I'd add that there is an important difference between Gaussian filtering and band-pass filtering: Gaussian filtering blurs (sharpens) everything by a specified amount, whereas low-pass (high-pass) filtering imposes a minimum amount of blurriness (sharpness). This often makes band-pass filtering the right choice for images with heterogenous resolution, because you often want to blur the noisiest, sharpest parts without blurring the smoothest, blurriest parts. Cryo-EM maps often fall in this category, and thus represent a common use case.
This is just like ChimeraX Gaussian filtering which does a convolution with a Gaussian in Fourier space. That is relatively fast — a few seconds for a 256**3 map. You can already do sharpening with the “invert” option to the gaussian filtering command (“vol gaussian #1 1.5 invert true”). Gaussian filtering is one form of low pass filtering — others could be added. I think it would be nice to allow a very fast (10 updates per second) test filtering on a small region using a mouse drag to figure out the desired parameters. But I never spent to the time to figure out a user interface (what small region, how do you undo, how do you then apply to full map, …).
Tom
> On May 6, 2017, at 10:27 AM, Oliver Clarke <olibclarke@gmail.com> wrote:
>
> Hi,
>
> Has any consideration been given to adding the capacity for fourier-space map sharpening/low pass filtering to ChimeraX? I’m not sure whether or not it is feasible speed wise, but if it is it would be a very useful addition for EM, allowing one to easily try different sharpening B-factors/low pass cutoffs and save the resulting map(s).
>
> Cheers
> Oli
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