A raster image's structure closely matches it's representation as shown on modern display hardware; the image is represented as a grid of filled square ``pixels''. Each pixel is considered to be a filled square of the same size and contains information describing its colour. This representation is simple and also well suited to storing images as produced by cameras and scanners. The drawback of raster images is that by their very nature there can only be one level of detail; this is illustrated in Figures \ref{vector-vs-raster} and \ref{vector-vs-raster-scaled}.
-A vector image contains information about the positioning and shading of geometric shapes. To display this image on modern display hardware, coordinates are transformed according to the view and then the image is converted into a raster like representation. Whilst the raster image merely appears to contain edges, the vector image actually contains information about these edges, meaning they can be displayed ``infinitely sharply'' at any level of detail --- or they could be if the coordinates are stored with enough precision (see Section \ref{Precision and Rounding}).
+A vector image contains information about the positioning and shading of geometric shapes. To display this image on modern display hardware, coordinates are transformed according to the view and then the image is converted into a raster like representation. Whilst the raster image merely appears to contain edges, the vector image actually contains information about these edges, meaning they can be displayed ``infinitely sharply'' at any level of detail --- or they could be if the coordinates are stored with enough precision.
Figures \ref{vector-vs-raster} and \ref{vector-vs-raster-scaled} illustrate the advantage of vector formats by comparing raster and vector images in a similar way to Worth and Packard\cite{worth2003xr}. On the right is a raster image which should be recognisable as an animal defined by fairly sharp edges. Figure \ref{vector-vs-raster-scaled} shows how these edges appear jagged when scaled. There is no information in the original image as to what should be displayed at a larger size, so each square shaped pixel is simply increased in size. A blurring effect will probably be visible in most PDF viewers; the software has attempted to make the ``edge'' appear more realistic using a technique called ``antialiasing''\footnote{We recommend disabling this if your PDF viewer supports it}.
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