CODEWITHSUNDEEP
phpimagemagicktransparencyimagick
yakobom
yakobom

Reputation: 2711

Detecting a pixel transparency with Imagick

I am trying to calculate what is the percentage of pixels that has transparency in a specific image. For that, I'm trying to detect if a pixel has transparency (using Imagick on PHP). I know that basically there's 'getPixel' and 'getColor' that returns an rgba array, but I'm getting various values for the 'a' for jpg and non-transparent pngs images as well... I have tried with and without normalization.

For example, for this image I get alpha values of 0, 1, 0.1, 0.9 etc. for various pixels enter image description here.

This is the code I am using:

$imageIterator = $image->getPixelIterator();    
foreach ($imageIterator as $row => $pixels) {
    foreach ($pixels as $column => $pixel) { 
        $color = $pixel->getColor(true);
        echo $color['a'] . PHP_EOL;
        ...

What am I doing wrong? Is there another way of getting this info?

Upvotes: 2

Views: 1529

Answers (1)

Mark Setchell
Mark Setchell

Reputation: 207445

You can check your version with:

php -i | grep -i -A10 magick

Mine is this:

imagick module => enabled
imagick module version => 3.3.0
imagick classes => Imagick, ImagickDraw, ImagickPixel, ImagickPixelIterator, ImagickKernel
Imagick compiled with ImageMagick version => ImageMagick 6.9.3-0 Q16 x86_64 2016-01-08 http://www.imagemagick.org
Imagick using ImageMagick library version => ImageMagick 6.9.3-0 Q16 x86_64 2016-01-08 http://www.imagemagick.org
ImageMagick copyright => Copyright (C) 1999-2016 ImageMagick Studio LLC
ImageMagick release date => 2016-01-08

Running this code, I get all ones for your image - i.e. no alpha layer or a fully opaque image:

#!/usr/local/bin/php -f
<?php
$image = new Imagick("budgie.png");
$pixel_iterator = $image->getPixelIterator();
foreach($pixel_iterator as $y => $pixels)
{
   foreach($pixels as $x => $pixel)
   {
      $color = $pixel->getColor(true);
      echo $color['a'] . PHP_EOL;
   }
}
?>

And likewise, if I run identify on your image, it shows no alpha layer present:

identify -verbose budgie.png | more
Image: budgie.png
  Format: PNG (Portable Network Graphics)
  Mime type: image/png
  Class: DirectClass
  Geometry: 296x383+0+0
  Units: Undefined
  Type: TrueColor
  Endianess: Undefined
  Colorspace: sRGB
  Depth: 8-bit
  Channel depth:
    red: 8-bit
    green: 8-bit
    blue: 8-bit

I think there is something up with your versions/configurations.

Upvotes: 2

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