Ian Thomas

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Storing Images
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Image
Different ways to store an image
Raster
Vector
Lossy
Lossless
No metadata
With metadata
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Raster data The image is digitized pixel by
pixel. Every pixel has colour data.
http//en.wikipedia.org/wiki/Raster_graphics
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Vector data The image is made up of shapes. The
shapes are painted to make the image.
http//en.wikipedia.org/wiki/ImageFace_with_objec
ts_selected.png
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Vector and Raster
A. Original B. Vector graphics C. Raster
graphics
http//en.wikipedia.org/wiki/Vector_graphics
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Vector graphics are good for removing too much
information.
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Raster graphics are easy to produce and display.
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Raster File Formats Many formats are available
for different jobs.
BMP GIF JPEG PNG TIFF
http//www.prepressure.com/image/bitmapvector.htm
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Vector file formats
GIS
EPS SVG
http//en.wikipedia.org/wiki/GIS
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Lossy and Lossless In lossy file formats, some
data is lost so that the file is smaller. In
lossless file formats, the image is exactly as
the original.
Lossy Lossless JPEG JPEG
lossless BMP TIFF
http//en.wikipedia.org/wiki/Png
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With/without metadata
Extra information can be added to the image file.
This information is about the camera parameters.
It is from a TIFF file.
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JPEG can also include some metadata
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Saving image data to a file
Image x size
A raster image file consists of a header
containing information about the image
(metadata), and the image data itself.
Image x size
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• We need to choose on of the many image formats.
  We do this based on decisions like
• Lossy or lossless?
• How much metadata do we need?
• Do we need a lot of compression?

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Comparison of popular Web image formats - GIF
and JPEG
GIF JPEG
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Lossless data - file size 111kbyte (TIFF)
Lossy data - file size 8kbyte (JPEG)
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Comparison of file sizes
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For medical data, using lossy compression can
lead to small changes in the image, which could
reduce the doctors ability to diagnose.
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For medical work there is another factor which we
need to consider - Integration. DICOM is a
standard for medical imaging which is easily
integrated. It can be used to produce a PACS.
http//www.ampronix.com/content/web/suite.asp
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DICOM metadata
http//www.leadtools.com/SDK/Medical/DICOM/ltdc1.h
tm