(Matlab) Performance of Gaussian filtering using imfilter on a binary image

Question

I am currently coding a program to keep track of a running fly in a small chamber, what I want is XY-coordinates of the center of the fly. For this I first filter each frame wit

Answer 1

It might be that the smoothing part is unnecessary, a simple thresholding of your image leads to a pretty clear identification of the fly:

f=rgb2gray(imread('frame.png'));
BW=f>30;
props=regionprops(BW, 'BoundingBox');
imshow(f)
rectangle('Position',props.BoundingBox, 'LineWidth',2, 'EdgeColor','b');

Result:

To answer your question about fast smoothing, you could use FFT-based low-pass filtering instead of a moving gaussian to smoothen your frames much faster. Example for one frame (the mask needs only to be done once):

f=rgb2gray(imread('frame.png'));
D=30;
[x,y]=size(f);

%Generating a disc-shaped binary mask with radius D:

Mask = fspecial('disk',D)==0;
Mask = ~imresize(padarray(Mask, [floor((x/2)-D) floor((y/2)-D)], 1, 'both'), [x y]);

% (Apply this to all the frames:)

MaskedFFT=fftshift(fft2(f));.*Mask;
Filteredf=abs(ifft2(MaskedFFT));

Result:

Original (f)

Filtered (Filteredf)