Color LCH Blend Mode for Colorizing in GIMP

This article explains the role and functionality of the Color (LCH) blend mode in GIMP when performing neutral colorizing on images. By utilizing the perceptually uniform LCH (Lightness, Chroma, Hue) color space, this blend mode allows users to tint or recolor grayscale and desaturated layers while preserving natural perceived brightness, preventing tone distortion, and delivering realistic colorization results.

Understanding the LCH Color Model

The Color (LCH) blend mode is based on the CIE LCH color space, which separates an image into three distinct components:

  • Lightness (L): Represents the perceptual brightness of a color, matching how human vision perceives light and dark.
  • Chroma (C): Represents the saturation or color intensity.
  • Hue (H): Represents the actual color family (e.g., red, green, blue).

Unlike traditional RGB or HSV color models, LCH is designed to be perceptually uniform. This means a change in color or saturation does not inadvertently change the perceived lightness of a pixel.

Function of Color (LCH) in Neutral Colorizing

When applied in GIMP, the Color (LCH) blend mode transfers the Hue and Chroma of the blend (top) layer to the base (bottom) layer, while completely preserving the Lightness values of the base layer.

In the context of neutral colorizing—such as tinting black-and-white photos, applying sepia tones, or balancing color casts:

  1. Maintains True Luminance: Traditional color blend modes often artificially brighten or darken specific colors (like yellow appearing brighter and blue appearing darker). Color (LCH) ensures that the target layer’s original contrast and exposure remain intact regardless of the applied hue.
  2. Eliminates Hue Shifts: When tinting neutral or desaturated areas, standard blend modes can introduce clipping or oversaturation in midtones. Color (LCH) applies a uniform tone smoothly across the entire tonal range.
  3. Preserves Shadow and Highlight Detail: Because the underlying lightness channel is preserved linearly, fine textures, deep shadows, and delicate highlights do not lose definition when new colors are introduced.

How to Use Color (LCH) for Colorizing in GIMP

  1. Open a grayscale or desaturated image in GIMP.
  2. Create a new transparent layer above the base image.
  3. Fill the new layer with the desired neutral tint or color (e.g., a subtle warm brown for sepia or a cool slate for cyanotype effects).
  4. In the Layers panel, change the Mode dropdown menu to Color (LCH) (located under the Color group).
  5. Adjust the layer Opacity to fine-tune the intensity of the colorization.