[boost] [gil] undocumented/unintended concept requirements in color_convert

Subject: [boost] [gil] undocumented/unintended concept requirements in color_convert
From: Michael Marcin (mike.marcin_at_[hidden])
Date: 2013-03-18 00:28:59

I was trying to add other color spaces support and noticed that the rgb 
to cmyk converter contains:

typedef typename channel_type<P2>::type T2;
T2 x = channel_traits<T2>::max_value()-get_color(dst,black_t());
if (x>0.0001f) {
     float x1 = channel_traits<T2>::max_value()/float(x);

T2 should model:
http://www.boost.org/doc/libs/1_53_0/libs/gil/doc/html/g_i_l_0264.html

but this code additionally requires T2 to be greater-than comparable to 
float and convertible to float.