Better Available Light Digital Photography : How to Make the Most of Your Night and Low-light Shots

Basic exposure 47

HDR in Photoshop

Both Adobe Photoshop CS2 and CS3 let you create High

Dynamic Range photographs by combining multiple individual

images that were captured at different exposures into a single

32-bit image that has an expanded dynamic range. The lumi-

nance values in an HDR image are directly related to the amount

of light in a scene. This is not true of 16- and 8-bits-per-channel

image fi les that store luminance values only from black to white,

and represent a small segment of the real world’s dynamic range.

For all the geeks out there, Photoshop stores all of an HDR

image’s luminance values by using a 32-bits-per-channel fl oat-

ing-point numeric representation. Floating point is a notation

system in which the decimal point is not fi xed, allowing very

large or very small numbers to be easily handled, and the data

are not subject to the kind of rounding errors that often occur in

image editing.

You can create your own HDR image using multiple photo-

graphs, each captured at a different exposure (a.k.a. bracketing)

by using Photoshop’s Merge to HDR (File > Automate > Merge

This HDR image fi le is a composite of three RAW fi les from the 12-shot series, and include fi les that are 1^1 / 3
stops over- and underexposed, as well as one from the middle exposure. We hope that the book’s reproduction
will help you see the difference between this and the “normal” image fi le. If not, it’s easy to try HDR and
see for yourself. © 2007 Joe Farace.