Hi,
I have got a remark, problem with CLAHE algorithm on applying 8 bit and 16 bit grayscale image. I use opencv-master build. So if i applying CLAHE algorithm on 8 bit grayscale image (CV_8UC1), the result was very good.
But unfortunately i have to work with 16 bit grayscale images (CV_16UC1).
If i normalized and converted the source 16 bit grayscale image to 8 bit and after that executed CLAHE, the result was beautiful, you can see it in this picture: 2.
If i executed CLAHE on the source 16 bit grayscale image, and after it normalized and converted to 8 bit, the result was very weird. Little grids appeared on the image and it was very unnatural, you can see it in this picture: 3.
I tried to different parametrization on CLAHE, but the point was the same.
I attached different pictures of my problem:
- Original 16 bit image normalize to 8 bit [0, 255] and convert to 8 bit (CV_8UC1).
- Applying CLAHE algorithm with default parameters (ClipLimit(40.0) and TilesGridSize(Size(8, 8))) on the previous (1.) image.
- Applying CLAHE algorithm with default parameters on the original 16 bit image. After executing, normalize CLAHE result to 8 bit [0, 255] and convert to 8 bit (CV_8UC1).
![Original 16 bit image normalize to 8 bit [0, 255] and convert to 8 bit (CV_8UC1).](http://kepfeltoltes.hu/161021/normalized8bitFromOriginalOutput_www.kepfeltoltes.hu_.jpg){kind=link}
![Applying CLAHE algorithm with default parameters on the original 16 bit image. After executing, normalize CLAHE result to 8 bit [0, 255] and convert to 8 bit (CV_8UC1).](http://kepfeltoltes.hu/161021/normalizedClaheOutput8Bit_www.kepfeltoltes.hu_.jpg){kind=link}
I have got some questions too:
- Why is limited the histogram bin size to 4096 when a 16 bit image has got (1<<16) == 65536 kinds shade?
- What do the grids mean on image 3? How can i eliminate them?
