Question about the coordinate system

May I ask what coordinate system is used in the yolo programming assignment?
Is the y-axis up or down?
Contrary to Cartesian coordinate system?


I believe (0,0) is in the upper left corner.

For image processing, as Tom said, (0,0) is the top-left corner. In this course, you learned convolutions. Filter handling also starts from a top-left corner.
In old TVs, a scan line starts from a top-left, then scan pixels to the right most pixel. Then, move one pixel down, and scan from left to right. I suppose it was reasonable to start from the top-left for image processing.