Using GIMP: Correcting and Touching Up Your Images - GIMP 2.6 for Photographers: Image Editing with Open Source Software - page 71

When saving TIFF formats, you can choose the lossless LZW compression
for reducing the file size— TIFF lossless compress . In any case, you should choose
the option that embeds the camera's own EXIF data into JPEG and PNG files.
For Create ID file , you should select Also . UFRaw ID files have the same
name as the output file but with a .ufraw filename extension. ID files contain
all the settings for generating the output file. Choosing Create ID file Also is
useful for keeping track of the setting used, or for making future changes on
top of the saved settings. The only option is useful if one doesn't want to wait
while the output file is being generated. The output file can be generated in
the background using the command: ufraw-batch ID-FILE . However, therefore
you have to use the command-line version of UFraw, ufraw-batch.exe . If you
don't need the settings, you can also select Never again . Select Just this once if
you want to apply the setting on a case-by-case basis.
EXIF
Exchangeable Image File Format (EXIF) is a standard format used by digital
cameras to store information about an image. The EXIF data includes the
camera model, date and time the image was taken, ISO speed, shutter time,
aperture, and focal length. You can find more information about EXIF data at
http://en.wikipedia.org/wiki/Exif.
You can't change any of the settings that appear when you click the EXIF
icon in UFRaw. You can only get basic EXIF data about the image. UFRaw
can save the EXIF data only for the JPEG output for a few supported formats:
Canon (CRW/CR2), Nikon (NEF), Pentax (PEF), Samsung (PEF), Sony (SR2, ARW),
Minolta (MRW), Fuji (RAF) and Adobe's DNG.
If you are interested in editing the EXIF information for your image files
after saving them on your hard drive, you should have a look at Phil Harvey's
ExifTool . You can find more information at the following website: http://www.
sno.phy.queensu.ca/~phil/exiftool/ (it includes a download for all three major
operating systems).
Live Histogram
The histogram of the preview image is updated as the settings on the image
are changed. You can right-click on the live histogram to set the curve's size
and representation.
There are two modes in which you can control the exposure. Clicking
the controls or buttons underneath the live histogram will show you the
overexposed and underexposed pixels in the image.
Activate the check boxes by clicking them. The corresponding pixels will
light up in the preview. Click each Indicate tab to view the over- or underexposed
pixels, respectively. The numerical values next to the controls indicate the
amount of overexposure or underexposure per channel in percentages. These
options provide you with objective guidelines to correct the exposure, always
keeping an eye on the color combination and mood in the picture.