Image comparison

[wolves]

someone knows how to compare one image to another one?
like

how many percent dog.gif is equal to dog1.gif ?

tks

[shocker-z]

huh??  ???

you mean like size of image or what?

Regards
Liam

[FrOzeN]

I *think* he means go through them pixel by pixel and adding one to a counter for every (x, y) pixel that corresponds to the other image. Then produce a percentage of pixels that match to the total of pixels in the image.

I haven't worked with images in php yet, so I'm not sure the code you would use, but the above would be the concept.

[wolves]

[quote author=FrOzeN link=topic=109181.msg439944#msg439944 date=1159022622]
I *think* he means go through them pixel by pixel and adding one to a counter for every (x, y) pixel that corresponds to the other image. Then produce a percentage of pixels that match to the total of pixels in the image.
[/quote]

yes, I think that this is the idea.

someone knows a script for it? tks

[Orio]

[code]<?php

if(imagesx($pic1)==imagesx($pic2) && imagesy($pic1)==imagesy($pic2))
{
echo("Equal");
}

?>[/code]

Something like this??

Orio.

[wolves]

image 1 has 4 squares and 2 circles
image 2 has 3 circles and 4 triangle
image 3 has 3 oval formas and 3 squares

so image 1 seems more to image 3 of image 2


 

[AndyB]

[quote author=wolves link=topic=109181.msg440106#msg440106 date=1159048916]
so image 1 seems more to image 3 of image 2
[/quote]

To a human, yes.  Comparing one image to another pixel by pixel assigns no relevance to the shapes made by all the pixels or their relative spatial arrangement.  For example: I have an image with four large squares in a row, and another image that's a copy of the first but half the width and half the size.  To a human those have some degree of 'match'. On a pixel-by-pixel basis those probably don't match at all.

[wolves]

[code]
those probably don't match at all.
[/code]
ok but, the image seem more with for large squares of another image with 6 small circles ?

[AndyB]

[quote author=wolves link=topic=109181.msg440111#msg440111 date=1159049540]
[code]
those probably don't match at all.
[/code]
ok but, the image seem more with for large squares of another image with 6 small circles ?
[/quote]

'Seem' is the human intuitive analysis result.  A php script in entirely logical, i.e. non-intuitive.  Here's another example. Image 1 is a coin; image 2 is the same image rotated 1 degree.  Human says they're the same, computer says they're different.  I don't know what you're trying/hoping to do, but it isn't going to happen with a logical language.

[wolves]

"Seem" sorry but english is not my native language so it is bad :(

ok I will put my problem..

I need to analyze images of pieces of wood, small pieces but good resolution

Im my database there are lots of diferent images

Now, I have a new image, so I have to compare to the others to see if I have this one or not.

Why not a script that look the all the images and return me some images that looks like to my image
not a perfect comparaison, but a aproximate

[Barand]

This will do a pixel-by-pixel comparison of 2 same-size gif images and produce a mask of those pixels where the color is different. It also reports the % different.

[code]
<?php
$filea = $_GET['f1'];
$fileb = $_GET['f2'];

$im1 = imagecreatefromgif($filea);
$im2 = imagecreatefromgif($fileb);

$w1 = imagesx($im1);
$w2 = imagesx($im2);
$h1 = imagesx($im1);
$h2 = imagesx($im2);
$w = min($w1, $w2);
$h = min($h1, $h2);
 
$im3 = imagecreate($w,$h+25);
$bg3 = imagecolorallocate($im3,0xff,0xff,0xff);
$fg3 = imagecolorallocate($im3,0xff,0x00,0xff);
$fg3t = imagecolorallocate($im3,0x00,0x00,0x00);

$total_pixels = $w*$h;
$diff = 0;

for ($x=0; $x<$w; $x++) {
    for ($y=0; $y<$h; $y++) {
        if (imagecolorat($im1, $x, $y) != imagecolorat($im2, $x, $y)) {
            $diff++;
            imagesetpixel($im3, $x, $y, $fg3);
        }
    }
}
imagerectangle($im3,0,0,$w-1, $h-1, $fg3t);
$pcdiff = number_format(floor($diff/$total_pixels * 100), 0) . '%';
imagestring($im3, 3, 4, $h+3, $pcdiff, $fg3t);

imagedestroy($im1);
imagedestroy($im2);

header("content-type: image/png");
imagepng($im3);
imagedestroy($im3);
?>[/code]

Call with
<img src='compareImage.php?f1=a.gif&f2=b.gif'>

where a.gif and b.gif are the images to be compared.

[wolves]

it is creating a new image with all diferences between img 1 and img 2
but always 0% of diference,

I will try to fix

tks

[Barand]

If it's very small % changes, change

$pcdiff = number_format(floor($diff/$total_pixels * 100), 0) . '%';

to

$pcdiff = number_format($diff/$total_pixels * 100, 2) . '%';

[wolves]

it is working but
see this images

http://www.set.eesc.usp.br/lamem/Texturas/Angelim.JPG
http://www.set.eesc.usp.br/lamem/Texturas/Cedrilho.JPG

they are total diferent analizing it by pixels, but not really total diferent
the number of pixel is the number of different pixels

so if u compare this other image
http://www.set.eesc.usp.br/lamem/Texturas/PauBrasil.JPG

will be 100% diferent too . . .

complex images will always return 100% of diference  :-\

[Barand]

try this version which converts to high contrast grayscale. Small adjustments to contrast have large effect on result.
[code]
<?php
$filea = $_GET['f1'];
$fileb = $_GET['f2'];

$im1 = imagecreatefromjpeg($filea);
$im2 = imagecreatefromjpeg($fileb);

$w1 = imagesx($im1);
$w2 = imagesx($im2);
$h1 = imagesx($im1);
$h2 = imagesx($im2);
$w = min($w1, $w2);
$h = min($h1, $h2);
 
$im3 = imagecreate($w,$h+25);
$bg3 = imagecolorallocate($im3,0xff,0xff,0xff);
$fg3 = imagecolorallocate($im3,0xff,0x00,0xff);
$fg3t = imagecolorallocate($im3,0x00,0x00,0x00);

$total_pixels = $w*$h;
$diff = 0;

imagefilter($im1, IMG_FILTER_GRAYSCALE);
imagefilter($im2, IMG_FILTER_GRAYSCALE);
imagefilter($im1,IMG_FILTER_CONTRAST, 88);
imagefilter($im2,IMG_FILTER_CONTRAST, 88);

for ($x=0; $x<$w; $x++) {
    for ($y=0; $y<$h; $y++) {
        if (imagecolorat($im1, $x, $y) != imagecolorat($im2, $x, $y)) {
            $diff++;
            imagesetpixel($im3, $x, $y, $fg3);
        }
    }
}
imagerectangle($im3,0,0,$w-1, $h-1, $fg3t);
$pcdiff = number_format(floor($diff/$total_pixels * 100), 0) . '%';
imagestring($im3, 3, 4, $h+3, $pcdiff, $fg3t);

imagedestroy($im1);
imagedestroy($im2);

header("content-type: image/png");
imagepng($im3);
imagedestroy($im3);
?>[/code]

[Barand]

[quote=php manual imagecolorat()]
$rgb = ImageColorAt($im, 100, 100);
$r = ($rgb >> 16) & 0xFF;
$g = ($rgb >> 8 ) & 0xFF;
$b = $rgb & 0xFF;
[/quote]

applies to truecolor images, GD2

[wolves]

tks all especially Barand =)

[wolves]

now I need to compare ".pgm" files

there is a away to do this in php?

i looked at docs, but I found nothing about .pgm