There is a lot of discussion about how best to remove noise in digital camera images and a lot of tools to do it. For this article I have compared just about every tool possible to try and find the best one.
CCD noise comes in two parts, luminance noise and chroma noise. Luminance noise makes an image look grainy on screen, but is usually not visible when printed. Chroma noise is visible as random red and blue pixels and is usually less obvious both on screen and printed. Removing luminance noise reduces the sharpness of the image and removing the chroma noise damages some of the correct color. So noise reduction is a balance between how much softness and color damage you are willing to accept vs. how much noise you want to remove. Unless you use an uncompressed mode with your camera, JPEG artifacts also get added into the mix.
I was interested in seeing how much noise each tool could remove before the image got too soft (for my tastes). I did not do any sharpening after the noise reduction (even if the tool had that capability built in), that will be another test.
I used the following three source images, each one providing a unique challenge. Click on the thumbnail for the original, straight out of the camera images.
Due to disk space constraints I can only show a 400x400 sample patch from each image. Rolling over a sample will show the original, noisy image. The sample patches for the top four tools are presented as PNGs to prevent introducing new JPEG artifacts, but for the runners-up I used JPEGs set to 90% for disk space and bandwidth considerations.
I tested the following 22 products: