# 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?

• Are the images of the same scene or can be totally different?
– Royi
Commented Aug 4, 2020 at 5:12
• Are you after local or global contrast?
– Royi
Commented Dec 2, 2020 at 5:16

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 $$a>1$$, you extend the range, hence the contrast, or if $$a>1$$, you shrink the range, hence the contrast again. How does the RMS behave? A quick computation should give you an answer.