Re: [Openexr-devel] On YUV support

[Billy Biggs]

Florian Kainz (address@hidden):

> A couple of weeks ago, two statements were made in this thread:
> 
> 1) The "Technical Details" page on the OpenEXR web suggests reserving
>    the channel names Y, U, and V for "YUV images", that is, images
>    with one luma and two chroma channels.  The channel names, and the
>    term "YUV image" are misleading and should be changed.
> 
> 2) The the luma and chroma channels in existing component video
>    systems were defined assuming that R, G and B fit into a normalized
>    zero-to-one range, and that RGB data are non-linear.  Outside the
>    zero-to-one range, the luma/chroma definitions are not necessarily
>    valid.  Therefore luma/chroma encoding of high-dynamic-range images
>    might not be possible or not desirable.
> 
> I agree with statement 1, except regarding the channel name "Y".
> 
> I disagree with statement number 2.  High-dynamic-range luma/chroma
> encoding is possible.  RGB image files can be converted to
> significantly luma/chroma files, in most cases with very little visual
> degradation of the image.

  Hi Florian,

  So long as a Y channel is for true luminance, the name is appropriate,
and defining your own luminance/chroma space is of course valid and very
useful.  However, I would recommend you avoid calling the Y channel
'luma', that's Poynton's term for non-linear luminance or Y', not a
short form for luminance. :)

  Great post, very clear, and the code was cool and readable.  Thanks.
  -Billy