 34a, 34b ... Amplifier (Amp.)
35. Color temperature detection circuit

Claims (6)

A dividing means for dividing color image data obtained from the image sensor into a plurality of screen areas;
Extracting means for extracting white pixel data from image data for each screen area divided by the dividing means;
A comparing means for comparing white pixel data of a specific screen area obtained by the extracting means with a preset reference value;
An image pickup apparatus comprising: white balance adjusting means for adjusting white balance of image data of the specific screen area by changing weighting with image data of other screen areas based on a comparison result of the comparing means. 2. The imaging apparatus according to claim 1, further comprising designation means for arbitrarily designating the specific screen area from a plurality of screen areas divided by the dividing means. The imaging apparatus according to claim 1, wherein the specific image region includes a central portion of the screen. The dividing means divides the image data into a plurality of screen areas so that the areas are not uniform.
The imaging apparatus according to claim 1, wherein the specific image area is a screen area having a maximum area divided by the dividing unit. 2. The image pickup apparatus according to claim 1, wherein an image area from which most white pixel data is extracted is set as the specific image area. A division step of dividing the color image data obtained from the image sensor into a plurality of screen areas;
An extraction step of extracting white pixel data from the image data for each screen area divided in this division step;
A comparison step for comparing the white pixel data of the specific screen area obtained in this extraction step with a preset reference value;
An image pickup apparatus comprising: a white balance adjustment step of adjusting white balance by changing a weight of the image data of the specific screen region with the image data of another screen region based on a comparison result of the comparison step White balance adjustment method.

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