Image resolution

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Image resolution

• Part 1 pixels and dots
• Part 2 scanning, printing and display

Part 1 Antti Karjalainen Part 2 Jere Koret
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What is a pixel

• Pixel - An abbreviation of the term 'picture
  element.'
• A pixel is the smallest picture element of a
  digital image.
• A monochrome pixel can have only two values,
• 0 and 1.
• Color and gray scale require more bits true
  color,
• displaying approximately 16.7 million colors,
  requires 24
• bits for each pixel.
• A pixel doesn't have a fixed size.
• A pixel may have more data than the
• eye can perceive at one time.

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Pixels in digital image

• Digital image consists of
• pixels that are laid out in a
• specific order.
• Width (x) and height (y)
• A pixel doesn't have
• an absolute size.
• File format which defines the components of the
  digital
• image (x y values, colour, compression, manner
  in which the pixels are laid out, etc.) and
  provides for the storage and redisplay of the
  digital image

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What is image resolution

• Digital image resolution means the size of the
  image in pixels, eg. 800X600 means that the image
  is 800 pixels wide and 600 pixels long.
• Image resolution may or may not be related. This
  is because of some discrete pixel sizes.
• Image resolution is always measured in pixels,
  not in DPI etc, except in the context of a
  specific display, printer or image capture device.

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What is a dot

• Dot The smallest unit that a printer can
  print.
• DPI or dots per inch A measure of the resolution
  of a
• printer is called DPI or dots per inch.
• It properly refers to the dots of ink or toner
  used by an imagesetter, laser printer, or other
  printing device to print your text and graphics.
  In general, the more dots, the better and sharper
  the image.
• DPI is printer resolution. DPI is NOT image
  resolution although frequently used that way.

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Laser printer

• The primary working principle
• Static electricity (the same energy that makes
  clothes in the dryer stick together or a
  lightning bolt travel from a thundercloud to the
  ground)
• Static electricity is simply an electrical charge
  built up on an insulated object, such as a
  balloon or your body. Since oppositely charged
  atoms are attracted to each other, objects with
  opposite static electricity fields cling together.

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Inkjet Printer

• Basics Principles
• An inkjet printer is any printer that places
  extremely small droplets of ink onto paper to
  create an image. If you ever look at a piece of
  paper that has come out of an inkjet printer, you
  know that
• The dots are extremely small
• The dots are positioned very precisely (with
  resolutions of up to 1440x720 dots per inch)
• The dots can have different colors combined
  together to create photo-quality images.

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• The paper you use on an inkjet printer greatly
  determines the quality of the image. (Standard
  copier paper works, but doesn't provide as crisp
  and bright an image as paper made for an inkjet
  printer).
• There are two main factors that affect image
  quality
• Brightness
• Absorption

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Brightness

• Normally determined by how rough the surface of
  the paper is.
• A course or rough paper scatters light in several
  directions, whereas a smooth paper will reflect
  more of the light back in the same direction.
  This makes the paper appear brighter, which in
  turn makes any image on the paper appear
  brighter. (example Comparing a photo in a
  newspaper with a photo in a magazine. Smooth
  paper reflects light back much better than the
  rough texture of the newspaper).
• Papers that is listed as bright are generally a
  smoother-than normal paper.

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Absorption

• The other key factor in image quality is
• Absorption
• When the ink is sprayed onto the paper, it
  should stay in a tight, symmetrical dot.
• The ink should not be absorbed too much into the
  paper. If that happens, the dot will begin to
  feather.
• The result is that page that looks somewhat
  fuzzy, particularly at the edges of objects and
  text.

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Absorption Example
Left is on coated paper and the dot on the right
is on low-grade copier paper.
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Scanners

• Primary information
• The scanner's dpi (dots per inch) is determined
  by the number of sensors in a single row
  x-direction sampling rate and y-direction
  sampling rate.
• Sharpness depends mainly on the quality of the
  optics (a bright xenon lamp and high-quality lens
  will create a much clearer, and therefore
  sharper, image than a standard fluorescent lamp
  and basic lens)