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View Full Version : Levr--what is it?


govinda
04-04-2007, 06:59 PM
There've been a lot of threads about Levr mode, which is useful for creating high-con procedural channel maps. But much like the soup at my nearest all-night Thai joint, its recipe is a mystery. What's never discussed is how Levr mode combines two layers, according to what RGB math? What results can be expected? Most designers know that overlay mode is a combination of multiply and screen, and even the most obscure layer modes are just a google away--except for Levr. No info that I can find quickly.

Help says, not so helpfully: 'The value of the blend pixel is used to apply contrast to the background pixel.'

Erik Heyninck
04-04-2007, 09:33 PM
The best description I ever read on it comes from Per:

http://www.peranders.com/tutorials/tutorials.php?index=5

bottom of the page

Per-Anders
04-04-2007, 09:44 PM
Well contrast is at heart just the formula contrast(pixelvalue - 50%)+50% so contrast of 0% will give you 50% or mid grey, 100% will give you the original value and 200% will give you a value that's twice as far away from 50% or mid grey, e.g. if you color was 25% grey then at 200% contrast it would be 0% or black, or if it was at 75% grey it would become 100% or white. If Levr is as the manual states using the contrast then then it would seems to shift the contrast point, i.e. that 50% in the equation by the overlying layer's own value, and then uses the layer strength to control the contrast (but in a more extreme fashion so that 100% is full contrast). The result is basically that one layer controls the cutoff of the underlying layer (but inverted), you can see the results ad how they interelate in the toon shading tutorial on my website.

georgedrakakis
04-05-2007, 08:40 PM
here is a usefull link that explains (with formulas & photo examples)
21 layer blending modes
http://docs.gimp.org/en/gimp-concepts-layer-modes.html#id2567210

govinda
04-05-2007, 09:38 PM
Cool link! And thanks as usual, Per and Erik. Though I haven't looked at it in awhile, I've used that cel shading method in a piece that generated a little controversy here over two years ago (hint: it involved the city of Baghdad). ;)

I've written some notes on Levr as I try it out with various inputs. The reason I don't use it more is probably a common one--it's dodgy to predict the results at first. Cheers.

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