Xrite Color Profiles ?

Started 10 months ago | Discussions thread
Jack Hogan Veteran Member • Posts: 8,008
Tone Curve to Squeeze DR into CR

ggbutcher wrote:

Jack Hogan wrote:

ggbutcher wrote:

"linear" refers to the original light measurements captured in the raw file. Sometimes called 'scene-linear". Usually looks dark and/or dull.

Good post Glenn. Two pet peeves:

1) Scene linear does not' look' dark, it only appears dark if the output medium is not properly color managed (i.e if it tries to apply a gamma curve where none is needed) , otherwise it will look 'properly' bright. It may on the other hand look dull but see 2) below.

"Non-linear", obviously, refers to a departure from scene-linear, through some kind of tone transform, or "curve". This almost always has to be done to a raw image to make it presentable, having to do with the non-linear response of human vision

2) Human vision expects a linear input. How could it not? Light behaves pretty well linearly right up until it hits the eyes. From then on the HVS behaves like it always does, non-linearly, based on a linear input.

But, isn't "perceptual" about what the brain does with the linear input?

Right. Linear input from the scene or, alternatively, linear output from an output medium, say a monitor. Ideally the output of the monitor is identical to what's coming from the scene; second best would be proportional to it. Meaning that the scene, the capture, the raw conversion, and the output render on the monitor are in the end ideally linearly related. We strive for the ideal but, alas, practice never achieves it (nor in many cases is it necessary to do so).

The 'curve' before the input, may be necessary mainly because today's cameras capture a larger DR than the output medium, so it's an easy way to squeeze the former into the latter. Absent that it looks 'dull'. Though it carries its own problems, such as chromaticity shifts. One of DcamProf/Lumariver's better attributes is that it tries its best to compensate for such.

So if we had a 12 stop DR scene, a linear pipeline and a 12 stop CR monitor, would we need a tone curve for maximum fidelity? In an ideal world not.

On the other hand, a 12 stop scene out of an 8 stop CR monitor definitely needs some sort of tonal compression lest the output look 'dull'. See for instance linearly rendered Figure 13 before the tone curve here (vs Figure 15 after):

https://www.strollswithmydog.com/raw-file-conversion-steps/

Jack

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