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Image formats
Characteristics
© Adolf Knoll, National Library of the Czech Republic
What a format does contain?
Information about: Resolution (vertical and horizontal) Colour depth Compression … a lot of other data to enable the correct
display or printing (ICC profiles, e.g.)
Some formats offer only selected opportunities.
Types of image formats
ISO initiatives (TIFF; JPEG, JBIG, /MPEG/)
De facto standards (PNG) Very proprietary formats (PSP, PSD,
ZMF, … - internal formats of graphical tools)
TIFF – Tagged Image File Format
ISO definition A container that can incorporate so
many parameters This may cause various problems with
reading or writing TIFF
TIFF and write/read problems
Black and White (1bit, 2 colours) Huffman RLE encoding CCITT Fax Group 3 CCITT Fax Group 4 (TIFF 4)
Colour (up to 24 bits, true colour) no compression LZW (TIFF 5) Mackintosh Packbits JPEG (TIFF 6) PNG
True Colour Black and White
Grey scale256 shades of grey
Grey scale16 shades of grey
Black and White2 colours
8 bit 4 bit 1 bit
24 bit/True colour 8 bit 4 bit
16,7 million colours 256 colours 16 colours
TIFF Fax Group 4
TIFF can also contain more images (multipage TIFF, gr. 6) in one.
BMPMicrosoft Windows Bitmap
It supports 16,7 million colours, frequently only with 256 colours
It supports RLE compression Fast reading as any other
uncompressed bitmap
Web image formats
There are 3 formats recommended by the WWW consortium for web:
GIF JPEG
PNG (latest recommendation) … and also SVG
GIFGraphic Interchange Format
256 colours - palette format each GIF has its own palette this is difficult to combine LZW compression scheme highly used on the web several modifications in the WWW environment used frequently as
the so-called transparent, interlaced, or animated GIF
Palettes of GIF images
Transparent GIF
One colour in the 256-colour palette can be indicated as transparent
Animated and Interlaced GIF
Animated GIF on web pages Interlaced GIF as many other formats
can appear successively step by step
JPEGJoint Photographic Expert Group
True colour, 24 bit Lossless or lossy compression: the
compression ratio must be tuned individually (software dependent)
Possibly progressive encoding (not recommended - read problems possible)
irreplaceable for compression of photorealistic images
PNGPortable Networks Graphic
True colour format; allows up to 48 bit encoding
PNG compression: lossless, 9 degrees Slightly more economic compression
than GIF, but more colours transparency (alpha-channel) possible,
interlaced character possible
WWW and images
3 formats are recommended by the WWW consortium:
GIF, JPEG, PNG (recently)
Other formats possible, but they require special components to be installed into web browsers (ActiveX, plug-ins).