How to decrease the computation time of this code? - matlab

Question

I am working on computing some features of an image data set and saving the features for later use. Below is the code:
tic
l = 9907 % size of image data set
% pre-allocating space for variables in the for loop
Icolor = cell(1,l);
Iwave = cell(1,l);
IglrlFeatures = cell(1,l);
for i = 1:l % l = size of image data set = 9907
IDB{1,i} = imread(strcat(path,strcat(num2str(i),'.jpg')));
Icolor{1,i} = colorMoments(IDB{1,i}); % 6-features in each cell
Iwave{1,i} = waveletTransform(IDB{1,i}); % 8-features in each cell
IglrlFeatures{1,i} = textureFeatures(IDB{1,i}); % 44-features in each cell
ICW{1,i} = [Icolor{1,i} Iwave{1,i} IglrlFeatures{1,i}];
end
toc
Here the computation time for each function on single image is:
colorMoments(single_image) = Elapsed time is 0.009689 seconds.
waveletTransform(single_image) = Elapsed time is 0.018069 seconds.
textureFeatures(single_image) = Elapsed time is 0.022902 seconds.
l = data set size = 9907 images
Computational times for different data set sizes (l):
l = 10; Elapsed time is 0.402629 seconds.
l = 100; Elapsed time is 2.233971 seconds.
l = 1000; Elapsed time is 21.178395 seconds.
l = 2000; Elapsed time is 44.510071 seconds.
l = 5000; Elapsed time is 111.393866 seconds.
l = 9907; Elapsed time is 238.924998 seconds. approximately (~4 mins)
I want to decrease this computational time, any suggestions?
Thanks,
Gopi

Answer 1

The measured times seem to indicate computational complexity of order O(n). I doubt that the order can be reduced further for this type of problem. So, I believe that, at best, we can only hope for a linear increase in performance.
One thing you should look into is whether the code is using multiple processor cores. If not, try restructuring the for-loop to be able to use parfor instead.