On 9/29/13, Michael Henning dra...@darkrefraction.com wrote:
Sorry for the delay in replying; I wanted to take the time to properly
look at everything you've said.
If you managed to make your way through *everything* I said in my
attempt to explain why the adapted values are the correct values
Sorry for the delay in replying; I wanted to take the time to properly
look at everything you've said.
Yes, Elle, you're right. I take what I said back; we should be using
the adapted values.
If anyone is still doubting this, you can try playing around with this
demo program I created:
A technically correct luminance-based conversion to black and white is
done using this formula:
L = R*Yr + G*Yg + B*Yb
where R, G, and B are the image RGB values for any given pixel and Yr,
Yg, and Yb are the Y values from the image's actual ICC profile. If
the profile white point isn't D50, the
On 9/21/13, Michael Henning dra...@darkrefraction.com wrote:
Both babl's RGB format and Y format are currently defined with a white
point of D65. Because of this, I believe the code's current luminance
values are correct.
In other words, I think that the whitepoints are all currently
I hope you don't mind; I reordered parts of your email when responding to it.
Isn't the second (adapted) transform going to give us a D50 Y instead
of a D65 Y?
Yes, it will, and that's precisely what you want if you want to
correctly calculate an sRGB image's Luminance values from its RGB
On 9/22/13, Michael Henning dra...@darkrefraction.com wrote:
Isn't the second (adapted) transform going to give us a D50 Y instead
of a D65 Y?
Yes, it will, and that's precisely what you want if you want to
correctly calculate an sRGB image's Luminance values from its RGB
values.
The main
Both babl's RGB format and Y format are currently defined with a white
point of D65. Because of this, I believe the code's current luminance
values are correct.
Out of curiosity, how did you determine the Y values from the code in
gegl/operations/external/lcms-from-profile.c ? If you're somehow
On 9/21/13, Michael Henning dra...@darkrefraction.com wrote:
Both babl's RGB format and Y format are currently defined with a white
point of D65. Because of this, I believe the code's current luminance
values are correct.
The whitepoint of an ICC profile might have a D65 white point without
a
Those conversion factors are attempting to get a D65 Y from D65 RGB.
So, we currently do a conversion like this, using unadapted values:
D65 Y = 0.212656 * D65 Red + 0.715158 * D65 Green + 0.072186 * D65 Blue
And you want us to do this, using the adapted values:
Y = 0.222491 * D65 Red + 0.716888
