The color image enhancement--ace algorithm of ISP module.

ACE (Automatic color enhancement), an automatic color enhancement algorithm, is a very effective method for color image enhancement. Its improved algorithm and fast implementation are presented in article Automatic Color Enhancement (ACE) and its fast implementation,2012 .

in the NXN image, thealgorithm complexity of ACE algorithm is O (n^4), the new ACE algorithm adopted two approximate methods, one is to use polynomial function approximation slope function (Slope functions) to reduce convolution calculation, The second is to use different degrees of interpolation to reduce the amount of convolution calculation.

The specific steps of the ACE algorithm:

The first step: separately processing the R,G,B channel of the color image, calculating the R (X) value of each pixel, where SA (t) is the slope function, which means that the first step adapts to the local image contrast, SA (t) can enlarge the small difference, and enrich the large difference, Ability to extend or compress dynamic range according to local content:

The second step: using the following formula to show R (x) between [0,1], the enhanced channel, the second step to obtain the global white balance.

The third step: to solve the optimization problem, the ACE algorithm can be regarded as a smoothing and local correction method for the normalized histogram equalization method.

Some of the factors considered in the improvement approach are:

1) Other slope function SA (t), polynomial function approximation

2) In addition to 1/| | x-y| | The selection of the weight function outside

3) in the summation process, Y can be limited to a small window around X

4) Some other standardized methods of L (x)

Experimental results: Download the source code on the official website, install the FFTW3 library before the normal operation to get results. The method has obvious effect on low contrast or fog image processing.

Source Code link URL: http://www.ipol.im/pub/art/2012/g-ace/

FFTW3 Library Download and configuration link: http://bbs.csdn.net/topics/390815673

Command line: Autocolorenhancement-a 5-w 1/r-M interp:12 input.bmp output.bmp

Original

After ace processing

Original

After ace processing

The color image enhancement--ace algorithm of ISP module.