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From: Thomas de Groot
Subject: Apparent circular pattern of scratches
Date: 25 Jan 2019 12:21:57
Message: <5c4aff65@news.povray.org>
See at same subject in povray.advanced-users.

OK. This is the best I can do presently.

-- 
Thomas


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Attachments:
Download 'circular scratches_test.png' (457 KB)

Preview of image 'circular scratches_test.png'
circular scratches_test.png


 

From: Thomas de Groot
Subject: Re: Apparent circular pattern of scratches
Date: 25 Jan 2019 12:34:59
Message: <5c4b0273@news.povray.org>
On 25-1-2019 13:21, Thomas de Groot wrote:
> See at same subject in povray.advanced-users.
> 

While increasing the bump_size.

-- 
Thomas


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Preview of image 'circular scratches_test.png'
circular scratches_test.png


 

From: ingo
Subject: Re: Apparent circular pattern of scratches
Date: 25 Jan 2019 13:31:15
Message: <XnsA9E293B70E4FFseed7@news.povray.org>
in news:5c4aff65@news.povray.org Thomas de Groot wrote:

> This is the best I can do presently.
> 

Comming along nicely. 
It still has a bit of 'leathery' quality to it, less metallic. Maybe it's 
the size/width of the scratches that give that impression,

ingo


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From: Bald Eagle
Subject: Re: Apparent circular pattern of scratches
Date: 25 Jan 2019 18:30:00
Message: <web.5c4b557e5e3f4450765e06870@news.povray.org>
ingo <ing### [at] tagpovrayorg> wrote:

> > This is the best I can do presently.

Which is indeed very nice.  :)

> Comming along nicely.
> It still has a bit of 'leathery' quality to it, less metallic. Maybe it's
> the size/width of the scratches that give that impression,
>
> ingo

Yes, I would say that probably the real test would be something like a
transparent piece of plastic or a dark plastic/glass, where there are in reality
a lot of scratches, but optically, only a few of these are ever really visible
at any given time - depending on the viewing angle.

So, sparser, finer scratches, and perhaps an animation where the object is
rotated a bit to see how a changing incident light angle affects the look.


Still, this has developed to a usable form for a lot of scenes in a very short
time.   Great work!   :)


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From: clipka
Subject: Re: Apparent circular pattern of scratches
Date: 25 Jan 2019 18:47:59
Message: <5c4b59df$1@news.povray.org>
Am 25.01.2019 um 19:29 schrieb Bald Eagle:
> ingo <ing### [at] tagpovrayorg> wrote:
> 
>>> This is the best I can do presently.
> 
> Which is indeed very nice.  :)
> 
>> Comming along nicely.
>> It still has a bit of 'leathery' quality to it, less metallic. Maybe it's
>> the size/width of the scratches that give that impression,
>>
>> ingo
> 
> Yes, I would say that probably the real test would be something like a
> transparent piece of plastic or a dark plastic/glass, where there are in reality
> a lot of scratches, but optically, only a few of these are ever really visible
> at any given time - depending on the viewing angle.
> 
> So, sparser, finer scratches, and perhaps an animation where the object is
> rotated a bit to see how a changing incident light angle affects the look.

I think one important feature overlooked so far may be that the 
scratches are presumably rough (in all directions, not only in cross 
section), while the remainder of the surface is rather smooth; so you'd 
either need different finish properties for the scratches (with larger 
highlights), or you'd have to somehow add a bit of noise to the scratches.


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From: Thomas de Groot
Subject: Re: Apparent circular pattern of scratches
Date: 26 Jan 2019 07:26:58
Message: <5c4c0bc2$1@news.povray.org>
On 25-1-2019 19:47, clipka wrote:
> Am 25.01.2019 um 19:29 schrieb Bald Eagle:
>> ingo <ing### [at] tagpovrayorg> wrote:
>>
>>>> This is the best I can do presently.
>>
>> Which is indeed very nice.  :)
>>
>>> Comming along nicely.
>>> It still has a bit of 'leathery' quality to it, less metallic. Maybe 
>>> it's
>>> the size/width of the scratches that give that impression,
>>>
>>> ingo
>>
>> Yes, I would say that probably the real test would be something like a
>> transparent piece of plastic or a dark plastic/glass, where there are 
>> in reality
>> a lot of scratches, but optically, only a few of these are ever really 
>> visible
>> at any given time - depending on the viewing angle.
>>
>> So, sparser, finer scratches, and perhaps an animation where the 
>> object is
>> rotated a bit to see how a changing incident light angle affects the 
>> look.
> 
> I think one important feature overlooked so far may be that the 
> scratches are presumably rough (in all directions, not only in cross 
> section), while the remainder of the surface is rather smooth; so you'd 
> either need different finish properties for the scratches (with larger 
> highlights), or you'd have to somehow add a bit of noise to the scratches.

Gentlemen, you are perfectly correct regarding these suggestions. We now 
enter the domain of subtlety and craftiness indeed. Let's see what we 
all come up with.

-- 
Thomas


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From: Thomas de Groot
Subject: Re: Apparent circular pattern of scratches
Date: 26 Jan 2019 08:56:25
Message: <5c4c20b9@news.povray.org>
Proof of concept using different finishes for surface and scratches. 
Still in flux...

-- 
Thomas


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Attachments:
Download 'circular scratches_test.png' (506 KB)

Preview of image 'circular scratches_test.png'
circular scratches_test.png


 

From: Thomas de Groot
Subject: Re: Apparent circular pattern of scratches
Date: 26 Jan 2019 12:10:38
Message: <5c4c4e3e@news.povray.org>
... and fulling following "The Teachings of Clipka" (Scroll 24F, Chapter 
"On Metals and their Finish").

-- 
Thomas


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Preview of image 'circular scratches_test.png'
circular scratches_test.png


 

From: ingo
Subject: Re: Apparent circular pattern of scratches
Date: 26 Jan 2019 13:10:48
Message: <XnsA9E3903F11149seed7@news.povray.org>
in news:5c4c20b9@news.povray.org Thomas de Groot wrote:

> Proof of concept using different finishes for surface and scratches. 
> Still in flux...
> 

The scratches are based on the random sticks? If so, try uses extremely 
stretched boxes as sticks to get a sharper 'impression'.

Maybe use a gradient 'depth map' texture on the sticks, the scratichg edge 
rgb 1 and going to rgb 0 to the other edges. Vary the rgb 1 on the sharp 
edge for depth variation. 
 
Render it with orthocam and a light at the camera location.

ingo


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From: Norbert Kern
Subject: Re: Apparent circular pattern of scratches
Date: 26 Jan 2019 14:15:01
Message: <web.5c4c6ae05e3f44501fbfafc10@news.povray.org>
Hello,

here is my attempt, using a layered texture and an imagefile for the scratches
(similar to what Thomas posted here -
http://news.povray.org/povray.advanced-users/message/%3C5c4970bb%40news.povray.org%3E/#%3C5c4970bb%40news.povray.org%3E
).


material {
        texture {
                pigment {color srgb <0.9284,0.9016,0.8678>}
  normal {
                        average
                        normal_map {
                                [1      bump_map {png "scratches"}
                                        bump_size -1
                                ]
                                [1      bump_map {png "scratches"}
                                        bump_size -1
                                        rotate x*90
                                ]
                                [1      bump_map {png "scratches"}
                                        bump_size -1
                                        rotate z*90
                                ]
                        }
                        accuracy 0.003
                }
                finish {
                        ambient 0
                        diffuse 0.1
                        specular 1
                        roughness 0.0003
                 phong 0.5
                        phong_size 10
                        brilliance 3
                        reflection {0.6, 1 fresnel on metallic}
                        conserve_energy
                }
        }
        texture {
  pigment {color srgbf <0.96,0.965,0.975,0.99/0.8>*0.8}
  finish {
          ambient 0
          diffuse 0.05
          reflection {0, 1 fresnel on}
          conserve_energy
          specular albedo 0.5
                        roughness 0.001
                        brilliance 7
                }
 }
        interior {ior 3.64}
        scale 1
 Reorient_Trans (z, 1)
}

Norbert


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Attachments:
Download 'scratch finish on metallic surfacea.jpg' (684 KB)

Preview of image 'scratch finish on metallic surfacea.jpg'
scratch finish on metallic surfacea.jpg


 

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