From: Timothy Hunter <cyclists@...>
Date: 2005-08-30T08:41:23+09:00
Subject: Re: rmagick question

Joe Van Dyk wrote:
>>Doing a 10000x10 pixel image (only 10 pixels high for unit testing
>>purposes), I could process:
>>
>>13k pixels/second with the bitshifting approach (and 16 bit IM)
>>13k pixels/second with the array lookup approach (and 16 bit IM)
>>21k pixels/second with 256 bit IM.
>>
>>I also found that building up an array of colors for one row and then
>>doing a @image.import_pixels had no speed improvements and the code
>>was uglier.
> 
> 
> Hm... I don't think that those pixels/second numbers are correct.  I
> was doing the timings inside a Benchmark.measure { ... } block and
> perhaps that makes things slower?
> 
> I was able to process a 8700x6000 pixel image when using 'time ./script.rb'
> 440.005u 9.917s 8:27.20 88.7%       0+0k 0+0io 52012pf+0w
> 
> So, around 7 minutes for 5 million pixels.. that's around 118000
> pixels per second.  Hm.  Oh well, it's fast enough for me.  This
> operation isn't done all that often.   Although, a while ago I did
> something like this in C with the GD library, and it took around 10-20
> seconds to process a similar sized image.
> 

I'm not surprised that the 256-color IM is the fastest solution. I'm 
also not surprised that a pure-C solution is faster than a Ruby 
solution. All those channel values have to be converted from integers to 
Fixnums and back to integers, not to mention constructing 5M 
Magick::Pixel objects.

Thanks for sharing what you learned. This'll be useful for the next guy 
to face a similar problem.