Note: SO converted above the reference image to JPEG. Here is a transparent PNG .
Below is an example of a code that recreates a png image on a new canvas and retains transparency. As you can see, this also allows you to manipulate the pixel level, for example. with a custom function like custom_func($r, $g, $b) , which is better illustrated at the bottom of this question.
Basically, this code recreates / redraws the above image on a new canvas successfully, as it is. Please note that in this image the sky is completely transparent.
$image = imagecreatefrompng('grass.png'); $x_dimension = imagesx($image); $y_dimension = imagesy($image); $new_image = imagecreatetruecolor($x_dimension, $y_dimension); // create a transparent canvas $trans_color = imagecolorallocatealpha($new_image, 0x00, 0x00, 0x00, 127); imagefill($new_image, 0, 0, $trans_color); for ($x = 0; $x < $x_dimension; $x++) { for ($y = 0; $y < $y_dimension; $y++) { $rgb = imagecolorat($image, $x, $y); $r = ($rgb >> 16) & 0xFF; $g = ($rgb >> 8) & 0xFF; $b = $rgb & 0xFF; $alpha = ($rgb & 0x7F000000) >> 24; //$pixel = custom_function($r, $g, $b); imagesetpixel($new_image, $x, $y, imagecolorallocatealpha($image, $r, $g, $b, $alpha)); } } imagesavealpha($new_image, true); imagepng($new_image, 'grass-result.png');
However, when I run the same code in this particular png image below.
It gives me an almost black image like this.
I would like to understand what is happening here and why? Most importantly, I would like to learn about the possible factors that may affect the process, so I could study it. Why is the result different from one png to another?
Ideally, I would like my code to be able to save and transmit the transparency state (transparent, translucent or opaque) of the original png image, as it is, to the recreated image. As you can see, I was able to achieve this, with the exception of the case described above.
Just in case, here is my environment. Windows 7 - 64 bit ** Wampserver2.5 ** Apache-2.4.9 ** Mysql-5.6.17 ** php5.5.12-64b. Also here is var_dump image with getimagesize() :
array (size=6) 0 => int 228 1 => int 230 2 => int 3 3 => string 'width="228" height="230"' (length=24) 'bits' => int 8 'mime' => string 'image/png' (length=9)
UPDATE Here is the proof that the sample image is truly transparent, and that it can be manipulated while maintaining transparency. Note that the bottom of the image is more brownish. This was achieved by slightly modifying this line of imagesetpixel($new_image, $x, $y, imagecolorallocatealpha($image, 100, $g, $b, $alpha));