The Gimp has two different options in how you can perform Gaussian blur: "IIR" and "RLE". What's the difference between them?

  • $\begingroup$ iir is likely "infinite impulse response" which is a type of filtering (the other being finite impulse response). Not sure what rle could stand for. It makes me think of "run length encoding" but I don't think that's what it stands for. $\endgroup$
    – Alan Wolfe
    Commented Aug 14, 2015 at 4:03
  • $\begingroup$ I guess I was right about rle but don't understand how it applies. docs.gimp.org/en/plug-in-gauss.html $\endgroup$
    – Alan Wolfe
    Commented Aug 14, 2015 at 4:08
  • $\begingroup$ "RLE Gaussian Blur is best used on computer-generated images or those with large areas of constant intensity." Makes me think it's some kind of optimization of the blur process, that's somehow data-dependent so it works better on certain kinds of images? Is there any visible difference between the results of the two? $\endgroup$ Commented Aug 14, 2015 at 21:32
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    $\begingroup$ This question seems very poorly formulated... You could have taken the time to do a quick search to at least get the definitions for the acronyms, since the previous commenters don't seem to know what they mean exactly. $\endgroup$
    – glampert
    Commented Aug 15, 2015 at 4:18

1 Answer 1


From the GIMP docs:


IIR stands for “infinite impulse response”. This blur works best for large radius values and for images which are not computer generated.


RLE stands for “run-length encoding”. RLE Gaussian Blur is best used on computer-generated images or those with large areas of constant intensity.

and also

They both produce the same results, but each one can be faster in some cases.

So the short answer is that IIR is optimised for photographs, and RLE is optimised for images with areas of flat colour.

The claim seems to be that the only difference is the time taken to calculate the blur, and that the end results are identical. I haven't tested this, so if you need to rely on that claim you should test both and check for any differences in the results.


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