What is available light? 13
What is exif and what is it good for?
The Exchangeable Image File standard was established in 1995
as a way to accommodate a range of image fi le formats and allow
playback of photos made with one kind of camera to be played
and viewed on other devices. As such, EXIF is part of Design
rule for Camera File system (DCF), a larger fi le system standard
designed to ensure image fi le compatibility between digital
cameras and printers. DCF-compatible devices allow image fi les
to be easily exchanged so that photographs made with a Canon
PowerShot SD40 can be viewed on a Nikon Coolpix S7c’s LCD
screen.
This EXIF standard is the fi le format used by most digital
cameras and defi nes fi lename standards and folder structures,
including how to store image and camera data. When a digicam
is set to capture and record a JPEG image fi le (named after
the Joint Photographic Experts Group), it’s actually recording
an EXIF fi le using compression to store additional photo
data within that fi le. This information can expand to make room
for future applications, enabling users to add new informa-
tion along with new camera features as the state of the art
progresses.
Right now, EXIF supports storage of extended camera informa-
tion within the image fi le’s header, such as the time and date the
image was made, device name, shutter speed, and aperture,
along with other capture data such as compression mode, color
space, and number of pixels. You can read all of this header
information externally using EXIF-compatible software, which
can use it for image fi le management (the subject in the fourth
part of this quadrilogy).
In addition to image data, the next most important feature of
EXIF is its inclusion of thumbnails. Thumbnails are small
versions of the original image and can be used by soft-
ware applications including image-management software
and image-editing software to display a series of image fi les.
Under DCF standards, the typical thumbnail size measures
160 × 120 pixels.
Together with the image data, the EXIF 2.2 standard—a.k.a.
EXIF Print—records all of the information set by the photogra-
pher, including capture parameters and scene information, in the
form of EXIF tags. The printer reads all of this photographic
information to ensure optimal printing. This can be especially
important when capturing an image using a digicam’s Scene
modes. Photographic scene information, for example, records
that the image was captured in Night Scene mode and printing
is optimized to suit the original effect without increasing image
brightness. Consequently, the output produced will faithfully
refl ect the photographer’s original intentions.
