HSM3 implements the Hasler and Süsstrunk M3 metric of image colourfulness (Hasler and Süsstrunck 2003).
The M3 metric is a linear combination of the mean and standard deviation of an opponent sRGB colour space defined by and
. The M3 metric is then calculated as
where
and
.
The interpretation of the metric is based on a category scaling experiment in which subjects rate the colourfulness attributes of images, with the following values of the M3 metric assigned to colourfulness attributes:
- not colourful = 0
- slightly colourful = 15
- moderately colourful = 33
- averagely colourful = 45
- quite colourful = 59
- highly colourful = 82
- extremely colourful = 109.
The only argument for HSM3 is x, which is an image loaded using imager::load.image.
To illustrate the function we can compare the colourfulness of the smoothed barcodes for the trailers to The Lego Batman Movie and John Wick: Chapter 3 - Parabellum.
The Lego Batman Movie
John Wick: Chapter 3 - Parabellum
The barcode of the trailer for The Lego Batman Movie has a colourfullness of 91.3, classing it as 'highly colourful,' whereas the trailer for John Wick: Chapter 3 has a colourfulness of 42.8, which is almost 'averagely colourful.'
Hasler, D. and Süsstrunk, S. E. (2003) Measuring colorfulness in natural images, Proc. IS&T/SPIE Electronic Imaging 2003: Human Vision and Electronic Imaging VIII (17 June 2003) 5007: 87-95. https://doi.org/10.1117/12.477378.