Forum: Photoshop


Subject: Alpha Channels

Watcher2K opened this issue on Feb 05, 2003 ยท 10 posts


Watcher2K posted Wed, 05 February 2003 at 1:50 AM

I am sure there is an easy explanation to this but I have been trying to work this out for ages now. I know a little about masking but I am no where near a pro. I am also aware that you can save Poser Images as PSD that include an alpha mask. The problem I am having is knowing how to use those Alpha Masks. I can not seem to figure out how to mask out the default grey background leaving me with just the people in the picture so I can then oput them into there own layer.

I hope this makes sense and again thanks for the info in advance.

:)


lundqvist posted Wed, 05 February 2003 at 3:11 AM

Okay. In Poser (I'm assuming Poser4 or Propack here and Photoshop 5 or up on Windows) render your scene and either Save the image to PSD (or use the export menu option). Now, open the PSD file in Photoshop, you should have the normal "background" layer showing your render and if you click on the "channels" palette, there should be the alpha channel - shown after the regular red, green and blue channels (Poser automatically supplies the alpha when the output format supports it such as PSD or TIF). Go back to the "layers" palette and double click on the "background" layer, this will cause Photoshop to convert it to a regular layer (named "layer 0" by default), capable of supporting a mask. Go to the "channels" palette and ctrl-click on the alpha channel that Poser created, this should load it as a selection. Return to the "Layers" palette (with the selection still active) and click on the "Add layer Mask" icon at the bottom (or from the menu, choose Layer->Add Layer Mask->Reveal Selection). You should now have applied the alpha to the render and have the background removed. Hope that helps. :)


Watcher2K posted Wed, 05 February 2003 at 4:15 AM

lundqvist, Thanks a million for that :) it worked like a dream. I have been trying to read up on how these masks worked from Poser but could never understand it. Common sense english always prevails :) Thanks again !


lundqvist posted Wed, 05 February 2003 at 4:35 AM

No problem. Glad it helped. :)


donhakman posted Wed, 05 February 2003 at 8:37 AM

ditto on the thanks


dpoosch posted Thu, 06 February 2003 at 10:16 AM

Finally......someone put this into a comprehensible piece of information that a normal human can understand. Many thanks.


dpoosch posted Fri, 07 February 2003 at 9:27 AM

Question about after alpha has been done. After the subject is cut from the background, I get a halo around the edges that is lighter than the subject. Also when I try and paint over the alpha, the selection seems to be active and can't paint outside the mask. Example:postworking hair on a poser render.


lundqvist posted Fri, 07 February 2003 at 10:16 AM

The haloing you see is probably due to the background color used in the render. Not sure here, but I don't know how accurate (with respect to the opacity of the pixels) in the render, Poser's alpha are. Once you have applied the alpha to a render, use Ctrl-D (to deselect any active selection), then go to the "Layers" palette and click on the layer mask icon (to the right of the layer thumbnail) - it should show an extra border around the layer mask icon once selected. If this is done correctly, Photoshop will change your foreground/background colors to grayscale and any painting you do will be on the alpha/mask, not the layer image itself. Optionally, you can go to the channel palette and paint directly on the layer mask. Also, if using PS7, ensure that the "lock transparency" option has not been set for the layer (it isn't by default). Sorry if this doesn't help, I may have missed the point.


Cheryle posted Thu, 20 February 2003 at 3:00 AM

With your alpha selected, go to select->modify-> contract and contract a pixel or 2, it will bring your selection inside - which makes sure that you don't have any unwanted background fringe in there. Also try feathering your selection 1 pixel or so (depending on resolution) so your edges blend more naturally into your background. You can also try the defringe option layer->matting-> defringe Before painting hair etc., flip back to layers and highlite your layer. Also try hitting ctrl+D (cmd+D) to make sure you dont have any hidden selections Yah yah i am late ;P been working ;P hope this helps


Cheryle posted Thu, 20 February 2003 at 3:02 AM

That should be- with your alpha loaded as a selection ( you should have your RGB channels on)(highlited-selected)