Flood Fill using matlab

Question

I am new in MATLAB, I am trying to implement flood filling using this algorithm in matlab, I dont know what I did wrong may be I didnt used recursive function right, but still I dont whats going wrong and this code make my matlab close I am using the following code I am trying to debug it since morning but failed to find the problem

function [ colored_Image ] = floodFill( image, target_Loc_x, target_Loc_y, targetColor, replacementColor )
colored_Image = image;

if (target_Loc_x >= 1) && (target_Loc_x <= size(image,1)) && (target_Loc_y >= 1) && (target_Loc_y <= size(image,2))
    if image(target_Loc_x,target_Loc_y) == targetColor
        colored_Image(target_Loc_x,target_Loc_y) = replacementColor;
        colored_Image = floodFill(colored_Image,target_Loc_x ,target_Loc_y + 1, targetColor, replacementColor); 
        colored_Image = floodFill(colored_Image,target_Loc_x + 1,target_Loc_y, targetColor, replacementColor);
        colored_Image = floodFill(colored_Image,target_Loc_x,target_Loc_y - 1, targetColor, replacementColor);
        colored_Image = floodFill(colored_Image,target_Loc_x - 1,target_Loc_y, targetColor, replacementColor);
    end

end


end

calling this function using

image = floodFill(im,1,1,0,127);
imshow(image);

im is my matrix image of 200 by 200 I want my black color(0) to grey color(127), any help will be thankful

Answer 1

You are probably hitting Matlab's recursion limit. My computer doesn't crash, but generates this error:

Maximum recursion limit of 500 reached. Use set(0,'RecursionLimit',N) to change the limit. Be aware that exceeding your available stack space can crash MATLAB and/or your computer.

The way around this is to rewrite floodFill so it does not use recursion. There are some alternative algorithms on Wikipedia.

Also: aardvarkk's answer makes an important point about Matlab's column-major indexing. You can fix your function by swapping all x and y variables.

Answer 2

I believe there are two things wrong with this:

a) You appear to be indexing the image matrix in the order (x,y). MATLAB matrices are in column order, so you have to (unintuitively) index them in the order (y,x). So the line:

image(target_Loc_x,target_Loc_y)

should probably be:

image(target_Loc_y,target_Loc_x)

Same goes for when you set the value in the colored image. Note also that size(image,1) will give the size in the y direction, not x!

b) You're using a recursive function to do a very simple operation. It very quickly hits MATLAB's recursion limit. In a 200x200 image, you'll have a stack of calls 40,000 deep, and MATLAB only allows a recursion limit of 500 by default. Why not try something like this instead:

colored_image = image;
colored_image(colored_image == targetColor) = replacementColor;