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13 years ago
trimImage ( resource $image , int $colour , int $tolerance )

trimImage() will return top-most, right-most, bottom-most and left-most positions of wanted pixels for an image (i.e. find minimum image area so you can then trim given colour from the outer edges of an image).

Parameters

image
An image resource, returned by one of the image creation functions, such as imagecreatetruecolor().

colour
colour to be 'trimmed'.  Allowable range 0 (black) to 255 (white).  if null (or outside 0 - 255) will use top/left corner colour as default.

tolerance
Acceptable range +- from colour.  0 (trim only exact colour) to 255 (trim all colours).

Return Values
Returns an array of outermost pixels which are outside the tolerance range from colour.  
array( int $top, int $right, int $bottom, int $left )

Example (and actual function)
<?php
function trimImage($im,$c,$t) {
  // if trim colour ($c) isn't a number between 0 - 255
  if (!is_numeric($c) || $c < 0 || $c > 255) {
    // grab the colour from the top left corner and use that as default
    $rgb = imagecolorat($im, 2, 2); // 2 pixels in to avoid messy edges
    $r = ($rgb >> 16) & 0xFF;
    $g = ($rgb >> 8) & 0xFF;
    $b = $rgb & 0xFF;
    $c = round(($r+$g+$b)/3); // average of rgb is good enough for a default
  }
  // if tolerance ($t) isn't a number between 0 - 255 use 10 as default
  if (!is_numeric($t) || $t < 0 || $t > 255) $t = 10;

  $w = imagesx($im); // image width
  $h = imagesy($im); // image height
  for($x = 0; $x < $w; $x++) {
    for($y = 0; $y < $h; $y++) {
      $rgb = imagecolorat($im, $x, $y);
      $r = ($rgb >> 16) & 0xFF;
      $g = ($rgb >> 8) & 0xFF;
      $b = $rgb & 0xFF;
      if (
      ($r < $c-$t || $r > $c+$t) && // red not within tolerance of trim colour 
      ($g < $c-$t || $g > $c+$t) && // green not within tolerance of trim colour 
      ($b < $c-$t || $b > $c+$t) // blue not within tolerance of trim colour
      ) {
        // using x and y as keys condenses all rows and all columns
        // into just one X array and one Y array.
        // however, the keys are treated as literal and therefore are not in
        // numeric order, so we need to sort them in order to get the first 
        // and last X and Y occurances of wanted pixels.
        // normal sorting will remove keys so we also use x and y as values,
        // this way they are still available without preserving keys. 
        $y_axis[$y] = $y;  
        $x_axis[$x] = $x;
        // note: $y_axis[] = $y; and $x_axis[] = $x; works just as well
        // but results in much much larger arrays than is necessary
        // array_unique would reduce size again but this method is quicker
      }
    }
  }
  // sort them so first and last occurances are at start and end
  sort($y_axis);
  sort($x_axis);  

  $top = array_shift($y_axis); // first wanted pixel on Y axis
  $right = array_pop($x_axis); // last wanted pixel on X axis 
  $bottom = array_pop($y_axis); // last wanted pixel on Y axis
  $left = array_shift($x_axis); // first wanted pixel on X axis

  return array($top,$right,$bottom,$left);
}

$image='test.jpg';
$im = imagecreatefromjpeg($image); // we need resource

$c = (isset($_GET[c])) ? $_GET[c] : null; // set trim colour via GET
$t = (isset($_GET[t])) ? $_GET[t] : null; // set tolerance via GET

list($t,$r,$b,$l) = trimImage($im,$c,$t); // find top, right, bottom and left

$w = $r-$l; // find width
$h = $b-$t; // find height

imagedestroy($im); // free resource

// below is just for visually testing function ---------------------------------

$html_display = <<<HTM

<style type="text/css">
#stage {
  position: relative;
  float: left; // so it is the same size as the image it contains
}
#canvas {
  border: solid 1px #FC3;
  width: {$w}px;
  height: {$h}px;
  position: absolute;
  top: {$t}px;
  left: {$l}px;
}
img { border: solid 1px #EEE; }
</style>

HTM;

?>
<html>
<head>
<?=$html_display?>
</head>

<body>
<div id="stage">
  <div id="canvas"></div>
  <img src="test.jpg" />
</div>

</body>
</html>
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