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Using GIMP I'm trying to cut out all white background from a picture of a pen and ink drawing in order put it on a colored T shirt, like a silk screen. Thanks for your help!

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  • Possible duplicate of How to remove background with Gimp? – Luciano Jun 30 '17 at 14:47
  • I have +1 your question because I have spent too much time to find that solution in Gimp a few years ago. They have this alpha-channel option, but depending on the origin of your file, you might need to add an alpha-channel first, before you even get certain tools activated. Anyway, some good answers below but I have compassion for your question. Hint: if you give us more context and detail (and maybe an example picture) of what you are doing, we can help you even better here. – Martin Zaske Dec 28 '17 at 11:55
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Just use Color>Color to alpha to remove the white (makes all the white transparent). And save the image as a PNG, JPEG doesn't support transparency.

But usually you want to clean things a bit first. If the image is a scan (lighting is regular), just using the Brightness/Contrast tool to blow out the white (increase contrast (much) and brightness (a bit)) is often enough. But don't overdo it, watch that the edges don't get pixellated.

If it's a photo (likely with uneven lighting), try this:

  • Duplicate the image
  • Apply a Gaussian blur to the top layer. This blur should be sufficient to make the lines disappear entirely (I typically use about 1/3 of the image)
  • Put the top layer in 'Grain merge' mode
  • Layer>New from visible to finalize things.
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You don't need to do that for printing. White is not reproduced as a separate colour in most printing processes, including regular screen printing, unless you have a specific need for it.

If the pen and ink drawing is monochrome, a screen can be made that will print in black ink, or any other single colour of ink. The white areas will be transparent.

If the drawing is coloured, it can be reproduced in CMYK printing - again no white ink is involved in the process.

As to answer your question directly, it is possible to remove a white background should the need arise. In GIMP click Colours > Colour to Alpha > OK - then export in a format that supports alpha transparency, such as PNG, GIF, PSD, TIFF, XCF.

  • I have just seen a few days ago a commercial photo service that lets you print stuff on t-shirts. They exist for ever, but now they offer very nice pre-views with nicely rendered t-shirts. So that would be one scenario, where the user-requested transparency would make a real difference. This is a made-up reason (but valid) because I get nervous when answers are starting with "you should not want that". Your start "you do not need that" can be very nice, if it reduces un-needed work and effort. But we do not know enough. @Fenwick should have provided more context to allow more precise answers. – Martin Zaske Dec 28 '17 at 11:50
  • @MartinZaske Sorry, but I disagree. Transparent images are not required to make a preview of a t-shirt either. It can easily be achieved using software such as Photoshop, or GIMP, and simply using a blending mode such as "multiply" on the image layer above the t-shirt layer. – Billy Kerr Dec 28 '17 at 19:08
  • disagree if it makes you happy. But the previews in this online shop look crapy, when you have white background in your artwork. The online shop is automatic and has got no inbuilt Photoshop. I gave a valid example where transparency is helpful. You can invent many more scenarios, that is fine with me. No need to haggle over transparency. I am glad we got such nice tools - compared to 20 years ago when we started at home with a scanner and some editor... – Martin Zaske Dec 29 '17 at 20:50
  • Also note that the only up vote on your answer is from me - I am with you, no worries. – Martin Zaske Dec 29 '17 at 20:53
  • @MartinZaske then that is the fault of the website developers. There are image processing/compositing functions available in software such as ImageMagick which could be used to achieve a "multiply" blending mode for images uploaded to websites. – Billy Kerr Dec 30 '17 at 8:04
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Open photoshop. Place the picture. Unview the background so that it's transparent (click the eye logo on the layer) Select the layer of the picture and manually select all the parts you want removed. Once all is selected (other than the ink) press delete. Save as .PNG and ta-da!

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    question is about how to do that in GIMP – Luciano Jun 30 '17 at 14:45
  • manually select "all white"?; I am not using Photoshop (never mind the question is about Gimp) but I am sure that there are powerful tools there too, for selecting certain colours, as the op has requested – Martin Zaske Dec 28 '17 at 12:01

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