  We propose a simple method for estimating noise level from a single color
image. In most image-denoising algorithms, an accurate noise-level estimate
results in good denoising performance; however, it is difficult to estimate
noise level from a single image because it is an ill-posed problem. We tackle
this problem by using prior knowledge that textures are highly correlated
between RGB channels and noise is uncorrelated to other signals. We also
extended our method for RAW images because they are available in almost all
digital cameras and often used in practical situations. Experiments show the
high noise-estimation performance of our method in synthetic noisy images. We
also applied our method to natural images including RAW images and achieved
better noise-estimation performance than conventional methods.
