Method and apparatus for selectively adjusting the brightness of large regions of an image
First Claim
1. A method for adjusting the value of each one of a plurality of select pixel groups comprising one or more individual pixels which collectively define an image comprising the steps of:
- comparing the value of each pixel group with at least one of a darkness threshold and a brightness threshold;
incrementally enlarging the comparison of each pixel group to an area encompassing surrounding select pixel groups until any pixel group within the comparison area exceeds the darkness threshold or is less than the brightness threshold up to a maximum area of comparison;
assigning a value of size and average to each select pixel group in accordance with the incremental amount of area thereabout entirely below the darkness threshold or above the brightness threshold up to a maximum size and average; and
comparing the size of each select pixel group with a certain maximum size and adding the assigned average value of that pixel group to the pixel group value when that pixel group is at least the maximum size or when any pixel group within a predetermined distance thereof is the maximum size, or alternatively multiplying the average value of each pixel group by a smoothing characteristic and adding the result to that pixel group value when that pixel group is less than the maximum size and no other pixel group within the predetermined distance is the maximum size.
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Abstract
The invention concerns a method for rendering scene information in images having a large dynamic range, i.e. sunny and shady areas. The method takes particular advantage of image segmentation and computations employed in compression of images for electronic still photography. In distinguishing large areas, the method selectively adjusts the brightness of all portions of the area without necessarily preserving contrast which avoids halo artifacts. Those portions in areas of intermediate size are subjected to a smoothing feature which avoids the production of artifacts in the form of a line at the boundary.
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Citations
28 Claims
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1. A method for adjusting the value of each one of a plurality of select pixel groups comprising one or more individual pixels which collectively define an image comprising the steps of:
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comparing the value of each pixel group with at least one of a darkness threshold and a brightness threshold; incrementally enlarging the comparison of each pixel group to an area encompassing surrounding select pixel groups until any pixel group within the comparison area exceeds the darkness threshold or is less than the brightness threshold up to a maximum area of comparison; assigning a value of size and average to each select pixel group in accordance with the incremental amount of area thereabout entirely below the darkness threshold or above the brightness threshold up to a maximum size and average; and comparing the size of each select pixel group with a certain maximum size and adding the assigned average value of that pixel group to the pixel group value when that pixel group is at least the maximum size or when any pixel group within a predetermined distance thereof is the maximum size, or alternatively multiplying the average value of each pixel group by a smoothing characteristic and adding the result to that pixel group value when that pixel group is less than the maximum size and no other pixel group within the predetermined distance is the maximum size. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A method for selectively adjusting the brightness of a plurality of select pixel groups comprising one or more individual pixels which collectively define an image comprising the steps of sequentially selecting pixel groups from the image;
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comparing the value of each pixel group selected with a threshold defining an acceptable level of brightness and expanding the comparison to other pixel groups in succeeding concentric adjacent sets if the value of the initial pixel group is not within the acceptable level of brightness and until the value of at least one of the other pixel groups in the concentric adjacent sets is within the acceptable level of brightness up to a maximum number of sets corresponding to a predefined large area; assigning a size and average value to each pixel group in the image in accordance with the number of concentric sets of other pixel groups compared and the average value of such other pixel groups so compared which are not within the acceptable level of brightness; and comparing the size of each pixel group with the size associated with the predefined large area and adding the average to that pixel group when the size of that pixel group corresponds to the size of the large area; and
if that pixel group does not correspond to the size of the predefined area, thereafter comparing the size of all other pixel groups within a selected number of pixel groups from that pixel group with the size associated with the predefined large area and adding the average to that pixel group when the size of the any other pixel group within the selected number of other pixel groups has a size corresponding to the predefined large area;
or alternatively multiplying the size of each pixel group times a smoothing factor when the size of that pixel group and all other pixel groups within the selected number of pixel groups is less than the size associated with the predefined large area and adding the resulting value to the size of that pixel group, so that the amount added to each pixel group operates to bring that pixel within the acceptable level of brightness. - View Dependent Claims (12, 13)
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14. A method for hierarchal processing of a digital image made up of an array of pixel groups of one or more pixels in which each pixel group is provided a value by selectively adjusting the brightness of pixel groups in large areas of generally uniform brightness of the image without the necessity of preserving contrast comprising the steps of:
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selecting incrementally a pixel group from the array; comparing the value of the pixel group with a threshold; producing a first signal when the selected pixel value is at a level in comparison to the threshold indicative of a pixel group of sufficient brightness and producing a second signal when the selected pixel group value is at a level in comparison to the threshold indicative of a pixel group which may require selective brightening adjustment; assigning a first size and average value to the selected pixel group and selecting the next succeeding pixel group in response to the first signal; selecting each one of a first set of other pixel groups surrounding the selected pixel group in response to the second signal and comparing the value of each of the other surrounding pixel groups with the threshold, producing the first signal when the value of any of one of the surrounding pixel groups is at a sufficient brightness and producing the second signal when the value of all the pixels in the surrounding set require selective brightening adjustment; assigning a next larger size relative to the first size and corresponding average value to the selected pixel group and selecting the next succeeding pixel group in response to the first signal; selecting each one of a second set of other pixel groups surrounding the first set and comparing as recited above to produce one of the first and second signals accordingly and assigning a next successive larger size and corresponding average value to the selected pixel group up to a maximum number of selections; and adjusting the value of the selected pixel group in accordance with the average and size assigned to the selected pixel group. - View Dependent Claims (15, 16, 17, 18, 19, 20)
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21. Apparatus for compressing the dynamic range of a digital image, made up of an array of pixel groups of one or more pixels in which each pixel group is provided a value, by selectively adjusting the brightness of pixel groups in large areas which are at an unacceptable level of brightness comprising:
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a selector for selecting pixel groups; a comparator responsive to the selector for sequentially comparing each selected pixel group with the acceptable level of brightness and producing a first output when the selected pixel group value is an acceptable level of brightness and producing a second output when the selected pixel group value is not an acceptable level of brightness indicative of a pixel group which may require selective brightening adjustment; means for causing the selector to increment to the next succeeding pixel group in response to said first output; means for assigning size and average values to the selected pixel group being responsive to the first output for assigning a corresponding size and corresponding average value for the selected pixel group, and being responsive to the second output for causing the selector to select other pixel groups in a set surrounding the selected pixel group for comparison by the comparator with the acceptable level of brightness, said comparator being responsive to produce said first and second outputs up to a selected maximum number of succeeding sets of surrounding pixel groups; a size comparator for comparing the corresponding size of each selected pixel group with the maximum size and the size of other pixel groups in a select surrounding set within the maximum size and producing a first size output when the size of the selected pixel group is the same as the maximum size or the size of any other pixel group within the select surrounding set is the maximum size and providing a second size output when the size of the selected pixel group or any other pixel group within the select surrounding set is less than the maximum; and means responsive to the first size signal for adding the value of the selected pixel group to the average value of that pixel group for the selected number of sets for that pixel group and means responsive to the second size signal for multiplying the value of the selected pixel group by a smoothing characteristic in accordance with the size of that pixel group and adding the resulting value to the value of the selected pixel group, said means producing outputs indicative of the amount of brightening adjustment for the selected pixel groups. - View Dependent Claims (22)
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23. Apparatus for selectively adjusting the brightness of a digital image made up of pixel data elements comprising:
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comparator means for comparing each pixel data element with a threshold representative of an acceptable level of brightness and producing outputs corresponding to acceptable and unacceptable levels of brightness; means for selectively producing a corresponding size and average value for each pixel data element in response to the comparator output representing acceptable brightness; means responsive to the comparator means for selectively varying the size of the pixel data element to include selected adjacent pixel data elements in response to the comparator output representing an unacceptable level of brightness up to a maximum size, each size having a corresponding average value; and means for adjusting the brightness of the pixel data element in accordance with the corresponding average value. - View Dependent Claims (24, 25, 26, 27, 28)
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Specification