According to the user on that site "alzayani": sort an array of all 16777216 image positions (x,y) randomly loop the positions array and for each position: r

According to the user on that site "alzayani": sort an array of all 16777216 image positions (x,y) randomly loop the positions array and for each position: read the pixel color at the position as a reference sample N random colors from the available colors list for each sample calculate the hypotenuse from the reference color Math.hypot(R - r, G - g, B - b). find the nearst color, use it for that position in the output image update the list of avalible colors (for practicality in chunks)