Rastar Scan

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Raster scan
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What is raster scanning?

• It is the process of displaying an image by
  updating each pixel one after the other, rather
  than all at the time.

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Raster scanning

• It is done by scanning each row of pixel one by
  one from left to right and scanning from top to
  bottom.
• It is the most common type of graphics monitor
  employing a CRT. While sweeping of electron beam
  row wise, then beam intensity is turned on and
  off to create a pattern of illuminated spots.
• Picture definition stored in memory area called
  Refresh Buffer or Frame Buffer.
• Memory area holds the set of intensity values for
  all the screen points.

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Raster scanning

• Each screen point is known as Pixel or (Pel)
  Pixel Element.
• Painted on the screen one row at a time.
• In Black and White system, each screen point is
  either on or off.
• 1 bit/pixel in Black and White system so frame
  buffer is known as Bitmap.
• For system with multiple bits/pixel it is called
  Pixmap.

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working

• In raster scan, the electron beam from electron
  gun is swept horizontally across the phosphor.
• After each horizontal sweep the beam is moved.
• After the bottom line is swept the beam returns
  to the top abd the sweep process begins again.
• HORIZONTAL RETRACE It is used to refer the beam
  moving back to left at the end of each line.
• VERTICAL RETRACE It refers to the movement from
  bottom to top.

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