CHAPTER 9 HOW SOFTWARE CHANGES PIXELS BY THE NUMBERS^159
The result is not the finished product. In fact, it may not
be particularly attractive. That’s because Photoshop
created an image with a greater dynamic range than
most monitors can display. At this point, Photoshop
invites you to set a white break point, which lets you
adjust the image to create something that works in the
16 bits per channel that are all your monitor displays.5
In Photoshop, you tell the program’s HDR feature the
shots you want it to combine. HDR analyzes the pho-
tos and assigns then an EV (exposure value)of 0,
+1, -1, +2, -2, and so on. If it’s able, Photoshop aligns
all the shots and adds together the extremes of light
and shadow from all the photos to produce a single
image that incorporates the highlights from the
underexposed areas and the lowlights from the
overexposed.4
The final image is created when
you open a 32-bit Preview
Options dialog box. There you
instruct Photoshop to adjust the
exposure and contrast to reduce
the image to 16 bits, to com-
press the highlight values in the
image so they fall within the
luminance range of a 16-bit
photo, or tinker with other
renditions so that you wind up
with a photo that is the sum of
many images. As you can see
from the four examples here,
the adjustments produce widely
different results. The final image
on the facing page came from
tweaking levels, curves, and
brightness.6