1. 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

2. 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

3. 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

4. Colour Depth Pixels make up an image ISYS 3074

5. 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. #FF00A3 #255,0,163 #11111111,00000000,01100011 240,200,171 ISYS 3074

6. 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. <BODY BGCOLOR=“#F0D200”> ISYS 3074

7. 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

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

9. 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

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

11. 1 2 3 4 5 6 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

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

13. 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

14. Compression - JPEG 212k original 31k 8% 12k 50% ISYS 3074

15. 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 25000 images on one CD. ISYS 3074