More Dynamic Range in GIMP

Exposure blend is a GIMP plugin which facilitates the process of creating contrast blended exposures. Contrast blending is a popular technique for getting more dynamic range from a set of bracketed images.

(Photoshop users might wanna check here for a few actions and a tutorial.)

The Gimp and HDR

It seems that there are lots of people that don't understand that The Gimp is not capable of doing HDR images. There is a simple reason for this, which involves the way The Gimp represents image files. Without being too technical, I'll try to explain.

The Gimp's basic model represents each pixel as 3 different numbers between 0 and 255. This means that it can represent only 16581375 different colors per pixel. I say only, because, if you were to use 3 floating point numbers, from 0 to 1, or 3 numbers from 0 to 65535, or some other power of 2 (minus 1), you then are able to represent many more colors; you become able to represent a higher dynamic range of colors.

Even if The Gimp supported more pixel values, our monitors can't, and we need to use a process like tone mapping to convert the computed HDR image (comprised of some combination of multiple exposures), back into something viewable; something where the range of pixels is made up of 3 integers from 0 to 255 (in the general case).

This doesn't mean The Gimp sucks, because it certainly doesn't; it just means that it has some limitations and one has to be mindful of them. This "problem" of image representation is only really visible if you're looking for ultra-high quality output, like movie producers, and most photo professionals. Amateurs need not worry.

One Exposure HDR

There's been much talk about HDR in the last year and how you have to take multiple shots of exactly the same thing. Unfortunately there are times when this isn't possible, whether it be because you are tripodless at the moment, or there's some action in the shot. Fortunately, if you're shooting RAW files there's hope. (You are shooting RAW right?) Eirikso has a technique for creating HDR images from one RAW file.

Qtpfsgui

Qtpfsgui is an free software (as in freedom, but also as in beer) application for creating HDR images. It's available for Mac OS X, GNU/Linux and Windows. Aside from the name, which seems to stem from the GUI toolkit it uses (Qt), and pfs (the set of commands it creates the gui for) it looks promising and is definitely a cheaper alternative to get into HDR imaging. I'm looking forward to taking a look at it soon.

High Dynamic Range Tutorial

With Adobe's release of Photoshop CS2, many photographer's became interested in High Dynamic Range (HDR). HDR uses 32-bits per channel rather than the usual eight or sixteen bits. However, your camera doesn't just magically take HDR images. Instead you take a series of images and compose them together. What you get from all this are photos with a greater range of brightness values, to which you can edit til you have the holy grail, the perfect photograph. Read Earthbound Light's tutorial on HDR.