I'm not getting any speed gain with this method, for 'real' image. Not sure, why to expect this gain, if instead of matching for sequence of non-zero bytes we just trying to match for non-zero byte followed by sequence of zeroes? And there's additional work to do: xor-ing, chopping, etc.

Plus, what if object "32" happens to be in 1st column?

$s = join '', map { chr } qw/ 32 0 1 1 0 0 2/;
$t = ' ' . $s ^ $s;
chop $t;
while ( $t =~ m[[^\0]\0*]g ) {
    printf "%d\t%d\t%d\n", ord( substr $s, $-[0], 1 ), $-[0], $+[0] - 
+1;
}

[download]

It looks we have to prepend a zero byte (because, it seems, original eily's solution was strictly for alphabetical strings). Then speed drops below that of "buk3" - loop spends lot of time finding bbox of background. Inserting "next unless $c", leads to, again, the same performance as "buk3".

Well, for now, "buk3"'s speed is "good enough" (amazingly good compared to 'elegant' PDL-only solution), thank you everyone who contributed.

In reply to Re^5: Faster regex to split a string into runs of similar characters? by vr
in thread Faster regex to split a string into runs of similar characters? by BrowserUk

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.