Spectrum 512 Enhanced file format

Spectrum 512 Enhanced    *.SPU

Spectrum 512 images with a 15-bit RGB palette.
Created by Sascha Springer: http://blog.anides.de/

These are identical to Spectrum 512 uncompressed images with two exceptions.
The very first long of the image data will be the file id: '5BIT'
Spectrum 512 can't display the first scan line anyway, so the id should cause no issues.

The upper 3 bits of a palette word are used to provide a 5th bit of RGB. Thus:
  red:  0xxx1432xxxxxxxx
  green x0xxxxxx1432xxxx
  blue: xx0xxxxxxxxx1432

These look like normal Spectrum 512 images by old viewers when the upper 3 bits are not used.

As described by the creator: 
The new least significant bit for each channel are now stored in the upper nibble of the
color word and so the image .SPU format itself is kept completely "backwards" compatible.

See also Spectrum 512 file format

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