Lab Colour Saturation
Everybody says that Colour Saturation in Lab is miles better than doing it in RGB - so lets put it to a really hard test.
Trying to take a picture of a sunset and then printing it is almost impossible because of the brilliance of the sun. A setting sun is a brilliant yellow-orange colour, but when we print it (or view it on the screen) the blank paper is as white as we can go. If we then try and add colours to this it can only get darker and trying to add both colours will make it worse!
Lab with it's complete range of colours, some which are called 'imaginary', can represent that colour because colour and brightness are separated. No such luck with RGB. In a sense this doesn't help if the camera could not capture the brilliant colours in the first place, but I digress.
The only thing to 'improve' this situation is to boost the colours in the hope of fooling the viewer into perceiving a colourful sun.
This picture exploits Lab's ability to make impossible colours. In RGB the brightest colour is 255,255,255 and any attempt to add colour will darken it. But in Lab, where colour and contrast live in separate channels we can have pure lightness at 100% and still add colour to it! However although Lab can hold these colours, Photoshop must try and make them visible and also convert them back into RGB/CMYK for printing - it just does the best it can with these out of gamut colours. So be slightly aware that when you convert a Lab image into RGB, the colours can change, but you will only notice this when they are wild impossible ones.