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Visual content
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Image production
Summary & activities
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Resolution
- Digital images are measured in 'pixels'.
- The document size multiplied by the resolution equals the pixel size.
- Images must be 'resampled' to change the pixel dimensions.
- Image resolution of 75ppi will make document size and screen display size
similar.
- When possible, set scanning software to use pixels as the size unit when scanning
for the web.
Compression
- A web page should be no more than 60kb, so images within web pages should
be even smaller.
- Compression may be 'lossy' (eg JPEG) or 'lossless' (eg GIF, PNG, TIFF) in
regard to image quality.
- Images should be saved in a 'lossless' format (eg TIFF, PNG24) for archiving
- Images with many colours, such as photographs, are best saved as JPEG which
provides full colour and efficient compression with some image degradation.
- Images with few colours, such as charts, logos, buttons, are best saved as
GIF which provides efficient, lossless compression with a reduced colour range.
- Use a standard 'eight dot three' naming convention for images, to ensure compatibility
across systems.
Web colours
- Photographs are best saved as JPEG, which contains 24-bit colour
- Graphics with a limited range of colours are best saved as give, with a web
safe or optimised palette.
- There are a range of palette options for optimising an index colour palette.
- Where dithering of colours may compromise legibility, web safe colours should
be used.
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