RMS contrast of image interpretation I have two grayscale images, say A and B, and I want to determine, which one is more contrast. For that I'm calculating an RMS contrast as it is described in Wikipedia. The results are about RMS_A = 0.4 and RMS_B = 0.1. Does it mean that image A is more contrast as its gray pixels are nearer to black/white values? How should I interpreter RMS value to determine contrast?
You defined to compute an RMS. I don't know why you choose it, but OK. How can we probe it as a contrast measure?  If you are considering images with positive pixel values, and consider that multiplying them by a scale factor $a&gt;1$, you extend the range, hence the contrast, or if  $a&gt;1$, you shrink the range, hence the contrast again. How does the RMS behave? A quick computation should give you an answer.

Indeed, those are hypotheses. Honestly, I would not consider RMS as a proper measure, as it does change with a value offset, which to be is substantially iso-constrast.