Lecture Four File Specification Standards

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Lecture FourFile Specification Standards
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Standards - Why Bother?

• Portability
• platform independence
• programmer portability
• Not tied to proprietary formats
• cost
• availability
• Problem of plethora of standards

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Common image file formats

• BMP raster widely used
• GIF raster Internet use
• JPEG raster compressed
• TIFF raster large standard
• PICT raster Mac-based
• IMG raster bit limited
• WMF / CGM vector specialist use

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Common video file formats

• MPEG / MPG / MPV
• AVI
• MOV - QuickTime

many other proprietary formats - e.g. Cinepak,
Intel Indeo
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Common audio file formats

• WAV sampled analogue sound
• AIFF
• AU
• MIDI records keys / instruments / time
• MP2 / MP3 audio track from MPEG
• RA / RAM RealAudio streaming technology

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The BMP file format

• Basic need to store pixel values - but what do
  they mean?

Colour Look-up Table (CLUT)
RGB Value
Pixel Value
Output Device
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Elements of the file specification

• Initial identifier BM
• Size of the file - allows for quick check
• Offset through the header to the pixel data
• Width height of the bitmap, in pixels
• Number of bits per pixel
• Type of compression in use (if any)
• Pixels / metre in x and y dimensions

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More elements

• Number of colours in the CLUT
• Number of important colours
• CLUT pixel data follows
• Questions
• Why is each element included?
• Are there any limitations to a BMP?