Re: note on problem reports
Re: note on problem reports
- Subject: Re: note on problem reports
- From: Steve Christensen <email@hidden>
- Date: Wed, 23 Jul 2008 19:52:03 -0700
On Jul 22, 2008, at 3:42 AM, Kristian Harms wrote:
Den 21. juli. 2008 kl. 18.32 skrev Darrin Cardani:
The third problem is only in Motion: If an FxPlug effect
generates pixels that are fully transparent, but have the R, G
and B channels set to some non-zero value (e.g. 127 if we're
talking UInt8), then Motion won't treat these pixels as fully
transparent, but will instead show any underlying layer as
"washed out", and the black default background will shine through
as grey. This is with the normal blending modes. (Apple guys, the
problem ID is #6079465.)
As Steve mentioned, this is a problem on your end (and you're not
the first person to have this problem). You just need to
premultiply your pixel values, and everything will work as expected.
Okay, but it seems that to provide consistent output for both
Motion and FCP, I'll have to premultiply in one host but not the
other.
No. If you look in FxImage.h in the comment right above the
declaration of the FxImageInfo struct, it says:
"isPremultiplied YES if the RGB values are premultiplied by the
alpha. Should always be YES."
Can you confirm that this is the normal way to do this? Also, since
I don't seem to get any information with which I can differentiate
between the two cases, except -hostIsMotion et al.
See above, but I just assume that I always have premultiplied pixels,
and don't check for which host application is currently running the
plugin.
Anyway, isn't half the point of making a generator instead of a
filter that I should simply include an alpha channel and leave it
to the host app to blend with lower layers?
No, the point of a generator is to produce an effect that isn't
dependent on a source image. The blending occurs with all the layers,
taking into account the alpha values at each pixel location within
the frame, irrespective of the type of effect plugin that was applied
to a particular layer.
steve
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