[Openexr-devel] EXR documentation change

[Florian Kainz]

The "Recommendations / RGB Color" section on page 12 of the
"Technical Introduction to OpenEXR" document says:

    The IlmImf library defines a "chromaticities" attribute, which
    specifies the CIE x,y coordinates for red, green, blue, and white;
    that is, for the RGB triples (1, 0, 0), (0, 1, 0), (0, 0, 1), and
    (1, 1, 1).  The x,y coordinates of all possible RGB triples can be
    derived from the chromaticities attribute. [...] If a file doesn't
    have a chromaticities attribute, display software should assume that
    the file's primaries and the white point match the display.

Since this recommendation is fairly useless, I will change the last
sentence to:

    If a file doesn't have a chromaticities attribute, display software
    should assume that the file's primaries and the white point match
    Rec. ITU-R BT.709-3:

                CIE x, y
        red     0.6400, 0.3300
        green   0.3000, 0.6000
        blue    0.1500, 0.0600
        white   0.3127, 0.3290

I will also change the exrdisplay program so that it performs a coordinate
transform from the file's to the display's RGB space.

Florian


P.S.:  I am aware that a simple coordinate transform is not a substitute
for proper color rendering.  Still, it is better than nothing; at least
it allows you to look at files whose primaries that from you display's,
for example, XYZ images where the xy coordinates for R, G, B and white
are (1,0), (0,1), (0,0) and (1/3, 1/3).