Am 23.02.2012 15:28, schrieb crowbait:

> This is screenshot of render window.
> http://blogimg.goo.ne.jp/user_image/69/3c/83e31ff151644d9a6a6c3f89583d54e9.png
>
> And this is the output file.
> http://blogimg.goo.ne.jp/user_image/57/ce/dcf2d63a98a4e0f8fd0c682d3d90b290.png
>
> The output gets color bands that haven't been in render window.
> 3.7RC3 makes bands too.

With 3.6, the render window would show the same color banding.

The reason is that 3.6 preview & file output (and 3.7 default file 
output) does not use any dithering, so you get color-aliasing due to the 
limited bit depth, resulting in visible banding of some "shallow" gradients.

> How could I get output that is equal to render window?

POV-Ray 3.7 supports dithering, but it's enabled only for render window 
output by default, as it might cause undesired effects when printing an 
output image (or so I am told). You can use "+th" (for "diTHer") or 
"Dither=yes" on the command line or in the INI file to enable 
Floyd-Steinberg dithering.

You can also choose a different dither method by specifying 
"Dither_Method=XX" or "+thXX", where XX is any of the following:

B2..B4: Bayer pattern dithering using a 2x2, 3x3 or 4x4 pattern

D1, D2: simple 1- or 2-dimensional error diffusion dithering

FS: Floyd-Steinberg dithering (the default).

(Reder window output always uses some Bayer pattern dithering; don't 
know off the top of my hat whether it's 2x2 or 4x4.)


Alternatively, you could use 16-bit output (not available with all 
output file formats), or the OpenEXR high dynamic range image format 
(Radiance HDR doesn't quite cut it, as it has color banding problems of 
its own.); both use a high enough precision to avoid color banding 
altogether. It would then depend on the image viewing software whether 
you see color banding or not (the image viewing software would have to 
use dithering itself in that case).

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