How to instead the "for" loop?
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Hello, I had a program which use for loop and if, but it take a long time, I want it faster.
How Can I instead of "for" and "if" so that it can make the program become faster?
Here is the program, Thanks
tic
clear all
close all
mov = mmreader('02.avi');
for i = 1: 7111 % number of the frame of the video
frame1 = read(mov, i);
if i == 750
for a = 300 :2: 303;
for b = 353 :2: 381;
for c = 301 :2: 303;
for d = 354 :2: 381;
frame1(a,b,:) = [0,0,0];
frame1(c,d,:) = [0,0,0];
end
end
end
end
for a = 300 :2: 303;
for b = 354 :2: 381;
for c = 301 :2: 303;
for d = 353 :2: 381;
frame1(a,b,:) = [153,153,153];
frame1(c,d,:) = [153,153,153];
end
end
end
end
end
if i == 760
for a = 300 :2: 303;
for b = 356 :2: 385;
for c = 301 :2: 303;
for d = 357 :2: 385;
frame1(a,b,:) = [153,153,153];
frame1(c,d,:) = [153,153,153];
end
end
end
end
for a = 300 :2: 303;
for b = 357 :2: 385;
for c = 301 :2: 303;
for d = 356 :2: 385;
frame1(a,b,:) = [0,0,0];
frame1(c,d,:) = [0,0,0];
end
end
end
end
end
for x = 1 : 478;
for y = 1 : 640;
if frame1(x,y,1) == frame1(x,y,2) && frame1(x,y,2) == frame1(x,y,3) && frame1(x+1,y,1) == frame1(x+1,y,2) && frame1(x+1,y,2) == frame1(x+1,y,3) && frame1(x+2,y,1) == frame1(x+2,y,2) && frame1(x+2,y,2) == frame1(x+2,y,3)
figure; imagesc(frame1);
title(['Frame ', num2str(i)])
xlabel('x-axis');
ylabel('y-axis');
coordinate = [x y]
frame1 = read(mov, i+1);
end
end
end
end
toc
Thanks
回答（1 个）
Richard Brown
2012-4-24
Un-nest your loops - your a,b and c,d loops are independent of each other. What you're doing is running your inner two loops gazillions of times more than you need to. I.e. replace your four-level loops with these:
for a = ...
for b = ...
frame1(a, b, :) =...
end
end
for c = ...
for d = ...
frame1(c, d, :) =...
end
end
3 个评论
Walter Roberson
2012-4-24
And your code
for c = 301 :2: 303;
for d = 354 :2: 381;
frame1(c,d,:) = [0,0,0];
end
end
can be replaced by
frame1(301 :2: 303,354 :2: 381,:) = 0;
with no loop at all.
Peony Lai
2012-4-24
Peony Lai
2012-4-24
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