对Canny边缘检测器的一个有趣的优化(2)

So now that we dropped the dependency tolibmand theatan2()call, let's do something even better.

We are still using floating point operations here, which is kind of a problem (for performances, and for architecture independent testing at least). Let's try to make some integer arithmetic instead.

several named ranges can be defined. a named range can represent multiple blocks of cells.。there should be no missing values in the range defined. otherwise, you get the error message shown in figure 156.。sumif function this function adds the values in a range if the cell with the value satisfies a user-defined criterion.。

This range is quite small, and multiplying these values by1<<16will largely fit in an integer, so it should be safe to use 16-bit arithmetic.

Instead of comparingGyagainst:

...like we did previously, let's do the comparison betweenGyx(1<<16)and:

The rounded values for these constants are:

These values will be multiplied toGx, and1020 x 158218fits into a 32-bit integer so it's still OK. Following, the optimized version:

We should now have a way faster version than our first naive implementation.

Following is a naivetimebenchmark, on a i7 Intel CPU, and usinggcc -O3:

Runnaiveno atan2integer

0.257

0.032

0.025

0.251

0.032

0.029

0.255

0.029

0.027

As usual, performances depend on a lot of various other parameters, but it looks like it was worth the effort since it's almost 10 times faster (and now bit exact).

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已翻译对Canny边缘检测器的一个有趣的优化

2017-09-2081126

翻译作者

nunu1234

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