It is easy to make good greyscale (or monochrome) single colour images in Photoshop…right? Well that’s not exactly true, read on if you want better quality colour to greyscale Photoshop conversions!
Basic colour handling knowledge in Photoshop will inform you that true single colour greyscale images can be achieved by simply converting the image to greyscale in the Image menu. This compresses all the lovely detail hiding away in the channels that make up your full colour image into one single colour channel, meaning you can loose a lot of detail.
However, in almost all cases you will achieve a much wider, better quality tonal range in your greyscale image by first converting the image to LAB colour mode. Then simply select the lightness channel in the channels palette, and then convert the image to greyscale.
Lab colour is useful for lots of little jobs in Photoshop, but you should always ensure you convert your image to the destination colour space for final production, usually RGB for multimedia or CMYK for printing to avoid any issues along the way.