Render psd images have embedded alpha info?

[April Henderson]

Sorry for having such newbie questions.
I just saw in the rendering dialoge that I have should chosen to render “alpha+RGB”, and this seems to do the trick?

Is there any way to salvage the old rendered images? Or should I just re-render “alpha+RGB”?

[Kelly Johnson]

You have to have an alpha channel to render one. If all the figures are on their own layer and the background is just a solid, then you can simply delete that layer (leaving the checkered background) and the alpha will render.

Otherwise, you need to create an extra channel in the channel palette that contains the outline in white of the figures.

[Jacob Wessler]

April,

AE understands alpha channels in your composition and uses them when you stack layers. Some layers have alpha built in (text, shapes, etc) and some layers don’t (video layers (unless they were created with an alpha channel!)).

When you render your composition, you have the option of including the alpha channel or not. If you choose just “RGB,” AE will render a video (or image sequence) that is the size of your composition (assuming you didn’t scale in the output module). This video will contain an alpha channel that is essentially completely white and the exact dimensions of your composition EVEN IF your composition has transparent areas visible in the comp window.

When you render with RGB+Alpha, AE will take into account any transparency in your composition and provide that information in the final video.

That’s the long answer for “you need to re-render.” There are some plug-ins that can remove the black background from your image, but I don’t remember their names and it’ll probably be easier (and better quality) to re-render your videos.

Now you get to decide on straight or premultiplied alpha channels and that’s another story entirely. The main difference comes from how AE handles edges that aren’t 100% black or 100% white. Premultiplied can have the tendency to bring some of your background color into the edge of your video (adding a black color to smoke edges, for example). However, most programs can interpret straight or premultiplied so it isn’t that big of a deal.

When you’re in photoshop, you do need to add an alpha channel for transparency. If you apply a mask to a layer, your alpha channel is automatically added.

That’s a lot of words that I certainly hope makes sense.

Good luck,
Jacob

[Touko Maksimainen]

I’ve found that “Save frame as” will not save alpha for PSD files due to a bug.

You can save it to something else, like PNG, but that will obviously not export the layers.