Mix ’em Up, Part 1: Introduction to Combining Images in Photoshop CS4

The advent of digital photography has opened up an array of new techniques for working with and combining multiple images in pursuit of technical perfection. Three of the most popular techniques in this category are panoramic stitching, focus blending, and high-dynamic range imaging.

As of Photoshop CS4, Adobe now includes some level of support for applying all three of these techniques without external tools. In this post, I’ll provide a brief overview of the three techniques and the problems they’re intended to solve. In future posts, I’ll address each of the three techniques individually, provide an example or two, and discuss both Photoshop’s built-in tools for applying those techniques as well as talking about third-party solutions and other alternatives.

Panoramic stitching is a technique which attempts to overcome the resolution limitations of the digital camera by creating a mosaic of the various images. Stitching tools attempt to identify where these images overlap, and then in the process of combining them attempt (with varying degrees of success) to clean up all the resulting artifacts caused by parallax, differences of exposure, and so on.

Focus blending is a technique which attempts to overcome depth-of-field limitations. When using long telephoto lenses, or alternately doing macro photography, it’s often optically impossible to get as much depth-of-field as you’d need to keep the entire scene in focus. Focus blending tools attempt to take a set of images of the same scene each taken at different focus settings, identify and extract the most detailed sections of each image, combining them to create a composite where all (or at least more) of the image is in sharp focus.

High dynamic range (or HDR) imaging refers to a set of techniques which attempt to overcome the dynamic range limitations of a digital camera sensor. HDR imaging tools attempt to take a set of images of the same scene each taken at different exposure values and combine them into a single image which contains a greater range of exposure information than any of the individual images could provide. Because the resulting images represent a much greater range of exposure information than can easily be represented on a print or on a computer monitor, HDR tools also provide tools for tone mapping. Tone mappers take an HDR image and convert it back into a an image with a smaller dynamic range using techniques that may or may not seem subjectively realistic. While I work for realism in my own work, there is a fair subculture of folks who enjoy some of the strangely graphic effects that come from unrealistic tone mapping.

Before we go on, however, a word of caution. While each of these techniques has it’s place, it is far too easy for any of these techniques to become parlor tricks or distractions. Each can be fussy and time-consuming, and each can be a way of focusing on how you photograph instead of deciding what to photograph. Being able to capture a great deal of detail or depth of field can be an important part of crafting a great photograph, but those abilities don’t make a photograph great by themselves.

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