There are a couple of good ways to temporarily alter the image to show up the problem areas and help you dodge and burn what you otherwise might miss. The first is simple, add a Hue/Saturation adjustment layer and pull the saturation slider to -100. After all, we’re dealing solely with luminosity, colour can be an unwanted distraction.
Secondly, you can use a curve to increase contrast to the areas you’re working on. The steepest part of a curve is the area of highest contrast, and we can manipulate this to help us work on problem areas. With this sample image I’m lucky enough to be able to significantly increase the steepness of the curve without losing much detail at either end;
This brings out a lot of detail that might otherwise be difficult to spot. To increase contrast in a specific area, such as the highlights in this collarbone, shift the curve so that the steepest part of the curve lies in the lightest part of the histogram;
Be aware that by doing this you’re decreasing contrast in the shadows and in danger of plugging the blacks, so you may need to steepen the curve there later to check you haven’t missed anything.
Group your de-saturation and contrast curve layers together and simply switch them off when you’re done.
Combating Colour Shifts
The problem with dodge and burn is that areas of shadow are more saturated than mid tones, and a lot more saturated than highlights. As we’re dealing solely with luminosity, those hues won’t change, meaning an area you’ve significantly lightened can appear over saturated and a darkened highlight can look ashy and dull.
To remedy this open two new Hue/Sat adjustment layers, one above each of your Dodge and Burn curves; Alt/Opt click between layers to clip a layer to the layer beneath. This means the effect of the clipped layer will only affect the appearance of the layer it’s clipped to. It will recognise masks, so clipping a Hue/Sat layer to your Dodge curve will affect only the dodged areas;
As we know that dark areas are likely to become (or rather remain) oversaturated when lightened, drop the saturation slider on your Burn adjustment. And as lighter areas are less saturated and will to remain so when darkened, raise the saturation slider for your Dodge adjustment. You can set the saturation slider according to how much of a shift you see in colour, frequently anywhere between no shift at all to plus or minus 20pts depending on the image.
Zoom in and check closely while you choose your slider setting, and don’t forget you can adjust the hue in the same dialog if you find it necessary.
Original Post Daniel Meadows a UK based professional retoucher viewable HERE.