if there is an object (say a line) in an image, how to find the xy coordinates of each pixel that makes the line?

The XY coordinate values of each pixel of the red line. Such that I can trace the line. Thank you.

Answer 1

[Walter Roberson]

Convert to grayscale. Threshold to select the part that is not as bright -- the brightest part will be the white background. Now you can regionprops() and ask it to return PixelList . (Or you might want to consider using bwboundaries or bwtraceboundary. Or you might want to bwmorph() to extract the skeleton and then ask for those pixels...