transform pixels to transparency?

I was wondering how i can transform certain colors or pixels in a picture. I don´t want to use the "save for web"-gif function. I know that the "color range"-function's does the same work as "save for web", but the problem is that only one color can be transformed to transparency there.

a little more clarification on what you're trying to do and why would be a bit helpful

chris

If I have a picture, let's say this one: http://www.takingaim.net/images/photos/bluescreen.jpg
I want to make the whole blue area that surrounds the boy transparent and I don't want to use the save for web-function.. The reason why I don´t use the extract tool is because I want to make a droplet that perform this specific action, and the extract tool doesn't work in a droplet, as far as I know. What should I do?

You are going to need to mask out the boy (as in your example). Your choice of selection methods are entirely yours. You could use a colour range command to isolate most of the colour, followed by a tidy up in quick mask, I find this method more organic and altogether more pleasing when used on images like this with no real 'edges'. Perhaps you would use the pen tool or some other masking method it doesnt matter really.

As for your saving options, JPEG will save with a white or a black background, not with transparency. GIF will save with binary transparency, either on or off, but the complex colour palatte of the photo may make it a large file. PNG's allow alpha transparency, so you can assign percentage fades to the transparency on a per pixel basis, down side is the IE's implementation of PNG's is woeful and improving slowly.

Depending on what your output is you could use clipping paths, created with the pen tool.

I would most likely use a copy of the blue channel inverted and run the dodge and burn tools over it for a mask.

Just my thoughts.

CryptoManiac

thanks for your help. I tried the different functions and the one that did the best job was "color range" in the select menu.