(.TIF file extension, pronounced Tiff)
TIFF is the format of choice
for archiving important images. TIFF is THE leading commercial and
professional image standard. TIFF is the most universal and most widely
supported format across all platforms, Mac, Windows, Unix. Data up to 48
bits is supported.
TIFF supports most color spaces, RGB, CMYK, YCbCr, etc. TIFF is a
flexible format with many options. The data contains tags to declare what
type of data follows. New types are easy to invent, and this versatility
can cause incompatibly, but about any program anywhere will handle the
standard TIFF types that we might encounter. TIFF can store data with
bytes in either PC or Mac order (Intel or Motorola CPU chips differ in
this way). This choice improves efficiency (speed), but all major
programs today can read TIFF either way, and TIFF files can be exchanged
without problem.
Several compression formats are used with TIF. TIF with G3 compression
is the universal standard for fax and multi-page line art documents.
TIFF image files optionally use LZW lossless compression. Lossless
means there is no quality loss due to compression. Lossless guarantees
that you can always read back exactly what you thought you saved,
bit-for-bit identical, without data corruption. This is very critical
factor for archiving master copies of important images. Most image
compression formats are lossless, with JPG and Kodak PhotoCD PCD files
being the main exceptions.
Compression works by recognizing repeated identical strings in the
data, and replacing the many instances with one instance, in a way that
allows unambiguous decoding without loss. This is fairly intensive work,
and any compression method makes files slower to save or open.
LZW is most effective when compressing solid indexed colors
(graphics), and is less effective for 24 bit continuous photo images.
Featureless areas compress better than detailed areas. LZW is more
effective for grayscale images than color. It is often hardly effective
at all for 48 bit images (VueScan 48 bit TIF LZW is an exception to this,
using an efficient data type that not all others use ).
LZW is Lempel-Ziv-Welch, named for Israeli researchers Abraham Lempel
and Jacob Zif who published IEEE papers in 1977 and 1978 (now called LZ77
and LZ78) which were the basis for most later work in compression. Terry
Welch built on this, and published and patented a compression technique
that is called LZW now. This is the 1984 Unisys patent (now Sperry)
involved in TIF LZW and GIF (and V.42bis for modems). It expires in 2003.
There was much controversy about a royalty for LZW for GIF, but royalty
was always paid for LZW for TIF files and for v.42bis modems.
Image programs of any stature will provide LZW, but simple or free
programs often do not pay LZW patent royalty to provide LZW, and then its
absence can cause an incompatibility for compressed files.
It is not necessary to say much about TIF. It works, it's
important, it's great, it's practical, it's the
standard universal format for high quality images, it simply does the
best job the best way. Give TIF very major consideration, both for photos
and documents, especially for archiving anything where quality is
important.
But TIF files for photo images are generally pretty large.
Uncompressed TIFF files are about the same size in bytes as the image
size in memory. Regardless of the novice view, this size is a plus, not a
disadvantage. Large means lots of detail, and it's a good thing. 24
bit RGB image data is 3 bytes per pixel. That is simply how large the
image data is, and TIF LZW stores it with recoverable full quality in a
lossless format (and again, that's a good thing). $200 today buys
BOTH a 60 GB 7200 RPM disk and 512 MB of memory so it is quite easy to
plan for and deal with the size.
There are situations for less serious purposes when the full quality
may not always be important or necessary. JPEG files are much smaller,
and are suitable for non-archival purposes, like photos for read-only
email and web page use, when small file size may be more important than
maximum quality. JPG has its important uses, but be aware of the large
price in quality that you must pay for the small size of JPG, it is not
without cost.
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