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Feature #10026

Background color of "Tone curve" (LAB)

Added by Rudolf Martin almost 6 years ago. Updated almost 6 years ago.

Status:
New
Priority:
Low
Assignee:
-
Category:
Darkroom
Target version:
-
Start date:
07/28/2014
Due date:
% Done:

0%

Estimated time:
Affected Version:
1.4
System:
Ubuntu
bitness:
64-bit
hardware architecture:
amd64/x86

Description

I'm new to dt and very interested in "Mastering color with Lab tone curves". I read the post[[http://www.darktable.org/2012/02/mastering-color-with-lab-tone-curves/]] and the recommended book “Photoshop LAB color: The Canyon Conundrum” by Dan Margulis.

Now I'm puzzled about the background colors of the tone curves in dt.

Dan Margulis shows something like
This is a good help. When you draw the curve to the red corner, the image becomes red. The same with green.

Another helpful background is and by Galileopress.

But dt shoes:
This background colors don't help.

IMHO the background in dt should be rotated by 90 degree.

Another good point would be the indication of black and white corners of the L-curve. Something like

History

#1 Updated by Rudolf Martin almost 6 years ago

Another improvement would be:
- userdefined presets for the grid, eg. 10 percent intervals - good to have
- switching the colors in channel a and b (can be done in Photoshop)- not important

#2 Updated by Rudolf Martin almost 6 years ago

Forget my proposal to rotate the background. This don't help.

The manual of dt says:

The horizontal line represents the color channel value of the input image pixels.
The vertical line represents the color channel value of the output image pixels.

So there should be the whole range from green(-128) to red/magenta (+127) at the bottom and at the left side of the diagramm. With this you can visual check the output color.

The graph for the colorpicker should start at the bottom (input), then vertical to the curveline, then horizontal to the left side (output).

Example for a-channel: together with a grid of 10 percent and accentuated centerlines.

Example for b-channel:

#3 Updated by Rudolf Martin almost 6 years ago

In the L-channel a value of zero is absolutely black and 100 absolutely white. So there should be the whole range from black(0) to white(100) at the bottom and at the left side of the diagramm.

Example for L-channel:

#4 Updated by Rudolf Martin almost 6 years ago

A better color gradiant of the a-channel is "green-gray-magenta".
A better color gradiant of the b-channel is "blue-gray-yellow".

Examples:

Together with a diagonal as initial position. So you can see at once whether your curve is higher or lower than the origin.

#5 Updated by Rudolf Martin almost 6 years ago

Another non-sophisticated way is to show only the gradiant of input(bottom) and output(left side). That's similar to photoshop, but with usage of colors instead of black and white.

Examples:

The graph for the color-picker(gray) should describe an angle from bottom to curve(white) to left side.
Example:

#6 Updated by Jochem Kossen almost 6 years ago

I like some of the ideas presented here, it makes that i have to think less about what changes to the curves are going to do to my images. The suggestion in #5 seems to be similar to what Rawtherapee has.

#7 Updated by Rudolf Martin almost 6 years ago

Another example (including color numbers) for comparison:

The gradiant for the L-channel seems not to be correct. It should be black to white (not gray) at the bottom and left side.

Also available in: Atom PDF

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