Converting Colour Images to Monochrome

Levels and Curves adjustments are generally best done prior to conversion to monochrome.

Method 1 - Greyscale

Method 2 - Hue and Saturation

Method 3 - Double Hue and Saturation Layers

Open a file and two hue/saturation adjustment layers .
Desaturate the second (top) hue/saturation layer to minus 100%.
Change the first hue/saturation layer to colour mode, and adjust the hue and saturation to give the required tonal balance.

Method 4 - Channel Mixing

Use the adjust/channel mixing control.
Tick the monochrome box.
Adjust the colour channels to change the tones (the total of three channel percentages should usually be 100%).

Method 5 - Lightness Channel

Open a file - image - mode - lab colour.
Choose channels - select lightness channel.
Image - greyscale - discard colour channels.
Copy background layer - select blend (screen for dark image or multiply for light image) - adjust the opacity to achieve the required tone.

Method 6 - Selective Colour

Open a file.
Open new layer - fill with 50% grey - colour blend.
Select the background layer - open selective colour adjustment layer - adjust the different colours to get right tonal balance.

Method 7 - Selective Colour

Open a file
Flatten the image.
Create a new hue/saturation adjustment layer using saturation mode, hue = -180, saturation = -100 and lightness = +100
Convert to LAB color and choose the flatten option if it is available.
Open the channels window and delete channels A and B.
Convert to greyscale.