Bitmap editing

Blend pictures with the GIMP

This tutorial by silentrainfall is a bit old (September 2005), but I thought it might be useful to learn how to make image blends with layer masks on the GIMP.

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Halftoning pictures with the GIMP for photocopies

The GIMP can conveniently complement a desktop publishing tool like Scribus; and if you are on a low budget, you can also prepare your pictures for the photocopying process by converting them to black & white halftone.

Photocopiers use powder toner, and they have a hard time reproducing grey hues. By preparing all of your documents pictures this way, you facilitate the photocopier’s work, allowing it to reproduce plain black or white shapes.

If you haven’t got the GIMP installed yet, you should be able to find a link to your OS version on the project’s web site.

First of all, make sure that you properly resize your image for black and white printing. A resolution of 300 dpi is the norm, although you could do with a minimum of 150 dpi. Basically, if you intend to send your work on a digital media (CD, DVD, USB key), you can go for a 300 dpi resolution. Otherwise, if the work needs to be sent through email, a 150 dpi image will take less than 1/4 of the disc space that a 300 dpi might.

In this example, the resolution is set to a 150 dpi.

Next, choose:
Image > Mode > Indexed

Set the colormap to use black and white (1bit) palette and choose between Floyd-Steinberg (normal) and Positioned dithering.

the original image in grey and the result in halftone

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