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I have this image:
Is there any way to get rid of the red background (make it transparent) yet keep all the glow effects? So far I've only been able to remove the pure-red parts of the image, yet that leaves a red-glow fringe.
So wherever there's red, I want it to be transparent, but wherever there's shadow-glow, I want the red to be gone but the shadow to remain. Is this possible?
Greenfish Icon Editor Pro has this functionality out of the box. It is a function called "Remove Matte", where you just specify the color component you want to be replaced with transparency. In your case red.
Here is the result of removing the red:
Is this possible?
It surely is somehow (you would need a tool that can take red as the reference colour, and then translates all deviations from red against a transparent background) but I think you're far better and easier off simply recreating the shadows using the tool of your choice, e.g. Photoshop.
Duplicate the layer and desaturate (image> adjustments > hue/saturation) it until the red becomes really dark grey and the detail of the gradients shadow is still visible. Then goto image > adjustments > levels and you should see to big spikes. The left one is the darker colour that was the red. Drag the sliders below the be around the right spike and you should only be able to see the white. The left slider should be just to the left of the 2nd spike, the right slider should be just to the right and the middle slider centered on the spike. Click Done
Now select all of the image, and copy to the clipboard. Select the original layer and create a layer mask. On the channels panel select and make visible the one named mask and paste into it. Click back to the layers, and click back to the image.
It should now be transparent. You may need to play around with it a bit but that is the general process I would use.
Good luck
GIMP can also do this. In fact, there are a couple of different ways.
The default output from the Color to Alpha tool looks exactly the same as awe's, complete with the slight greenish fringing where the original image had shades of gray. To avoid that effect, I applied the Color to Alpha tool only to the red parts of the image:
Change the image from indexed to RGB mode with Image → Mode → RGB. That's always the first step to do when editing an indexed-color image, unless you want to be constrained to the original image's color palette.
Select the red areas of the image using the Select By Color 
tool. A threshold of around 130 seems to work fine in this case.
Open Colors → Color to Alpha... and select pure red (#ff0000) as the color to make transparent. You can use the eyedropper from the color picker dialog for this.
There's still a tiny bit of green fringing left near the edges of the formerly red areas, where some pixels in the original had a pinkish shade due to anti-aliasing. To get rid of that, a quick and dirty solution is to use Colors → Desaturate....
Finally, convert the image to grayscale (optional, but recommended to minimize file size) with Image → Mode → Grayscale and save it as PNG:
Another way to achieve the same result is by using the Bucket Fill 
tool with the Color Erase mode. The workflow is basically the same, except that you need to click each of the red areas separately with the tool, rather than selecting them all at once and then using Color to Alpha.
The Background Eraser tool in Photoshop works well for this example
Just do it in Illustrator - simply set the properties on the stroke and leave out the foreground - no filters no nothing.
