Understanding
File Format
o All
files are packaged in different formats
o Format
is often determined by file origin
o Graphic
files can be reduced in file size with compression
Lossy vs. lossless
·
Lossy: Image data is “lost” or reduced for
smaller size files but can cause poor image quality
·
Lossless: Retains image data for higher quality
files
Graphic formats
·
TIF, JPG and GIF and the three most common file
formats
·
PNG is a common web format; high quality and can
save with transparency
·
Color format for files: TIF can be RGB or CMYK,
JPG is only RGB, GIF has indexed color.
TIF
·
Tagged Image Format
·
Common format for printing
·
Is LOSSLESS so it retains image data
·
Results in larger file size, not fit for
Internet use.
JPG
·
Joint Photographers Group
·
Made for digital photography
·
Lossy format
·
Can reduce image size by 10:1 without showing
significant compression artifacts
·
Level of compression is adjustable
GIF
·
Graphics Interchange Format
·
Is best for graphics, especially ones with flat
colors
·
Reduces image size by indexing color
·
Is adjustable by changing color levels
·
Contains no DPI, so it is bad for printing
Which format to
use?
·
Best quality = TIF or PNG
·
Best file size
(photo)= JPG
·
Best file size (graphics) = TIF, GIF, PNG
·
Worst choice for photography = GIF
·
Worst choice for graphics = JPG
Pixel types
·
TIF and JPG are best for images with pixels that
blend in color, called contiguous
·
Gif is best for images with flat tones, or
non-contiguous
·
Aliased = non-contiguous
·
Anti-aliased = contiguous
