Imaging File Formats
Photographic images in the digital world are
stored in a variety of digital file formats. Each
file type has its own particular positives and
negatives. The file formats utilised for the majority
of photographic tasks are listed below, together
with a brief explaination of their own unique
properties.
To start with, file formats used for holding
image data fall into two general categories: Lossy
and Lossless file formats.
Lossy formats reduce file
size through discarding some of the less important
information in the image. The more information
that is discarded, the smaller the file size but
the lower the image quality. Some formats will
discard additional information with each adjustment
and resaving of an image.
Lossless formats will retain
all the image information, although some of the
more recent file formats have clever mathematical
algorithms that also allow a reduction in their
file size.
| RAW |
 |
RAW format
is more of a category of file types
than a distinct file specification. |
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RAW refers to camera
manufacturers proprietary file formats,
which capture “raw” data
and save it to file without any in-camera
processing. This data is then able to
be manipulated and exported using Raw
processing software, which allow a considerable
range of adjustments to be made to the
data without loss of information. RAW
files are then typically exported to
JPEGs or TIFF format. |
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Most RAW files are a
lossless format, certainly all those
from the major camera manufacturers.
They usually incorporate some form of
compression, allowing somewhat small
file sizes, whilst retaining the maximum
amount of information. |
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They allow the maximum
amount of flexibility in post-production,
and access to the highest levels of
image quality. |
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Typical file extensions
are CRW, CR2, NEF |
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Require specialised software to process |
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| JPEG |
|
A very popular
and widely used format, with support
from virtually all operating systems
and software programs |
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JPEG is a lossy file
format. |
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Considerable compression
is possible, the level of which is adjustable
when saving the file. However, the higher
the level of compression, the more pixelated
the image will look. At the highest
level of quality (lowest compression
level), there is almost indiscernible
degradation in the image, whilst obtaining
a considerably smaller file than an
equal resolution TIFF file. |
|
Medium quality JPEGs
are normally used for web applications
as this offers the best compromise between
image quality and file size. |
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JPEGs do not handle multiple editing of the same file as further degredation occurs with every opening and saving of the file. They are typically used for final purpose output. |
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| TIFF |
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TIFF files
are another highly accepted format,
supported by the vast majority of software. |
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They are a lossless format,
and are also saveable in 16-bit format |
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The highest quality files
are often provided as TIFFs |
|
TIFF files save with
the largest file size as they are completely
uncompressed. |
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| DNG |
|
Stands for
“Digital NeGative”. This
format was developed by Adobe to help
create some consistency between the
many competing RAW formats, whilst still
allowing those camera manufacturers
to retain a certain level of proprietary
information in the file. |
|
Developed as an open license
format, it’s primary purpose was
to ensure the future proofing of RAW
formats and the readability of those
files long after the original camera
manufacturers software stops being supported.
|
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DNG files are a compressed,
but lossless format |
|
| PNG |
|
Pronounced
“ping”, this is a royalty
free format that was developed to replace
the GIF format and in some circumstances
the TIFF format. |
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PNG utilises lossless
compression and can often achieve very
high compression levels, consistently
greater than those of the GIF format. |
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This format, whilst becoming
more common, is still not often used
for photographic purposes. |
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| GIF |
|
Uses a specific
lossy compression technique, part of
which reduces the number of colours
available to a maximum of 256. As photographic
images contain millions of colours,
GIFs are therefore unsuitable for this
use. They are most often used for web
graphics or block colour graphics. |
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GIF files are very commonly
used for web graphics including banners
and buttons. |
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| BMP or Bitmap |
|
A Microsoft
format similar in some ways to TIFF.
Seldom used. |
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| PDF |
|
PDF files
are another format created by Adobe.
Although they are not primarily an image
format, they act like a package for
images as well as text and other objects,
and will often contain images. |
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They maintain the formating
of a document (including graphics) as
designed by the document creator. |
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PDF files are use in
print production. |
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Images are usually internally
converted to JPEGs within a PDF file. |
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| PSD |
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PSD are Adobe
Photoshop files. |
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Once again, whilst not
a primary image format, Photoshop is
by far the most commonly used software
program for image manipulation and hence,
images may sometimes saved as PSD files. |
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Commonly, Photoshop files
are converted to JPEGs or TIFF files
after image enhancement or manipulation. |
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PSD files are a lossless
format, with low levels of compression. |
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