Creating a High Dynamic Range image
Introduction
A High Dynamic Range (HDR) image represents the whole range of values of light reflected by a scene, from its deepest shadows to brightest hightlights. In order to store the range of values with sufficient precision, HDR images are stored in floating-point representation, which is why they are referred to as 32-bit images (32 bits/channel) as the floating point type is encoded with 32 bits in computing.
The dynamic range of real-world scenes is often much higher than the dynamic range digital cameras can capture. For this reason, a single photograph, regardless of whether it is a RAW or jpeg file, is considered Low Dynamic Range as the camera sensors can only capture partially the dynamic range of a scene. The part of the range captured depends on the exposure setting. Capturing the dynamic range in its totality therefore requires that you take multiple exposures.
So, in order to create an HDR image, you will first need to take several exposures of the scene. Then, Photomatix will combine the photos to create a 32-bit HDR image from them. The number of photos needed depends on the dynamic range of the scene as well as the EV spacing separating each exposure.
For more information on how to shoot a High Dynamic Range scene, see the section Taking differently exposed images.
To create an HDR image from differently exposed photos:

1.
On the HDR menu, click on the Generate item.
2.
Click on the Browse button to go to the location of your differently exposed images and select them using the SHIFT+Arrow keys or your mouse and CTRL key. Then click on the OK button.
The calculation of the HDR image requires the exposure value of each input image. If the exposure time can not be found in the Exif data, Photomatix will show a window where you can input the Exposure Values for each one of your images (see note below). This window will also show if two or more source images have the same exposure setting.
3.
Check the option Align images if you did not use a tripod to take the differently exposed shots. Even when you used a tripod, it is still a good idea to check it in order to correct potential slight shifts between images.
4.
If the scene is not still, check the option Attempt to reduce ghosting artifacts. When the movements in the scene are objects or persons distinct from the background, select the option moving objects/people. When the movements are periodic and involve the background (for instance rippling water), select the option ripples.
Once the HDR image has been created, you will need to process it in order to properly show its details in highlights and shadows. For that, go to menu HDR and click on the Tone Mapping item.
Note for the case of missing exposure information:
The Exposure Values need to be entered as relative values (i.e. values of -2, 0, +2 are the same as 0, +2, +4 for instance). A doubling of the exposure time relates to an increment of 1 in the Exposure Value, provided that the aperture and ISO settings did not change.
Note regarding tone curves:
The default option Take tone curve of color profile looks up the Tone Reproduction Curve data in the ICC color profile associated with the source images in order to determine the non-linear function applied to the raw sensors data. If no profile is available, it takes the tone reproduction curve of Adobe RGB.
The option No tone curve applied is enabled with source images in 16 bits/channel mode and should only be checked if you are sure that your images have been converted from RAW without any tone curve applied, i.e. linearly relative to luminance. Please note that this is not the case with the "linear" curve in Adobe Camera Raw for instance.

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