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Am 06.01.2011 10:40, schrieb zalakainz:
> Le_Forgeron<lef### [at] free fr> wrote:
>> Le 06/01/2011 09:31, zalakainz a écrit :
>>> I have a problem with windows64 version 3.7 RC1:
>>> The image in the window POVRAY not match the saved to disk.
>>> Am I doing something wrong or is the fault of povray?.
>>> Thanks
>>
>> Both png seems similar to me.
>
> I clearly observed bands of color in the image saved to disk.
Yup, I see those as well.
A bit of technical background here:
With the default setting, PNG can only represent 256 different shades of
grey; POV-Ray uses much higher precision internally, but when the color
values are simply rounded to the nearest representable level of grey,
what you get is color banding.
You will most probably see the same effect with POV-Ray 3.62 - with one
difference: POV-Ray 3.6 will also show the banding in the preview,
because the display has the same 256-level limitation.
The banding no longer shows in POV-Ray 3.7's render preview because it
always uses /dithering/: By adding some randomness to the rounding, the
eye can be tricked into perceiving a smooth transition between the two
color levels.
Of course POV-Ray 3.7 also supports dithering for file output, but this
is disabled by default, as it may lead to even worse problems when
printing such an image, if the dithering method does not play nice with
the printer driver. However, it can be turned on using the command-line
parameter
+TH
(This activates Floyd-Steinberg dithering by default; you can choose
between six different modes, though in practice they're all doing a
sufficiently good job.)
Alternatively, you can choose a file format with a higher bit depth
(e.g. 16-bit PNG rather than 8-bit) or the floating-point based OpenEXR
format.
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