The 50% algorithm is incorrect and, as other commentors note, basically only considers red.
The test colors are flawed, too; they are all completely saturated (or exactly grey). This means that even an incredibly naïve algorithm like the 50% one will always have contrast simply because both white and black always contrast against saturated colors — and because when r = g = b (grey) then it doesn’t matter if red is over-represented.
I really feel the article needs updated to reflect this. It’s that big a deal, and I think 24 Ways commands enough respect that readers expect/deserve a correction.
Alan Hogan
The 50% algorithm is incorrect and, as other commentors note, basically only considers red.
The test colors are flawed, too; they are all completely saturated (or exactly grey). This means that even an incredibly naïve algorithm like the 50% one will always have contrast simply because both white and black always contrast against saturated colors — and because when r = g = b (grey) then it doesn’t matter if red is over-represented.
I really feel the article needs updated to reflect this. It’s that big a deal, and I think 24 Ways commands enough respect that readers expect/deserve a correction.