Adobe Photoshop CS3 User Manual

Page 85

PHOTOSHOP CS3

User Guide

Merging images of different exposures to create an HDR image
A. Image with shadow detail but highlights clipped B. Image with highlight detail but shadows clipped C. HDR image containing the dynamic
range of the scene

In Photoshop, the luminance values of an HDR image are stored using a floating-point numeric representation that’s
32 bits long (32-bits-per-channel). The luminance values in an HDR image are directly related to the amount of light
in a scene. This is not so with (non-floating point) 16-bits-per-channel (bpc) and 8-bpc image files, which can store
luminance values only from black to paper white; this represents an extremely small segment of the dynamic range
in the real world.

Adobe Photoshop CS3 now offers layers support for 32-bpc images, as well as access to more tools, filters, and
commands. 32 bit has been added as an option when creating new documents in Photoshop. For more information,
see below.

Another added feature is painting on 32-bpc images. Enhancements have been made to the Adobe Color Picker so
you can specify colors that have a brightness intensity that exceeds 1.0 (the equivalent of the 255 level in an 8-bit RGB
document). See also “About the HDR Color Picker (Photoshop Extended)” on page 83.

You can create an HDR image using multiple photographs, each captured at a different exposure. In Photoshop, the
Merge To HDR command lets you create HDR images from multiple photographs. Because an HDR image contains
brightness levels that far exceed the display capabilities of a standard 24-bit monitor or the range of tones in a printed
image, Photoshop lets you adjust the preview of the HDR image so it can be viewed on a computer monitor. If you
need to print the image or use Photoshop tools and filters that don’t work with HDR images, you can convert the
HDR image to an 8- or 16-bpc image.

Photoshop support for 32-bpc images

Use the following tools, adjustments, and filters with 32-bpc HDR images:

Adjustments

Levels, Cut Down Saturation, Hue/Saturation, Channel Mixer, Photo Filter, and Exposure.

Note: Although the Exposure command can be used with 8- and 16-bpc images, it is designed for making exposure
adjustments to 32-bpc HDR images.