If you choose to Pre-multiply on rendering or interpreting footage, the original RGB values are still not changed. You can use the set channels filter to ignore if you wish to ignore the alpha or change the mode on a particular layer. The alpha channels in AE, whether created, rendered, or interpreted from footage, have no effect on the RGB portions of the image unless you choose to have the alpha control a chosen property of the rgb channels.īy default, AE assigns an alpha channel to all layers and interprets the alpha as a straight alpha. But it would still be using multiple copies of the footage internally, the same way a studio switcher does, to achieve the control needed for a seamless composite.Įvery time I've seen the black fringe problem you describe it's been an error in interpretation of the footage, or an error in rendering settings for the alpha channel in the first place that causes the problem. This would definitely clean up the timeline and probably speed up workflow. A good programmer could write a plug in with 3 or more selectable value ranges and apply different operators or transfer modes to those ranges so you’d have only a single copy of your footage in the comp and a single plug-in applied. Using one instance of the footage it’s impossible to add the rgb values over black, screen the values between black and white, and use the values over white normally. Even the shadow on the weather map from the forecasters arm on the evening news comes from splitting off alpha channel information derived from the keyer into multiple copies that are mixed internally to produce a believable shadow. Using multiple copies of the alpha channel footage, or routing a single instance through different busses of a switcher or different levels of a plug-in, you can manipulate the pixel values in any area covered by any alpha value using different equations. It’s similar to the render pipeline problem with the text plug-ins. I do see that there is a problem with AE’s render pipeline when you choose Luminescent premultiply and want to pre-comp and/or mask the layer. (Some apps default to the opposite behavior (black used - white blocked) I don’t see the flaw. White in the alpha means pixels in the other channels are used 100%, black means the pixels are not used, somewhere between black and white they are used in proportion to the value in the alpha channel. AE-Photoshop-Combustion-Commotion-Flame-and the Sony switcher in the HD room at Victory Studios in LA all handle alphas the same. I can't give you a way to control information inside and outside of the alpha channel and maintain control of the pixels on each side of the alpha and in the gray area between (your black fringe) using a single layer or a single plug-in. Post a link to a frame of your footage/bg/comp problem, not jpgs with no alphas, but the actual footage you’re using, and I'll give you a multi layer solution with complete control over every part of the image. The fundamental flaw that I see in your procedure is trying to do everything in a single layer with a single click.
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