Digital camera file formats
Most digital cameras record files in JPEG format (they have a .jpg filename
extension), but they use a special variation of JPEG called Exif. This is a
standard that allows extra information to be recorded by the camera into the
image file. The Exif standard was developed by the Japanese Electronics Industry
Development Association (JEIDA) and is used in almost all models of digital
camera.
The extra information in the file relates to picture-taking conditions, camera
settings, color encoding information, sounds recorded when the picture was taken,
and Global Positioning System (GPS) information. Exactly what is recorded depends
on the model of camera.
If you select a digital camera file in Photo Explorer and use the File->Properties
function you will see various information about the file. Digital camera files
that have been directly transferred to the PC (without using TWAIN) will have
an additional tab group called "Camera Information (Exif)". Here you
can see information about the picture taking conditions such as the date the
picture was taken, the shutter speed, aperture, and others. This information
is contained in the JPG file and will be retained even if the photos are copied
to CD or to other computers. But be careful, this information is often lost
when pictures are saved from image editors and other software.
More About JPG/JPEG
What is JPG? JPG is stands for Joint Photographic Experts Group. This
is the right format for those photo images which must be very small files, for
example, for web sites or for email. JPG is often used on digital camera memory
cards, but RAW or TIF format may be offered too, to avoid it. The JPG file is
wonderfully small, often compressed to perhaps only 1/10 of the size of the
original data, which is a good thing when modems are involved. However, this
fantastic compression efficiency comes with a high price. JPG uses lossy compression
(lossy meaning "with losses to quality"). Lossy means that some image
quality is lost when the JPG data is compressed and saved, and this quality
can never be recovered.
File compression methods for most other file formats are lossless, and lossless
means "fully recoverable". Lossless compression always returns the
original data, bit-for-bit identical without any question about differences
(losses). We are used to saving data to a file, and getting it all back when
we next open that file. Our Word and Excel documents, our Quicken data, any
data at all, we cannot imagine NOT getting back exactly the original data. TIF,
PNG, GIF, BMP and most other image file formats are lossless too. This integrity
requirement does limit efficiency, limiting compression of photo image data
to maybe only 10% to 40% reduction in practice (graphics can be smaller). But
most compression methods have full lossless recoverability as the first requirement.
Digital cameras also offer JPG quality choices too. Large image files do fill
memory cards fast. You can buy more and larger cards, or you can compromise
by sacrificing image quality for small file size (but I hope you won't go overboard
with this). The camera menu will have two kinds of resizing choices. One size
choice actually creates a smaller image size (pixels), resampled smaller from
the original standard size of the CCD chip, for example perhaps to half size
in pixel dimensions. The correct image size in pixels is related to your goal
for using the image. For example you may need enough pixels to print 8x10 inches
on paper (6 megapixels), or you may only want a small image for video screen
viewing (1 megapixel).
Related: What
is Exif?
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