Seperate the Colors
The first thing we`re going to do is to remove all shades from the image. The result will be solid shapes of color. Follow the steps below to learn this technique.
Open a photo you would like to edit. Resize (Image> Image Size) the image to the output size you would like. It is fine to upscale a low resolution image before using this effect.
Duplicate the layer (Layer> Duplicate Layer or Ctrl+J) and change the blending mode of the new layer to Luminosity.
With the top layer selected, Invert (Image> Adjustments> Invert or Ctrl+I).
Reduce the opacity of the current layer to 50%.
Press Ctrl+Shift+Alt+E to create a new layer of the visible and delete Layer 1.