Patent ID: 8270759

Claim:
A method for transforming a video image from a High Dynamic Range (HDR) image on an array of pixels to a Low Dynamic Range (LDR) image on the array of pixels, said array characterized by NY rows of pixels oriented in an X direction and NX columns of pixels oriented in a Y direction, said NX and NY each at least 5, said method comprising: generating an old luminance l old (x,y) on the array of pixels from a color space of the HDR image, wherein x and y are indexes of pixels in the X and Y directions, respectively; generating a scaled luminance l(x,y) for each pixel on the array of pixels according to l(x,y)=αl old (x,y)/l image , wherein α is a target average luminance for the image, and wherein l image is a geometric luminance of the image; segmenting the scaled luminance into S stripes subject to 1≦S≦NY, wherein each stripe consists of one row or a contiguous sequence of rows of the array of pixels; selecting a search strategy T(x,y) for searching for a target zone Z(x,y) of N zones for a current pixel P(x,y) of each stripe such that N is at least 3, wherein the N zones are denoted as zone 0, zone 1, . . . , zone N−1, wherein the search strategy T(x,y) is either a linear search strategy or a zone history-based search strategy; determining a start search zone of the N zones based on the selected search strategy; determining the target zone Z(x,y) for the current pixel P(x,y) of each stripe, using the search strategy and the start search zone; computing a convolution V zone (x,y) of the scaled luminance l(x,y) at the current pixel P(x,y) of each stripe using a convolution kernel k zone (x,y) specific to the target zone Z(x,y); generating a tone mapped pixel luminance l′(x,y) for the current pixel P(x,y) of each stripe according to l′(x,y)=l′(x,y)/(1+V zone (x,y)), which converts the stripes to tone-mapped luminance stripes; collecting the tone-mapped luminance stripes to form a tone mapped luminance pixel array; transforming the tone mapped luminance pixel array to the color space to form the LDR image; and storing, displaying, or both storing and displaying the LDR image, wherein zone i (i=1, 1, . . . , N−1) of the N zones corresponds to a square of pixels in the array of pixels, said square comprising the current pixel P(x,y) at a geometrical center of the square if i is an odd integer and offset from the geometrical center of the square by one pixel if i is an even integer, each side of the square having a length L i that is measured in pixels and is a monotonically increasing function of i subject to L i ≧3.