ISYS 3074 Graphics File Formats File formats have developed with applications. At least 50 currently in use. Examples include: GIF, JPEG, TIFF, BMP, DIB, PCD, PNG ……. Each has been developed for specific reasons.

ISYS 3074 Graphics File Formats File formats have developed with applications. At least 50 currently in use. Examples include: GIF, JPEG, TIFF, BMP, DIB, PCD, PNG ……. Each has been developed for specific reasons. Many are obsolete, irrelevant, and there is much crossover in functionality.

ISYS 3074 Makeup Graphics files typically contain info on –Type / subtype (e.g. GIF 87a, GIF 89a, Greyscale) –Size - width and height (e.g. 120x80) –Colour depth in bits (2, 4, 8, 16, 24, 32) –Palette information (if less than 16 bits in depth) –Internalised image data (e.g. PCD has 5 sub images)

ISYS 3074 Colour Depth Pixels make up an image

ISYS 3074 #FF00A3 #255,0,163 # , , Colour - Depth Each pixel has a colour depth. A certain number of ‘bits’ are used to define a pixels colour e.g. held as an RGB value. For 256 (or less) colours a palette is used as an index describing which 256 actual colours to use in an image. 240,200,171

ISYS 3074 Colour Depth The colours themselves consist of up to 24 bits of information to descibe them. 8 bits for Red, Green and Blue - 256x256x256 colours = 24 Million possible colours. In web page design we use these 24 bits to define our colours for page detail. e.g.

ISYS 3074 Size / Depth Obviously, less colour - less size in the final image. e.g (in uncompressed raw format). –300x200x1 (2 colours)= 8k –300x200x4 (16 colours)= 30k –300x200x8 (256 colours) = 60k –300x200x24 (full colour) = 180k

ISYS 3074 Size / Depth 8k 60k 1 bit8 bit 180k 24 bit 30k 4 bit

ISYS 3074 Colourspace Less colour /size also means lower quality. When working / creating / manipulating images for production we should use 24 bit colour. To conserve space (or transmission time), we can reduce colour depth - but only at the end of the process. Continual reduce/ increase cycles lowers quality in a noticeable manner.

ISYS 3074 Compression We can compress images to further reduce size. –LZW / RLE - lossless –JPEG- lossy –Wavelet - lossy –Fractal- lossy greater compression

ISYS 3074 Compression - LZW / RLE This technique is used in common lossless compression formats - GIF / TIFF / BMP... Runs of colour can be defined in a simple Run / Colour / Number format. e.g. for yellow R0206, for gray R0304, for red R04FE, R0101 for white, R0614 for blue - taken from the palette below

ISYS 3074 Compression - LZW / RLE TIF uncompressed = 289k TIF lzw compressed = 248k TIF uncompressed = 90k TIF lzw compressed = 5k

ISYS 3074 Compression - JPEG JPEG (Joint Pictures Expert Group) uses advanced mathematical techniques to store image information. It is ‘lossy’ - compression causes the loss of image data. Compression can be tailored to need. Useful on post production only. TIF lzw compressed = 248k JPEG (15%) = 29k

ISYS 3074 Compression - JPEG 212k original12k 50%31k 8%

ISYS 3074 Compression - Fractal Patented (not public domain) technique, again, using very complex maths. Images are represented as mathematical expressions. Used by commercial business to store large image databases. E.g. Microsoft Encarta uses FIF files to allow over images on one CD.