On 25-12-2018 8:27, Thomas de Groot wrote:
> On 24-12-2018 12:52, clipka wrote:
>> Am 24.12.2018 um 08:45 schrieb Thomas de Groot:
>> ...
>>> #declare F_hf =
>>> function {
>>>    pigment {
>>>      image_map {
>>>        tga "My_image.tga" gamma 1.0
>>>        map_type 0
>>>        interpolate 2
>>>      }
>>>      //adding some warp
>>>    }
>>> }
>> ...
>>> However, I do not know /why/ the artefacts happen, nor if this should 
>>> be expected or not.
>>
>> Interpolation I presume. Unless you specify the "once" keyword, at the 
>> edges the image is interpolated with the opposite edge.
> 
> Ah! That is an interesting thought. Never thought of it but makes sense. 
> I shall investigate. I'll come back.
> 
> Thanks! and Merry Christmas!
> 

Back again. The answer is yes and no. Yes, because interpolation 
definitely creates artefacts from the opposite side of the image_map / 
height_field; no, because adding the "once" keyword only makes the 
artefacts in the x-axis direction disappear, but /not/ in the z-axis 
direction.

To illustrate this, I add a test file with image_map. Run with "once" 
(at line 65) commented out or not to see the difference.

-- 
Thomas

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