Sorting image colours by RGB in descending order

colour_sort.py

# Processing 3.0.1 Python mode
# Original artist: https://medium.com/@GroundTruth/in-living-color-antarctica-s-vibrant-wildlife-under-the-sea-54ee6f09d662#.maye8r6ws
'''Sorts an image by rgb colour and draws them in gradient'''

bar_width = 50
w = 1980
h = 1366

def setup():
    size(1980, 1366)
    img = loadImage('test.png')
    px = []

    image(img, bar_width + 3, 0)

    for x in range(img.width):
        for y in range(img.height):
            c = img.get(x, y)
            px.append((red(c), green(c), blue(c)))
            
    px.sort(reverse=True)
    
    total = img.width * img.height
    for i in range(total):
        c = color(*px[i])
        ti = i / float(total) * h
        stroke(c)
        line(0, ti, 50, ti)
        
    noLoop()
        
def draw():
    pass