Photomatix Pro 2.2 Help 6
V - Generating an HDR image
Introduction
The Dynamic Range of an image is the ratio between its brightest and darkest parts. The ability to
reproduce the dynamic range of a scene depends on two types of limitations.
-
First limitation: the capturing device. Images produced by digital cameras are considered Low
Dynamic Range. Once the influence of noise and other limiting factors have been taken into
account, the maximum dynamic range avaible from most camera sensors is about 1,000:1 or
less.
-
Second limitation: the reproducing media. Standard computer screens can only reproduce a
dynamic range of about 100:1.
The dynamic range of real-world scenes however is much higher (ratios of 100,000:1 are common in
the natural world). Given that the human eye can accommodate a dynamic range of approximately
10,000:1 in a single view, there is a need for images that can hold a higher dynamic range than the
limited range available in images encoded with 8 bits per color channels. Those are referred to as
HDR images and are usually stored in 32-bit image formats.
Photomatix uses images of the same scene shot under different exposures in order to reconstruct the
dynamic range of the scene and generate the corresponding HDR image. The number of images
needed depends on both the stop spacing and the dynamic range of the scene considered. If your
scene has a high dynamic range (e.g. the interior of a room with an outside view on a sunny day), a
stop spacing of two will limit the number of shots necessary to cover the whole dynamic range.
For more information on how to shoot a High Dynamic Range scene, see the above section “Taking
differently exposed images”.
To create a High Dynamic Range Image from bracketed shots:
1.
On the HDRI menu, click on the Generate HDR 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.
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 displays a window where you
can enter the Exposure Values for each one of your images (see note below).
3.
If you did not use a tripod to take the differently exposed shots, check the option Align LDR
images.
Note for the case of missing exposure information:
The Exposure Values needed to be entered are 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.
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