Dynamic range compression of high dynamic range imagery

Abstract

An improved apparatus and method adaptively compresses the dynamic range of an image from a sensor by rescaling the value of every pixel to fit within the dynamic range of a low dynamic range display while preserving local image contrast and global scene appearance.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is high level block diagram of one example of the invention.

FIG. 2 is a block diagram of the high frequency boost circuit of FIG. 1.

FIG. 3 is a block diagram of the dynamic range remap circuit of FIG. 1.

FIG. 4 is a specification of the logistic remapping circuit of FIG. 3.

FIG. 5 is a graph of the sigmoid function used to map high dynamic range input pixels to a lower dynamic range output display.

FIG. 6 is an illustrative example of an image produced by this invention.

Claims

1. An adaptive dynamic range compression apparatus, comprising: (a) a high frequency boost circuit that receives an input image comprising a plurality of input pixels, each of the input pixels being represented by a pixel value having a first predetermined first number of bits, the high frequency boost circuit producing an output image comprising a plurality of output pixels as a function of: (i) a first region of the input image neighboring each input pixel, the first region having a first area,(ii) a second region of the input image neighboring each pixel, the second region having a second area larger than the first area, and(iii) a third region of the input image neighboring each pixel, the third region having a third area larger than the second area; and(b) a dynamic range mapping circuit that receives the output image produced by the high frequency boost circuit and maps the output image to a target image comprising a plurality of target pixels, each of the target pixels being represented by a pixel value having a predetermined second number of bits, the second number of bits being less than the first-number of bits.

2. The apparatus of claim 1, in which the high frequency boost circuit produces an output image as a function of a convolution of each input pixel and its neighbors in the second region of the input image with a Gaussian distribution.

3. The apparatus of claim 1, in which the high frequency boost circuit produces an output image as a function of a statistical function of pixel values in the third region of the input image.

4. The apparatus of claim 3, in which the statistical function is the mean of pixel values in the third region of the input image.

5. The apparatus of claim 1, in which the high frequency boost circuit produces an output image as a function of: (a) a convolution with a Gaussian distribution of each input pixel and neighboring input pixels in the second region of the input image and(b) a statistical function of pixel values in the third region of the input image.

6. The apparatus of claim 5, in which the statistical function is the mean of pixel values in the third region of the input image.

7. A method of adaptively compressing the dynamic range of an image having a plurality of pixels, comprising the steps of: convolving each pixel of the image and a first region of the image around each pixel with a Gaussian operator to produce a processed pixel value; andadaptively normalizing the processed pixel value based on a mean value in a second region of the image around each pixel, the second region being larger than the first region, but smaller than the entire image.