Saturation is a tool I often use. Saturation adjustments can be used to tweak a piece of video to give extra impact by making colours more vibrant, or a very different feeling can be evoked by making the colours washed out.  Some groovy special effects can be done with ease - remember the little girl with the red coat in Schlinder's list?

Firstly lets get it clear what saturation is - paint is a good analogy.  If we start with grey paint and add purple the paint will slowly go from grey to very purple, from saturation down to saturation up in the picture on the left, we are increasing the amount of colour.  Now look at the brightness boxes, the saturation has not been changed, the amount of colour is the same but we see it brighter or dimmer as the level of brightness changes.  At their extremes saturation fully down would give a grey box, saturation right up would be a very purple box, brightness right up would be white, right down would be black. 

In the previous tutorial on curves we were adjusting brightness only - we were changing how a particular brightness level was altered by the plug in depending on the shape of the curve we used.  The saturation adjustment tool works in a similar way but looks a bit different.

This artistic still life is a still taken direct from the camera.  It contains some strong areas of colour, highly saturated, and some areas that are much less saturated.  The saturation filter is set to flat.

I am not going to explain what the sliders do, it is much easier to learn by fiddling with them than by me droning on.

 
In this picture you can see the result of boosting the colour in areas of low saturation, click to enlarge.  Strong areas of colour on the bottle are unchanged but weaker areas look stronger - even the very weak green colouration from reflected light off the plant is visible on the wall.  This is a good way of jazzing up footage for more impact.

In this example only the high levels are boosted.  All the colours look identical to the flat version except that the bright colours are now fully saturated.

Now if you want that effective girl in the red coat trick from Schindler's list all you need to do is film the scene with the object you want in colour as the strongest colour in the scene and use the low cut to remove the colour from everything else.

Click here for some movie action showing the effect.  It hasn't worked that well because there was a lot of red in my skin tones so to make me b/w I had to lose some of the red in the fag packet.  With more careful filming this effect can look more 'real'.
 

A final word of caution.  When pushing saturation levels really high, and especially when using this plug in at the same time as using 'curves' to boost visual impact you need to watch out for 'jaggies' getting worse.  The colour resolution of DV is actually much lower than the raw resolution, so boosting levels and saturation can create jagged edges at the boundaries between colours as this low resolution becomes visible.  Applying these effects to more compressed footage such as wmv or divx can produce some nasty artefacts too.