Tinting a photo
This is simple easy way to turn a photo (or any picture) into
a monochrome picture. In this example we will take a colour
photo and turn into a monochrome photo using blue. The sample
photo we are using is below:

First we want to remove any colour information by
selecting Image -> Adjust and then Desaturate, or Ctrl+Shift+U.
This turns the picture into black and white.
Now select Image -> Adjust and then
Hue/Saturation or Ctrl+U. Set the settings as per my example for a
blue tint. Otherwise just play with the sliders to obtain the
desired effect. Make sure you select colorize or it won't work.

Lets adjust the levels to get the picture just
right. Select Image -> Adjust and then Auto Levels, or
Ctrl+Shift+L. That should get a result similar to that below. Easy!

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