The dynamic range of a scene or image is the range of brightness values between its darkest and brightest parts. Generally speaking, a standard camera cannot capture a scene's entire dynamic range and a standard image cannot represent it because its color component values cannot cover a broad enough range.
High Dynamic Range (HDR) images solve this problem by combining multiple exposures of the same scene into a single image file, which has a much greater range of illumination than a standard image. Therefore, it can accurately represent real-world lighting.
Because the amount of light in a scene can be virtually unlimited, HDR images need to be able store much larger color component values (RGBA, for example) than their low-dynamic-range counterparts. Instead of storing color component values as integers between 0 and 255 like an 8-bit image, HDR images store them as floating point values (decimal point values like 1.23123), which can range from 0 to 100000 and higher. This lets an HDR image's pixel values correspond accurately to the amount of light in the real world.
HDR images that you wish to use in Softimage should be saved in one of several formats supported by both Softimage and mental ray. For more information about converting images to supported formats, see the next section Creating HDR Images for Softimage. Supported formats include:
mental ray color texture (.ct ) is a commonly used format. .ct images tend to be quite large, and may increase render time when loaded in memory by mental ray. .ct files can be saved at 8, 16, or floating point-bit depth.
mental ray memory mapped texture (.map) images are good to use when memory and/or rendering time is an issue because mental ray maps them into memory rather than loading them completely. This saves render time and reduces disk swapping, especially with large images. .map files can be saved at 8, 16, or floating point-bit depth.
For more information about .map files, see Using Memory-Mapped Textures [Texturing].
HDR (.hdr) is a widely used high dynamic range image format that produces very compact files. However, the format does not support an alpha channel, so you'll need to use a different format if you intend to modify the image using the alpha channel. In addition to using them in the Fx Tree, you can adjust their brightness using the Exposure setting in the image clip property editor. .hdr files are saved at floating point bit-depth.
OpenEXR (.exr) images have the advantage of being both highly precise and highly compact. In addition to modifying them in the Fx Tree, you can adjust their brightness using the Exposure setting in the image clip property editor. .exr files can be saved at 16-bit floating-point (half) or 32-bit floating-point bit depth.
Creating HDR Images for Softimage
Before you can use your HDR images in Softimage, you may have to convert them to a different format. You can do this using the imf_copy standalone.
Type the path of the folder where the file(s) that you want to convert are stored (for example: C:\projects\myproj\pictures).
To convert an image, type the following command (all on one line):
imf_copy [-v] [-p] inimage outimage [outformat [outtype]] imf_copy -v myhdrimage.tif myhdrimage_test.map map rgba_fpYou can also use imf_copy for other image conversions, .map to .ct for example, or .ct to .exr.
For more information about using imf_copy, type imf_copy -h at the command prompt for command line usage or see Standalones.
HDR Files and Image Management
Using your HDR images in Softimage usually means creating source and clip instances of them. It's best to set any HDR image's image management mode to Use From Disk or Broadcast, either of which passes the image's name and path directly to mental ray instead of loading it in memory.
For more information about image management modes, see Displaying and Rendering Gamma Correction.
Adjusting HDR Image Exposure and Display Gamma
If you are working with HDR files saved in the .hdr or .exr formats, you can adjust their exposure, and correct their display gamma from several places in Softimage.
If you've created an image clip from a .hdr or .exr image, you can adjust its exposure and display gamma from the image clip property editor, as described in this section.
If you've imported a .hdr or .exr image into the Fx Tree, via a File Input operator, you can adjust the image's exposure and display gamma from the File Input property editor, as described in Setting File Input Properties [Compositing and Effects].
If you're previewing a .hdr or .exr image in a standalone flipbook, you can adjust the image's exposure and display gamma from the flipbook's Display Options dialog box, as described in Previewing Animation in a Flipbook [Viewing and Playback].
To adjust a .hdr or .exr image clip's exposure and/or display gamma
Edit the image clip's properties as described in Editing Image Clip Properties.
On the Adjust tab, set the following values as needed:
HDR and OpenEXR 
Display Gamma: if the image format is .hdr or .exr, this setting performs a gamma correction for display purposes only. For example, 2.2 is the correct value for displaying
images on a monitor.
Exposure Exposure (f-stop): if the image format is .hdr or .exr, this setting offsets the exposure to brighten or darken the image.
The exposure value is measured in f-stops, so a value of 0 is the image's default exposure, while non-zero values offset the default by the specified number of f-stops in either direction.
