Comments on Image Denoising by Sparse 3-D Transform-Domain Collaborative Filtering

In order to resolve the problem that the denoising performance has a sharp drop when noise standard deviation reaches 40, [1] proposed to replace the wavelet transform by the DCT. In this comment, we argue that this replacement is unnecessary, and that the problem can be solved by adjusting some numerical parameters. We also present this parameter modification approach here. Experimental results demonstrate that the proposed modification achieves better results in terms of both peak signal-to-noise ratio and subjective visual quality than the original method for strong noise.