How to make a transparent banner

I’m very much not a graphical person but when forced to dabble in any kind of image manipulation have always tried to use The GIMP, over any commercial offerings.

Just this afternoon I’ve spent some time trying to make the background of a very simple image transparent. The image is a filled shape on a white background. I wanted the white background to be transparent.

I think I’ve finally found the best way to achieve this but may be way off mark.

Here’s how to make a transparent banner:

1. Open the original image (jpeg image in this case).
2. Use the ‘magic wand’ (Select contiguous regions) and select the coloured shape.
3. Move the selected shape to the side of the image.
4. In the Layers view you should now have a new ‘Floating Selection (Floated Layer)’. Right click on this layer and select ‘New layer’. This converts the transient layer into a real layer.
5. Click on the background layer to ‘select’ the background of the image.
6. Select Layer > Transparency > Add Alpha Channel.
7. We can now set the background to transparent by using Layer > Transparency > Colour to Alpha and selecting our background colour (white in my case) as the From colour.
8. Click Ok to set the background to transparent.
9. Click on the Floated Layer (this is what the layer will be called unless you renamed it) to display it to the side of the image.
10. Click the cross-hair (Move layers & selections) tool and move the shape onto the now transparent background.
11. That’s it, apart from saving the image in a format that either saves the layers (.xcf at least, maybe more) or at least deals with transparency (.gif and .png).

http://chrisroos.co.uk/blog/2005-09-09-set-background-transparency-in-gimp