[Octave-patch-tracker] [patch #8709] fixes to color conversion functions (mainly rgb2ntsc and ntsc2rgb)

[Carnë Draug]

Follow-up Comment #8, patch #8709 (project octave):

Since you also agree, I have then pushed those changes with a bunch more
tests.  I have also added support for signed integer images (image package
supports int16 but this adds support for int16 and int8).  See

http://hg.savannah.gnu.org/hgweb/octave/rev/a5ed88c9eb14
http://hg.savannah.gnu.org/hgweb/octave/rev/a278de349250
http://hg.savannah.gnu.org/hgweb/octave/rev/67e6343cd29a

One thing that I noticed while writing the tests is that the conversion from
integers to double by ntsc2rgb does not really work.  The reason is that we
are currently scaling the values into the [0 1] range. However, ntsc values
are not meant to be on that range (do not believe Matlab documentation, it's
all wrong).  Just consider the values from its sister function rgb2ntsc


octave> rgb2ntsc ([0 1 0])
ans =

   0.58700  -0.27400  -0.52300



How should we be scaling integer values for NTSC?

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