[vlc-devel] [PATCH 5/5] direct3d11: pass the Whitepoint shifts as a Matrix

[Steinar H. Gunderson]

On Tue, Mar 07, 2017 at 02:41:41PM +0100, Steve Lhomme wrote:
>> If 0 => 0.0 and 255 => 1.0, then surely 127 => 127.0/255.0 =~ 0.498.
> My comment says I'm using 128, not 127. IMO the middle between 0 and
> 255, in integer, is 128 not 127.

Yes, my bad. But 128/255.0 is 0.502, so same problem. :-)

> But anyway the 128 value comes from 3.4 and 4.6 in BT.709. I picked the
> name "achromacy" from there. It should be 128/255 though.

Yes, that was my point. And for 10-bit, it should be 512/1023, which is a
subtly different value (0.500488 versus 0.501961). So you can't just set a
single constant here independent of the bit depth and get accurate results.

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