CG Sketchbook , notes and tutorials

Un-blurry filters in blender nodes

A bit of background :I’ve always been fascinated by the ‘HDR look’ ,  not so much by  its main function : compressing luminosity range  .That’s very important ,but not the fun part.The fun part is ‘local contrast enhancement’ : but  how does it work exactly ? idea : hdr ToneMapping Operators are very complex stuff trying to reproduce the human vision.

So for the artist .. can it be broken down to some simpler tools ?something that can be more controllable and reliable than using strange TMOs like fattal or mantiuk ?In CG that could be good ,keeping a full artistic control, better than blindly using a tool meant for realworld photos, that is often too ‘aggressive’  .

I always felt that many experienced cg artists don’t use strange tmos , because they can get those results with simpler procedures ! :

Ok . That’s very broad and vague : but  in the image below  you can see 2 filters (done with a series of nodes) :  these have their own names and purpose (highpass and bloom), also they give a nice  ‘local contrast enhancement’ : or at least something similar, but much simpler/lighter  of  what you get in e.g. QtpfsGui. And what’s nice is that it won’t be too aggressive on a cg render that’s already tonemapped (in terms of luminosity range) and more controllable.

Notes :  i took ideas from vasrious places :

–Gimp plugin repository ‘Highpass filter’and ‘retinex’ (great stuff !)

–Blender game engine GLSL filters : By MartinSH found on Blenderartist forums (here) : there i discovered retinex is the inverse of bloom .  So  wondered if both could be used togheter ? yes, using different radiuses.

BTW, The proper NASA  ‘Retinex’ is more complex than this . But sure this makes a nice bloom effect  : it darkens highlights making image more readable (retinex) and .. at same time gives a nice bloom halo . 🙂

–The higpass filter is similar to un-sharp mask . I admit i never understood or never got really working the unsharp node explainend by Mike Pan .(Edit : Actually , it’s Matt Ebb who did the tutorial on unsharp mask nodes , and about SSAO ( here ), Mike pan explained a similar node setup for SSAO)

So i prefer this highpass  , the  procedure comes from a PS tutorial  (here)  adapted to blender nodes.

EDIT : another experiment , still not a proper retinex but i added 2 more radiuses to the highpass section (so now it’s 3 blooms and 3 highpass)

The effect is a bit too intense  to better show the result  :




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