Re: [Openexr-devel] Luminance/chroma images, transform equation

[Florian Kainz]

The header file ImfRgbaYca.h declares this function:

    Imath::V3f computeYw (const Chromaticities &cr);

Given a set of chromaticities, it returns the vector
V3f (w_r, w_g, w_b).  If you are interested in how the
values are computed, take a look at the function definition
in ImfRgbaYca.cpp and at the function RGBtoXYZ() in
ImfChromaticities.cpp.

By the way, ImfRgbaYca.h defines a set of functions will
perform a high-quality conversion from RGB to luminance/chroma
(with sub-sampled chroma) and back to RGB.  See the comments in
the file for more information.

Florian

Hồ Châu wrote:
> For luminance/chroma images, if have chromaticities and white point 
> coordinates, what algorithm should my program use for calculate w_r, 
> w_g, w_b for this equation?
> Y = R × w_r + G × w_g + B × w_b
> from EXR Technical Introduction document.
>
> Châu
>
>
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