{"id":626,"date":"2005-03-24T23:25:18","date_gmt":"2005-03-24T23:25:18","guid":{"rendered":"http:\/\/beta.robertprice.co.uk\/robblog\/2005\/03\/grayscaling_images_with_perl-shtml\/"},"modified":"2005-03-24T23:25:18","modified_gmt":"2005-03-24T23:25:18","slug":"grayscaling_images_with_perl-shtml","status":"publish","type":"post","link":"https:\/\/www.robertprice.co.uk\/robblog\/grayscaling_images_with_perl-shtml\/","title":{"rendered":"Grayscaling Images With Perl"},"content":{"rendered":"

\nOne thing that caught my interest today was how to convert a colour image into grayscale.\n<\/p>\n

\nIt turns out the basic algorithm is very simple. Basically it’s just…\n<\/p>\n

grey = 0.15 * red + 0.55 * green + 0.30 * blue;
\n<\/code><\/div>\n

\nThis can be turned into a Perl<\/a> subroutine using the following code.\n<\/p>\n

sub grayscale {
\nmy ($r, $g, $b) = @_;
\nmy $s = 0.15 * $r + 0.55 * $g + 0.30 * $b;
\nreturn int($s);
\n}
\n<\/code><\/div>\n

\nHere we pass in the RGB<\/acronym> values of the colour we want to turn into gray. We apply the algorithm and return the integer value of gray.\n<\/p>\n

\nThe value we get for gray is used to replace each of the values for red, green and blue.\n<\/p>\n

\nWe can test this subroutine out with the help of the Perl GD module (available for free on CPAN<\/a>).\n<\/p>\n

#!\/usr\/bin\/perl -w
\nuse GD;
\n## grayscale subroutine
\nsub grayscale {
\nmy ($r, $g,$b) = @_;
\nmy $s = 0.15 * $r + 0.55 * $g + 0.30 * $b;
\nreturn int($s);
\n}
\n## create a new GD object with the data passed via STDIN
\nmy $image = new GD::Image(*STDIN);
\n## iterate over the number of colours in the colour table
\nfor (my $i = 0; $i < $image->colorsTotal(); $i++) {
\n## get the RGB values for the colour at index $i
\nmy ($r, $g, $b) = $image->rgb($i);
\n## convert the RGB to grayscale
\nmy $gray = grayscale($r,$g,$b);
\n## remove the original colour from the colour table
\n$image->colorDeallocate($i);
\n## add in the new gray
\n$image->colorAllocate($gray,$gray,$gray);
\n}
\n## make sure we output binary
\nbinmode STDOUT;
\n## pass the image as a raw GIF to STDOUT
\nprint $image->gif;
\n<\/code><\/div>\n

\nThis code takes an image piped in from STDIN and outputs a grayscale GIF version of the image to STDOUT.\n<\/p>\n

\nIf the code was called convert.pl<\/code> it would be called as .\/convert.pl <test.gif >>test_result.gif<\/code>.\n<\/p>\n

\nHere’s a conversion I did earlier of a GIF image of Kitt, Bev and Justin at the Emap Performance Awards 2004 using the above Perl code.\n<\/p>\n

\n\"Kitt,\n<\/p>\n

\n\"Kitt,<\/p>\n","protected":false},"excerpt":{"rendered":"

One thing that caught my interest today was how to convert a colour image into grayscale. It turns out the basic algorithm is very simple. Basically it’s just… grey = 0.15 * red + 0.55 * green + 0.30 * blue; This can be turned into a Perl subroutine using the following code. sub grayscale … Continue reading “Grayscaling Images With Perl”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"inline_featured_image":false,"footnotes":""},"categories":[2],"tags":[17,47],"class_list":["post-626","post","type-post","status-publish","format-standard","hentry","category-dev","tag-dev","tag-perl"],"yoast_head":"\nGrayscaling Images With Perl - Robert Price<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.robertprice.co.uk\/robblog\/grayscaling_images_with_perl-shtml\/\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Grayscaling Images With Perl - Robert Price\" \/>\n<meta property=\"og:description\" content=\"One thing that caught my interest today was how to convert a colour image into grayscale. It turns out the basic algorithm is very simple. 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