ImageData:getPixel
Gets the color of a pixel at a specific position in the image.

Valid x and y values start at 0 and go up to image width and height minus 1. Non-integer values are floored.

In versions prior to 11.0, color component values were within the range of 0 to 255 instead of 0 to 1.
r, g, b, a = ImageData:getPixel( x, y )
x number The position of the pixel on the x-axis.
y number The position of the pixel on the y-axis.
r number The red component (0-1).
g number The green component (0-1).
b number The blue component (0-1).
a number The alpha component (0-1).