RGB-Levels should give some assurance that a full black is achieved
without any reference to the underexposure indicator.
David
On 2022-01-25 21:45, Top Rock Photography wrote:
The proper point to clamp black and white in scene-referred is filmic RGB.
Correct to some extent, in scene-referred pipeline. The “why” is important,
though, and not relevant to non-filmic pipelines.
…could eventually produce problems in other parts.
With a floating-point pixel pipeline, we do not have the general problems
which come with an integer pipeline as in Ps/Lr. They have integers which
MUST be between 0 & 255/65,535 (8-bit/16-bit). If at any point in the
pipeline, the number falls below or above those values, it clips to the
extreme value. That leads to banding in the shadows/highlights.
With floating-point, the colours are represented by 0 for blackest black,
and 1 for whitest white. If at any point, the number falls below or above
those values, they remain at whatever the value is, until another module in
the pipeline adjusts it again. At the end of the pipeline, before
exporting, there are three ways to handle ‘out-of-gamut’ values.
1. clip any value below zero or above one.
2. normalise the values to fall within the range. (The lowest value
becomes zero, the highest value becomes one, and all other values are
squeezed in.
3. I cannot recall.
The problem with the filmic module is that it uses a log function, and
there is no log defined for a negative number. Therefore, the filmic module
might crash or give incorrect interpretations for negative numbers. There
are several ways to fix that.
1. clip negative numbers before the filmic module.
2. normalise negative numbers before the filmic module.
3. replace the log function with trigonometric substitution, or
something, where negative numbers can be handled.
4. I am really not sure. I would really have to think about it.
Currently, I have tried to switch my workflow from LabCIE to FilmicRGB,
and, despite the warning, have still been sometimes adjusting my black
level with the [exposure]→[black level correction] slider. So far, the
[filmic rgb] module has not crashed out on me, nor messed up my subject.
One reason may be that, because I use the {clipping indication} to ensure
that no part of my subject goes too far beyond that 2% margin, (actually,
in 3.8, it is -12.27 EV), very few pixels, if any, (in the subject), goes
into the negative. I suppose I could use the {gamut checking} option
instead of the clipping option for a more certain outcome, but the end
result is more or less the same; no negative values to worry about.
Another reason may be that the [input colour profile] module —which has
options for handling out-of-gamut colours— comes AFTER the [exposure]
module and BEFORE the [filmic rgb] module.
A third reason could be great error-handling routines in the [filmic rgb]
module to handle the log of negative numbers.
Whatever the reason, so long as I do not end up clipping (crushing) my
shadows in the [exposure] module into negative values, the image seems to
be just fine at the end of my pixel pipeline. (Truth be told, I do not
actually know what would happen IF I dropped the blacks into the negative).
If one is NOT using [filmic rgb], —or any other module which does functions
where the result of a negative number input is NAN,— then using
the [exposure]→[black level correction] slider is not really a problem.
Sincerely,
Karim Hosein
Top Rock Photography
754.999.1652
On Tue, 25 Jan 2022 at 11:33, Guillermo Rozas<guille2...@gmail.com> wrote:
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