[Leica] Tip: Local contrast control in Photoshop

[Martin Howard <mvhoward@mac.com>]

First of all, thanks to BD, Mr Deadman, and Tina Manley (and anyone 
else who answered my call for help).  After getting home and playing 
around with Photoshop (and a manual), I've come up with what I consider 
to be a pretty good solution to the problem of local contrast control.

Unfortunately, this will only work in 8-bit images, because it requires 
layers.  The key lies in how the "Soft Light" blending mode works: if 
the blend colour (light source) is lighter than 50% grey, the image is 
lightened.  If it is darker than 50%, the images is darkened.  Painting 
with pure white or black creates a lot of change, but will not result 
in pure white or black.

So, this is what you do:

1) Create a new (standard) layer (not an "Adjustments layer" nor a 
"Fill layer").

2) Fill this layer with 50% grey. Make the layer blend mode "Soft 
Light". This means that it should have no effect on the underlying 
image.  Set the layer opacity to 50% and fill to 100%.

3) Get soft brush of suitable size.  The size depends upon how large an 
area you wish to dodge or burn.  Set the paint mode to "Normal" and 
opacity to 75%.

4) Make sure that the new layer is the one you're painting on, but also 
make sure that you can see the background layer.  I'd also recommend 
opening a new window which allows you to see the whole image in one go.

5) To lighten an area, select a grey lighter than 50%.  I use 75% for 
rough work and 55% for fine tuning.  To darken an area, select a grey 
darker than 50%.  Again, I use 25% for rough stuff and 45% for fine 
tuning.  To remove the dodge or burn from an area where you've 
previously applied it, select a grey of exactly 50%.

6) Paint away.  As you paint, you can see how the contrast changes in 
the image.  If you do too much, just "Undo", or use the history list to 
click back several steps.

The cool thing about this method is that all the contrast control is in 
a separate layer, so it does not affect the original images' pixels.  
Also, using different brush sizes it is possible to do very fine work, 
and the combination of paint shade, brush opacity, and layer opacity 
allows very fine control over the final appearance.

M.

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