Adobe Photoshop CS5 One-on-One

the background for a perfume ad (top middle). Now let’s say
I lose the original image and the lightened background copy
is all I have. If I apply the Auto Color command to restore
the highlights and shadows, I can revive a semblance of the
original image. But you can see how few colors remain (top
right). The corrected image is rife with color banding as well
as flat highlights and shadows.

This would not have been a problem if I had
chosen the Image→Mode→16 Bits/Channel
command before creating the perfume ad (the
command doesn’t do me any good after the
colors are lost!). Choosing Auto Color would
have restored the image to nearly its original
coloring, as demonstrated by the lower-right
example. It would have also produced a much
healthier histogram. When you’re working
with 8 or 16 bits per channel, the histogram
shows you just 256 levels of brightness. But
when you stretch out a squished histogram,
the 8-bit histogram reveals gaps and the 16-
bit histogram is smooth, as the examples on
the right show.

If you convert to 32 bits per channel (also
known as high dynamic range, or HDR), you
gain still more theoretical wiggle room. Sud-
denly, you are no longer bound by the con-
ventional histogram. Colors can float outside
the boundaries of the visible range, permit-
ting you to regain blown highlights and flat
black shadows.

What does all this have to do with Camera
Raw? By default, Camera Raw reduces the
bit depth to 8 bits/channel when opening an
image in Photoshop. That makes sense given
that the major benefit of a higher bit depth is
the freedom it gives you when applying color
adjustments, and chances are you’ll do most
of the destructive work in Camera Raw be-
fore setting foot in Photoshop. However, if
you plan on applying a few more dramatic
color adjustments, or you’re merely keen on

Original photographLightened using LevelsAuto Color

produces banding

Radically

lightened image

Auto Color

in 8-bit/channel

Auto Color

in 16-bit/channel

protecting every single color that you can, click the blue link

below the image preview in the Camera Raw interface. This

displays the Workflow Options dialog box. Set the Depth

option to 16 Bits/Channel and then click OK. From now on

(or until you restore the default Depth setting), all your raw

photos will open in Photoshop’s 16 bits/channel space.

Exploring High Bit Depths 303