Re: Out of range premultiplied images in FxPlug/FCP
Re: Out of range premultiplied images in FxPlug/FCP
- Subject: Re: Out of range premultiplied images in FxPlug/FCP
- From: Paul Schneider <email@hidden>
- Date: Mon, 2 Aug 2010 17:02:01 -0500
Hi Eberhard,
It sounds like your plugin may be generating some illegal pixel values. FxPlug output must be premultiplied; that is, the color components must be <= the alpha component. You have to be careful not to break the premultiplied state of the pixels during processing.
FCP will unmultiply your images after processing, so you will immediately see artifacts if you produce non-premultiplied images. In the simple case, Motion will often just display the color buffer to the screen, so issues with non-matching alpha won't be visible. But you will still see artifacts if you do more complicated processing, such as compositing the output over other layers.
Can you double-check your algorithm to make sure that you are always generating premultiplied pixels?
- Paul
On Jul 29, 2010, at 12:42 PM, Eberhard Ammelt wrote:
> Hello,
>
> we have a problem with some of our OpenGL based fxplug filters.
> In some cases the rendered image doesn't look as expected where alpha is > 0 and < 1.
> This problem does only occur with FCP but not with Motion at any bit depth.
> It seems that the color values of the filter output get out of range when unpremultiplied by FCP internally (?)
>
> As Motion seems to handle this, is there a way we could change this behavior in FCP - maybe by changing an OpenGL attribute?
>
> Thanks,
> Eberhard Ammelt - Pixlock _______________________________________________
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