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Mike Williams wrote:

>> Hash: SHA1
>>
>> Mike Williams wrote:
>>> Wasn't it Nicolas Alvarez who wrote:
>>>> Nicolas Alvarez wrote:
>>>>> It will supersample even if there is a completely color.
>>>> OK that got messed up... I meant "It will supersample even if there is a 
>>>> completely plain color." Even if your whole image is the exact same 
>>>> color, +a0.0 will supersample it...
>>> It is sometimes useful to supersample images for which the colour is
>>> exactly the same at integer pixel positions, but which have sub-pixel
>>> features.
>>>
>>> For example:
>>>
>>> camera {location  <0,0,-10> look_at 0}
>>>
>>> plane {z,0 
>>>   pigment {gradient x
>>>     colour_map {[0.005 rgb 0][0.005 rgb 1]}
>>>   }
>>>   finish {ambient 1}
>>> }
>>>
>>> If you render that with any non-zero antialias threshold then it will
>>> miss some of the lines where the line happens to squeeze between pixels.
>>> How many lines are missed depends on the image size: at 320x240 all the
>>> lines are missed.
>>>
>>> If you render it with +a0.0 then it finds all the lines.
>>>
>>> That's a bit of an extreme example, but it's possible to encounter the
>>> same sort of effect in real scenes.
>>>
>>       In that case, render at a higher resolution with +a0.1, then
>> downscale the image with an external tool. This will be faster than
>> +a0.0 for an equivalent quality.
> 
> Depends how large you want the final image. If you want a 640*480 image
> of the above example, then it's faster to use +a0.0 at 640*480. On my
> machine it takes 4.8s to render at 640*480 +a0.0, but in order to see
> all the lines at +a0.1 it needs to be scaled up to about 2300*1725 which
> takes 9.4s.
> 
	Here, it takes 26s at 640x480 with +a0.0 and 15s at 3200x2400 with
+a0.1 +r1 (which gives the same potential resolution). The result is
actually better in the second image.

	Result images are here:
http://jeberger.free.fr/public/povray/

		Jerome

PS: This is all done with method 2 of course. When using method 1,
the render is faster (4s), but the result is much worse:
http://jeberger.free.fr/public/povray/aa-640x480x1-0.0-m1.png

PS2: I also tried it at 1920x1440 with +a0.1 +r2. It renders in 6s,
but some lines are imperfect. All in all, I'd consider its quality
on a par with the method 1 result (some lines are worse, some are
better).

- --
+------------------------- Jerome M. BERGER ---------------------+
|    mailto:jeb### [at] freefr      | ICQ:    238062172            |
|    http://jeberger.free.fr/     | Jabber: jeb### [at] jabberfr   |
+---------------------------------+------------------------------+
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