MacBlend

Calibrate images containing a Macbeth ColorChecker directly in Blender.

MacBlend samples chart patches, calculates forward and inverse color transforms, creates compositor or shader nodes, and exports the results as .cube LUTs. It calculates the $3 \times 3$ matrix that best conforms the sampled input to a specified color-space gamut or to a chart sampled from another image.

Requirements

• Blender 4.2 or newer
• A source image containing a Macbeth chart
• Scene-linear source and target data
• Correct image input transforms (IDTs) in Blender

The image Color Space setting in the Image Editor sidebar must describe the image encoding. When Use reference values as target is enabled, the target gamut must match Blender's scene-linear working gamut after that input transform. MacBlend auto-detects supported working gamuts when a calibration source image is selected and shows the detection status below the target selector. When no explicit alias matches, it reports the failure and keeps Linear Rec. 709 selected as a manually overridable fallback.

Tutorial

1. Image Editor

Align the chart sampler with the chart in the image, set the patch sample size, and select Sample Chart.

Optionally repeat this process on a second image to create an image-to-image transform, such as matching camera A to camera B.

2. Compositor or Shader Editor

Select the sampled source image. Choose the reference-target gamut, configure normalization and separate exposure-node creation, name the transform, and select Forward or Inverse.

To use the second sampled image as the target, disable Use reference values as target and select that image. Select Export LUTs to write both transform directions as .cube files.

Method and limitations

MacBlend perspective-warps each patch footprint from rectified chart space, averages its RGB values, and uses a least-squares fit across all 24 patches to calculate one $3 \times 3$ matrix. Optional normalization uses the Neutral 5 patch to separate a global exposure scale from the matrix.

This is a linear approximation, not a general color grade or full camera characterization. It cannot reproduce gamma changes, tone curves, clipping, local adjustments, or hue-selective corrections. Results are most reliable with scene-linear, minimally processed, evenly exposed material. Built-in chart values are based on D65; substantial differences between the capture illuminant and D65 can increase error.

Installation

Install MacBlend from the Blender Extensions platform.

The simplest installation methods are:

1. Search for MacBlend in Blender's Edit > Preferences > Get Extensions view and select Install.
2. Open the Blender Extensions page in a browser and drag the install link onto a running Blender window.

If the Extensions platform is unavailable, download an extension ZIP from GitHub releases, then use Edit > Preferences > Get Extensions > Install from Disk.

Development checkouts can be launched directly with the Blender Development extension for VS Code.

Documentation

The user manual is available at manuelhouben.github.io/macblend. It covers IDTs and scene-linear data, chart sampling, matrix calculation, assumptions and limitations, node workflows, and LUT export.

Report bugs through the issue tracker. Include the Blender and MacBlend versions, image color-space settings, and reproduction steps.

License

MacBlend is licensed under the GNU General Public License v3.0 or later.

Acknowledgements

MacBlend owes much to Marco Meyer's mmColorTarget, Jed Smith's CalibrateMacbeth, and Paul Schlichter's Colour Chart Camera Matcher add-on.