Transcript File Formats

File Formats
The most common image file
formats, the most important
for cameras, printing,
scanning, and internet use,
are JPG, TIF, PNG, and GIF.
JPG




Compresses the data to be much smaller in the file.
Uses lossy compression, which is a strong downside.
Used when a small file size is more important than
maximum image quality (web pages, email, memory
cards, etc). But JPG is good enough in many cases, if we
don't overdo the compression.
If you are concerned with maximum quality for archiving
your important images, then you do need to know two
things:


1) JPG should always choose higher Quality and a larger
file, and
2) Do NOT keep editing and saving your JPG images
repeatedly, because more quality is lost every time you
save it as JPG (in the form of added JPG artifacts... pixels
become colors they ought not to be - lossy). More at the
JPG link at page bottom.
TIF
 TIF
is lossless, which is considered the highest quality
format for commercial work.
 TIF is the most versatile, except that web pages
don't show TIF files.
 For other purposes however, TIF does most of
anything you might want, from 1-bit to 48-bit color,
RGB, CMYK, LAB, or Indexed color. Most any of the
"special" file types (for example, camera RAW files,
fax files, or multipage documents) are based on TIF
format, but with unique proprietary data tags making these incompatible unless expected by
their special software.
GIF
 GIF
always uses lossless compression, but it
is always an indexed color file (8-bits, 256
colors maximum), which is poor for 24-bit
color photos.
 GIF is still very good for web graphics (i.e.,
with a limited number of colors). For
graphics of only a few colors, GIF can be
much smaller than JPG, with more clear
pure colors than JPG).
PNG



PNG can replace GIF today (web browsers
show both), and PNG also offers many options
of TIF too (indexed or RGB, 1 to 48-bits, etc).
PNG was invented more recently than the
others, designed to bypass possible LZW
compression patent issues with GIF, and since
it was more modern, it offers other options too
(RGB color modes, 16 bits, etc).
PNG remains excellent. Less used than TIF or
JPG, but PNG is another good choice for
lossless quality work.
Color data mode -bits per pixel
JPG
TIF
JPEG always uses lossy JPG compression, but its degree is selectable, for higher quality and
larger files, or lower quality and smaller files. JPG is for photo images, and is the worst possible
choice for most graphics or text data.
TIF files, most programs allow either no compression or LZW compression (LZW is lossless, but is less
effective for color images). Adobe Photoshop also provides JPG or ZIP compression in TIF files
too (but which greatly reduces third party compatibility of TIF files). Many specialized image file
types (like camera RAW files) are
PNG also supports animation (like GIF), showing several sequential frames fast to simulate
motion.
PNG uses ZIP compression which is lossless, and somewhat more effective color compression
PNG than TIF LZW. For photo data, PNG is somewhat smaller files than TIF LZW, but larger files than JPG
(however PNG is lossless, and JPG is not.) PNG is a newer format than the others, designed to be
both versatile and royalty free, back when the patent for LZW compression was disputed for GIF
and TIF files.
GIF
GIF is an online video image. Designed by CompuServe for online images in the days of dialup
and 8-bit indexed computer video, whereas other file formats can be 24-bits now. However, GIF
is still great for web use of graphics containing only a few colors, when it is a small lossless file,
much smaller and better than JPG for this. GIF also supports animation, showing several
sequential frames fast to simulate motion.
What is Resolution?
 Dots
of color or electronic pixels that make
up a picture whether it is printed on paper
or displayed on-screen.
DPI
 DPI
(Dots per inch): The number of 'dots'
or pixels per each inch of a printed or
scanned document.
Pixels
 Pixels:
The exact number of 'dots' both
horizontally and vertically that make up
the file.
How Many Dots?
 In
black & white printing, the size and shape of the
black dots and how close or far apart they are
printed creates the illusion of shades of gray.
 The more little dots that are used (up to a point) the
clearer the picture.
 The more dots in a picture, the larger the size of the
graphic file.
 Each type of display device (scanner, digital
camera, printer, computer monitor) has a
maximum number of dots it can process and
display no matter how many dots are in the
picture.
Resolution Examples
A
600 DPI laser printer can print up to 600 dots of
picture information in an inch. A computer monitor
can typically display only 96 (Windows) or 72 (Mac)
dots of picture information in an inch.

When a picture has more dots than the display device
can support, those dots are wasted. They increase the
file size but don't improve the printing or display of the
picture. The resolution is too high for that device.
 Pictures
on the Web are usually 96 or 72 DPI
because that is the resolution of most computer
monitors.
 If you print a 72 DPI picture to a 600 DPI printer, it
won't usually look as good as it does on the
computer monitor.