Problem with a slope

Hi,

Why does the slope result I get from these two points is opposite?

Code:

clc;
clear;
figure, imshow('pout.tif');
b1 = impoint(gca,[]);
b2 = impoint(gca,[]);

pos1 = getPosition(b1);
x1=pos1(1,1);
y1=pos1(1,2); 

pos2 = getPosition(b2);
x2=pos2(1,1);
y2=pos2(1,2); 

slope = (y2-y1)/(x2-x1);

plot([x1,x2 ],[y1,y2],'Color','r','LineWidth',2);

Answer 1

[Azzi Abdelmalek]

Maybe you should write

slope = ((y1-y2)/(x2-x1))

You can notice that the origin is not in the left bottom, but in the left top corner. check it with

x1
x2
y1
y2

[Image Analyst]

The direction can be changed with set(gca,'YDir','reverse'). Or maybe it already is since that's what imshow does. In that case, try set(gca,'YDir','normal').