Imagick::setImageCompressionQuality()

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设置图片压缩的质量

说明

Imagick::setImageCompressionQuality(int $quality): bool

设置图片压缩的质量

参数

$quality

配置压缩质量的整数

返回值

成功时返回TRUE。

错误／异常

错误时抛出 ImagickException。

I had strange results when trying to get good png compression.
I used Imagick::COMPRESSION_ZIP
Here are a few file sizes for a few compression levels.
0: 236,100
1: 274,035
9: 258,379
50: 241,282
100: 240,156
Note the best result at 0. Also I got thrown off for a long time trying to get similar results to gimp. Make sure your image depth is set to 8, it appears to be 16 bits per channel, at least for me.
You can check with identify -verbose filename.png
You can also strip a bit more file size with $image->stripImage();

For a PNG image, `setImageCompressionQuality()` is not work at all, length of the generated files are totally same.
But I found an effective way, that is use `setOption('png:compression-level', 9)`, the value range is 0-9.

This example shows how to set the compression type, set the compression quality, create a thumbnail and remove unnecessary data in order to reduce file size.
This will use the following functions in reference:
Imagick::setImageCompression
Imagick::setImageCompressionQuality
Imagick::stripImage
Imagick::thumbnailImage
Imagick::writeImage
<?php
  $image = 'image.jpg';
  $directory = '/path/to/image';
  $image_location = $directory . "/" . $image;
  $thumb_destination = $directory . "/t" . $image;
  $compression_type = Imagick::COMPRESSION_JPEG;
  
  $im = new Imagick($image_location);
  $thumbnail = $im->clone;
  $thumbnail->setImageCompression($compression_type);
  $thumbnail->setImageCompressionQuality(40);
  $thumbnail->stripImage();
  $thumbnail->thumbnailImage(100,null);
  $thumbnail->writeImage($thumb_destination);
?>
Now, obviously you don't have to do so much with the variables and the file location. I only used so many to demonstrate where the images are coming from and where they are going.
NOTE: The $thumbnail->thumbnailImage(100,null); keeps the aspect ration by setting the second parameter to null. Read about this at Imagick::thumbnailImage
There is another way to create thumbnails that works quite well if you want to crop the image rather than using the entire image. Check out Imagick::cropThumbnailImage

The default value fot the JPEG compression quality appears to be 86.