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I'm currently trying to work with pictures and PHP, thanks to GD functions.
Now I would like to modify the size of PNG pictures. Here is an example of a PNG I'd like to resize :
The dotted line represent the border of the PNG, the background is transparent, and I only have a star lost on the middle of a large space. I'd like to crop this star, to get a simple square of the star (even if the new background becomes blank, It doesn't matter).
How could I do something like that efficiently ? I thought about doing a loop checking every pixel of the picture.. Trying to find where the image is, to finally crop with a little margin based on the minimum x / maximum X and minimum y / maximum y values, but If I start working with hundreds of pictures, It would be really long.
EDIT :
<?php
$file = "./crop.png";
$ext = pathinfo($file, PATHINFO_EXTENSION);
$image;
switch ($ext){
case 'png':
$image = imagecreatefrompng($file);
break;
case 'jpeg':
case 'jpg':
$image = imagecreatefromjpeg($file);
break;
case 'gif':
$image = imagecreatefromgif($file);
break;
}
$cropped = imagecropauto($image, IMG_CROP_DEFAULT);
if ($cropped !== false) { // in case a new image resource was returned
echo "=> Cropping needed\n";
imagedestroy($image); // we destroy the original image
$image = $cropped; // and assign the cropped image to $im
}
imagepng($image, "./cropped.png");
imagedestroy($image);
538
If you read and follow the php php-gd documentation, you'll find a function called imagecropauto which does exactly what you want, it crops the alpha channel of the image.
Crop an PNG image with alpha channel
$im = imagecreatefrompng("./star-with-alpha.png");
$cropped = imagecropauto($im, IMG_CROP_DEFAULT);
if ($cropped !== false) { // in case a new image resource was returned
imagedestroy($im); // we destroy the original image
$im = $cropped; // and assign the cropped image to $im
}
imagepng($im, "./star-with-alpha-crop.png");
imagedestroy($im);
You can try it dirrectly to a php page using this code:
<body>
<img src="star-with-alpha.png">
<?php
$im = imagecreatefrompng("./star-with-alpha.png");
$cropped = imagecropauto($im, IMG_CROP_DEFAULT);
if ($cropped !== false) { // in case a new image resource was returned
imagedestroy($im); // we destroy the original image
$im = $cropped; // and assign the cropped image to $im
}
imagepng($im, "./star-with-alpha-crop.png");
imagedestroy($im);
?>
<img src="star-with-alpha-crop.png">
</body>
The result
http://zikro.gr/dbg/php/crop-png/
164
[This is for ubuntu 12]
The only problem with the imagecropauto is that it works only on Mac & Windows.
And since most of the servers today use ubuntu/debain - this function is of no use.
Instead use Imagick() for this.
Here is a sample code I wrote which does exactly this:
//Add background transmparent
$background = 'none';
$image = new Imagick($path);
$image->trimImage(0);
//add transparent border
//border add start
/** Set border format **/
$borderWidth = 20;
$borderColor = 'none';
$borderPadding = 10;
$imageWidth = $image->getImageWidth() + ( 2 * ( $borderWidth +
$borderPadding ) );
$imageHeight = $image->getImageHeight() + ( 2 * ( $borderWidth +
$borderPadding ) );
Create Imagick object for final image with border
$imageWithBorder = new Imagick();
// Set image canvas
$imageWithBorder->newImage( $imageWidth, $imageHeight, new ImagickPixel(
'none' ));
// Create ImagickDraw object to draw border
$border = new ImagickDraw();
// Set fill color to transparent
$border->setFillColor( 'none' );
// Set border format
$border->setStrokeColor( new ImagickPixel( $borderColor ) );
$border->setStrokeWidth( $borderWidth );
$border->setStrokeAntialias( false );
Draw border
$border->rectangle(
$borderWidth / 2 - 1,
$borderWidth / 2 - 1,
$imageWidth - ( ($borderWidth / 2) ),
$imageHeight - ( ($borderWidth / 2) )
);
// Apply drawed border to final image
$imageWithBorder->drawImage( $border );
$imageWithBorder->setImageFormat('png');
Save Image
// Put source image to final image
$imageWithBorder->compositeImage(
$image, Imagick::COMPOSITE_DEFAULT,
$borderWidth + $borderPadding,
$borderWidth + $borderPadding
);
$imageWithBorder->writeImage($path);
Recenter and fit to original image height and width
$imageWithBorder->scaleImage(FINAL_WIDTH, FINAL_HEIGHT, true);
$imageWithBorder->setImageBackgroundColor($background);
$w = $imageWithBorder->getImageWidth();
$h = $imageWithBorder->getImageHeight();
$imageWithBorder->extentImage(FINAL_WIDTH, FINAL_HEIGHT, ($w -
FINAL_WIDTH) / 2, ($h - FINAL_HEIGHT)/ 2);
$imageWithBorder->writeImage($path);
Hope it helps. Cheers!
1
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