Trim an image using PHP and GD

Submitted by zavaboy on October 6, 2007 - 4:19pm.

I was looking for a way to trim images with the GD library. So I made a function to do just that. The function, which I only naturally called imagetrim(), trims a image much like Photoshop's trim feature. Additionally, you may add padding too if desired.

So, here's the function:

<?php
// Trims an image then optionally adds padding around it.
// $im  = Image link resource
// $bg  = The background color to trim from the image
// $pad = Amount of padding to add to the trimmed image
//        (acts simlar to the "padding" CSS property: "top [right [bottom [left]]]")
function imagetrim(&$im, $bg, $pad=null){

    // Calculate padding for each side.
    if (isset($pad)){
        $pp = explode(' ', $pad);
        if (isset($pp[3])){
            $p = array((int) $pp[0], (int) $pp[1], (int) $pp[2], (int) $pp[3]);
        }else if (isset($pp[2])){
            $p = array((int) $pp[0], (int) $pp[1], (int) $pp[2], (int) $pp[1]);
        }else if (isset($pp[1])){
            $p = array((int) $pp[0], (int) $pp[1], (int) $pp[0], (int) $pp[1]);
        }else{
            $p = array_fill(0, 4, (int) $pp[0]);
        }
    }else{
        $p = array_fill(0, 4, 0);
    }

    // Get the image width and height.
    $imw = imagesx($im);
    $imh = imagesy($im);

    // Set the X variables.
    $xmin = $imw;
    $xmax = 0;

    // Start scanning for the edges.
    for ($iy=0; $iy<$imh; $iy++){
        $first = true;
        for ($ix=0; $ix<$imw; $ix++){
            $ndx = imagecolorat($im, $ix, $iy);
            if ($ndx != $bg){
                if ($xmin > $ix){ $xmin = $ix; }
                if ($xmax < $ix){ $xmax = $ix; }
                if (!isset($ymin)){ $ymin = $iy; }
                $ymax = $iy;
                if ($first){ $ix = $xmax; $first = false; }
            }
        }
    }

    // The new width and height of the image. (not including padding)
    $imw = 1+$xmax-$xmin; // Image width in pixels
    $imh = 1+$ymax-$ymin; // Image height in pixels

    // Make another image to place the trimmed version in.
    $im2 = imagecreatetruecolor($imw+$p[1]+$p[3], $imh+$p[0]+$p[2]);

    // Make the background of the new image the same as the background of the old one.
    $bg2 = imagecolorallocate($im2, ($bg >> 16) & 0xFF, ($bg >> 8) & 0xFF, $bg & 0xFF);
    imagefill($im2, 0, 0, $bg2);

    // Copy it over to the new image.
    imagecopy($im2, $im, $p[3], $p[0], $xmin, $ymin, $imw, $imh);

    // To finish up, we replace the old image which is referenced.
    $im = $im2;
}
?>

Comments

Using it myself

Submitted by Voiceover on January 4, 2010 - 4:50am.

Seems that we had almost exactly the same idea. I needed a tim-functionality for the users of my site and wrote a function that could be a trim borther, errr, TWIN brothers to yours.

Transparant background?

Submitted by John on August 10, 2009 - 4:35pm.

Is it possible to trim an image with an transparant background in your example here above?

Can you give an example?

I'm wondering the same, can

Submitted by Dan on October 7, 2009 - 7:16am.

I'm wondering the same, can this function be used to trim off 'empty space' from a PNG 24's alpha channel?

thanks for the post but i

Submitted by wow gold on December 30, 2008 - 8:39am.

thanks for the post but i agree with Bill.you are right.thanks for the example you submitted.that was really helpfull for us.
hope have more interesting things in future from this site.thanks!

I will be agreeing that my

Submitted by facia plate on April 25, 2009 - 9:12am.

I will be agreeing that my mate.Thanks for the example you have submitted.And thanks for the good post.Thanks a lot for sharing.

Yes I agree with him. You

Submitted by PC repair on March 26, 2009 - 12:18am.

Yes I agree with him. You chosen right path.I thank you a lot for the nice info.

I think there's a minor correction - pls confirm...

Submitted by Bill Ortell on November 20, 2008 - 5:23pm.

came across your script, and it fits PERFECTLY for what i was trying to do... but i think the 2nd to last line needs to switch the $p[0] and $p[3] to get it to align on the canvas correctly... Anyways, I tried that and it worked - with the change.

Just fyi.

God bless!

<?php

$imw = 500; $imh = 500;
$im = imagecreatetruecolor($imw,$imh); // Create image

// Create some colors
$bg = imagecolorallocate     ($im,0xFF,0xFF,0x00);     // Background color (yellow)
$ln = imagecolorallocatealpha($im,0xFF,0x00,0x00,110); // Line color (transparent red)

imagefill($im,0,0,$bg);

// Generate something a little random.
$r = $imh/10; $t2 = array($r,0);
for ($a=0;$a<360;$a++){
  $noise = rand(-$r,$r);
  $t1 = $t2;
  $t2[0] = (($r+$noise) * cos(deg2rad($a)));
  $t2[1] = (($r+$noise) * sin(deg2rad($a)));
  imageline($im, ($imw/2)+$t1[0], ($imh/2)+$t1[1], ($imw/2)+$t2[0], ($imh/2)+$t2[1], $ln);
}

// Padding: 1px top, 2px right, 3px bottom, 4px left
//imagetrim($im,$bg,'1 2 3 4');

// Padding: 1px top, 2px right, 3px bottom, 2px left
//imagetrim($im,$bg,'1 2 3');

// Padding: 1px top, 2px right, 1px bottom, 2px left
//imagetrim($im,$bg,'1 2');

// Padding: 5px top, 5px right, 5px bottom, 5px left
//imagetrim($im,$bg,'5');

// Padding: 0px top, 0px right, 0px bottom, 0px left
imagetrim($im,$bg);

// Set the header and output image.
header('Content-type: image/png');
imagepng($im);
imagedestroy($im);

?>

Hope this helps! :)

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