[Chimera-users] Saving image and rendering

[Eric Pettersen]

On Jun 22, 2009, at 3:53 PM, Ibrahim Moustafa wrote:

> Dear Chimera team,
>
>    Recently, I have some trouble saving images with POV-RAY option  
> “true”. The process of rendering is too slow (both on the mac and  
> windows version).
> To give the feeling of how slow: rendering an image with 1700 lines  
> takes 7 hrs (with quality 9 in pov-ray options) and 2 hrs (quality  
> 5). I used to get the images rendered much faster than that (with  
> older versions; however, I’m not exactly sure of when I started to  
> see such a slow rendering behavior).

I'm guessing you're using transparent surfaces.  We've made  
improvements in the fidelity of translation of transparent colors  
between Chimera and POV-Ray since the 1.3 release.  In 1.3, the  
transparent colors were much darker than they appeared in Chimera.   
This change increases the rendering time because the amount of  
supersampling that POV-ray performs depends on how much color  
variation there is in the image and the new scheme provides a lot more  
variation than its uniformly dark predecessor.  One example I tried  
produced slightly more than a factor of two in rendering times between  
the 1.3 version and the current daily build.

Now, if you're rendering such a high-resolution image you don't really  
need as much effort expended on each individual pixel as you do for a  
smaller image.  I find that if I increase the "Antialias threshold"  
POV-Ray option from 0.3 to 1.0 then I get an almost unchanged image in  
approximately the same time as as the 1.3 version required.  You might  
even be able to go higher than that and still get a good image.

>    There is another related problem but only with the windows  
> version: If I want to save an image, with depth cue, using the fast  
> mode (POV-RAY false), the image output lacks any depth used in the  
> model, with poor quality and darker than it should be. Somehow, the  
> camera orientation is messed. In addition, the depth cue will be no  
> longer available for the rest of the session (I have to restart over  
> again). To get the depth cue I want, I need to turn the POV-RAY  
> option “true”....but then too slow to create a good figure.

I understand that Greg (who works on this code) recently made some  
depth-cueing related bug fixes.  Please try the very latest daily  
build and see if you still get this problem.  If you still do then  
please use Help->Report a Bug to send us a bug report which will  
automatically include detailed information about the system you're  
using.

>    I’d appreciate any comment or explanation from Chimera people;  
> and what is the best way to overcome this problem?

An alternative to ray tracing is to turn on "glossy lighting" (from  
the Lighting tab of the Side View).  That may look good enough for  
what you want and works with Chimera's non-raytraced image saving.

--Eric

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