Metamers – Visualizing Spectral Reflectance

As part of my ongoing book project States of Minds, I am looking for a way to visualize the concept of metamers (interactive demonstration) as well as how little we differentiate even within the light frequencies we can see (Interactive Color Booth of different illuminants).

I have previously written about this (Color Sensation – Why Red + Yellow is not Orange), but am still looking for ways to drive the point of metamers, light spectra, etc. forward via visualization, metaphor or the like.

The code is written in python and quite loosely based on ColorPy by Mark Kness. You can find the complete python code for this project here: ReflectanceViz-0.7.tar.gz.

It now also features a genetic algorithm for finding metamers, and can visualize these properly.

The Setup

As light sources I used:

  1. Fluorescent(like neon tubes)
  2. High Pressure Sodium Vapor(often used in industrial and outdoor applications)
  3. Incandescent(a classical filament light bulb)
  4. Compact Triphosphorus bulb (many energy saving bulbs)
  5. Sunlight
  6. White RGB LED lamp

All light sources are calibrated in such a way that their apparent brightness to a human observer is the same. Any differences in the brightness of reflected materials is due to spectral absorbtion.

Comparison of ColorChecker materials under different illuminants

Simulation of selected ColorCheck squares under different Illuminants (compared to sunlight). CC-BY Jonas Tullus"

Spectral Reflectance of an Apple






Spectral Reflectance of Blue Boots






Pink Fabric






The Light Sources






Resources:

This is part of the stream Programming – find previous and follow-up posts there.

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