Re: Row-wise vs. column-wise image processing

In article <1169724559.422594.10530@xxxxxxxxxxxxxxxxxxxxxxxxxxxx> mark_bluemel@xxxxxxxxx writes:
On 25 Jan, 11:00, Enrique Cruiz <jni6l03mdo6n...@xxxxxxxxxxx> wrote:
I am currently implementing a fairly simple algorithm. It scans a
grayscale image, and computes a pixel's new value as a function of its
original value. Two passes are made, first horizontally and second
vertically. The problem I have is that the vertical pass is 3 to 4
times slower than the horizontal, although the code is _exactly_ the
same in both cases?!
....
You are almost certainly right, and there's probably not a lot you can
do to change it with this processing style.
In your horizontal pass you can process a cache's worth of data at a
time before pulling the next cachefull. In the worst case, your
vertical pass could have a cache miss for each pixel accessed.

Indeed. Cache misses can give a huge loss of cycles.
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