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  1. 1. Seeing Invisible Things <ul><li>We will find out: </li></ul><ul><li>Review the terms ‘pixel’ and ‘resolution’ </li></ul><ul><li>Understand how images can be gathered using pulses of sound or radiation </li></ul>
  2. 2. Pixel <ul><li>A pixel is a ‘Picture Element’ – it is the smallest part of the reconstructed image. </li></ul>
  3. 3. Resolution <ul><li>Resolution is smallest discernible feature or smallest detectable difference on an image </li></ul><ul><li>To calculate it: </li></ul><ul><li>Resolution = image dimension/number of pixels </li></ul><ul><li>for an image from the scale and number of pixels </li></ul><ul><li>e.g. what is the resolution of a 15cm x 10cm image made up of 15000 pixels? </li></ul>
  4. 4. Resolution <ul><li>e.g. what is the resolution of an image of a 15cm x 10cm area made up of 15000 pixels? </li></ul><ul><li>Number of pixels = Area / Pixel Size </li></ul><ul><li>Therefore Pixel Size = Area/ Number of pixels </li></ul><ul><li>Area = 15cm x 10cm = 150cm 2 </li></ul><ul><li>Number of pixels = 15000 </li></ul><ul><li>Therefore Pixel Size = 150 / 15000 = 0.01cm 2 = 1mm 2 </li></ul><ul><li>Resolution = 1mm 2 </li></ul><ul><li>This is the smallest distinguishable detail – but what if the image represented an actual area of 150m x 100m? </li></ul>
  5. 5. Resolution of an image <ul><li>This is an image of East Midlands Airport – it shows an area of 2km x 1km </li></ul><ul><li>What is the resolution if it is displayed on the screen as previously discussed? </li></ul>
  6. 6. Showing Resolution <ul><li>Using a sheet of A4 squared paper, put the picture of EMA underneath and draw around it. </li></ul><ul><li>Count the number of squares. </li></ul><ul><li>What is the resolution if the area shown in the image is 100m x 150m assuming that each square on the paper is 1 pixel? </li></ul>
  7. 7. Imaging with Sound <ul><li>Ultrasound can be used to form images </li></ul><ul><li>Pulses are sent and reflections are timed: </li></ul><ul><li>Distance = Speed x Time </li></ul><ul><li>Pulses are sent so that sound does not become ‘muddled’ – sent and reflected pulse. </li></ul>

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