Splitting hair for wider range
I face situations where I may want to accommodate a wide tonal
range in an image that has too much contrast. I picked a sample
image to use here showing two garages with white paint under direct
sunlight with a heavy shadow area behind a fence.
In this tutorial, I will use the combined RGB channel and not be
concerned with color corrections. The purpose is to illustrate a
technique on controlling the range. You may save and use the image
above to follow the rest of the tutorial.
Simple curves adjustment
I made a decent effort to adjust the curves to open the highlights
while retaining some detail on the white parts of the garage. Here
is the result:
I have managed to adjust the whites and, to some extent, the mid-tones
but the shadow area on this side of the fence is still too dark.
Here, the split adjustments of the highlights and the shadows will
give me a greater control on maintaining the tonal range that I
First, I need to create a mask that consists of the luminosity of
the image. To achieve that, click on the "Channels" tab,
then Ctrl-click on the RGB combined channel. This will select the
luminosity of the image. Press Ctrl-C to copy this selection. We
now need a new channel, click on the fly-out menu arrow on the top
right corner of the channels panel and select "New channel"
from the menu, accept the suggested name "Alpha 1." You
will see a blank channel. Make sure to click on this channel and
press Ctrl-V to paste the image in the clipboard. Now we have a
B&W image of the luminosity of the original. Press Ctrl-D to
release the selection so that no part of the image is selected.
Since I want the mast to control the shadows, I will invert the
image before making the final adjustment to create the mask. To
do this, press Ctrl-I (making sure that you have already pressed
To make the mask work the way we want, we should enhance its contrast.
Summon the "Curves" tool, press Ctrl-M and make the curve
to look as follows. The important thing to remember is to create
a smooth curve. Here's my curve.
After this adjustment, my Alpha 1 channel looks like this:
Now I have a high contrast channel that I can use, I want to use
it to select the appropriate parts of the original image. Press
Ctrl-click on the Alpha 1 channel to select the mask, then click
on the RGB channel. The mask has created the selection on the RGB
channel which will control the areas that will be affected by subsequent
Curves, part I
Now, click on the "Layers" palette and using the black-and-white
circle at the bottom of the palette window, create a "Curves"
layer. This adjustment layer will only affect the shadow areas of
the image and to a lesser extent some of the mid-tones. I have adjusted
my curves as follows. This retains the highlights the way they were,
makes slight adjustments to the mid-tones, and significant adjustments
to the shadows.
The resulting image after this stage looks like this:
I can see more in the shadows, even the reddish patio tiles and
other detail are visible.
Curves, part II
Now I will turn my attention to the highlights which requires the
exact opposite of the mask that I have created for the shadows.
Using the mouse, Ctrl-click on the curves mask, which shows the
high contrast B&W image on its thumbnail. (Alternately, you
can switch to the channels palette, and Ctrl-Click on the Alpha
1 channel.) We want to mask the exact opposite of the selection,
so press Ctrl-Shift-I to select the inverse. Again, using the B&W
circle at the bottom of the Layers palette, create a new curves
layer which will affect only the selected areas, highlights. Any
adjustments we make on this curve will affect the highlights and
to a lesser extent the mid-tones. Here is my curve for this adjustment.
And the resulting adjusted image has the correct highlights and
reasonably open shadows. Since we have both curves layers active,
the image shows the combined adjustment and yields full tonal range.
If you think the same result can be obtained by using a single
curves layer on the original image, you may be (may be) right. Try
it and observe how fussy you have to be to make it look half way
decent. Where this method of split level curve adjustments are quite
tolerant of substantial adjustments on their respective curves.