Nest your composition in a new one and apply echo to the nested composition. Echo must be applied to the layer it is working on that layer must be either a movie or a composition.
These are items 1, 3 and 5 from the list above. By "precomposed layer" I mean the nested composition that is created when you precompose layers. I wonder what the problem can be.
Try this. Add a 100 x 100 pixel solid to a new pump and animate from screen left to screen right over two seconds. Pre-compose that layer making sure to move all attributes to the new composition. Apply echo to your pre-comp. Set the number of repeats the three and delay to .5
That works, even when using composite in front. I wonder why it isn't working for video.
You have to use a blend mode like add or multiply or have transparency
Ok. Do you know the answer to question B then? Aside from manually adjusting colors, is there a way to not cause changes in brightness when using add or blend? It is not a brightness adjustment, I think. I know how to rather tediously visually make the color levels match. I am asking about a formula. I would think almost everyone who uses echo, and not using composite, would go through this process.
If you are trying to create the images in trail effect then Echo is the wrong approach unless you Roto the portion of the image you want to repeat.
Blend modes do just that, they blend pixel values. Please describe in detail exactly what you are trying to accomplish and provide a screenshot if possible.
By analogy, if someone were painting a representation of something that they dreamed and they were currently deciding on a color of some clothing, they would not ask "what paint should I use to paint clothes"? The artist doesn't know. A more likely question is about a specific property of this or that paint.
So, exactly, what I am trying to accomplish is to use the echo effect in after effects, with video and to gain some understanding of how it works in order to see if it helps with a minor aspect of a project.
You want to be using CC Time Blend FX, far more flexible and fun and far more confusing. For instance, you need two copies of the effect on the same layer, one to copy the effect from and one to receive, paste, the effect into. And they're reversed in the stack; the copy goes on the bottom below the paste--quite unintuitive.
You cannot understand the paragraph above until you've read all of the online support for the CC Time family of effects.
Thank you, that looks interesting. I see a manual here: http://cycorefx.com/downloads/cfx_hd_std/CycoreFX%201.7%20Manual.pdf
Part of why someone would do the work of answering people's questions is that it is interesting or fun to work on the task. I am usually asking abstract questions that don't lead to some fun activity in solving the problem. Sorry. It's similar to asking for help with algebra and people tell you that you can use a calculator to achieve the same result... Yes, but I'm asking about algebra.
The fun of participating around here is helping people solve real problems in real jobs on real projects. There are no rewards around here. Adobe doesn't give us anything. People often resent our suggestions, they rarely say thanks, and they hardly ever close their threads with helpful advice for those who come after.
After Effects is not a calculator. It's like a set of watercolors that came with drafting tools instead of a brush. You must be able to apply paint creatively (which is difficult enough) but you must also think like an engineer.
One interesting part of that cycore manual:
Force motion blur should always be applied to a composition because it uses data from previous and subsequent
frames and this is only possible if the effect is pre-composed.
I think that explains why the help text about echo says that you have to pre-compose.
I think I have figured it out, at least partly.
Composite means something that is composed. Maybe it's this definition Digital compositing - Wikipedia, the free encyclopedia
So, as opposed to adding or averaging pixel values, it includes opacity. That may be what Rick Gerard was getting at.
The things being composed are adjacent frames. Precomposition is necessary, or a layer with a composition as it's source, because it compares rendered frames. If the source were not a composition, rendering will not have happened yet.
You can get the echo effect with the composite operator to work when adjacent frames do not have opacity by adding opacity using the starting intensity parameter, which adds opacity of the source frames.
I don't have an answer about correcting colors when using additive operators. But, that is probably better as a separate question.
Incidentally, the effect accumulates, meaning it will initially have a different number of frames to composite. If that is undesirable, a solution i can think of is to append or preprend a copy of the range of frames, then use the rendered result to select a portion in which all of the frames are composed of the same number of frames, e.g.:
A B C D A B C D A B C D A B C D