POV-Ray

The Persistence of Vision Raytracer (POV-Ray).

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Attached to Project: POV-Ray
Opened by Timwi - 2013-03-24
Last edited by William F Pokorny - 2017-04-21

FS#282 - Unrendered region should be transparent, not black

When rendering only a region of a file, using the command-line options +sc/+sr/+ec/+er, the area of the image that is excluded comes out as black in the final PNG.

Expected behaviour is for it to be transparent.

Thorsten Fröhlich commented on Sunday, 24 March 2013, 14:28 GMT

The behavior is expected. The pixels are never filled, as you explicitl requested them to not be renderd. The background in a scene only applies to pixels rendered.

Timwi commented on Sunday, 24 March 2013, 20:54 GMT

This report is not referring to the background in a scene at all. The unrendered region should simply always be transparent — after all, as you correctly pointed out, it is not rendered. It should not be filled with black.

Please reopen as the closer misunderstood the bugreport.

Thorsten Fröhlich commented on Sunday, 24 March 2013, 21:00 GMT

Did you read the response to your report 283?

Timwi commented on Sunday, 24 March 2013, 21:19 GMT

Report 283 is completely unrelated to this one. Report 283 is about “background { ... }”. This one is not. This one is about +sc/+sr/+ec/+er.

Timwi commented on Sunday, 24 March 2013, 21:21 GMT

But to answer your question, yes, I read it, and I tried +UA, and it still comes out as opaque black.

Admin
Christoph Lipka commented on Sunday, 24 March 2013, 22:30 GMT

I think it is reasonable to expect unrendered portions of the image to come out transparent when alpha support is enabled for the output file. After all, the preview window also still shows the checkerboard pattern in those regions. I therefore re-opened this issue as a feature request.

Thorsten Fröhlich commented on Monday, 25 March 2013, 07:55 GMT
I think it is reasonable to expect unrendered portions of the image to come out transparent when alpha support is enabled for the output file. After all, the preview window also still shows the checkerboard pattern in those regions. I therefore re-opened this issue as a feature request.

I agree, it would be a useful feature. Of course, we had been discussing if we want a full image generated for a partial render or not for a long time anyway. Once we add a choice for that, we can also change the current behavior.

Simon commented on Tuesday, 26 March 2013, 18:36 GMT

Just an opinion to consider: outputting a partial render with transparent unrendered parts can be extremely useful. In cases when a small part of the image changes, and the rest stays the same (this is ok if there's no radiosity and reflections), rendering speed can be significantly increased if only the changing part is rendered, and then the partial image is composited over a single render of surroundings. Let's say, a render of animation that includes a rotating or morphing object in static environment (common in scientific presentations). Having a transparent background makes the compositing a trivial operation. The same technique can be used to distribute rendering across different machines (such as ad-hoc cluster over ssh): chunks can be easily merged if the unrendered parts are transparent.

William F Pokorny commented on Friday, 21 April 2017, 11:30 GMT

Now tracked on github as issue #279.

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