What are HDR Images and HDR Files?
HDR images and HDR files are two components of high dynamic range photography are at the heart of the matter. These are the things in HDR photography that put the H and the D in the R. Sometimes the terminology of high dynamic range photography can be confusing. Everything is HDR this and HDR that.
Create, generate, save, shoot, publish, manipulate HDR — these other activities help create, manage, or transform the images and files.
HDR images and files have the following general properties:
HDR image: An HDR image is a high-bit–depth image (normally 32 bits per channel) that contains color and brightness information across a very wide dynamic range. When you generate HDR or load a saved HDR file in an application, something like this figure shows up onscreen.
This is an HDR image comprising bracketed photos. It doesn’t look very good in this format, though, because the clouds are blown out and parts of the greenery are too dark. The data is in the file, but the image has more dynamic range than the system on which it’s being displayed can handle.
An HDR image is an ephemeral thing: It exists to be transformed. You can edit HDR images in most HDR software before you get to tone mapping (mapping data with a large dynamic range into a smaller dynamic range). You may be able to reduce the level of noise in the HDR image, rotate it, examine properties (such as bit depth), look at the histogram, or crop it.
HDR file: An HDR file is an HDR image encoded and saved by HDR software to retain the high dynamic range nature of the originally generated data. HDR files use an internal scheme defined by the unique HDR file format you choose.
Oddly enough, there is very little you can do with HDR images and files besides view them with specialized software or turn them into something else. The something else, for HDR photographers, is a low dynamic range TIFF or JPEG that displays properly on monitors, plays well with Web browsers and iPhones, and can be printed.
An HDR file is simply a stepping stone. It rests between the photographs you take with your camera and the final file you proudly show everyone. You won’t print it out, post it online, or even look at it very much on your monitor.