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blackandwhite

render solids without zero alpha

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anyone know how to render solids/layers in ae so that they appear in the RGB channels but do not "contribute" or add white to the alpha channel. In other programs this is sometimes called "matte opacity" where you can set certain layers to render visibly in the RGB channels, but render BLACK in the alpha.

 

I guess the best way to describe this is that i have a bunch of text layers and i also have an image serving as the background. I would like to render to a qt and i want this image plane to be visible in the background, but still have the alpha ONLY from the text layers.

 

in the past what i would normally do is render the text layers on top of the image with no alpha, then i would render again hiding the background image and this time with alpha. that way i would end up with 2 files, one that appears correctly and one that has the alpha. well this seems a bit redundant as it causes me to render twice and then i have 2 files to keep track of. Just trying to streamline the workflow a bit so that i can render once, and have everything appear correctly visually if i ignore the alpha but then if i need i have that hidden alpha channel embedded in the qt so i can easily overlay the text over a different background.

 

anyone know how to do this?

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ah FANNY if you would only follow your own advice, i could spend the other half of my day animating instead of teaching you how to animate ;)

 

 

ok well sorry for the premature post. I figured the answer. Ill post the solution just for anyone else who was wondering. and well there is something tricky going on as well which explains the hang-up i was having. also there is some chrunchyness associated with the STRAIGHT alpha channel which is unfortunate but necessary i guess.

 

so what i did was make a black solid the size of the comp background and used that layer as a luma matte for everything that i wanted to remain black in the alpha. well when you do this ae it makes your layer totally disappear? On a hunch i decided to render this out anyways and see if it looked right. lo and behold when you render it with a straight alpha channel your background comes back! and your alpha channel is there hidden as a straight alpha channel so when you import it back in you can choose to ignore or interp as straight. pretty much what i wanted. seems like it would be handy if there was an effect that would allow you to apply to the layers you wanted to render hidden in the alpha channel. this way works, but makes the comp extra complicated as i have to make luma mattes for everything i want visible in the rgb but hidden in the alpha. oh well cant get everything eh?

 

by the way the only other side effect of this method i noticed was by rendering to a straight alpha channel the borders of the alpha appear a bit chrunchy in the RGB channels which makes not so good for client presentations... oh well.

Edited by blackandwhite

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Try this

 

The key is that you have to render your composition with staright alpha..

 

 

Create composition with your text layers

 

Place that composition above your background image

 

Precompose those two layers.

 

Again place once again your text composition here it will become your alpha source

 

Apply 'set matte' Fx to your precomposed layer.

Set take matte layer to text composed layer and make sure use for matte set to alpha channel.

 

In composition monitor it will knockout the background image and will leave you only those texts visible.

 

But if you change view mode to RGB staight it will still show the background.

 

Time to render. add this composition to render queue.

Set color attribut inside output module to straight(unmatted).

 

If you view the rendered video on regular player it will still show your background but it has an alpha.

When you import back to AE it will depend on your footage interpretation setting

 

Hope it help

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ah ok great response i forgot all about set matte... i spend more time in 3d so i tend to think in those terms more.

 

as a side note i found a way to streamline this even more....

 

since i really just want NO ALPHA in the background layer, instead of precomping, applying matte effect, setting the precomp as the alpha source..

 

what ill do is use the set matte effect on the background layer that i want with no alpha, and in the effect ill pick THAT BACKGROUND layer, select alpha then ill invert the matte. this is exactly what i was looking to do. just makes it one step easier than precomping stuff etc....

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Have you compared the result of your direct compositing.. with my precompose stuff

..

 

The reason i suggested those precomposes thing is that it could affect the render result.. if you do compositing with alpha edit within one composition for straight alpha the rendered video will seem to be aliased (chrunchy) around its alpha edge area. But if you precompose layers and do alpha edit on its parent it will look nice and might suit your presentation need ;)

Edited by Harry.noeg

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Have you compared the result of your direct compositing.. with my precompose stuff

..

 

The reason i suggested those precomposes thing is that it could affect the render result.. if you do compositing with alpha edit within one composition for straight alpha the rendered video will seem to be aliased (chrunchy) around its alpha edge area. But if you precompose layers and do alpha edit on its parent it will look nice and might suit your presentation need ;)

 

 

yea good point...

 

still confused though. looks like i get crunchy alpha even by the method you suggest. unless im doing something wrong.

 

im going to prep some files to explain this better

 

 

please note that you will have to save these images and open them in pshop or like... the browser doesnt show the alpha properly.

this image shows the standard (how it SHOULD look)

www.paraportable.net/images/good_straight.tif

 

 

this image shows a render using the method you descibed above (or at least i think it does)

www.paraportable.net/images/precomp_straight.tif

still crunchy

 

 

ive posted the ae project as well if you want to tell me mabye im not following your method to the T.

www.paraportable.net/images/renderBackgroundAlpha.zip

Edited by blackandwhite

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Hmmmn....

 

Ok i've dig your project file

 

and i've update the project file to include my solution:

http://www.hotlinkfiles.com/files/1357380_...undAlpha_V3.zip

 

and here the simplified version:

http://www.hotlinkfiles.com/files/1357393_...V3_simplify.zip

hope it give the best way to describe our topic here :)

 

 

sory for the late post

i've trouble with my connection..

my whole networks going down..

that turned all my render nodes falling apart :(

i have to fix it all night before i able to back online..

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By d way..

I'm curious why you use 'fill' effect for your text layers..

 

If your intention to alter your texts color, why you didnt use its builtin color attribute since your fill effect will affect your text's alpha and cause it to become "chrunchy"

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By d way..

I'm curious why you use 'fill' effect for your text layers..

 

If your intention to alter your texts color, why you didnt use its builtin color attribute since your fill effect will affect your text's alpha and cause it to become "chrunchy"

 

 

will it?

 

I usually use it because its easier to control the color from an expression.

 

I dunno, I just tried a test, where i stacked 20 fills on top of a text layer... zoomed in to test the edges and didnt notice any "crunchyness". I guess I have always been suspicious of using fills and loosing the quality of the edges.. but I dont have the proof to back it up.

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