Compiled Thoughts by John Ciacia » gd

Basic OCR

John — Tue, 05 Jan 2010 03:40:11 +0000

This is a very basic optical character recognition script written in PHP. This is untested and serves merely a proof of concept. As noted in the comments, adjusting the sample size can improve results, since with a large sample size on a small image there can be many collisions. A database is needed to compare output results of this script with known values.

[code lang="PHP"]

/* create a test image */
$im = @imagecreate(100, 20) or die("Cannot Initialize new GD image stream");
$background_color = imagecolorallocate($im, 255, 255, 255);
$text_color = imagecolorallocate($im, 0, 0, 0);
imagestring($im, 1, 5, 5, "Hello, World!", $text_color);

/***
* Assumptions:
* A monochrome image where characters are black
* A single character is connected
* Characters are disjointed by white space
*/

$width = imagesx($im);
$height = imagesy($im);

/***
* Notes:
* The smaller the sample size the more accurate it will be,
* however, it will take longer. Larger images can use a larger
* sample size wihtout compromizing much accuracy.
*/
$x_sample = 1;
$y_sample = 1;

$last = 0;
for($i = 0; $i < $width; $i++) {
$col = array();

for($j = 0; $j < $height; $j++) {
$col[$j] = imagecolorat($im, $i, $j);
}

if(($current = array_sum($col)) > 0) {
if($last == 0) {
$l = 0;
}

for($k = 0; $k < $height; $k++) {
if(($l % $x_sample) == 0) {
if(($k % $y_sample) == 0) {
$sample .= $col[$k];
}
}
}

$l++;
$last = $current;
} else {
$last = 0;
}

if(!empty($sample) && $last == 0) {
echo $sample . "\n";
$sample = "";
}
}
?>[/code]

Output (each line represents a character)

00000011111100000000000000001000000000000000000010000000000000000011111100000000
00000000011000000000000000001011000000000000000011010000000000000000010100000000
000000100001000000000000001111110000000000000000000100000000
000000100001000000000000001111110000000000000000000100000000
00000000011000000000000000001001000000000000000010010000000000000000011000000000
000000000001000000000000000001100000000000000000010000000000
00000011111100000000000000000110000000000000000001100000000000000011111100000000
00000000011000000000000000001001000000000000000010010000000000000000011000000000
00000000111100000000000000000100000000000000000010000000000000000000010000000000
000000100001000000000000001111110000000000000000000100000000
00000000011000000000000000001001000000000000000010100000000000000011111100000000
00000001110100000000

Using PHP and GD to add border to text

John — Mon, 04 Jan 2010 23:41:03 +0000

[code lang="PHP"] /**
* Writes the given text with a border into the image using TrueType fonts.
* @author John Ciacia
* @param image An image resource
* @param size The font size
* @param angle The angle in degrees to rotate the text
* @param x Upper left corner of the text
* @param y Lower left corner of the text
* @param textcolor This is the color of the main text
* @param strokecolor This is the color of the text border
* @param fontfile The path to the TrueType font you wish to use
* @param text The text string in UTF-8 encoding
* @param px Number of pixels the text border will be
* @see http://us.php.net/manual/en/function.imagettftext.php
*/
function imagettfstroketext(&$image, $size, $angle, $x, $y, &$textcolor, &$strokecolor, $fontfile, $text, $px) {

for($c1 = ($x-abs($px)); $c1 <= ($x+abs($px)); $c1++)
for($c2 = ($y-abs($px)); $c2 <= ($y+abs($px)); $c2++)
$bg = imagettftext($image, $size, $angle, $c1, $c2, $strokecolor, $fontfile, $text);

return imagettftext($image, $size, $angle, $x, $y, $textcolor, $fontfile, $text);
} [/code]

[code lang="PHP"] $img = imagecreatefrompng("/home/john/Desktop/test.png");
$font_color = imagecolorallocate($img, 0, 0, 0);
$stroke_color = imagecolorallocate($img, 255, 0, 0);
imagettfstroketext($img, 10, 0, 10, 50, $font_color, $stroke_color, "abstract.ttf", "Hello, World!", 2);
?>[/code]

Basic CAPTCHA

John — Mon, 04 Jan 2010 23:01:18 +0000

Very basic code demonstrating the use of the GD library by creating a simple CAPTCHA.
[code lang="PHP"] function randomString($length){
$pattern = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";
if(empty($length)){
$length = "10";
}

for($i=0; $i<$length; $i++){
$string .= $pattern{rand(0,61)};
}

return $string;
}

function captcha() {
header("Content-type: image/png");
$im = @imagecreate(100, 50) or die("Cannot Initialize new GD image stream");
$background_color = imagecolorallocate($im, 0, 0, 0);
$text_color = imagecolorallocate($im, 255, 0, 0);
$string = randomString();
imagestring($im, 10, 5, 5, $string, $text_color);
imagepng($im);
imagedestroy($im);
}

captcha();
?>[/code]

imagettftext only displays yellow text

John — Sat, 09 May 2009 23:44:42 +0000

Lately I have been doing some work with the PHP GD library. I wanted to put text on an image so I naturally used imagettftext(). I started by copying the example code provided by the manual and intended on modifying the code to fit my needs. When I executed the code my my browser, the text was yellow. I took a look at the code, and the results did not match. The text should have been black. I tried adjusting the imagecolorallocate parameters to reflect a different color. However, this time with I executed the code, no text showed up. It turns out I needed configure PHP –with-freetype-dir. After a recompile with the new configuration it worked fine.

./configure \
–disable-magic-quotes \
–enable-bcmath \
–enable-sockets \
–with-mysq=/usr/local \
–with-apxs2=/usr/local/apache2/bin/apxs \
–with-curl \
–with-gd \
–with-freetype-dir=/usr
–with-png \
–with-jpeg \
–with-ttf