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Graphics in the web

Graphics in the web. Digital Media: Communication and Design. 06.03.2007. Comments. Mandatory assignment Don’t panic!! Photoshop photoshop.html in public_html Picture of yourself. Goals of the lecture. What is a digital image Different formats we can use in the web GIF, JPEG, PNG

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Graphics in the web

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  1. Graphics in the web Digital Media: Communication and Design. 06.03.2007

  2. Comments • Mandatory assignment • Don’t panic!! • Photoshop • photoshop.html in public_html • Picture of yourself

  3. Goals of the lecture • What is a digital image • Different formats we can use in the web • GIF, JPEG, PNG • Basic things about Photoshop • Continued in the assignment

  4. Index • Digital image • GIF • JPEG • PNG • Image editing

  5. Digital image • Rectangular grid of pixels • Resolution: width x height in pixels • 9 x 12 = 108 pixels • Colour depth: amount of information in each pixel

  6. Digital image II

  7. Vector image • Shapes are defined by mathematical expressions • Can scale without losing detail • Example with Flash

  8. 600 400 800x600 1024x768

  9. Resolution

  10. Resolution • 2272 x 1704 • 3.8 megapixels • 11.1 MB uncompressed • 1.5 MB JPEG • 640 x 480 (web size) • 0.3 megapixels • 900 KB uncompressed • 106 KB JPEG

  11. Colour depth • Bit: unit that represents either a 0 or a 1 • Binary image: • Black and white • 1 bit per pixel • 80x100 = 80 Kbits = 10 KB

  12. Colour depth II • Greyscale image: • 8 bits per pixel = 256 possible values

  13. Colour depth III • RGB colour: • Combine Red, Green and Blue light • Values usually given in hexadecimal base • R: 241 = #F1 • G: 21 = #15 • B: 109 = #6D

  14. Colour depth IV • True colour: • 24 or 32 bits per pixel = 16.777.216 values • 8 bits for each colour and alpha channel • 85% of users (thecounter.com)

  15. Colour depth V • Indexed colour • 8 bits per pixel = 256 colours at one time • The possible colours are stored in a palette (colour map)

  16. Index • Digital image • GIF • JPEG • PNG • Image editing

  17. GIF • Graphic Interchange Format • Indexed images with max 8 bits per pixel • Lossless compression • May contain transparent areas • May contain multiple images

  18. GIF II: Palette • Contains the colours that can be used • Maximum of 8 bits = 256 colours • Common palettes: • Exact • Adaptive • Perceptual • Selective (default in Photoshop) • Example: blue.jpg, brown.jpg

  19. GIF III: Compression • Lossless compression • Good when compressing areas with the same colour • Not good for gradients or photos

  20. GIF IV • Number of colours: • Find minimum number of colours needed • Dither: “create” colours with a limited palette • Example

  21. Index • Digital image • GIF • JPEG • PNG • Image editing

  22. JPEG • Joint Photographic Experts Group • RGB 24-bit colour image • Lossy compression • No transparency

  23. JPEG II • Very good compressing photographic images • Not good compressing flat colours • Example in Photoshop • Lossy compression: • It’s possible to specify the degree of compression

  24. Index • Digital image • GIF • JPEG • PNG • Image editing

  25. PNG • Portable Network Graphic • Created for the web • 24- or 48-bit colour, 16-bit grayscale and 8-bit indexed colour images • Lossless compression • 8- or 16-bit alpha channel • W3C and ISO standards

  26. PNG II • Better compression than GIF • Larger files than JPEG • But better quality • IE6 doesn’t support transparency

  27. Which format to choose PNG GIF JPEG

  28. Index • Digital image • GIF • JPEG • PNG • Image editing

  29. Some basic Photoshop Dark Light Mid

  30. Some basic Photoshop II

  31. Some basic Photoshop III

  32. Some basic Photoshop IV

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