Reset value of pixels of side of imagine line.

Hi.

I have two known coordinates in a colorful image. I wanna reset value of pixels in one side of the line. for more clarifying, I've shown my process in following picture.

any help would be appreciated.

Answer 1

[Walter Roberson]

You can use the coordinates to get slope and intercept of the dividing line. From there you could work row by row zeroing out the pixels to the right of where the slope meets the row; or you could vectorize it all using ndgrid or meshgrid on indexing matrices...

[Y, X] = ndgrid(1:size(YourIm,1), 1:size(YourIm,2));
NewIm = YourIm;
NewIm(repmat(Y < m*X+b,1,1,3)) = 0;  %the repmat duplicates the 2D mask into all bit planes

If you have a sufficiently new MATLAB, R2016b or later, you can do it without the ndgrid:

Y = (1:size(YourIm,1)).';   %column vector
X = 1 : size(YourIm,2));    %row vector
NewIm( repmat(Y < m*X+b, 1, 1, 3) ) = 0;  %the repmat duplicates the 2D mask into all bit planes

[Amin Ghasemi]

Thanks, unfortunately I have 2016a :( btw could you give some hint y ndgrid command needs at all??!!

[Walter Roberson]

ndgrid() is the full vectorized method.

You can use calculations such as

NewIm = YourIm;
for X = 1 : size(YourIm,2))
  Y = m*X + b;
  NewIm(ceil(Y):end, X, :) = 0;
end

but that requires a loop. If you want to test each location in the image "simultaneously" then you need to create grids of indices.

[Amin Ghasemi]

thanks