3.19. Retinex
| 3. Color filters |

### 3.19. Retinex

Revision History
Revision $Revision: 1710 $ | 2006-11-12 | j.h

#### 3.19.1. Overview

Figure 16.60. “Retinex” example

Note new details in the upper right corner.

Retinex improves visual rendering of an image when lighting conditions are not good. While our eye can see colors correctly when light is low, cameras and video cams can't manage this well. The MSRCR (MultiScale Retinex with Color Restoration) algorithm, which is at the root of the Retinex filter, is inspired by the eye biological mecanisms to adapt itself to these conditions. Retinex stands for Retina + cortex.

Besides digital photography, Retinex algorithm is used to make the information in astronomical photos visible and detect, in medicine, poorly visible structures in X-rays or scanners.

#### 3.19.2. Activate the filter

You can find this filter through Filters → Colors → Retinex.

#### 3.19.3. Options

Figure 16.61. “Retinex” filter options

These options call for notions that only mathematicians can understand. In actual practice, user has to grope about for the best setting.

Level

  Here is what the plug-in author writes on his site (www-prima.inrialpes.fr/pelisson/MSRCR.php): “To characterize color variations and the lightor, we make a difference between (gaussian) filters responses at different scales. These parameters allow to specify how to allocate scale values between min scale (sigma 2.0) and max (sigma equal to the image size)”...

  - Uniform: FIXME

  - Low: FIXME

  - High: FIXME

Scale

  FIXME

Scale division

  FIXME

Dynamic

  As the MSR algorithm tends to make image lighter, this slider allows you to set color saturation.

3.18. Max RGB |  | 3.20. Semi-Flatten