Using PIL to find separator pages

Steve Holden steve at
Sat Jun 2 22:15:43 CEST 2007

Steve Holden wrote:
> Larry Bates wrote:
>> I think I've come up with something that will work.  I use PIL
>> Image.getcolors() to get colors and take the top 10 colors of my
>> background page.  I then calculate the average of the R, G, B
>> components.  That becomes my reference.  Then I read a page and
>> make the same calculation.  I then calculate the absolute value
>> of the difference of R, G, B of the two values.  Sum those
>> together gives something like the average difference between
>> the two average colors (at least that is what I think it does).
>> This seems to give me small numbers when the pages are the same
>> and large numbers when they are different.  It isn't super fast
>> but it is working.
>> Thanks for pushing me in the right direction.
>> -Larry
> Well done! Thanks for letting me know that the basic approach was correct.
> regards
>   Steve

Oh, by the way: instead of averaging over the *whole page*, now average 
over (say) eight samples each of 10 x 10 pixels or thereabouts. They 
should all be roughly the same, and they should all be close to the 
color of the separator color.

Seems to me (again, without bothering to actually write the code, which 
you are far more motivated to do than I anyway) that the much smaller 
amount of arithmetic will compensate for any loss in accuracy (which I 
surmise will anyway be trivial if the separator is something like DayGlo 
green or yellow).

Or maybe it's already running "fast enough", and you are already on to 
the next job?

Steve Holden        +1 571 484 6266   +1 800 494 3119
Holden Web LLC/Ltd 
Skype: holdenweb
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