Hi I have been cutting a lot of the stuff out for getting a perfect alpha on this image , but then when I try to transform this into an alpha channel it gets reallybad with lots of white halo etc , how can I do to use the actual cutted out part to form a decent alpha?

Flatten your image on a white BG
Adjust curves or levels til all your stuff is black against white
Ctrl-A Ctrl-C
Paste in your alpha channel

(and you might want to mix a little Ctrl-I in there)

Priors way is good if you want the gray tones in the image to make it into the alpha. If you don't you can also right click the layer and hit select pixels and then create a black fill on a new layer.

Also helps sometimes to use one of the Red, Green, or Blue color channels to start from. Like if the image is green leaves against a blue sky, then the red channel will have more contrast than the combined RGB image.

Photoshop has a bunch of other methods too, like Select > Color Range, etc.

White halo where, in Photoshop, or in your 3D application (or whatever you're displaying it in).

As mentioned, CTRL-clicking this layer will make a new selection based on the existing transparency, you can then fill this selection in as white on a black background.

However, you will then need to make sure your diffuse has some padding. I suspect the white pixel "bleeding" you're talking about is due to not padding the diffuse out at all, so the transparent background is showing through when you apply the alpha channel in your 3D app.

If the parts you want alpha-d are on a separate layer, you can double click on it to open up the layer properties, color overlay and select black, make sure the background is white, and that should give you what you want.

cool tips!

have you tried going to 'layer-matting-remove white matte' or defringe. these will choke your matte slightly


if your lucky enough to have your subject against a primary colour you can use the channel mixer to create a alpha.
Put in in monochrome mode. put the background colour to as low as it will go and then ramp up the constant slider.
then use the result as a layer mask.
This one was quick, you can get more subtle with it




If your feeling fruity you could also try After effects or Shake and pull a key with keylight. hell Max and maya come with a compositor now. they should have good keying features.

Ijust want all the pixels I cutted away transparent to become actually alphed out in the alpha channel and the rest be opaque , no shade degrees..

ctrl+cklick layer to load it as a selection, create alpha channel, fill with white.

Indeed. Basically, do what I said (or what ivars said). ;)