This is a technique that I’ve used for years, but I’ve just learned a new wrinkle!  Above is a  photograph I made of some trees in Yosemite. In the upper part of image, you can see a slight problem—the sky peeking through the leaves is the brightest thing in the image, which I find distracting.  It was made in May, around 6 PM in deep shade, and since the upper branches were very close and I wanted most everything in focus, I stopped down to f/16. This  required an exposure of around 2 seconds (it was dark in there!)  Thus, any sky or granite cliffs showing through the leaves would be completely white and blown-out.  Since you cannot effectively darken these areas, they must be cloned out.  (Short diatribe:  “Cloning” like this is not  unique to digital!  When I printed a similar image in my dye transfer days, I would take a retouching brush to the print and darken out such bright parts with dyes—accomplishing the exact same thing.  Except I had to do it on every print—in Photoshop, we only have to do it once).  Here’s a tiny detail of one of the problem areas below, showing before (on left), and after (on right):

                 

How do you clone just the leaves and not mess up the many dark branches?   Actually, very easily.  The area of leaves I was cloning from (not seen in the detail above) was lighter than any of the branches.  So I used Photoshop’s Darken Mode.  This allows the clone tool to only change pixels that are lighter than the sampled area.   Since the branches are darker, they will not change, but the bright spots will.  This technique can be very handy!

The previous way I used this technique worked fine.  But, at my recent “alumni”  workshop, I learned an even better way to implement this technique from Cindy Walpole.  Here’s what to do:

You’ll need to create a new empty layer in Photoshop—this should be immediately above the background/image layer and choose “darken” instead of “normal” for the blending mode.   I’ve named it appropriately:

And, since you’re practicing “safe computing”  by cloning into a separate layer (which keeps changes reversible), you need to select “current and below”  in the cloning tool options at the top of the screen:

The options for the cloning tool itself should stay in “normal”.  This new cloning layer, since it is in a special blending mode, will only work as I described above:  The only pixels that will change are those that are lighter than our sampled area.   If you want to do “regular”  cloning, then you’ll need another cloning layer in normal mode.  In this image, be sure that the sampled areas of leaves is sufficiently brighter than the tree branches to avoid any partial clones or ghosting.

This technique can also help with problem masks.  I try to avoid “accurate”, hard-edge masks, but they are necessary in certain cases.  Below is a mountain peak before dawn, and I wanted to lighten the mountain, but not the sky, and thus had to create a hard-edged mask selecting just the mountain.  I made the mask from one of the color channels, and even using various tricks, I still had a slight haloing in certain areas.  Below is a section seen at 200% magnification:

By cloning from the sky into the ridge line using this darken mode technique, you can easily clean this up.  The halo is lighter than the sky, so the halo gets darker.  But the mountain is darker than the sky, so it doesn’t change:

If you want to fix this in your “master” file,  you’ll need to put this special cloning in darken mode layer above the mask that caused the problem in the first place.   I always advise that any cloning layers be directly above the image layer, but in this case it will need to be above whatever adjustment layer has that problem mask.