Vijay Pandurangan writes about his visualization of movie posters since 1914:

I first made a unified view of colour trends in movie posters since 1914. Ignoring black and white colours, I generated a horizontal strip of hues in HSL. The width of each hue represents the amount of that hue across all images for that year, and the saturation and lighting were the weighted average for all matching pixels. Since HSL has a fixed order, comparisons can be made between years visually.