On 26-1-2019 21:00, Bald Eagle wrote:
> "omniverse" <omn### [at] charternet> wrote:
>> "Norbert Kern" <nor### [at] t-onlinede> wrote:
>>> Hello,
>>>
>>> here is my attempt, using a layered texture and an imagefile for the scratches
> 
> .....
> 
>>> Norbert
> 
> Holy crap.  :O

I agree. The important thing is to use a bump_map of some quality.

> 
> 
> 
>> I like that, fine scratches or scuffed. Great how it follows the curvatures and
>> reflected light.
> 
> 
> I think that's an important part of the effect - the halo of concentric
> scratches.

See image attached. Playing with different bump_maps and strength of the 
bump_size.

> 
> 
>> Any criticism I can think of would be that some lines appear to radiate outward
>> from the lit areas, showing up as bright as the other, non-radial lines. Which
>> is what was mentioned before about the original idea, so I wonder how that
>> directional condition could be achieved? Seems like a polarization effect needed
>> to do that anyhow.

Maybe, that comes from the fact that the scratches are not very linear, 
more "curvy" as it were. I noticed that also with different bump_maps. 
The more linear the scratches are, the more the effect is visible.

> 
> 
> 
> Yeah - I'm also still very curious as to what gives rise to that selective
> effect IRL.  I'd be tempted to predict that only a series of oriented lines
> would reflect strongly - not a circular pattern.  I mean, it's not like
> completely random scratches adopt a circular pattern - so it must necessarily be
> a purely optical effect.
> 

It /is/ an optical effect of course, based imho on the strength of 
incident light reflecting from the scratch surfaces. The closer the 
incident light angle is to 90 degrees with regard to (part of) the 
scratch surface, the stronger the scratch reflects. Inversely, the 
scratch will hardly or not light up when the incident light angle is 
very low. The cumulation of strongly reflecting scratches will dominate 
the view in the end, giving rise to the optical illusion.

-- 
Thomas

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