| 摘要 |
This invention relates to a system and method for improving the uniformity in exposure and tone of a digital image using a locally adapted histogram equalization approach. This approach involves first segmenting the digital image into a plurality of image patches (302). For each of these patches, a pixel brightness level histogram is created (304). The histogram for each patch is then optionally averaged with the histograms associated with a prescribed number of neighboring image patches (306). A normalized cumulative distribution function is generated for each patch based on the associated averaged histogram (308). This normalized cumulative distribution function identifies a respective new pixel brightness level for each of the original pixel brightness levels. For each of the original pixel brightness levels, the associated new pixel brightness levels from one or more of the image patches are blended (314). Preferably, this blending is accomplished using either a bilinear or biquadratic interpolator function. Finally, for each image patch, the original pixel brightness level of each pixel in the image patch is replaced with the blended pixel brightness level corresponding to that original brightness level (316). A further refinement can also be implemented to mitigate the effects of noise caused by areas of a single color in the scene depicted in patch. In one embodiment, this refinement entails employing a partial equalization approach. In another embodiment, the refinement entails limiting the gain exhibited by any of the blended pixel brightness levels associated with an image patch, in comparison to its associated original pixel brightness level, to a prescribed level.
|
