Re^3: Perl Image Analysis

Yes, this is looking more promising. The triplet values were not as useful as hoped for. I tried to use the getsamples() method to sample just one pixel, however, and the results were like:


巷褘『檄噙橙姍~蟋禿w
U=9dy菽苠I*\ZGp諞
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I'm not sure how to compare those values to each other... My code to do this was as follows:

###
#it appears there may actually be a way to read the grey channel
#using the "getsamples" routine
my $ycoord = 5;
my $xcoord = 5;
my $sample = $img->getsamples(y => $ycoord, x => $xcoord);
print "we sampled 5,5 to have a value of $sample\n";
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I tried sampling two different points that I knew to be quite different by this method, which is how I got those two odd strings above. I'll have to look further into the Perldocs for Imager, it appears :)

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Re^4: Perl Image Analysis
by tonyc (Friar) on Oct 06, 2006 at 01:10 UTC

getsamples() uses the context you call it in to decide whether to produce samples packed into a string or a list of samples
if you don't supply a width getsamples() returns samples from the given x position all the way to the right side of the image.

my ($sample) = $image->getsamples(x => $x, y => $y, width => 1);
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for my $y ( 0 .. $image->getheight() - 1 ) {
  for my $sample ($image->getsamples(y => $y)) {
    # do something with the sample
  }
}
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Re^5: Perl Image Analysis

by lparsons42 (Novice) on Oct 06, 2006 at 18:58 UTC

this site

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Re^6: Perl Image Analysis

by BrowserUk (Patriarch) on Oct 06, 2006 at 20:05 UTC

I loaded the image using Opera and used it's zoom function to blow the image up 1000%. It is then fairly obvious that the "white" area immediately surrounding the black squares is full of slightly off-white pixels, including #f2f2f2, #f1f1f1, #ededed, #f6f6f6, #f5f5f5, etc. This is probably an artifact of the JPEG 'lossy' compression system, though it could also be an artifact of the drawing program you used to constuct it.

Update: Actually, looking at it again (looking at my lcd from an oblique angle), the black isn't entirely black either. bThere are several pixels in both squares that are variously #0f0f0f, #030303, #0c0c0c etc.

Redo your image using the non-lossy .png or .tiff formats. If the artifacts go away, it was the JPEG compression biting you. If they don't, it is your drawing program that may be attempting to antialias something. Either look for a configuration option to turn that off or use a 'dumb' graphics editor (like mspaint.exe) that doesn't attempt to do anything clever :) (The had to be some advantage to paint didn't there :)

Also, be wary of what program you use to zoom the image. For example, Ifranview will resample the image as you zoom it unless you explicitly turn that option (view->properties->view->Use resample) off. This results in the edges of the squares getting antialiased, and the corners getting rounded as the image is zoomed.

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

Lingua non convalesco, consenesco et abolesco. -- Rule 1 has a caveat! -- Who broke the cabal?

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

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Re^7: Perl Image Analysis

by lparsons42 (Novice) on Oct 06, 2006 at 21:14 UTC

Re^8: Perl Image Analysis

by BrowserUk (Patriarch) on Oct 06, 2006 at 21:36 UTC

Some notes below your chosen depth have not been shown here

Re^6: Perl Image Analysis

by grep (Monsignor) on Oct 06, 2006 at 20:22 UTC

identify -verbose identify -verbose artificial_black_n_white.jpg


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