How Photoshop Multiplies
a Photo’s Dynamic Range
158 PART 3 HOW THE DIGITAL DARKROOM WORKS
This photo is a “normal”
exposure, meaning it’s a
picture that was impossi-
ble to expose correctly.
The light coming through
the windows is overex-
posed, burning out the
details of a lovely
delicate design in the
curtains. At the other
extreme, the rocks in
the vase exist only in
silhouette, and the wood
grain in the table is
smothered in darkness.1
Here is a photo of the still
life that hides nothing with
excessive light or dark. But
in truth, it’s really eight pho-
tos that have been blended
in Photoshop.2
High dynamic range begins by taking at least three pictures of the same subject, with at least a two-
stop difference from one shot to the next. The changes in exposure were accomplished by varying the
shutter speed so that aperture, and therefore the depth of field, remain the same. High dynamic
range images open up a world of possibilities because they’re allowed 32 data bits for each of the
three color channels.3
The holy grail of all photographers is to
stretch the dynamic range of their pic-
tures so that it captures details in the
deepest shadows and the brightest
whites. But there has yet to be invented
a film or a digital sensor that captures
the range of light and shadow as well as
the human eye. We’re left with a
photo that looks as if it was
taken by a camera that
“squinted,” cutting out light
carrying the details that gave the
scene life when the picture
was taken. Adobe, with
Photoshop CS2, introduced
high dynamic range (HDR),
a tool that captures the dark
and light details of a scene
by ganging up on them with
multiple photographs.