heya,
On Thu, Jun 26, 2014 at 10:06 PM, Robert William Hutton <[email protected]>
wrote:
> Hi Stéphane,
>
> As far as I know the reason for the base curve is there to convert between
> the different way our eyes and digital
> sensors see light, the digital sensor being linear and the eye (kind of)
> logarithmic.
yes, true, but technically the srgb space (or similar, whatever your output
profile) at the very end of the pipeline accounts for this gamma correction
with a curve already. the base curve will add some additional eye-popping
contrast. i find that it sometimes really looks better or closer to what i
thought the scene appeared to me when taking the picture. however
especially in high contrast scenarios (back-lit portrait or so) i think
sometimes the version without base curve looks a lot better. in this
context i find very little use for canned styles which already include a
certain curve, i think it's a shot-by-shot decision.
-jo
> That is, you have to convert from
> what the camera sees, being uniform in terms of the number of photons
> falling on a particular pixel, to what the eye
> would see, i.e. a "perceptually uniform" space. An example of this is
> that the human eye sees 18% grey as "middle
> grey", i.e. half-way between white and black, whereas the sensor sees 50%
> grey as half-way between white and black.
> This is also the reason for "expose to the right" as there is far more
> information in the highlights than the darks.
>
> http://en.wikipedia.org/wiki/Lightness_(color)
> http://www.luminous-landscape.com/tutorials/expose-right.shtml
>
> The s-shaped curve for increasing contrast is distinct from that. I would
> normally do that in the tone curve as this
> has the ability to handle saturation in an intelligent way (increasing it
> in areas that are being brightened and
> decreasing it in areas that are being darkened).
>
> HTH,
>
> Rob
>
> On 26/06/14 10:30, Stéphane Gourichon wrote:
> > Le 26/06/2014 10:54, Artur de Sousa Rocha a écrit :
> >> it
> >> would be an interesting project to have some software that would take
> >> corresponding raw file and JPEG from camera and figure out a
> >> color/curves/etc. profile and lens correction.
> >
> > There is a tool that figures out a basecurve *and* a tone curve from a
> bunch of JPEG+RAW (or from RAW only when it
> > embeds a JPEG).
> > See about basecurves | darktable <
> http://www.darktable.org/2013/10/about-basecurves/>
> > http://www.darktable.org/2013/10/about-basecurves/
> >
> >
> > Regarding what is written there, I don't understand well why the
> basecurve is applied so early in darktable pipeline.
> > (And since it is mentioned in places, yes, I read 3.4. Modules | user
> manual | darktable
> > <http://www.darktable.org/usermanual/ch03s04.html.php> 3.4.2. Tone
> group | user manual | darktable
> > <http://www.darktable.org/usermanual/ch03s04s02.html.php> Mastering
> color with Lab tone curves | darktable
> > <http://www.darktable.org/2012/02/mastering-color-with-lab-tone-curves/>
> and did run ./tools/iop_dependencies.py in a
> > source tree, see the generated PDF and, oh, something is complicated in
> there.)
> >
> >
> > 3.4. Modules | user manual | darktable <
> http://www.darktable.org/usermanual/ch03s04.html.php> says:
> >> Camera sensors provide data in linear RGB format, the original image
> appears flat and dull.
> >
> > To me, the first reason why it appears flat and dull is that paper (and
> computer monitor with usual luminosity set so
> > that full white is not aggressive to the eye) actually have low dynamic
> range, lower than most photographed scenes (and
> > virtually any scene under a visible sun).
> >
> > So, the "“S-shaped” view transform." mentioned in about basecurves |
> darktable
> > <http://www.darktable.org/2013/10/about-basecurves/> is a way to
> /compensate/ for the poor dynamic range of the final
> > medium/display device (computer screen, projector, or even photographic
> paper).
> >
> > To put it short and incomplete : the S shape curve enhances contrast on
> the "medium luminance" areas for a pleasing
> > apparent contrast, which mathematically "eats" most the the available
> dynamic range. This forces to compress further the
> > shadows and highlights, and it looks better to have compressed
> highlights than clipping anyway.
> >
> > Indeed, you can experience that a linear scene (no base curve, no tone
> curve) displayed on a monitor set to high
> > luminosity looks better (natural rendering, more details in shadow and
> highlights) than the same scene with S-shaped
> > curve on a limited dynamic medium (paper, or the same monitor with
> regular luminosity settings).
> >
> > Does that make sense to you ?
> >
> > Back to my question, why is base curve applied so early in darktable ?
> Am I misguided about the S-shaped curve, the base
> > curve, the tone curve ? The documents referenced above do not explain
> well why there are already two S-shaped curves
> > (base curve, tone curve) offered.
> > Anyone had experience with other similar tools and how they do that ?
> >
> > Thank you for your attention.
> >
> > --
> > Stéphane Gourichon
> >
> >
> >
> >
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>
>
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> Quickly connect people, data, and systems into organized workflows
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Open source business process management suite built on Java and Eclipse
Turn processes into business applications with Bonita BPM Community Edition
Quickly connect people, data, and systems into organized workflows
Winner of BOSSIE, CODIE, OW2 and Gartner awards
http://p.sf.net/sfu/Bonitasoft
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