RE: purpose of Granger rainbow chart?
RE: purpose of Granger rainbow chart?
- Subject: RE: purpose of Granger rainbow chart?
- From: Roger Breton <email@hidden>
- Date: Mon, 08 Mar 2010 14:47:42 -0500
Jacob,
Please correct me if I am wrong, you seem to have an engineering video
background I don't have. But the Granger chart, to my knowledge, is just a
collection of discrete RGB values arranged in such a way to assure
monotonicity along every dimensions. I never thought it could be used for
anything be putting color conversions to torture. To me, however deficient
the chart be, numerically, it never struck me as critical as I've used it
many times to test output profiles smoothness. Never thought I could
attribute the tonal discontinuities or smooth tonal transitions I saw as a
function of the chart numerical makeup or mathematical deficiencies. Could
you briefly enlighten me up? And please, do excuse my ignorance in advance.
Best / Roger
> Sorry, I suppose there are no "discontinuities" in the luminous landscape
> max-for-each-hue-and-luma, but neither will there be in the same thing
> piped through a CMM and printed. What I meant to say is that the function
is
> not smooth (continuously differentiable), and in particularly noticeably
has a
> nasty diagonally slanted edge in lightness (L*), where the derivative
changes
> abruptly. This visual artifact is clearly visible <http://www.luminous-
> landscape.com/images31/Granger_Chart.jpg>. I don't understand why it
> wouldn't make more sense to create test images with lightness rather than
> luma on the vertical axis, especially considering that most CMMs use
CIELAB
> as a PCS. I suppose it would take crunching some numbers to make such a
> test image, and wouldn't be quite as easy to manage in Photoshop.
>
> Cheers,
> Jacob
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