How to disable alpha interpolation ?
I want to have just 0 or 255 as alpha value in the resulting tif image of a render. How to setup the render to do that ?
ShadingInterpolation, PixelFilter ??
Or do i need to post-process the render ?
If I understand correctly,
Display "filename.tif" "file" "rgba"
should do the trick.
You'll get an rgba image with the alpha in it. You could also render out the alpha to a separate file
Display "+additionalfilename.tif" "file" "a"
You can also specify quantization on the display line
Display "filename.tif" "file" "a" "float quantize" [zeroval oneval minval maxval]
Thanks for the quick answer George.
I think I have to use quantize(?) because I want to have only alpha value equals to 0 or 255. Not 12, 127, 223 etc. that is resulting from anti-aliasing. Setting PixelSamples 1 1, alpha values are only 0 or 255 but using PixelSamples 2 2 they are interpolated. Can I prevent that using quantize ?
I think you want
Quantize "a" 1 0 1 0
This will give you a 1 bit alpha. You can't get a 0- and 255-only 8 bit alpha unless you swith pixel filtering off by setting PixelFilter "box" 1 1 and make sure you don't have any semiopaque primitives.
Probably easier & better (since your color is still nicely pixel-filtered) to promote the 1 bit alpha up to 8 bits after rendering is finsihed, using an imaging application.
Note that I switched of dithering in above statement -- this will give you 'nicer' edges on a 1 bit image.
You can also use:
DisplayChannel "rgb" "quantize" [ 0 255 0 255 ] "dither" [ 0.5 ]
DisplayChannel "a" "quantize" [ 0 1 0 1 ] "dither" [ 0 ]
Display "foo.tif" "rgb,a"
Haven't tested this though.
Also see this page: http://www.dotcsw.com/doc/quantize.html
Thanks for the answer Moritz. Ill' try this solution.
In fact I only need the Z buffer data not the alpha. How to ouput a file with Z buffer information ?
It seems Pixie does not support zfile but tsm or other formats (tx?). I'm a bit confused with shadow and other display configurations.
And as I have to parse this file, how the file is built ? chunks, float data etc.
You can output z using
Display "+file.tif" "file" "z"
Which is different to doing
Display "+file.tx" "shadow" "z"
which premakes a pixie shadowmap.
The file is in standard tiff format, and can be read with libtiff, the data is float by default.
Thanks for the answer George.
I can read this file and get the z depth float values as expected.
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