Duotone in GIMP

[kmll]

Hi
I have been using a duotone effect in Photofiltre on a student project. However that software is now too old to be installed and I am considering GIMP. Do anyone know if a duotone effect similar to the attachment is possible in GIMP, and if yes how?

As you can see the effect makes the image duotone and at the same time make the quality "reduced", more grainy.

Please see Link to image

(https://ibb.co/jk2ysW3G)

[rich2005]

(Yesterday, 04:58 PM)kmll Wrote: Hi
I have been using a duotone effect in Photofiltre on a student project. However that software is now too old to be installed and I am considering GIMP. Do anyone know if a duotone effect similar to the attachment is possible in GIMP, and if yes how?

As you can see the effect makes the image duotone and at the same time make the quality "reduced", more grainy.

Please see Link to image

There will be a few ways but using basic tools is a good way of looking in the menus.

(1) Starting with a colour image but with plain background. Use Colors -> Threshold. Experiment with the slider but usually the default is ok.  Make sure that merge filter option is on.
(2) Make the white transparent using Colors -> Color-to-Alpha  White is default but you can change that. Make sure that merge filter option is on.

   

(3) Change the color Colors -> Colorize You can select a color but use the Lightness slider and Hue slider to get your choice. Make sure that merge filter option is on.
(4) Add a new layer Layer -> New Layer and drop it under the subject.  Fill it with the required background color.

   

Always Save your work as a Gimp .xcf which keeps layers...etc  You can flatten the layers if satisfied also Exporting as a jpeg or png flattens to a single layer.

I think in Gimp 2.10 someone made a duotone plugin but Gimp 3 is a bit recent, not many plugins made for it yet.

[rich2005]

This a quicker way - Start off as before, Colors -> Threshold (split view enabled just for info )
then
Set the foreground and background colors to what you require
then
Colors -> Map -> Gradient Map.

   

[kmll]

Great! Thank you both for the advice :-)
When I try the Gradient map it goes all white?? I must be doing something wrong.

[rich2005]

(Yesterday, 07:39 PM)kmll Wrote: Great! Thank you both for the advice :-)
When I try the Gradient map it goes all white?? I must be doing something wrong.

It is probably the layer effect (fx) not merged when you used the filter(s)  If there is the fx in the layer click on it and merge.  For the gradient, make sure you are using one of the FG/BG type.