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I'd like to use this image on a web site.

enter image description here

What I need to do is change the background from black to transparent, so I can use the arrow on my site maintaining the page background.

I used Gimp to convert the image to .png. I have no graphics experience so forgive me for this question, but how do I proceed now?


Image credits: this web site.

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3 Answers

up vote 15 down vote accepted

GIMP's Color to Alpha tool is very handy if you know how to use it, and this task seems particularly well suited for it:

  1. Open the image in GIMP, and change it to RGB color mode if necessary.
  2. Select Layer → Transparency → Color to Alpha...
  3. Select black (#000000) as the color to make transparent.
  4. Click "OK".
  5. Save the resulting image in PNG format:
    Image with transparency
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+1 I've been using Gimp since forever, and I never noticed that tool. Thanks! –  Paul d'Aoust Jun 22 '12 at 23:31
Fantastic- that was just the answer I needed! Just a heads up- if the 'colour to alpha' option is greyed out, it means that your image is in indexed colour mode. To rectify, please go to Image--> Mode--> RGB. Cheers! –  user8704 Nov 21 '12 at 10:54
@Heather: Thanks for spotting that, I've added a note about it to the answer. In fact, converting to RGB is usually the first thing you want to do to indexed images in GIMP anyway, unless you want your edits to be constrained to the existing palette. –  Ilmari Karonen Nov 21 '12 at 17:27
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You could use the GIMP's select by color tool or the Magic Wand tool. Anyhow you do it, just select all the black pixels. Then, instead of deleting the selected pixels, apply a layer mask:

Layer -> Mask -> Add layer mask

Select the "Selection" radio button and be sure to select the "Invert mask" checkbox. Now, all the black pixels are transparent.

Export as PNG or GIF.

The problem is in the edges around the arrow, where you might have some black pixels to form a matte. I don't know in GIMP but Photoshop has a nice feature to remove the previous matte and/or add a matte of your choice.

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I don't use gimp, but this image is a simple case where it should be straightforward to derive a decent transparency.

If you select the entire image, and then use that (or rather the greyscale version) as an alpha channel, you are pretty much done.

Depending on your software export features, you can just pick the alpha as the PNG transparency or you can use the alpha channel as a selection mask and delete the selection (bad) or use the slection as a layer mask (non-destructive), then export.

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