The illustration of the ellipse parameters.

(a) The raw image of the fish head region; (b) (x_o,y_o) denotes the extreme point and the violet color shows the grayscale distribution of the extreme point region. Variables length, width and represent the long axis, short axis and angle of the fitted ellipse respectively; (c) The variable contrast in the direction of the z-axis represents the contrast change of the ellipse and its surrounding region.