JP2009239974A - Automatic exposing device and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging device for recording image data inputted from an image pickup device, obtaining adequate exposure from the taken image data while reducing both hardware and software loads substantially. <P>SOLUTION: The automatic exposing method includes the steps of: splitting image data into a plurality of block areas (A04); integrating an image data luminance signal from each of the plurality of block areas (A05); comparing the obtained integral values of the plurality of block areas and determining backlight from the result of comparison (A06-A08), and correcting the exposure when the result is determined to be backlight (A00). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an automatic exposure apparatus and method particularly suitable for a digital still camera.

  Regardless of whether it is a digital still camera or a silver salt camera, a relatively high-class camera equipped with many functions, in particular, splits the screen into several parts as one of the AE (Auto Exposure) functions. Most models have multi-pattern photometry, multi-division photometry, and evaluation photometry (hereinafter abbreviated as “multi-photometry mode”) to obtain the optimum exposure by measuring multiple parts. Yes.

  In such multi-metering mode, by matching many photometric patterns prepared in advance with the photometric pattern obtained at that time, more optimal exposure is possible even when shooting with extreme backlighting or excessively strong light sources. The probability of obtaining is improved.

  However, when the subject is photographed in a backlit state where the background is very bright, the subject image tends to become dark due to the influence of the brightness of the background.

  In this case, especially when considering the case where the backlight is determined by comparing the brightness of the center of the screen with the brightness of the top of the screen excluding this center, when the subject is positioned at the center of the screen, This is a very typical composition, and relatively effective correction can be applied. On the other hand, when the subject is located off the center of the screen, this is a common composition, but it is adequately corrected. The probability of being applied is low.

  In particular, when the AE of the multi-metering mode is set on the digital camera and the white balance is set to the automatic adjustment, the brightness is always adjusted according to a constant reference. Even if the subject is actually white or black, it is photographed so that it becomes a reference value of halftone gray, so it is difficult to faithfully reflect the atmosphere at the time of photographing on the photographed image.

  For such problems, conventionally, a histogram was created from the brightness value of each pixel of image data obtained with a digital camera to determine the correct exposure, and it was used for shooting at the original timing. Things are also considered.

  However, in recent years, the number of constituent pixels of a CCD or the like that is an image sensor of a digital camera has been dramatically improved, and the amount of image data obtained by photographing is accordingly very large.

  As means for creating a histogram from such a large amount of image data and determining an accurate exposure, processing is performed in software using a DSP (Digital Signal Processor), or for performing histogram calculation. It is possible to implement a dedicated hardware circuit.

  In the case of processing by software, since the burden on the DSP is large and a lot of calculation time is required, it takes too much time to shift to the original shooting, and the shooting environment including the subject changes and the histogram changes. May not be able to be used effectively.

  In addition, when a dedicated hardware circuit is used, the circuit scale of the entire digital camera is increased because a relatively large circuit must be added and mounted only for one means for obtaining appropriate exposure, and The cost as a product will increase significantly.

  The present invention has been made in view of the above circumstances, and the object of the present invention is to obtain appropriate exposure from captured image data while making the burden on both hardware and software sufficiently small. It is an object of the present invention to provide an automatic exposure apparatus and method.

  According to the first aspect of the present invention, an image sensor that captures image data, a dividing unit that divides the image data into a plurality of regions, and a luminance signal are generated from the image data for each of the plurality of regions divided by the dividing unit. The generation means, the integration means for integrating the luminance signals for each of the plurality of areas generated by the generation means, and the integration value for each of the plurality of areas obtained by the integration means are compared between a plurality of areas adjacent in the vertical direction. The first comparison means for calculating the difference in luminance of the upper area relative to the luminance of the lower area, and the luminance calculated by the first comparison means for a plurality of areas including the central area of the image data And the difference in luminance obtained by summing the difference in luminance calculated by the first comparison means for a plurality of regions that are above the image data and do not include the central region of the image data. When larger than the predetermined value Characterized by comprising a determination means backlit.

  According to a second aspect of the present invention, in the first aspect of the present invention, the integrated values for a plurality of regions obtained by the integrating means are compared between a plurality of regions adjacent in the left-right direction, and the luminance of the central region is compared. Second comparison means for calculating a difference in luminance between the left and right areas is further provided, wherein the determination means calculates the luminance calculated by the first comparison means for a plurality of areas including a central area of the image data. And the difference in luminance calculated by the first comparison means for a plurality of areas that are above the image data and do not include the central area of the image data, and between the difference between the brightness of the image data If the difference in luminance obtained by adding together the luminance difference calculated by the second comparison means for a plurality of areas not including the central area is larger than a predetermined value, it is determined that the backlight is backlit. Features.

  According to a third aspect of the present invention, in the first or second aspect of the invention, the determination means is a luminance calculated by the first comparison means for a plurality of areas including a central area of the image data. And the difference in luminance obtained by adding the difference in luminance calculated by the first comparison means for a plurality of areas including the uppermost area of the image data is larger than a predetermined value. It is determined that the light is backlit.

  According to a fourth aspect of the present invention, in the first aspect of the present invention, the determination unit adds the luminance difference calculated by the first comparison unit in each part of the image data. Multiplying by weighting factors according to the above, and adding together.

  According to a fifth aspect of the present invention, in the second aspect of the invention, the determination means adds up the luminance differences calculated by the first comparison means or the second comparison means in each part of the image data. In this case, the weighting coefficients corresponding to the positions of the respective regions are multiplied and then added.

  The invention according to claim 6 is the invention according to any one of claims 1 to 5, wherein the determination means determines that the light is backlit when the difference in luminance obtained by summing is positive, and is negative. In this case, it is characterized in that the light is determined as follow light.

  The invention according to claim 7 is the invention according to any one of claims 1 to 6, further comprising backlight correction means for correcting backlight when the determination means determines backlight.

The invention according to claim 8 is the invention according to claim 7, in which the calculation means for calculating the distribution state of the luminance from the integral value for each of the plurality of regions obtained by the integration means, and the luminance calculated by the calculation means Brightness correction means for correcting the brightness in accordance with the distribution state.
According to the ninth aspect of the present invention, an imaging step for capturing image data, a dividing step for dividing the image data into a plurality of regions, and a luminance signal are generated from the image data for each of the plurality of regions divided in the dividing step. The integration step for integrating the luminance signal for each of the plurality of regions generated in this generation step, and the integration value for each of the plurality of regions obtained in this integration step are compared between a plurality of regions adjacent in the vertical direction. The first comparison step for calculating the difference in luminance of the upper region with respect to the luminance of the lower region and the luminance calculated by the first comparison step for a plurality of regions including the central region of the image data And the luminance difference calculated in the first comparison step for a plurality of areas that are above the image data and do not include the central area of the image data. The difference in brightness is is characterized in that and a determination step of determining a backlit is greater than a predetermined value.

  According to the present invention, the image data is divided into a plurality of regions, the integral value of the luminance signal is calculated for each region, and the integral value is compared between the plurality of regions adjacent in the vertical direction to determine the luminance of the lower region. The brightness difference calculated for a plurality of areas including the central area of the image data by the comparison means for calculating the brightness difference of the upper area with respect to the image area, and the comparison means is an upper part of the image data. If the luminance difference obtained by adding together the luminance differences calculated for a plurality of areas not including the central area of the data is greater than a predetermined value, it is determined that the subject is an Even in the case of being located in the central region of the photographing range or in the case of being located in the region shifted upward from the center of the photographing range, it is possible to perform appropriate backlight correction.

1 is a block diagram showing an electronic circuit configuration of a digital camera according to a first embodiment of the present invention. 7 is a flowchart showing processing contents corresponding to the multi-photometry mode in the recording mode according to the embodiment. The figure which shows the division | segmentation state to the several block area | region of the image data which concerns on the embodiment. 10 is a flowchart showing processing contents corresponding to the multi-photometry mode in the recording mode according to the second embodiment of the present invention. The figure which shows the division | segmentation state to the several block area | region of the image data which concerns on the embodiment. The figure which shows the histogram of the luminance value for every division | segmentation block area | region which concerns on the embodiment.

(First embodiment)
A first embodiment when the present invention is applied to a digital still camera will be described below with reference to the drawings.

  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.

  This photoelectric conversion output is appropriately gain-adjusted for each primary color component of RGB in the state of an analog value signal, and then is sampled and held by a sample and hold (S / H) circuit 15, and an A / D converter (A / D) ) 16 is converted into digital data, and color process processing including interpolation processing and γ correction processing is performed in the color process circuit 17 to generate a digital luminance signal Y and color difference signals Cb, Cr, and DMA (Direct Memory). Access) controller 18.

  The DMA controller 18 once converts the luminance signal Y and the color difference signals Cb and Cr output from the color process circuit 17 into a buffer inside the DMA controller 18 using the synchronization signal, memory write enable, and clock output from the color process circuit 17. Write and perform DMA transfer to DRAM 20 via DRAM interface (I / F) 19.

  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.

  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.

  The display unit 25 is composed of, for example, a backlit color liquid crystal display panel and its driving 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.

  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.

  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 captured from the CCD 12 to the DRAM 20 at that time, and records and saves them. Transition to the state.

  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 out and written to the JPEG circuit 27. The JPEG circuit 27 compresses the data by a process such as ADCT (Adaptive Discrete Cosine Transform) or Huffman coding which is an entropy coding method. The encoded data is read out from the JPEG circuit 27 as one image data file 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.

  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.

  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

  In addition to the shutter key described above, the key input unit 26 indicates a recording / replay mode switching key for switching between a recording (REC) mode and a reproduction (PLAY) mode, and indicates up / down / left / right directions for image selection. Cursor keys, “Enter” key, etc., and signals accompanying key operations are sent directly to the CPU 21.

  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 YUV data for one frame is 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 one frame of YUV data expanded and stored in the VRAM 23 and displays it on the display unit 25.

  Next, the operation of the above embodiment will be described.

  Here, the operation will be described assuming that automatic backlight correction is performed when the multi-metering mode is set in the metering mode during the recording mode.

  FIG. 2 mainly shows the processing contents performed by the CPU 21. At the beginning, it is determined whether or not the metering mode is the multi-metering mode (step A01). If not, the shutter key of the key input unit 26 is determined. The process of determining whether or not an operation has been performed (step A02) is repeatedly executed at a predetermined cycle, thereby waiting for them.

  If it is determined in step A01 that the multi-metering mode is selected, shooting is performed by AF (auto focus), AE, and AWB (automatic white balance) adjustment in order to obtain image data for immediately performing backlight determination. Image data is acquired (step A03).

  Then, at the stage where the acquired image data is stored in the DRAM 20, the luminance signal Y is divided into a total of 50 block areas, for example, 5 × 10 in the vertical direction as shown in FIG. 3 (step A04).

  The luminance signal Y for each block area divided in this way is integrated (step A05). Assuming that the integration values for each block area obtained by integration are “Sum00” to “Sum49” as shown in the figure, these integration values “Sum00” to “Sum49” are used next, and two block areas adjacent in the horizontal direction are used. Are subdivided into 25 block areas shown in FIG.

In this case, assuming that the integration value of each block area is “a0” to “e4”, the average value of the level of the luminance signal Y per pixel first becomes a certain reference value by the integration value of all the block areas. It shall be adjusted to the exposure time. That is,
Yref = (sum00 + sum01 + ... + sum49) / (50 * n) (1)
(However, Yref: luminance reference value per pixel,
n: Number of pixels per block. )
The backlight coefficient calculation formula is executed using the integrated value for each block area in the state matched with the reference value Yref (step A06). That is,
add1 = b1 + b2 + b3 (2)
add2 = a1 + a2 + a3 (3)
L = (add1 * X / c1 + add1 * X / c2 + add1 * X / c3−X * 9) (4)
M = (add2 * Y / b1 + add2 * Y / b2 + add2 * Y / b3−Y * 9) (5)
N = ((a1 + a3) * Z / a2-Z * 2) (6)
Against = L + M + N (7)
(However, Against: Output coefficient,
X, Y, Z: The effect on the size of the output coefficient is determined by the position of the block area.
It is a constant that is weighted accordingly. "1" when not weighted. )
Expression (4) that defines the variable L used in the above expression (7) is for comparison at the center of the image data, and the block area located at c1, c2, and c3 and the three blocks above it. This is to determine whether there is a difference in luminance from the areas b1, b2, and b3.

  The equation (5) defining the variable M used in the above equation (7) is for comparison at the uppermost part of the image data, and the block region located at b1, b2, b3 and 3 above it. This is for determining whether there is a difference in luminance between the two block areas a1, a2 and a3.

  Further, the equation (6) defining the variable N used in the above equation (7) is for comparing the left and right uppermost portions of the image data. The block region located at a2 and the left and right block regions a1, This is for determining whether there is a difference in luminance from a3.

  The output coefficient Against obtained in this way is used as a backlight determination coefficient, and a comparison process for backlight determination is executed based on the value (step A07).

  Here, if the image data has uniform brightness over the entire surface and the integrated value of the brightness data in each block area is equal, the variables L, M, and N in the above equations (4) to (6). After the comparison of the center, top and left and right of the top of the image data, the coefficient Against which is the final calculation result is subtracted from the value equivalent to the product of the coefficient and the number of comparison blocks. Becomes “0 (zero)”.

  On the other hand, the coefficient Against is “+ (plus)” in the case of backlight, and the coefficient Against is “− (minus)” in the case of direct light. This point will be described below.

  For example, let us consider a case where the face of a person who is the most important part of the subject is located in the block region c2 which is the center of the shooting range shown in FIG.

  In this case, since the integration value is compared with Yref which is a predetermined reference in advance, if a brighter block area exists in the image data, a dark block area similarly exists.

  When the face of a person is located in the block area c2 and the background is bright backlight, the value obtained by comparing the block area c2 with the three block areas b1 to b3 above is “+ (plus)”. .

  On the other hand, the comparison results between the block areas c1 and c3 on the left and right of the subject's face and the three block areas b1 to b3 above are equivalent to each other, and the compared value is almost “0 (zero)”. . Therefore, the variable L in the above equation (4) is “+ (plus)”.

  Further, if the same comparison is made in the three block areas b1 to b3 positioned above the block area c2 of the face portion of the subject and the three block areas a1 to a3 positioned further above, the same brightness is obtained. Therefore, the comparison value that is the variable M in the above equation (5) is almost “0 (zero)”.

  Further, in the comparison between the uppermost center block area a2 and its left and right block areas a1 and a3, the brightness is equivalent, and the comparison value as the variable N in the above equation (6) is almost “0 (zero)”. It becomes.

  As a result, as a whole, the numerical value of the comparison value “+ (plus)” between the block area c2 where the face of the person who is the subject is located and the three block areas b1 to b3 above the block area c2 is the output coefficient Against itself. In particular, when the difference in the integral value of the luminance value is large between the block region c2 and the three block regions b1 to b3 above the block region c2, the numerical value of the comparison value also increases accordingly.

  Next, consider the case where the face of the person, the most important part of the subject, is located in the block area c1 shifted to the left by one from the center of the shooting range shown in FIG.

  Also in this case, when the face of the person is located in the block area c1 and the background is bright and the backlight is bright, only the value obtained by comparing the block area c1 with the three block areas b1 to b3 above is “+ (plus ) ”, And in most other cases,“ 0 (zero) ”. Therefore, as a whole, the block area c1 where the face of the person who is the subject is located and the three block areas b1 to b3 above the block area c1 The numerical value of the comparison value “+ (plus)” becomes the output coefficient Against itself.

  Similarly, even if the face of the person who is the most important part of the subject is located in any of the block areas b1 to b3 that are shifted up by one from the center of the shooting range shown in FIG. When the surrounding block area as the background is bright backlight, only the value obtained by comparing the block area b1 (or b2, b3) with the three block areas a1 to a3 further above is “+ (plus)”. In other cases, the value is almost “0 (zero)”. Therefore, as a whole, a comparison value “+ () between the block area b1 where the face of the person who is the subject is located and the three block areas b1 to b3 above the block area b1. The numerical value of “plus)” becomes the output coefficient Against itself.

  Furthermore, even when the face of the person, the most important part of the subject, is located in the uppermost block area a2 of the shooting range shown in FIG. In this case, the value obtained by comparing the block area a2 with the left and right block areas a1 and a3 is “+ (plus)”. In other cases, the value is almost “0 (zero)”. The numerical value of the comparison value “+ (plus)” between the block area b1 where the face of the person who is the subject is located and the three block areas b1 to b3 thereabove becomes the output coefficient Against itself.

  Thus, when the backlight is generated in this way, it can be determined by the output coefficient Against. In the process of FIG. 2, the result of the comparison operation of the backlight determination in the step A07 results in the backlight. Whether or not has occurred has been determined (step A08).

  Then, only when it is determined that backlighting has occurred, the AE exposure value is corrected corresponding to the output coefficient value, specifically, the exposure value is corrected and set in the positive direction by the amount corresponding to the output coefficient value. (Step A09) Then, the process proceeds to Step A02 to wait for the shutter key to be operated.

  However, in the process of waiting for the shutter key to be operated while repeatedly executing the processes of steps A01 and A02, when the multi-metering mode is set, the processes of steps A03 to A09 are sequentially performed. Even when backlighting occurs, the exposure value can be corrected in real time.

  When it is determined in step A02 that the shutter key has been operated, the process immediately shifts to shooting, and AF (automatic focusing) is first performed to obtain an accurate focusing distance of the subject (step A10).

  Next, in the focused state, it is determined whether or not the multi-metering mode is set (step A11), and when it is determined that the multi-metering mode is not set and the other metering mode is set. While performing AE in accordance with the photometry mode (step A12), if it is determined that it is the multi-photometry mode, the latest exposure at that time when the backlight correction is performed as necessary by the processing in step A09. A value is set (step A13).

  Thereafter, after performing AWB adjustment (step A14), image data is shot (step A15), the obtained image data is compressed by the JPEG circuit 27, and the obtained image data is flash memory as a recording medium. 28 is written (step A16), and then the process returns to step A01 in preparation for the next shooting.

  In this way, the image data is divided into a plurality of block areas, and the luminance signal is integrated to obtain an integrated value for each block area, and the backlight is determined based on a comparison result between the integrated values. Because the amount of data handled is sufficiently small while processing by software, the calculation can be completed in a short time, and the backlit state can be quickly determined from the captured image data and used for actual shooting to obtain the proper exposure output. It is possible to execute the shooting.

  Further, although the upper three block areas are used as the pattern to be compared with the blocks, it goes without saying that the combination can be changed.

(Second Embodiment)
A second embodiment when the present invention is applied to a digital still camera will be described below with reference to the drawings.

  Note that the circuit configuration itself is basically the same as that shown in FIG. 1, and the same parts are denoted by the same reference numerals, and the illustration and description thereof will be omitted.

  Next, the operation of the above embodiment will be described.

  Here, the operation will be described assuming that the brightness is corrected when the multi-metering mode is set in the metering mode during the recording mode.

  FIG. 4 mainly shows the processing contents performed by the CPU 21. At the beginning, it is determined whether or not the metering mode is the multi-metering mode (step B01). If not, the shutter key of the key input unit 26 is determined. The process of determining whether or not an operation has been performed (step B02) is repeatedly performed at a predetermined cycle, thereby waiting for them.

  If it is determined in step B01 that the multi-metering mode is selected, shooting is performed by AF (auto focus), AE, and AWB (automatic white balance) adjustments in order to obtain image data for performing backlight determination immediately. Image data is acquired (step B03).

  Then, at the stage where the acquired image data is stored in the DRAM 20, the luminance signal Y is divided into a total of 50 block areas, for example, 5 × 10 × 10 as shown in FIG. 5 (step B04).

  The luminance signal Y for each block area thus divided is integrated (step B05). The integrated values for each block region obtained by the integration are “Sum00” to “Sum49” as shown in the figure.

  It is assumed that the histogram using the integration values “Sum00” to “Sum49” of these luminance signals has a distribution as shown in FIG. In this case, the horizontal axis represents the integral value of luminance expressed by 8-bit numerical values, the vertical axis represents the number of blocks, and the total number of blocks is “50”.

  This figure shows a luminance distribution when a subject having a very monotonous image pattern, such as white paper, is photographed, and the brightness distribution is concentrated in almost one place.

  Therefore, the image data has a uniform brightness, and the backlight correction as shown in the first embodiment is not performed.

  However, when the luminance distribution is concentrated in such a very narrow range, gray that is a halftone is processed as it is faithfully as it is, but some of the luminance values such as white and black are extreme. If it matches the standard, it will be processed as gray.

  This means that even if a single blue sky is photographed, it is processed as a gray image, that is, a cloudy sky, and brightness adjustment is required.

Therefore, first, the integrated values “Sum00” to “Sum49” are used, and the average value of the level of the luminance signal Y per pixel is adjusted to the exposure time at which a certain reference value is obtained. That is,
Yref = (sum00 + sum01 + ... + sum49) / (50 * n) (8)
(However, Yref: luminance reference value per pixel,
n: Number of pixels per block. )
A brightness comparison value is calculated using the integrated value for each block region in a state in accordance with the reference value Yref (step B06). That is,
VALUE = (Aperture F value) ² / Exposure time (9)
(However, VALUE: Relative brightness (= EV).)
The brightness comparison value VALUE is calculated as follows, and the right side of the equation (9) may be further multiplied by a variation coefficient of the digital camera 10 solid.

  Therefore, the above equation (9) indicates that the comparison value VALUE is inversely proportional to the exposure time, and when the exposure time when the reference value Yref is adjusted is doubled, it is darkened by one step. The brightness comparison value is ½.

  Thus, the comparison value VALUE calculated in this way is compared with a threshold value prepared in advance (step B07), and brightness correction is performed depending on whether or not the comparison value VALUE is larger than the threshold value. It is determined whether or not (step B08).

  Only when it is determined that the brightness is to be corrected, the aperture F value, the shutter speed, and the CCD 12 output adjusted by the A / D converter 16 are adjusted so that a brighter image can be obtained during actual shooting. The gain and the like are corrected and set (step B09), and then the process proceeds to step B02 to wait for the shutter key to be operated.

  However, in the process of waiting for the shutter key to be operated while repeatedly executing the processes of steps B01 and B02, when the multi-metering mode is set, the processes of steps B03 to B09 are sequentially performed. When it is necessary to correct the brightness, the exposure value can be corrected and set appropriately.

  When it is determined in step B02 that the shutter key has been operated, the process immediately shifts to shooting, and AF (automatic focusing) is first performed to obtain an accurate focusing distance of the subject (step B10).

  Next, in the in-focus state, it is determined whether or not the multi-metering mode is set (step B11). When it is determined that the multi-metering mode is not set and the other metering mode is set. While performing AE according to the photometry mode (step B12), if it is determined that the multi-photometry mode is selected, the brightness is corrected as necessary by the processing in step B09, and the most at that time. A new exposure value is set (step B13).

  Thereafter, after performing AWB adjustment (step B14), image data is photographed (step B15), the obtained image data is compressed by the JPEG circuit 27, and the obtained image data is flash memory as a recording medium. 28 (step B16), and then returns to the processing from step B01 in preparation for the next shooting.

  In this way, the image data is divided into a plurality of block areas, and the luminance signal is integrated to obtain an integrated value for each block area, and the brightness is determined based on the comparison result with the threshold value of the integrated value. Since the amount of data handled while being processed by software is sufficiently small, the calculation can be completed in a short time, and the brightness state can be quickly determined from the captured image data, for example, gray in a dark environment The correct exposure can be used for actual shooting by adjusting the exposure as necessary to accurately represent the halftone between the white paper that is visible and the white paper that appears white correctly in a bright environment. It becomes.

  Note that the method of performing exposure correction by backlight shown in the first embodiment and the method of performing exposure correction corresponding to the brightness distribution shown in the second embodiment are executed in combination. Thus, more accurate exposure control can be realized.

  In such a case, in a case where a large difference appears in the luminance value between blocks where backlighting occurs, the histogram of luminance values tends to have a large distribution. On the other hand, in the case where backlighting does not occur and the overall brightness is almost uniform, the exposure is adjusted from the brightness distribution according to the brightness at that time. It becomes possible to do.

  In each of the above embodiments, the image data is divided into, for example, 50 block areas. In that case, if the range is less than 2% of the entire image, even if there is a remarkably large difference in luminance, it will not be reflected in the distribution of luminance values, and will have an adverse effect on obtaining an appropriate exposure value in the multi-photometry mode. It can be judged that there is no effect.

  Similarly, if the number of block areas into which image data is divided becomes smaller, the barrel system that bears exposure correction will decrease, but if it is up to a certain range, even if there is a significantly large luminance difference, The effect can be absorbed.

  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.

  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.

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

Claims (9)

An image sensor for imaging image data;
Dividing means for dividing the image data into a plurality of regions;
Generating means for generating a luminance signal from image data for each of a plurality of areas divided by the dividing means;
Integrating means for integrating the luminance signals for each of the plurality of regions generated by the generating means;
A first comparing means for comparing the integral values for each of the plurality of areas obtained by the integrating means between a plurality of areas adjacent in the vertical direction and calculating a difference in luminance of the upper area with respect to the luminance of the lower area;
The luminance difference calculated by the first comparison means for a plurality of areas including the central area of the image data and a plurality of areas that are above the image data and do not include the central area of the image data. An automatic exposure comprising: a determination means for determining that the object is backlit when the luminance difference obtained by adding the luminance difference calculated by the first comparison means as a target is larger than a predetermined value. apparatus. A second comparing means for comparing the integrated values of the plurality of areas obtained by the integrating means between a plurality of areas adjacent in the left-right direction, and calculating a difference in luminance between the left and right areas with respect to the luminance of the central area; Prepared,
The determination means includes a luminance difference calculated by the first comparison means for a plurality of areas including a central area of the image data, and an upper area of the image data and a central area of the image data. The difference in luminance calculated by the first comparison unit for a plurality of non-regions and the second comparison unit for a plurality of regions that are above the image data and do not include the central region of the image data. 2. The automatic exposure apparatus according to claim 1, wherein when the difference in luminance obtained by adding together the difference in luminance calculated by the above is larger than a predetermined value, it is determined as backlight.   The determination means targets a plurality of areas including the central area of the image data and the plurality of areas including the uppermost area of the image data and the luminance difference calculated by the first comparison means. 3. The automatic exposure apparatus according to claim 1, wherein when the difference in luminance obtained by adding together the difference in luminance calculated by the first comparison means is larger than a predetermined value, it is determined that the light is backlit. .   The determining means, when summing up the luminance differences calculated by the first comparing means in each part of the image data, sums up after multiplying by a weighting factor corresponding to the position of each area. The automatic exposure apparatus according to claim 1.   The determining means multiplies a weighting factor corresponding to the position of each area when adding up the luminance differences calculated by the first comparing means or the second comparing means in each part of the image data. The automatic exposure apparatus according to claim 2, wherein the sum is added.   6. The determination means according to claim 1, wherein when the difference in luminance obtained by summing is positive, it is determined as backlight, and when it is negative, it is determined as follow light. Automatic exposure device.   7. The automatic exposure apparatus according to claim 1, further comprising a backlight correction unit that corrects backlight when the determination unit determines that the backlight is back. A calculation means for calculating a luminance distribution state from an integral value for each of a plurality of areas obtained by the integration means;
8. The automatic exposure apparatus according to claim 7, further comprising brightness correction means for correcting brightness according to the luminance distribution state calculated by the calculation means. An imaging step for imaging image data;
A division step of dividing the image data into a plurality of regions;
A generation step for generating a luminance signal from the image data for each of the plurality of regions divided in the division step;
An integration step for integrating the luminance signals for each of the plurality of regions generated in this generation step;
A first comparison step for comparing the integration values for each of the plurality of regions obtained in this integration step between a plurality of regions adjacent in the vertical direction, and calculating a difference in luminance of the upper region with respect to the luminance of the lower region;
The luminance difference calculated by the first comparison step for a plurality of areas including the central area of the image data, and a plurality of areas that are above the image data and do not include the central area of the image data. An automatic exposure comprising: a determination step for determining that the object is backlit when the difference in luminance obtained by adding the difference in luminance calculated in the first comparison step as a target is greater than a predetermined value; Method.

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