Re: Gamma transfer function - my second try


Timo Autiokari wrote:
ronviers@xxxxxxxxx wrote:

> Light intensity vs. signal input/output results in a curve.

No. Light behaves absolutely linearly. Also CCD and CMOS raw data are
detecting light linearly.

> The 'gamma transfer function' is used to flatten this curve so the
> relationship of encoded image data to intensity will be a simple
> ratio.

No. The gamma function is the property of cathode ray tubes. Their
native tonal reproduction curve is about gamma 2.5. So input voltages
and the respective screen luminances follow the gamma function at gamma
= 2.5 (a power law function with exponent of 2.5).

> In a well corrected system, humans will see luminance as lightness.

No! The lightness is a totally different thing than the various surface
luminances that we see in the scene. The lightness is what illuminates
the scene surfaces.


I will not respond point by point because I am going to start over,
this time with different sources. I used reference material from TV
electronics not color theory to develop my definitions. Luckily there
is tons of material online.
My thinking on the luminance/lightness statement was an attempt to make
the luminance definition derived from RGB color space and the L*
definition derived from the CIELAB color model meet in reality. I
thought it was a stretch when I wrote it.

Thank you for your time,
Ron

.

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