opencv clahe parameters explanation

Question

I would like to know proper explanation of the clahe parameters i.e clipLimit and tileGridSize. and how does clipLimit value effects the contrast of the image and what factors(like image resolution, object sizes) to be considered to select tileGridSize. Thanks in advance

Answer 1

this question is for a long time ago but i searched for the answer and saw this,then i found some links which may help,obviously most of below information are from different sites.

AHE is a computer image processing technique used to improve contrast in images. It differs from ordinary histogram equalization in the respect that the adaptive method computes several histograms, each corresponding to a distinct section of the image, and uses them to redistribute the lightness values of the image. It is therefore suitable for improving the local contrast and enhancing the definitions of edges in each region of an image. and , AHE has a tendency to over-amplify noise in relatively homogeneous regions of an image ,A variant of adaptive histogram equalization called contrast limited adaptive histogram equalization (CE) prevents this by limiting the amplification.

for first one this image can be useful:

CLAHE limits the amplification by clipping the histogram at a predefined value (called clip limit)

tileGridSize refers to Size of grid for histogram equalization. Input image will be divided into equally sized rectangular tiles. tileGridSize defines the number of tiles in row and column.

it is opencv documentation about it's available functions: https://docs.opencv.org/master/d6/db6/classcv_1_1CLAHE.html

and this link was good at all: https://en.wikipedia.org/wiki/Adaptive_histogram_equalization#Contrast_Limited_AHE http://www.cs.utah.edu/~sujin/courses/reports/cs6640/project2/clahe.html