{"id":514,"date":"2008-11-15T22:56:59","date_gmt":"2008-11-16T03:56:59","guid":{"rendered":"http:\/\/www.phpied.com\/?p=514"},"modified":"2008-11-15T22:56:59","modified_gmt":"2008-11-16T03:56:59","slug":"image-diff","status":"publish","type":"post","link":"https:\/\/www.phpied.com\/image-diff\/","title":{"rendered":"image diff"},"content":{"rendered":"

Was having fun today with idiff.php<\/code> - a PHP shell script to tell you if two images are visually different by comparing them pixel by pixel. If there's a difference, the script creates a third image - black background with the different pixels in green. Only after writing the script I found that there's an imagemagick command compare<\/code> that does the same \ud83d\ude42<\/p>\n

the script<\/h3>\n

The idea is that two GD images are created from the input files, also a third GD image with black background to store the diff. Loop through all the pixels and compare them one by one. If one is different, write a green pixel at the same location of the diff image. <\/p>\n

\n
<?php<\/span>\r\n<\/span>\/*<\/span>*\r\n * Shell script to tell if two images are identical.\r\n * If not, a third image is written - black background with the different pixels painted green\r\n * Code partially inspired by and borrowed from <\/span>http:\/\/pear.php.net\/Image_Text<\/span> test cases\r\n <\/span>*\/<\/span>\r\n \r\n<\/span>\/\/<\/span> check if there's enough input<\/span><\/span>\r\n<\/span>if<\/span> <\/span>(<\/span>empty<\/span>(<\/span>$argv<\/span>[<\/span>1<\/span>]<\/span>)<\/span> || <\/span>empty<\/span>(<\/span>$argv<\/span>[<\/span>2<\/span>]<\/span>)<\/span>)<\/span> <\/span>{<\/span>\r\n    <\/span>echo<\/span> <\/span>'<\/span>gimme at least two image filenames, please.<\/span>'<\/span>, <\/span>"<\/span>\\n<\/span>"<\/span>;\r\n    <\/span>echo<\/span> <\/span>'<\/span>e.g. "php idiff.php img1.png img2.png"<\/span>'<\/span>;\r\n    <\/span>echo<\/span> <\/span>"<\/span>\\n<\/span>"<\/span>, <\/span>'<\/span>third filename is the image diff, optional, default is "diffy.png"<\/span>'<\/span>;\r\n    <\/span>exit<\/span>(<\/span>1<\/span>)<\/span>;\r\n<\/span>}<\/span>\r\n \r\n<\/span>\/\/<\/span> create images<\/span><\/span>\r\n<\/span>$i1<\/span> = @<\/span>imagecreatefromstring<\/span>(<\/span>file_get_contents<\/span>(<\/span>$argv<\/span>[<\/span>1<\/span>]<\/span>)<\/span>)<\/span>;\r\n<\/span>$i2<\/span> = @<\/span>imagecreatefromstring<\/span>(<\/span>file_get_contents<\/span>(<\/span>$argv<\/span>[<\/span>2<\/span>]<\/span>)<\/span>)<\/span>;\r\n \r\n<\/span>\/\/<\/span> check if we were given garbage<\/span><\/span>\r\n<\/span>if<\/span> <\/span>(<\/span>!<\/span>$i1<\/span>)<\/span> <\/span>{<\/span>\r\n    <\/span>echo<\/span> <\/span>$argv<\/span>[<\/span>1<\/span>]<\/span> . <\/span>'<\/span> is not a valid image<\/span>'<\/span>;\r\n    <\/span>exit<\/span>(<\/span>1<\/span>)<\/span>;\r\n<\/span>}<\/span>\r\n<\/span>if<\/span> <\/span>(<\/span>!<\/span>$i2<\/span>)<\/span> <\/span>{<\/span>\r\n    <\/span>echo<\/span> <\/span>$argv<\/span>[<\/span>2<\/span>]<\/span> . <\/span>'<\/span> is not a valid image<\/span>'<\/span>;\r\n    <\/span>exit<\/span>(<\/span>1<\/span>)<\/span>;\r\n<\/span>}<\/span>\r\n \r\n<\/span>\/\/<\/span> dimensions of the first image<\/span><\/span>\r\n<\/span>$sx1<\/span> = <\/span>imagesx<\/span>(<\/span>$i1<\/span>)<\/span>;\r\n<\/span>$sy1<\/span> = <\/span>imagesy<\/span>(<\/span>$i1<\/span>)<\/span>;\r\n \r\n<\/span>\/\/<\/span> compare dimensions<\/span><\/span>\r\n<\/span>if<\/span> <\/span>(<\/span>$sx1<\/span> !== <\/span>imagesx<\/span>(<\/span>$i2<\/span>)<\/span> || <\/span>$sy1<\/span> !== <\/span>imagesy<\/span>(<\/span>$i2<\/span>)<\/span>)<\/span> <\/span>{<\/span>\r\n    <\/span>echo<\/span> <\/span>"<\/span>The images are not even the same size<\/span>"<\/span>;\r\n    <\/span>exit<\/span>(<\/span>1<\/span>)<\/span>;\r\n<\/span>}<\/span>\r\n \r\n<\/span>\/\/<\/span> create a diff image<\/span><\/span>\r\n<\/span>$diffi<\/span> = <\/span>imagecreatetruecolor<\/span>(<\/span>$sx1<\/span>, <\/span>$sy1<\/span>)<\/span>;\r\n<\/span>$green<\/span> = <\/span>imagecolorallocate<\/span>(<\/span>$diffi<\/span>, <\/span>0<\/span>, <\/span>255<\/span>, <\/span>0<\/span>)<\/span>;\r\n<\/span>imagefill<\/span>(<\/span>$diffi<\/span>, <\/span>0<\/span>, <\/span>0<\/span>, <\/span>imagecolorallocate<\/span>(<\/span>$diffi<\/span>, <\/span>0<\/span>, <\/span>0<\/span>, <\/span>0<\/span>)<\/span>)<\/span>;\r\n \r\n<\/span>\/\/<\/span> increment this counter when encountering a pixel diff<\/span><\/span>\r\n<\/span>$different_pixels<\/span> = <\/span>0<\/span>;\r\n \r\n<\/span>\/\/<\/span> loop x and y<\/span><\/span>\r\n<\/span>for<\/span> <\/span>(<\/span>$x<\/span> = <\/span>0<\/span>; <\/span>$x<\/span> < <\/span>$sx1<\/span>; <\/span>$x<\/span>++<\/span>)<\/span> <\/span>{<\/span>\r\n    <\/span>for<\/span> <\/span>(<\/span>$y<\/span> = <\/span>0<\/span>; <\/span>$y<\/span> < <\/span>$sy1<\/span>; <\/span>$y<\/span>++<\/span>)<\/span> <\/span>{<\/span>\r\n \r\n        <\/span>$rgb1<\/span> = <\/span>imagecolorat<\/span>(<\/span>$i1<\/span>, <\/span>$x<\/span>, <\/span>$y<\/span>)<\/span>;\r\n        <\/span>$pix1<\/span> = <\/span>imagecolorsforindex<\/span>(<\/span>$i1<\/span>, <\/span>$rgb1<\/span>)<\/span>;\r\n \r\n        <\/span>$rgb2<\/span> = <\/span>imagecolorat<\/span>(<\/span>$i2<\/span>, <\/span>$x<\/span>, <\/span>$y<\/span>)<\/span>;\r\n        <\/span>$pix2<\/span> = <\/span>imagecolorsforindex<\/span>(<\/span>$i2<\/span>, <\/span>$rgb2<\/span>)<\/span>;\r\n \r\n        <\/span>if<\/span> <\/span>(<\/span>$pix1<\/span> !== <\/span>$pix2<\/span>)<\/span> <\/span>{<\/span> <\/span>\/\/<\/span> different pixel<\/span><\/span>\r\n            <\/span>\/\/<\/span> increment and paint in the diff image<\/span><\/span>\r\n            <\/span>$different_pixels<\/span>++;\r\n            <\/span>imagesetpixel<\/span>(<\/span>$diffi<\/span>, <\/span>$x<\/span>, <\/span>$y<\/span>, <\/span>$green<\/span>)<\/span>;\r\n        <\/span>}<\/span>\r\n \r\n    <\/span>}<\/span>\r\n<\/span>}<\/span>\r\n \r\n \r\n<\/span>if<\/span> <\/span>(<\/span>!<\/span>$different_pixels<\/span>)<\/span> <\/span>{<\/span>\r\n    <\/span>echo<\/span> <\/span>"<\/span>Image is the same<\/span>"<\/span>;\r\n    <\/span>exit<\/span>(<\/span>0<\/span>)<\/span>;\r\n<\/span>}<\/span> <\/span>else<\/span> <\/span>{<\/span>\r\n    <\/span>if<\/span> <\/span>(<\/span>empty<\/span>(<\/span>$argv<\/span>[<\/span>3<\/span>]<\/span>)<\/span>)<\/span> <\/span>{<\/span>\r\n        <\/span>$argv<\/span>[<\/span>3<\/span>]<\/span> = <\/span>'<\/span>diffy.png<\/span>'<\/span>; <\/span>\/\/<\/span> default result filename<\/span><\/span>\r\n    <\/span>}<\/span>\r\n    <\/span>imagepng<\/span>(<\/span>$diffi<\/span>, <\/span>$argv<\/span>[<\/span>3<\/span>]<\/span>)<\/span>;\r\n    <\/span>$total<\/span> = <\/span>$sx1<\/span> * <\/span>$sy1<\/span>;\r\n    <\/span>echo<\/span> <\/span>"<\/span>$different_pixels<\/span>\/<\/span>$total<\/span> different pixels, or <\/span>"<\/span>, <\/span>number_format<\/span>(<\/span>100<\/span> * <\/span>$different_pixels<\/span> \/ <\/span>$total<\/span>, <\/span>2<\/span>)<\/span>, <\/span>'<\/span>%<\/span>'<\/span>;\r\n    <\/span>exit<\/span>(<\/span>1<\/span>)<\/span>;\r\n<\/span>}<\/span>\r\n<\/span>?><\/span><\/pre>\n<\/div>\n
usage<\/h3>\n
Type in the command line something like:<\/p>\n
php idiff.php img1.png img2.png result.png<\/code><\/p>\n
This command will compare img1.png<\/code> with img2.png<\/code>. If they are not the same dimensions, will exit with error code. If their pixels exactly the same will exit with success code 0 and print a success message. If the images are not the same, will write the file result.png<\/code>. <\/p>\n
If you omit result.png<\/code>, the generated file will be called diffy.png<\/code><\/p>\n
example<\/h3>\n
img1.png:
\n\"\"<\/p>\n
img2.png
\n\"\"<\/p>\n
running the command:<\/p>\n
>php idiff.php img1.png img2.png\r\n70\/24600 different pixels, or 0.28%<\/pre>\n
the result diffy.png:
\n\"\"<\/p>\n
imagemagick<\/h3>\n
yep, so after I did this I found that imagemagick has a command called compare<\/code> that does the same, only with more features<\/a>, like the -fuzz<\/a> option for example that allows you to specify how different should the pixels be, in order to consider them important.<\/p>\n
the command:<\/p>\n
>compare img1.png img2.png diffy-im.png<\/pre>\n
the diffy-im.png<\/code> result
\n\"\"<\/p>\n
As you can see the different pixels are red and the actual image is a very pale background. Nice.<\/p>\n","protected":false},"excerpt":{"rendered":"
Was having fun today with idiff.php – a PHP shell script to tell you if two images are visually different by comparing them pixel by pixel. If there’s a difference, the script creates a third image – black background with the different pixels in green. Only after writing the script I found that there’s an […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[41,40],"tags":[143,142,381,380],"_links":{"self":[{"href":"https:\/\/www.phpied.com\/wp-json\/wp\/v2\/posts\/514"}],"collection":[{"href":"https:\/\/www.phpied.com\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.phpied.com\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.phpied.com\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.phpied.com\/wp-json\/wp\/v2\/comments?post=514"}],"version-history":[{"count":0,"href":"https:\/\/www.phpied.com\/wp-json\/wp\/v2\/posts\/514\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.phpied.com\/wp-json\/wp\/v2\/media?parent=514"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.phpied.com\/wp-json\/wp\/v2\/categories?post=514"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.phpied.com\/wp-json\/wp\/v2\/tags?post=514"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}