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kinor
Posts:
181
Registered:
11/19/09


Re: speeding up assigning values to a matrix
Posted:
Apr 8, 2013 3:52 AM


"Luca " <l.presottoRE@MOVE.campus.unimib.NOTit> wrote in message <kjmuap$gaq$1@newscl01ah.mathworks.com>... > I do not understand what you are saying. > What does it mean "there is a way which is slower than" ? Is it a question for me to find a slower way? > Now... > I tried a lot of different operations and I discovered that it is extremely slow to do > A=(mask==num)*255; (1) > (casting or not num to uint8 changes less than 0.1%) > > I found it insted to be very fast, acceptably for my scope, to do > A= uint8(mask==num)*uint8(255); (2) > > the difference between the (1) and (2) is 300ms for the first one and 15ms for the second one!!! > A factor 20. > Very curious indeed. > > That works for now. > (still wondering wether I can use logical indexing to do something like: > aa = (mask==num); > maskC(aa,1)= 250; > and get the best performances of "vectorialized" matlab)
Hi Luca
i wanted to say there is a way of logical indexing which is not faster lately this version was slightly faster than all others i tested:
tic t = uint8(cat(4,(mask==uint8(2)),(mask==uint8(4)),(mask==uint8(6)))) * uint8(255); toc
best kinor



