Auto white balance apparatus and white balance adjusting method
View Patent ↗To provide an auto white balance apparatus capable of performing stable white balance adjustment. A parent block is divided into child blocks by a block-dividing circuit 110, and a typical value is calculated every child block by a typical-value calculating circuit 120, and then the distance between the typical color difference component of each parent block and the typical color difference component of each child block is obtained on a color difference plane. A child block satisfying a condition equal to or less than a threshold value S is selected to recalculate reliability of a parent blocks by using only selected child blocks. Moreover, a white balance evaluating circuit 130 corrects reliabilities of parent blocks in accordance with the number of unselected child blocks.
1. An auto white balance apparatus for applying white balance adjustment to a picked-up image, comprising:
block-dividing means for dividing an input image into a plurality of blocks;
typical-value calculating means for calculating, for each block, a typical value including luminance and color difference representing the block in accordance with each color value in the block; and
white balance adjusting means for applying white balance adjustment to the image in accordance with the typical value of each block; wherein
the block-dividing means includes
parent block-dividing means for dividing an input image into a plurality of parent blocks, and
child block-dividing means for dividing each parent block into a plurality of child blocks;
the typical-value calculating means includes
parent typical-value calculating means for calculating a typical value including luminance and color difference representing a parent block in accordance with each color value in a parent block,
child typical-value calculating means for calculating a typical value including luminance and color difference representing a child block in accordance with each color value in a child block,
child block selecting means for selecting several desired child blocks out of a child block group included in a parent block in accordance with comparison between parent typical color difference and child typical color difference of each child block included in the parent block, and
parent typical value recalculating means for recalculating the typical value of a parent block in accordance with the typical value of each selected child block; and
the white balance adjusting means performs white balance adjustment for the image in accordance with the typical value of each recalculated parent block.
2. The auto white balance apparatus according to claim 1 , further comprising:
block reliability estimating means for obtaining a distance between color difference of a white object under each light source and the typical color difference of each parent block on a color difference plane on each assumed light source every parent block; and
reliability correcting means for correcting the reliability of each of the parent blocks in accordance with the number of child blocks selected by the child block selecting means; wherein
the white balance adjusting means performs white balance adjustment for the image in accordance with the recalculated typical value of each parent block and the corrected reliability of each parent block.
3. The auto white balance apparatus according to claim 2 , wherein
the reliability correcting means performs correction such that, as the number of child blocks selected by the child block selecting means decreases, the reliability of a parent block lowers.
4. The auto white balance apparatus according to claim 1 , wherein:
the child block selecting means selects several desired child blocks from among a child block group included in a parent block in accordance with the distance between parent typical color difference and child color difference of each child block included in the parent block on a color difference plane.
5. The auto white balance apparatus according to claim 1 , wherein:
the child block selecting means obtains the distance between parent typical color difference and child typical color difference of each child block included in the parent block on a color difference plane and selects, as desired child blocks, child blocks in which the distance is equal to or less than a predetermined threshold value.
6. The auto white balance apparatus according to claim 5 , wherein
the predetermined threshold value is determined in accordance with the typical color difference of each parent block.
7. The auto white balance apparatus according to claim 1 , further comprising:
child block division determination means for determining whether to divide the image into child blocks in accordance with the object luminance of the image, wherein
when a determination is made that the image is not to be divided into child blocks, the white balance adjusting means applies white balance adjustment to the image in accordance with the typical value of each parent block calculated by the parent typical-value calculating means.
8. The auto white balance apparatus according to claim 7 , wherein
the child block-dividing means determines to divide the image into child blocks when the object luminance of the image is included in a luminance range which can be assumed by a plurality of light sources.
9. The auto white balance apparatus according to claim 7 , wherein
when the object luminance of the image is included in a luminance range which can be assumed by daylight and fluorescent light or daylight and tungsten light, the child block division determination means determines to divide the image into child blocks.
10. The auto white balance apparatus according to claim 7 , wherein:
when determining to divide the image into child blocks in accordance with the object luminance of the image, the child block division determining means further determines whether the light source of the image is estimated as a predetermined light source in accordance with the average of typical color differences of all parent blocks constituting the image, and only when the light source is estimated to not be the predetermined light source, finally determines to divide the image into child blocks.
11. The auto white balance apparatus according to claim 10 , wherein:
the predetermined light source is a light source included in an area of overlap between each light source area defined on a color difference plane.
12. The auto white balance apparatus according to claim 11 , wherein:
the light source included in the overlapped area is fluorescent light and tungsten light.
13. The auto white balance apparatus according to claim 7 , wherein
when a determination is made to divide the image into child blocks in accordance with the object luminance of the image, the child block division determination means further determines whether the light source of a parent block is estimated to be a predetermined light source in accordance with the typical color difference of each parent block constituting the image and finally determines to divide into child blocks only a parent block for which the light source is determined not to be the predetermined light source.
14. A white balance adjusting method for applying white balance adjustment to a picked-up image, comprising:
a parent block-dividing step of dividing an input image into a plurality of parent blocks;
a child block-dividing step of further dividing each parent block into a plurality of child blocks;
a parent typical value calculating step of calculating a typical value including luminance and color difference representing a parent block in accordance with each color value in the parent block;
a child block selecting step of selecting several desired child blocks from among a child block group included in the parent block in accordance with comparison between parent typical color difference child typical color difference of each child block included in the parent block;
a parent typical-value recalculating step of recalculating the typical value of a parent block in accordance with the child typical value of each selected child block; and
a white balance adjusting step of applying white balance adjustment to the image in accordance with the typical value of each recalculated parent block.
15. The white balance adjusting method according to claim 14 further comprising:
a block reliability estimating step of obtaining, for every parent block, the distance between color difference of a white object and a typical color difference of each parent block on a color different plane under each light source on each assumed light source and estimating the reliability when each of the light sources illuminates the scene of each of the parent blocks in accordance with each of these distances; and
a reliability correcting step of correcting the reliabilities of the parent blocks in accordance with the number of child blocks selected in the child block selecting step; wherein
in the white balance adjusting step, white balance adjustment is applied to the image in accordance with the typical value of each recalculated parent block and the reliability of each corrected parent block.
16. The white balance adjusting method according to claim 14 , further comprising:
a child block division determination step of determining whether to divide the image into child blocks in accordance with the object luminance of the image; wherein
when a determination is made not to divide the image into child blocks, white balance adjustment is applied to the image in accordance with the typical value of each parent block calculated in the parent typical value calculating step.