maxWidthHeight:: grayscale::
srcCanvas
(R + G + B) / 3
R/4 + G/2 + B/4 // Y(CgCo)
0.299*R+0.587*G+0.114*B // BT.601
0.2126*R+0.7152*G+0.0722*B // BT.709
(max(R,G,B)+min(R,G,B))/2// HSL
max(R,G,B) // HSV
CIEXYZ([R,G,B])[1]