Suggestion : Probing images and palette patches for modifying control points

[pierrelabreche]

Context
This suggestion is about the capability of using input and output images for creating control points on curves :

To make part of an image lighter or darker, shift-click on the input image to insert a new point on the curve corresponding to the brightness level at that point in the image. Then drag the new control point up to make that part of the image lighter or down to make it darker.
If nothing is happening when you click or shift-click on the input image, click on a blank part of the curve control to reset its probe.

It is also about the new Palette patches displayed in the main image area:

Palette Tool: a checkbox to let you display a copy of the palette color patches in the lower right corner of the main image area. For many transformations and controls, you can click or shift-click on one of these color patches and the effect will be the same as if you clicked or shift-clicked on that color in the image. You can use this feature, for example, to create new control points on curves or to set control points for selective color correction.

Need
The existing procedure by dragging a control point is not so easy to execute. A complementary procedure using the color probe would allow to define or reset control point for desired input and output values.

Suggestion
Allow users to define "input" and "output" colors or their components by using the probe for sampling. Sampling would be in addition to the existing dragging capability for defining the relationship between the input and the output. The following tasks would be doable by sampling, i.e. probing the input image, the output image, or the palette patches :

In curves, let X be a component value in the input image and let Y be the desired value in the output image:

• creating a a new control point, where X is sampled ( existing capability )
• resampling an existing control point to X on the input axis, while maintaining Y on the output axis ( new )
• resampling an existing control point to Y on the output axis, while maintaining X on the input axis ( new )

In a selective color correction, let A and B be a pair of hue-sat control points defining a color shift from A to B :

• Sampling a new control point A ( existing capability )
• Sampling a new control point B for completing the pair ( new )
• Resampling A in an A-B vector, while keeping B unchanged ( new )
• Resampling B in an A-B vector, while keeping A unchanged ( new )

User interface
Clicking variants ( right-left ) or Key presses ( Shift, Alt, Ctrl ) could define the desired sample assignment to input ( X or A ) or to output ( Y or B )

Affordance
To make this capability usable without knowing the clicking method, right-clicking on an existing control point could unfold a menu ( "sample input", "sample output" ) and the cursor would then change to a probe to sample the input image, the output image, or the palette patches.

[jsachs]

What problem is this trying to solve?

[pierrelabreche]

What problem is this trying to solve?

• User would have the option to assign the output value of a control point by sampling rather than by dragging. For example, in a hue curve, the output hue can be probed rather than guessed by trial and error using dragging. Another example is when creating the output hue-saturation in a selective color correction.
• In a curve transformation, the input or output coordinate of a control point can be sampled again using the probe without affecting the other coordinate. Useful, for example, If user accidentaly moved a curve control point's input or output.
• One hue-saturation control point of a pair can be probed again without affecting the other hue-sat control point. Useful, for example, If user accidentaly moved a selective color transformation control point.

[jsachs]

It turns out there is already a feature in the Selective Color Correction transformation that lets you do most of this. Shift-clicking on the palette displayed under the color wheel sets just the arrowhead of the current control point. This lets you match the color in the input image to any color in the palette, including colors sample from some other image. Or, for example, you can load a palette of skin tones and match to one of those.

I am still looking at Curve controls. Using various combinations of shift and ctrl (plain click and alt are not available) is just too confusing. I could add something to the Settings menu for the Curve control, but this is not really ideal, and there is no room to add more buttons. All in all, the benefit does not seem worth the added complication of the interface.

[pierrelabreche]

Suggestion for simplicity :

For consistency with selective color correction, when an existing point is selected on a curve, or just after a point has been created, Shift-clicking could set the point's target value ( Y axis ) without changing the input value ( X axis ).