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  1. 1. More Information in Images
  2. 2. More Information in Images <ul><li>We found out last time: </li></ul><ul><li>How pixels in an image have different ‘shades’ depending on the number of bits </li></ul><ul><li>Binary numbers represent decimal values in digital systems </li></ul><ul><li>The number of alternatives is 2 n for n bits </li></ul><ul><li>10101 = 21 what is the number of alternatives? </li></ul><ul><li>Hint, it’s 5 bits… </li></ul>
  3. 4. More Information in Images <ul><li>We will find out today: </li></ul><ul><li>How to calculate the data capacity needed to store an image </li></ul><ul><li>How to calculate data transfer rates </li></ul><ul><li>How to use Logarithms to calculate values </li></ul>
  4. 5. Number of alternatives = 2 number of bits Log 2 Number of Alternatives = Number of bits
  5. 6. Number of alternatives = 2number of bits Log 2 Number of Alternatives = Number of bits But what is needed to store an image or other information..?
  6. 7. Capacity How much data is needed to store an image??? Windows tells us the size of a file, but why is it that value? Remember 1 Byte = 8 bits ( Bi nary Digi ts )
  7. 8. <ul><li>Data Required in Bits = Number of pixels x bits per pixel </li></ul><ul><li>Data required in Bytes = Data required in Bits / 8 </li></ul><ul><li>For image above </li></ul><ul><li>Number of Pixels = 1600 x 1200 = 1.92 Million </li></ul><ul><li>Bits per pixel = 22 (there are 4.2 million alternatives) </li></ul><ul><li>Data required in Bits = 1.92M x 22 = 42.3Mbits </li></ul><ul><li>Data required in Bytes = 42.3M/8 = 5.3MB </li></ul>
  8. 9. Image Capacity of available memory = Memory Available/ Memory Required for Image How many of these images could be stored onto a 20GB disc? 20 x 10 9 / 5.3 x 10 6 = 3774 images It doesn’t matter what the data is for; images, text or music. Capacity is calculated the same way…
  9. 10. Data Transfer <ul><li>100011110100010101 </li></ul><ul><li>How long would it take to send a bit stream…? </li></ul><ul><li>It depends on the data rate… </li></ul><ul><li>Time to transfer = Amount of Data </li></ul><ul><li>Data Transfer rate </li></ul>

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