1. Remove the
background with any technique you like. I made a mask in Inkscape,
because the Path (Bezier) Tool is very easy to use, so all i had to do is export the mask-image in the correct pixelsize and open it as a layer in
If you use a
selection to render your image, just invert the selection and fill with white. Deselect, invert the image so that you get a negative and jump to step 3. Also make sure you save that selection to a channel for
future use !
You can use as
many colors as you like for your posterization, but between two and five seems like a good value. The famous 'Obama Hope' poster by Shepard
Fairey has five colors (actually four plus one additional tone that is achieved by
mixing two colours).
2. Im going with
Preparing the mask
a) Add a layermask
to your image.
b) Copy the mask
layer and paste it into the layermask. A floating selection will
appear. Anchor that layer, by clicking the little anchor symbol.
We want the
background to be white, so i put a new white layer under the original
c) merge your
original image with the layermask down, then invert the image
(Colours → Invert).
This image will be
Set up the tone layers
To set up the
layers, copy the final mask-layer image to the clipboard, and create a new (in my case, yellow) layer.
Add a layermask with a right-click and
with the layermask selected, paste and anchor the copied mask-image.
In case you dont fully understand layermasks, here is a good short summary i picked up from Glyn Dewis youtubechannel:
"Black conceals and White reveals."
So a layermask acts like a filter, showing all the colour (in this case yellow) where there is white on the layermask, and blocking all the yellow where there is black on the mask. Shades of grey gives you transparent yellow.
4. Duplicate that
layer as many times as you want colors, minus two.
Your first, lightest
color, doesnt need a layermask and the background needs a different
5. Add a layermask
to the darkest colour layer and copy/paste the mask you used to
render your image, but invert it (click on layermask, then 'Colors → Invert').
6. Finally add all
the inbetween colours, by drag and dropping them to your layers (or use the Bucket Tool).
Darkest colours on
top, lightest to the bottom.
Threshold the layers
Now its time for
the creative fun part.
By manipulating the values of the layermask, we can control what the mask reveals or conceals.
Select the layermask
and call up the Threshold Tool.
Move the slider to
the right, until you have the amount of shadows you want. In my case
im focusing on the eyes.
8. Repeat this for
all the other tone-layers, from top to bottom.
If you are unhappy
with a particular layer of your finished result, you can re-paste the original mask and try again.
You can use this
method to colorize an image and give it a pop-art effect.
If you want to
simplifiy and clean up the thresholded mask you can blur it before
you apply the thresholding.
In this example i
used a value of 3px for the shadows to preserve detail and a value of
8px for the lighter shades.
What you can also do
is make two images with the same colours but different levels of
simplification and later composite them with a layermask.
For this image i
used a version of the posterized image, where every layermask had a
Blur of 20px applied before thresholding.
I used the strongly
blurred mask version as the base and combined it with the detail of the eyes and
lips of this tutorial's image.
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Of course you can
also use textures instead of colours. For a hatching effect i used a