Graphics workshop

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Graphics workshop

• 2 July 2003

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Structure

• Raster vs vector graphics
• Scanning
• Purpose of use
• Decreasing file size
• File formats

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Vector graphics
1. Raster vs vector graphics

• object-oriented graphics or drawings
• consist of a series of mathematically defined
  points that are joined together by a line
• Object
• independent unit
• characterised by e.g. colour and shape.
• independent of other objects

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Raster graphics
1. Raster vs vector graphics

• Also called bitmaps
• The image consists of many pixels.
• Each pixel has its own colour.
• Pixels are arranged that a pattern is formed.

Original image
Same image 4x its original size
Original image is enlarged 6x.
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Scanning
2. Scanning

• Scanning only captures an incomplete
  representation of the original image.
• Have a clear idea of the use of the image at the
  time of scanning it.
• Print
• On-screen presentation
• Long-term preservation (?)
• Resolution

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Resolution
2. Scanning

• Frequency at which samples are taken from the
  original image during the process of scanning.
• expressed as dpi (dots per inch) or ppi (pixels
  per inch)
• Capture image at appropriate resolution.
• Avoid interpolated resolution.

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Purpose of use
3. Purpose of use

• Print
• On-screen
• Long-term preservation

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Print
3. Purpose of use

• Dont exceed resolution of printer.
• On non-professional equipment
• Not much difference between different file
  formats
• Resolution can be relatively low.
• On professional equipment
• File formats TIFF (Tag(ged) Image File Format)
  or EPS (Encapsulated Postscript).
• Contact printer prior to scanning your images
  about details.

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On-screen presentation
3. Purpose of use

• Issues involved
• Image quality
• Downloading time/ file size
• Browser compatibility
• File formats
• GIF (Graphics Interchange Format)
• JPEG (Joint Photographic Experts Group)
• PNG (Portable Network Graphics)
• Resolution 72 ppi

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Long-term preservation?
3. Purpose of use

• The standard archival format is uncompressed
  TIFF.
• Documentation and metadata are important.
• A conversion from JPEG or GIF to TIFF will not
  restore the information that has been filtered
  out during the process of saving the initial
  file.

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Decreasing file size
4. Decreasing file size

• Cropping Selecting part of the image
• Resizing Decreasing dimensions of the image
• File compression
• Colour models

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Cropping
4. Decreasing file size
Select part of the image you want to display
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Brightness and contrast
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Resizing
4. Decreasing file size

• Dont drag image

• Use softwares resize option

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Compression
4. Decreasing file size

• Reducing the file size of the image whilst
  maintaining image quality
• Different forms of compression
• Lossy some information is discarded (JPEG)
• Lossless all image information is preserved
  (GIF, PNG)
• Compression level can be variable

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Colours
4. Decreasing file size

• Images can contain a variable number of colours
• 8-bit colour (256 colours)
• 24-bit colour (16.7 million colours)
• Using more colours increases file size

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GIF
5. File formats

• Compression
• Lossless
• Reduction in the number of colours, which may
  have a negative influence on image quality
• Colour models

• Black white
• file size 8Kb

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JPEG Compression
5. File formats

• Lossy compression, i.e. data not necessary for
  on-screen display filtered out
• Loss of image quality through compression

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JPEG Colour models
5. File formats

• Greyscale
• 256 shades of grey
• 0 (black)
• 255 (white)

• RGB
• 256 shades each for red, green and blue
• values between 0 and 255
• red, green and blue 255 white
• red, green and blue 0 black

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PNG
5. File formats

• Compression
• Lossless
• Supported colour models
• Greyscale
• Palette
• RGB
• Not all browsers support PNG

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Comparison GIF, JPEG, PNG
5. File formats