Using c4d alpha in PS?

[Mike Abbott]

Open the image in PS and double click the Background and OK the dialog to convert the Background to a layer.

Select the tab of the channels palette and Ctrl (PC), Cmd (Mac) on the thumbnail of the Alpha Channel - this will load the alpha channel as a selection - you'll see the marqee ('marching ants').

Click on the RGB composite channel thumbnail, then click the layers palette tab to return there.

Now click the 'add layer mask' button at the bottom of the layers palette (it looks like a rectangle with a circle inside).

Your layer is now 'cut-out' using a layer mask.


Mike Abbott

[JamesMK]

Additionally, for PS in particular since it doesn't necessarily handle premultiplied alpha correctly, you'll want to use the "straight" option for the alpha. This will make the RGB look slightly weird along the edges, but that's corrected once the matching alpha is applied to the layer mask.

[3dj]

Hi, Mikes method is right on, but if you don't want to use a mask, keep a duplicate of the layer, do as Mike said, only delete instead of adding the mask. I do this sometimes, as the image can have a dark or light edge to it depending on the background it was rendered on, and you can easily get rid of this under Layer>matting>remove black (or white) matting.
You could adjust your mask too if you wanted to go that route, but I find this pretty fast and simple.
-Jim

[moka.studio]

Just go on the Channels window, and Ctrl+click on the alpha mask channel,
and you will get a selection from it.
That's it.

[rob rhodes]

Thanks guys interesting to see everyone has a slightly different approach. I have to say moka.studios way is very quick and effective - it does exactly what i was after. So thanks again guys.

[rubyscooby]

Hi I am also trying to removethe outline when compositing in photoshop. I tried using straight alpha and the mask is worse than not using it. it leaves an even bigger gap between itsepf and the object? I am using 10.5 Is this a bug perhaps? From what i understand the straight alpha is supposed to render the object a bit over the mask and not antialias it with the background color. If this is the case than the image should not have any kind of outline. Do I need to have multipass for this to work? Not sure wht I am missing here. Thanks for any help.

[PetrolUk]

Another tip for using C4d Alpha's in PSD

In the top menu go to the LAYER and under this menu (at the bottom of the list) you'll MATTING. Select REMOVE BLACK MATTE (if you rendered on black. It gets rid of the black fringe

[rubyscooby]

Thanks but i thought the whole point of checking the straight alpha was to avoid the fringe in the first place. Also any idea why it would be worse ?

[Simon Wicker]

you must be doing something wrong but without any more information it is impossible to know what.

using a straight alpha channel allows you to use a render directly in photoshop (it is something that i do literally every day).

you just render and then apply the alpha (i have an action already made that duplicates the colour channel and adds the alpha as a layer mask so i can then drag this clipped layer into another document).

a test scene that doesn't work would allow us to see where you are going wrong.

cheers, simon w.

[geoffr]

apple, alt 4 (mac). This'll load the fourth channel (which should be your alpha). If you look at the channels, they have a number next to them. You don't have to go into the channels list for this method.
You can then press apple J to duplicate the selection onto another layer. In versions past this was called the 'jump' command.

[Tysus]

Another tip for using C4d Alpha's in PSD

In the top menu go to the LAYER and under this menu (at the bottom of the list) you'll MATTING. Select REMOVE BLACK MATTE (if you rendered on black. It gets rid of the black fringe

You know...

This is probably one of the best tips for PS I've ever read, lol.

For years I've been Loading the alpha via the Select Menu, then Contracting it by 1 pixel, then deleting it; your method is soooo much better!

Thanks for the tip!

[alienesque]

Another tip for using C4d Alpha's in PSD

In the top menu go to the LAYER and under this menu (at the bottom of the list) you'll MATTING. Select REMOVE BLACK MATTE (if you rendered on black. It gets rid of the black fringe

VERY cool:)

ive noticed though that since i upgraded last week to 10.5 im getting real bad alpha channels..really horrible black edges..FAR worse than in my previous 9.6 version of C4d...something has definitely changed here..

[Per-Anders]

If you use straight alpha you should not need to use defringing or removing of black/white mattes. As Simon says if you ave a scene that shows a problem with straight alpha not working you should share it.

[imashination]

Remove the sky objects, its a bug/limitation, it screws up straight alphas.

[Per-Anders]

Remove the sky objects, its a bug/limitation, it screws up straight alphas.

Or give them a Compositing tag to not be seen by transparency.

It's simply a limitation, not of Cinema but of compositing in general. To explain - if you had just the normal alpha then what you'd get would be ghosting/fringing because it would be mixing down a mix between the object color and the sky/background color. In addition to this the rule is that Alpha cannot be darker than the surface luminosity (think of it this way - if it was darker then things like specular highlights wouldn't show up correctly). As the surface luminosity on transparent objects includes what's transmitted through them to the surface, e.g. sky/background objects then that brings the alpha brightness up again so long as it comes through transparent objects. Thus the compositing tag is what you need when you have sky/background and need an alpha. Bear in mind though that the same fringing/ghosting will occur at the edges of things, so in general it's best to also turn off seen by camera.

Think of it as if you were filming ordinarey material and wanted to now cut that material out off it's background, in the real world you'd film against a green/blue screen for that purpose that's as flat/matte looking as possible and use software to extract everything that's not green/blue as best as possible from that surface (and you can still get nasty borders that require work on them), in 3D you're dealing with the same problems when you have a background in there, however you have a few fancy tricks up your sleave, like only allowing the background to show up in reflections and not through transparent objects or in the background, thus getting rid of all those nasty fringing problems, you just have to set it up to be like that in the first place (and after all if you want the alpha then why do you have the background there in the first place, it's only there to be removed...).

[alienesque]

Or give them a Compositing tag to not be seen by transparency.

It's simply a limitation, not of Cinema but of compositing in general. To explain - if you had just the normal alpha then what you'd get would be ghosting/fringing because it would be mixing down a mix between the object color and the sky/background color. In addition to this the rule is that Alpha cannot be darker than the surface luminosity (think of it this way - if it was darker then things like specular highlights wouldn't show up correctly). As the surface luminosity on transparent objects includes what's transmitted through them to the surface, e.g. sky/background objects then that brings the alpha brightness up again so long as it comes through transparent objects. Thus the compositing tag is what you need when you have sky/background and need an alpha. Bear in mind though that the same fringing/ghosting will occur at the edges of things, so in general it's best to also turn off seen by camera.

Think of it as if you were filming ordinarey material and wanted to now cut that material out off it's background, in the real world you'd film against a green/blue screen for that purpose that's as flat/matte looking as possible and use software to extract everything that's not green/blue as best as possible from that surface (and you can still get nasty borders that require work on them), in 3D you're dealing with the same problems when you have a background in there, however you have a few fancy tricks up your sleave, like only allowing the background to show up in reflections and not through transparent objects or in the background, thus getting rid of all those nasty fringing problems, you just have to set it up to be like that in the first place (and after all if you want the alpha then why do you have the background there in the first place, it's only there to be removed...).

the problem has got worse though in the 10.5 update from 9.6..i use alphas every day in my work and have never had this strange fringe around things..but since ive updated i do..

i use sky objects for my GI so i cant get rid of them..

[Per-Anders]

You should have no additional fringing between versions, if you have a scene that shows this change then please share it.

As I said you can apply a compositing tag to remove the sky from the visible render, if you don't do so then you will always have fringing/ghosting unless you manually matte it out in your compositing app for very obvious reasons already explained.

[CGTalk Moderation]

This thread has been automatically closed as it remained inactive for 12 months. If you wish to continue the discussion, please create a new thread in the appropriate forum.