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File Formats

File Formats . COM 366 Web Design & Layout. Native file format Format native to software program . psd > PhotoShop default Preserves layers Use “Save for Web ” in PhotoShop to export as jpeg file. Graphic files. Raster or bitmap graphics Use pixels PhotoShop. Vector graphics

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File Formats

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  1. File Formats COM 366 Web Design & Layout

  2. Native file format • Format native to software program • .psd> PhotoShop default • Preserves layers • Use “Save for Web” in PhotoShopto export as jpeg file

  3. Graphic files • Raster or bitmap graphics • Use pixels • PhotoShop

  4. Vector graphics • Use mathematical formulas • Combine lines, points, curves • Fill with colors • Flash

  5. GIF format (.gif) • Graphic interchange format • GIF images use indexed color • Maximum of 256 colors • Compressed • Reduce file size • “lossless” means image doesn’t lose any quality by being compressed

  6. Biggest advantage is that one color can be transparent • Allow background on Web page to show thru • Can be interlaced • Download in layers with each layer adding more detail

  7. Interlaced file displaying every 8th row; this is how the file first loads. Interlaced file displaying all rows; this how the file appears after the entire graphic has loaded.

  8. Best used for text or illustrations or cartoons

  9. JPEG file (.jpeg) • or .jpg • Joint Photographic Experts Group • Best used for photos • Uses “lossy” compression scheme • Some detail is lost • Reduces file size

  10. Progressive JPEG • Similar to interlacing for GIF file • Downloads in waves or layers

  11. Big advantage of jpeg is that it can contain millions of colors • Can choose from various compression levels • Low = more degradation • Higher the quality level, greater file size

  12. Quality = 10, 4.7 kB Quality = 50, 15.1 kB Quality = 100, 83.2 kB

  13. Best used for photos

  14. File sizes • File sizes measured in bytes • Bit smallest unit of measurement on computer • On / off, 1 or 0 • 8 bits = 1 byte • One byte equals about one letter “A”

  15. A 1,000 bytes = kilobyte (kB) • A million bytes = megabyte (MB) • A trillion bytes = gigabyte (GB) • Lowercase b would mean bits • Mb

  16. Other formats • PNG (.png) • Portable network graphics • Developed as replacement for GIF • Not patented • Lossless compression • Transparent background • Can have more colors than gif (PNG-24)

  17. PNG-8 uses 8-bit color • 256 colors • Comparable to gif • PNG-24 • Supports millions of colors • Comparable to jpeg • Larger file size than jpeg • But uses lossless compression

  18. What a cat image looks like saved as a PNG-24 and placed against a patterned background on the HTML page:

  19. .html • Hypertext markup language • All web pages have to be in this format • Only format Web browsers (Safari, Firefox) can read

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