Hi, I will explain my situation. i have a render saved with an alpha channel and I have a background image that I want to put beneath the image as to give a background to my windows (http://www.renderosity.com/messages.ez?ForumID=12385&Form.ShowMessage=2357575). How can I comp these images together, I really just can't seem to figure out how to get this to work. I have looked at the Adobe help files and can't seem to find what I am looking for. I am sure this is a pretty easy thing to do, but feel I am missing something really fundamental. Any help is appriciated Cheers Will

Normally you would use the alpha channel as a selection, to select the details you want to change. Not sure exactly on what your trying to do though:)

I'm not sure if I understand, but I'll try to help: Open both images (the one you want to use as the background, and the rendered one). Start with the image you have saved with the alpha channel. Go to Select (the menu at the top), then choose "Load Selection" and then choose "Alpha 1" from the dropdown menu. Click OK. That should put a selection around the figure(s) in the render. Do CTRL-C or Edit: Copy. Go to the "background" image. Make sure it's the active window and do CTRL-V or Edit: Paste. That will paste the selection from the other image on a new layer. Manipulate at will. bonni

In addition to what elizabyte said, you can also get somewhat better results by tweaking the alpha. If your render has a black background and your image is light, for example, sometimes you'll get dark fuzz at the edges of your render selection when it's pasted because of antialiasing with the black background.

Usually I copy the selection to a new document with a transparent background, paste it and do the following:

-Select All
-Save Selection
-click on the appropriate channel (whatever you named it or the default, Alpha 1) so you see the black and white
-apply a slight gaussian blur to the alpha
-go back to your regular view on the layer
-Load Selection
-Select Inverse
hit your backspace/Delete key - each time you do, a little more of the fringe will be deleted until you get the result you want.

There's probably some faster way of doing this, but I've been using Photoshop since version 2 and am stuck in my ways :)
EDIT - after all that, Select All, copy and then paste to your composite image... /EDIT
.m

Message edited on: 08/06/2005 00:13

midazolam, a quicker way could be to feather the selection. If that's any help=)

Yeah, i just find I have more control over it with gaussian blur, plus there's a preview, which always helps...

True;)

midazolam, that's very helpful. I usually actually do the edges manually (with a soft, low-opacity smudge brush and a pen tablet) because I'm a glutton for punishment (actually, I'm one of those weird peole who finds minute pixel manipulation enjoyable, hehe). I've done the feather selection trick, but find it less than precise and the results vary considerably. Gaussian Blur on the alpha channel, though, that's a good trick to try. Thanks! bonni

Lets just say there are many ways to do the same thing in PSHop;)

Another trick with the gaussian filters and alphas is that you can blur something gradually - let's say you have a picture of a car, and the depth of field is really shallow, so just the front 1/8th or 1/4 is in focus. Let's assume the car is at a 45 degree angle from the camera, front of the car toward the left of the frame. The car is the selection, and you want to paste it into a CG background. The rear end of the car has a lot more blur to it than the front. Easy way to deal with this (or at least to create a quick n dirty fake) is to have your car alpha (once you've selected it), then create an all-new alpha channel. Do a black to white gradient from left to right (so black is left, white is at right). Make this alpha the selection, then make your active channel the car selection. Now you can apply a gaussian blur to the car alpha, and it will blur more pixels where your gradient alpha was white. If this makes no sense, I can do up a screen shot tut so you can see what I mean... .m

Put the rendered picture above the background. Go to channels and select the alpha channel. Its important that the parts of alpha channel where it should be the background must be filed with white color. Aplly gaussian blur depending on resolution and file size (biger resolution-biger blur) just to soften the selection. CTRL+click on alpha channel and go back to layers pallete. Make aktive the layer with the rendered picture and click on layer mask (its next to the layer effects). Voila that`s it, its good to add the curve adjustment layer on top of all ;)
Hope it will help you :)

Message edited on: 08/12/2005 09:48