Local Adjustments

Local adjustments - Lab

Author : Jacques Desmis (12 september 2020)

Introduction

Local editing in RawTherapee is based on RT-spots, which are similar in principle to the U-Point concept originally used in Nikon Capture NX2 © and subsequently in the Nik Collection ©, DxO PhotoLab © and Capture NXD ©. RT-spots use algorithms developed specifically for RawTherapee by Jacques Desmis.

This approach is completely different to the more familiar local editing methods used in applications such as the GIMP, Photoshop © etc., which primarily use selection tools such as lassos, magic wands etc., associated with brushes, layers and blend masks. These methods can be time consuming and difficult to use accurately when complex shapes are involved.

An RT-spot consists of either an ellipse or a rectangle with a variable-diameter spot at the center. The shapes have four control points, which can be adjusted independently or symmetrically, and future developments will provide enhanced shape manipulation.

The RT-spot algorithm uses shape detection based on ΔE (the change in the visual perception of two given colours) to select the parts of the image to be modified inside the ellipse or rectangle . The extent to which these modifications are applied can be finely controlled allowing for very precise selections. Further refinement is possible with additional parametric masks but the shape-detection algorithms should be sufficient for the vast majority of local editing requirements. RT-spots can also be used to exclude the algorithm from influencing certain parts of the image . The modifications that can be carried out are extensive and incorporate most of the functions available in RawTherapee’s global adjustment tools along with some additional tools available only in the Local Adjustment tab.

The tools are grouped in the following modules:

Getting start

Activating local adjustments

• In the tab bar, select the "hand" icon (Local Adjustments tab)
• Turn on the "Local Adjustments" power button (if it is not already activated) and expand the "Settings” module.
• Select "Add"

Original

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