I'm currently working on a piece of code which prepares an image for thresholding, although there seems to be a mismatch between the output image and the pixel data which is returned.
I'll talk you through the code. First, I define the function which takes three parameters - IMAGE, the image that will be thresholded; r the radius which defines a neighbourhood around a central pixel, from which pixel data can be calculated; and k, the 'kernel' which determines the detail of the thresholding.
function [t] = imadaptive ( IMAGE, r, k )
I then call functions I've previously defined, which create images in which the mean and standard deviation of each pixel is stored:
meanpic = immean (IMAGE, r);
stdpic = imstd (IMAGE, r);
Next, I create a new image t, where each pixel has an intensity of 0. This will be used to store the appropriate thresholding values for each pixel:
t = zeros(size(IMAGE));
I then work out the size of the image to tell the for-loop when to stop:
[nx, ny] = size(IMAGE);
Next, I start the for-loop and run a series of if-statements to stop the program from trying to inspect pixel values in positions like (-2,-2):
if x-r <= 0
startx = 1;
else
startx = x-r;
end
if x+r > nx
endx = nx;
else
endx = x+r;
end
if y-r <= 0
starty = 1;
else
starty = y-r;
end
if y+r > ny
endy = ny;
else
endy = y+r;
end
Finally, I run the code to work out the work out the appropriate threshold values for each pixel and then add that value to the image t:
R = 128;
for xp = startx : endx
for yp = starty : endy
if (x-xp)^2 + (y-yp)^2 <= r^2
thresh = meanpic(xp,yp) * (1 + (k * (((stdpic(xp,yp) / R) - 1))));
end
end
end
t(x,y) = thresh;
The problem is: when I run this code, I get an image identical to my stdpic: the picture which shows the standard deviation values of each image. I can't figure out why this is, though. The equation seems to be correct - and when I remove the ; from the equation, I see that the values it outputs are very varied and between 0 and 255, so the output image t should look wildly different.
Can anyone point out what I've got wrong here?
The thresh is reassigned each time through the loop. Thus only one pixel in the neighborhood contributes to each output pixel. If changing thresh doesn't help, would you please post the whole file here or on pastebin? The walkthrough format is very useful, but it's always possible the bug is in the code not shown.
Edit: at lines 163-165 of the paste, change uint8to double. At line 211, add code to use a pixel count or something similar. I think the division by R is happening in uint and truncating to zero. Change back to uint at the very end, after the math, or else imshow won't give you the results you expect. Hope this helps!