Deconvolution vs UnsharpMask

[Dimitris Platis]

I would like to know the difference between Deconvolution and UnsharpMask...and in which cases we should use each....pros/cons.
I would appreciate any substantiated opinions on the matter

[oldwexi]

Hi Dimitris!
The main difference i see between Deconv and UsharpMask is:
Deconv is using the Point Spread function of a series of stars to bring the real
data, influenced by the seeing, back into the complete picture.
UnsharpMask is increasing the contrast between bright and dark areas, so
it destroys data to give you the impression of sharper stars, which most of the time than get
also either bright or dark rings.
So, as i  am interested in getting the real data out of my images instead of destroying and painting i would
never use UnsharpMask, i alway use Deconvolution on the linear calibrated images.

Gerald

[MortenBalling]

Well, I use both. Deconvolution as step 1 after integration, and UnsharpMask as one of the final steps.

Unless you want to use the data for scientific purposes, and lets face it, most of us are amateurs, I think the main target is to make an image with as much visible information as possible. That means that all tricks are acceptable, as long as it "looks good".

Deconvolution can also produce "panda eyes" around stars, but with both processes using a star mask and finely tuned deringing can solve that. Ringing in itself isn't a bad thing. When you resample using a Lanczos algorithm it uses a slight ringing, and that can produce excellent results when upscaling.

Using the PSF is a great idea, but often you are able to get equally good (and sometimes better) results, by tweaking the manual settings.

Best regards

Morten 

Edit: Even though Deconvolution works best on linear images, it's also a fantastic tool when working on non linear images. I do that a lot. Actually, the deringing sliders are easier to use on nonlinear images.

Oh yes, I also forgot: Deconvolution also gives you the possibility to reduce noise slightly, whereas UnsharpMask is pure ringing, but you can get an almost similar effect by using a luminans mask together with sharpening.

[jkmorse]

Got to side with Gerald here.  I never use UnsharpMask.  Other tools are much better and truer to the data, including Deconvolution, LHE, and HDRMultiscaleTransform to name a few. 

For what its worth (probably not much  )

Best,

Jim

[MortenBalling]

I don't know the english expression, but in danish you say something like "There are many ways to cross the river". And I absolutely agree, that Deconvolution is better than UnsharpMask, but my point is, that once you finish everything else, it's still worth a try, to see if UnsharpMask does any good. My experience is that sometimes it does.

I normally use a special "nebula mask", which I make by subtracting a star mask from a luminance mask. That way you only sharpen the bright parts of the image, and not dark areas or stars. Then I try to sharpen stars separately using a star mask.

Br

Morten 

[Dimitris Platis]

Well, the idea is whether Unsharp basically does the same job as Decon........more or less.....

[oldwexi]

Dimitris,
in short
UnsharpMask destroys data
Deconvolution recovers data from seeing blur.

So Deconv is the choice.
if you need later on sharpening - MMT can be the choice, see:
http://pixinsight.com/forum/index.php?topic=3556.msg25794#msg25794

Gerald

[Geoff]

See this article http://en.m.wikipedia.org/wiki/Unsharp_masking
There is a specific section on USM vs deconvolution.
Geoff

[jkmorse]

Morten,

Love the "river" analogy.  Applies to so much of PI.

Best,

Jim

[Warhen]

Sometimes we say 'More than one way to skin the cat', can't say I like it, because I like cats! Anyway Dimitris, think of it this way also, which will perhaps help. Deconvolution is restorative- it attempts to correct for atmospheric blurring. USM like LHE, or wavelet tools are enhancements. While LHE is a wonderful contrast enhancer, sometimes we may want to use an 'edge sharpening filter' like USM to make fine detail pop. I wouldn't use it on stars. I typically run LHE, ATWT for sharpening, and perhaps a taste of USM.