In PHP, imagepng() accepts a filter parameter. How do these filters affect the function's output?

Posted by Joe Lencioni on Stack Overflow See other posts from Stack Overflow or by Joe Lencioni
Published on 2010-06-15T19:32:30Z Indexed on 2010/06/15 19:52 UTC
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php

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image

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png

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gdlib

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php-gd

How do these filters affect the output of imagepng() in PHP?

PNG_NO_FILTER
PNG_FILTER_NONE
PNG_FILTER_SUB
PNG_FILTER_UP
PNG_FILTER_AVG
PNG_FILTER_PAETH
PNG_ALL_FILTERS

The documentation simply says, "A special PNG filter, used by the imagepng() function" for each of them.

It seems that using PNG_NO_FILTER will reduce the filesize of the output, but other than that, I am unsure as to how it is affected. Any insight would be really appreciated.

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