This is a good introduction to local contrast:

Everything from this point on: this is my understanding, and could easily
be wrong - probably is, in parts.

I think coarseness of the local contrast is analogous to the radius of USM
described above. Contrast and detail are like amount, although I don't know
the exact inner workings.
I usually use the equalizer. It works like an audio equalizer. Lower
frequencies provide a low-resolution view of your image; boosting them will
increase local contrast (such as a dark cup will stand out more when placed
on a white table cloth). High frequencies are the details; boosting them
will sharpen the image (the individual pixels that form e.g. the edge
between a stand of fiber in the cloth or a fissure in the cup will stand
apart more from their neighbours). Playing with frequencies in between will
let you smooth skin without eliminating all detail like pores).
Local contrast, sharpen and equalizer always take into consideration the
surrounding pixels when determining how a given pixel should be modified.

Contrast, tone curve, base curve, zone system just check the values of an
individual pixel, without looking at its neighbours.
Base curve is in "RGB", in camera colour space, unless I'm mistaken. Each
channel is mapped individually, thus colour is affected: applying a steep
curve to a pixel with high red value and low blue will increase red and
decrease blue, making the colour more saturated (and shifting its hue?).
Tone curve operates in Lab, you adjust the L channel and darktable
auto-adjusts colour (a and b), unless you tell it you want to do it
Contrast applies a kind of centered tone curve.
The zone system tool is also like the tone curve, as far as I know.

I haven't had time to watch the videos in the open source photography
course, but I guess it covers most of these. Maybe Robert Hutton and others
have some useful and free videos, too.


On 19 Sep 2016 16:22, <> wrote:

On Mon, 19 Sep 2016 06:33:31 +0200
KOVÁCS István <> wrote:

>Please read the manual.

I did:

Much more versatility for contrast and brightness adjustment is
offered by the tone curve, levels, and zone system modules


Likewise you may adjust color saturation in a more detailed way with
the tone curve, color contrast, and color zones modules


This slider adjusts the image's contrast.

This slider adjusts the image's brightness.

This slider adjusts the color saturation.

Is there some table that compares the various multiple ways of doing
the same thing in DT?


darktable user mailing list
to unsubscribe send a mail to

darktable user mailing list
to unsubscribe send a mail to

Reply via email to