如何使用Imagick :: quantizeImage将300,000色PNG图像减少到100,000种颜色？

Question

I tried to reduce a 300,000 color PNG image to 100,000 with Imagick::quantizeImage, but it becomes about 65,000 colors. Can't you get more than 65,000 colors?

PHP version: 7.1.27 Imagick module version: 3.4.3

reference: https://www.php.net/manual/en/imagick.quantizeimage.php

I tried to put various values for $colorspace and $treedepth as arguments, but it was only about 65,000 colors at most.

$img = new \Imagick('/path/to/300000-colors-image.png');
$img->quantizeImage(100000, \Imagick::COLORSPACE_SRGB, 0, false, false);
$img->writeImage('/path/to/result.png');
$img->clear();
$img->destroy();

// Confirm the result
$img = new \Imagick('/path/to/result.png');

// Expected: 100,000
// Actual: 65,000
echo $img->getImageColors(); 

$img->clear();
$img->destroy();

Answer 1

It turned out that up to 65,536 colors can be reduced with Imagick::quantizeImage.

reference(source code):

• https://github.com/ImageMagick/ImageMagick/blob/429e32167d55f505ce5644c3cefeb757dbe32bea/MagickCore/quantize.c#L2672
• https://github.com/ImageMagick/ImageMagick/blob/57b308b170bb9e0ab184602bb1fed47bafe5a9d4/MagickCore/magick-type.h#L74