"y-direction of the coordinate system should be reverted"

I m kinda confused with this statement in matlab

I m trying to get x,y coordinat of and image, and someone told me that:

"y-direction of the coordinate system should be reverted"

Anyone can help me with this? ty so much

[Adam Danz]

> I m trying to get x,y coordinate of and image

Does this mean you are indexing an image array and you'd like to vertically flip the image array or does that mean you want to verticallly flip the image?

Answer 1

[Nathan Hardenberg]

Normally the coordinate system starts at the top left of the image. Right is the positive x-axis and down is the positive y-axis. So the pixel in the top left would be (0,0) or (1,1) in MATLAB

Mabe this illustration helps:

Source: https://knowthecode.io/labs/basics-of-digitizing-data/episode-14

Answer 2

[Steven Lord]

Images and "regular" plots have different conventions for whether the Y axis should be increasing or decreasing as you move towards the bottom of the page or screen. You can use the axis function to switch between the conventions, specifying 'ij' as the ydirection input argument to put the origin in the upper-left corner rather than the lower-left.

figure
plot(1:10)
title('image xy')

figure
plot(1:10)
axis ij
title('image ij')