Selective Desaturation Tutorial
I don't use selective desaturation much, but as a technique it can be used to highlight a subject in a photograph. Here's some interesting examples:
You can jump straight to sections from here:
First load our image up into photoshop. We're going to take the red leaf that is the subject of this photo, and desaturation everything else. To do this we need to make a mask that is the shape of the leaf and to do that the shape of the leaf needs to be selected.
There are many ways to create masks in Photoshop. I am going to show you one method here, which is generally the method I use. I'm not saying it's the best, but it's the method I prefer.
The magic wand tool selects a region in the image that is similar to the seed point where you click the wand. This is clearly only useful if the object you want to highlight is of a single colour. You may need to seed it in various places holding down the SHIFT key to ADD to the selection. You can alter the threshold of the magic wand to make it select more or less (the higher the number the more it will select).
Clearly the magic wand has been a bit over enthusiastic, but rather than turning the threshold down (which will mean we spend ages trying to get rid of little dots within the leaf that we want selected), we'll use the lasso tool that allows us to make a selection freehand.
We can press the SHIFT-key and drag the lasso tool around areas that we want to include in the image. Pressing the CTRL-key will allow us to select parts of the image to remove from the selection. We keep adding and removing bits from our selection, until the selection surrounds the leaf and there are no unselected areas within the leaf.
An alternative way to create the mask is to paint onto the mask layer using a black or white paintbrush.
Now we turn this selection into a mask on our image. However, we're going to apply this mask to an adjustment layer. Adjustment layers in Photoshop will apply some adjustment (such as desaturation) to all layers that are below it in the layer stack. To create an adjustment layer use the adjustment layer button in the layers panel. As we want to desaturate part of the image use the Hue/Saturation adjustment.
A new layer appears with the mask that came from the selection.
The Hue/Saturation dialog will appear. Drag the Saturation level to -100%.
You will notice that your leaf has desaturated, but the background has stayed normal, like this:
The reason for this is that the mask is masking off the background rather than the leaf. Look at the mask above. The mask is white where the adjustment layer will have an effect, and black where it will not. You can see that our leaf is white in the mask and so it gets desaturated. This is easy to fix, by clicking on the mask in the layers panel (make sure that the white box surrounds the little mask thumbnail), and select Invert from the Image Adjustment menu:
The mask gets inverted and the background desaturates.
If you find your mask is not complete (e.g. parts of the leaf get desaturated) you can use the paint brush with a black or white colour selected and paint onto the mask to fill in holes.
Here's our completed picture: