Flattening a blended layer while preserving style — colour to alpha

I've seen all sorts of archived forum topics on how to convert a particular colour to alpha, but I found the only way to do it while taking into account levels of that colour was to go to layer > layer style > blending options... and set the mode to 'multiply'.

In practical terms, this does exactly what I wanted. I had some heavily anti-aliased text on white in the layer in question, and now the layers below come through fine where the white is

BUT

the white is still there. Flattening the layer just discards the blending options, and generally I can't export this as an alpha png-24. Is there any way I can 'solidify' or rasterise the effects of the layer style?

Merge it with a transparent Layer.

Thanks for the suggestion Ed, sadly this loses the multiply effect and just creates an entirely opaque layer.

"creates an entirely opaque layer". It does? Just text with a Layer Style on it? Not sure what you mean.

You can set it to Multiply in the Layers Palette after you merge. Then do whatever else you need to do. I guess I'm not understanding what you are trying to do.

EDIT: Maybe you need to remove the white background from the layer? Is that it?

EDIT: Maybe you need to remove the white background from the layer? Is that it?

Ed, that's exactly what I'm trying to do. The image in question is a completely flat bitmap with a lot of white. Essentially I am trying to replace the 'whiteness' or lack of colour with alpha.

Mutiply does exactly what I want for the purposes of using the image within a psd file but the transparency can't be transfered beyond that. Whenever I flatten, merge or directly save-for-web the layer in question, it's plain old colour-on-white again.

There are various techniques for doing this, and some plugins as well. Depends on the image.

Here's one possibility:
<http://www.cybia.co.uk/alphaworks.htm>

There are ways to do it in Photoshop without plugins, but that depends on the image. Can you post it?

Once you get rid of teh background white Save for Web as PNG. Don't worry about making an Alpha channel.

Thanks for the link!

AlphaWorks looks like good fun. From playing with it for these couple of minutes it seems that the line-art tool works well for my image, except for the fact that it loses all pigment:

<http://barneycarroll.com/favicon.gif>

When I asked the question it seemed pretty simple but the tool makes me realise there can be many approaches. What I'm trying to get is a layer composed of pixels with hue and saturation but no brightness whatsoever, and, what would be brightness in the current image be replaced by alpha.

If your base layer is just black and white, you can do this easily with advanced layer blending (right click layer - advanced layer blending) - drag the triangles on the blending bars untill you eliminate the white...