Image display based on multiple brightness indicators
Methods for controlling light sources in displays in response to image data determine both a central tendency for brightness and an upper extreme for brightness of an area of an image. Brightness of a light source is controlled based upon both the central tendency and the upper extreme. Controllers in displays such as televisions, computer monitors, digital cinema and the like may control light source in a manner that reduces or avoids perceptible haloing.
1. Apparatus for controlling an illumination element of a backlight in a display, the apparatus comprising:
a processor configured to:
for image data corresponding to an image, select from the image data a first subset of image data and a second subset of image data, wherein the subsets correspond respectively to a first region of the image and a second region of the image, wherein the second region encompasses the first region, and wherein the first region and the second region are at least partially illuminated according to a point spread function of the illumination element;
determine a first image brightness indication from the first subset of image data;
determine a second image brightness indication from the second subset of image data, the second image brightness indication different from the first image brightness indication; and
control the illumination element based at least in part on a combination of the first and second image brightness indication.
2. Apparatus according to claim 1 wherein the first image brightness indication comprises an upper extreme brightness indication.
3. Apparatus according to claim 2 wherein the first subset of image data or the second subset of image data comprises a plurality of candidate subsets, and wherein the upper extreme brightness indication comprises a value typifying a maximum brightness in one of the plurality of candidate subsets having image data with the greatest number of image elements with a brightness above a threshold among the plurality of candidate subsets.
4. Apparatus according to claim 3 wherein the maximum brightness for one of the plurality of candidate subsets corresponds to at least two discontiguous spatial regions of the image.
5. Apparatus according to claim 1 wherein combining the first and second image brightness indications comprises adding a first product and a second product, the first product comprising a product of the first image brightness indication and a first weight, and the second product comprising a product of the second image brightness indication and a second weight.
6. Apparatus according to claim 5 wherein a ratio of the second weight to the first weight comprises a function that increases with an absolute difference between the first and second image brightness indications.
7. Apparatus according to claim 5 wherein a ratio of the second weight to the first weight comprises a function that increases with a dispersion indication of the first subset or the second subset of image data, and wherein the dispersion indication is an indication of variability or spread of intensities of light required to be provided to a light modulator to make the bulk of a set of image elements appear as specified by image data.
8. Apparatus according to claim 7 wherein the dispersion indication comprises at least one of a range, a variance, a standard deviation, an interquartile range, a mean difference, a median absolute deviation, an average absolute deviation, and a dimensionless statistical measure of dispersion or variability of the brightness of a set of image elements.
9. Apparatus according to claim 1 wherein determining at least one of the first and second brightness indications comprises computing a function of color space components of the image data that are representative of brightness.
10. Apparatus according to claim 1 wherein determining at least one of the first and second brightness indications comprises computing a function of the image data scaled according to a point spread function of the illumination element.
11. Apparatus according to claim 1 wherein the processer is configured to downsample the image data and to determine at least one of the first and second brightness indications from downsampled image data.
12. A method for controlling an illumination element in a display, the method comprising:
for image data corresponding to an image, selecting from the image data a first subset of image data and a second subset of image data, wherein the subsets correspond respectively to a first region of the image and a second region of the image, wherein the second region encompasses the first region, and wherein the first region and the second region are at least partially illuminated according to a point spread function of the illumination element;
determining a first image brightness indication from the first subset of image data;
determining a second image brightness indication from the second subset of image data, the second image brightness indication different from the first image brightness indication;
combining the first and second image brightness indications to yield a combination; and
controlling the illumination element based at least in part on the combination.
13. A method according to claim 12 wherein combining the first and second image brightness indications comprises adding a first product and a second product, the first product comprising a product of the first image brightness and a first weight, and the second product comprising a product of the second image brightness indication and a second weight.
14. A method according to claim 13 wherein combining the first and second image brightness indications comprises
determining the first weight based at least in part on a first function; and
determining the second weight based at least in part on a second function;
wherein at least one of the first and second functions depends at least in part on at least one of the first and second image brightness indications, and
wherein a ratio of an output of the second function to an output of the first function increases with an absolute difference between the first and second image brightness indications.
15. A method according to claim 14 comprising normalizing the first weight and the second weight so that the sum of the first weight and the second weight is equal to a constant value.
16. A method according to claim 13 wherein combining the first and second image brightness indications comprises
determining the first weight based at least in part on a first function; and
determining the second weight based at least in part on a second function;
wherein at least one of the first and second functions depends at least in part on at least one of the first and second image brightness indications, and
wherein a ratio of an output of the second function to an output of the first function increases with a dispersion indication of the at least one subset.