# What is the difference between a range filter and a low-pass filter?

A low-pass filter attenuates the high frequencies, preserving only smooth variations in the provided image. The result of an image which is low-pass filtered is an image with blurred edges (hence certain details and noice are removed after the application of the low-pass filter). There are different low-pass filters: ideal, Butterworth, and Guassian.

However, I don't have an intuitive definition of range filters. Intuitively, how would you describe a range filter? How is it different from a low-pass filter?

I am more interested in receiving answers in the context of image processing (and computer vision), so you should assume that signals are images.

• I think that by range filters we mean filters that are applied to the range of the image (if we consider coloured images as functions of the form $\mathbb{R}^2 \rightarrow \mathbb{R}^3$). If the domain of the image are the position of the pixels (coordinates x and y), then the range of an image are the colours at those positions. – nbro Mar 29 '19 at 15:14
• when I google “range filter” I get hits from Home Depot. I don’t see any obvious associations to image processing. please add a link to where you see “range filter” mentioned. this could be a great question – user28715 Mar 30 '19 at 14:16
• @StanleyPawlukiewicz I have seen it in some slides, which I can't share with you (I think). But, as I said above, I think that range refers to the range (codomain, i.e. pixel values) of the image. – nbro Mar 30 '19 at 14:24