So because I suffer from severe procrastination and should be studying now, I've decided to write this quick tutorial to explain one very simple technique to colourise your photo and make it look a bit less cheap.

I personally really like associating my characters or factions with particular colours. And in some cases it's good to have that type of association because it makes the characters a bit more memorable. To show it, I tend to use a way of colourising the photos in transmissions or stories. There are some very simple techniques (such as throwing an Overlay layer filled with the colour over the photo). It's quick and simple, but also awfully cheap and not very well-looking. There is however a rather well-known solution to that problem called luminosity masking that I'm intending to show off in this little tutorial.

So imagine I want a character to be a bit more with my faction colour, for instance, just to pick a name out of a hat, this one. I'm also going to use this picture of the photographer Lara Jade as our subject for the purpose of the tutorial.

To show you what we're going to be doing,


So now that we've established what we're making fun of, let's tear it apart. You're going to need GIMP for this, so if you don't have it, you can get it at http://gimp.org.

So first we're going to create luminosity channels for our photo - for light and dark regions. To do that, first duplicate the photo layer. To do that, select the layer in the layers window (if you don't have it open for some reason, you can open it by pressing Ctrl+L) and press Ctrl+Shift+D. I'm going to rename my layers to main and desaturate respectively - to do that select the layer and press Space.


Now we're going to desaturate one of the layers. Select the layer desaturate and go to Colors -> Desaturate. Select Luminosity and click OK.


That has made one of the layers greyscale, however it's not immediately visible. To see how it looks now, you need to hide the top layer - do that by clicking the little eye icon to the left of the layer name.


Now we're going to add the luminosity channels. Open the channels window (Windows -> Dockable Dialogs -> Channels). It is divided into two sections - the four basic channels (Red, Green, Blue and Alpha) on top and our own defined channels on the bottom. The bottom part is empty, but we're going to add two channels of our own - Lights and Darks.

First, drag one of the RGB channels to the custom section. It doesn't matter which one you select, because since we desaturated the picture, all of them are the same. Then rename it to Lights.


Now we're going to create the inverse of that channel - Darks. To do that, first select the entire picture (do that by pressing Ctrl+A or going to Select -> All). Then right click the Lights channel and select Subtract from selection.


Now go to Select -> Save to Channel. This is going to create a new channel called Selection Mask copy. Rename it to Darks.


So now we have our channels created. Let's colour in the picture.

This part is going to be relatively easy. We don't need the desaturate layer any more so you can delete it by selecting it and going to Layer -> Delete layer. Then we're going to duplicate the main layer and rename the duplicate to colour. Then select the colour layer and pick Add Layer Mask. As the type of mask we're going to pick Channel. Then, select Darks from the dropdown menu. Click Add.


Now select the layer colour (remember to do that by clicking the normal layer icon rather than the black-and-white mask one). Adding in the mask means we're now only operating on the darker channel of the picture, leaving the main colours intact. Go to Colors -> Colorize and start playing with the colours. When you're done, click OK and you're ready to save or export your picture.

And that is it. Luminosity masking is a very simple yet very effective technique which goes well with other enhancement operations. You can play around with colouring the other channels, sharpening the image (Filters -> Enhance -> Sharpen) and other stuff.

I hope this helped you in some way, enjoy.