How is your image saved?
If you have e.g. matrix A with the pixel values for each (x,y) pair, and you want all the pixels above y = mx + c (i.e. y - m*x - c > 0) to be zero, then:
m = -1;
c = 1;
x = 0:0.01:1; % your x values
y = 0:0.01:1; % your y values
% logical matrix for each x/y pair
logical_matrix = false(length(x),length(y));
for i = 1:length(x) % for each x value
for j = 1:length(y) % for each y value
logical_matrix(i,j) = (y(j) - m*x(i) - c > 0);
end
end
% now set corresponding values in your A matrix to the desired value
A(logical_matrix) = 0;
You can of course do this more efficiently without for loops, but the exact form will depend on how you saved your matrix/object/whatever it is you have.
