1） 通过扩展WP_Image_Editor_GD 问题是如何在更改中间jpeg图像的质量之前访问图像大小。

请注意image_resize() 函数为deprecated.

我们可以使用jpeg_quality 从公众中筛选get_quality 摘要方法WP_Image_Editor 类别：

$quality = apply_filters( \'jpeg_quality\', $quality, \'image_resize\' );

或者wp_editor_set_quality 滤器

以下是一种基于图像大小（宽度/高度）设置图像质量的方法：

/**
 * Set image (jpeg) quality based on the image size (width/height)
 * @see http://wordpress.stackexchange.com/a/165241/26350
 */
add_filter( \'wpse_make_image_arguments\', function( $arguments, $filename, $size, $function ) 
{   
    // Only target jpeg cases, i.e. with the quality set in $arguments[2]       
    if( ! isset( $size[\'height\'] ) || ! isset( $size[\'width\'] ) || ! isset( $arguments[2] ) )
        return $arguments;

    // Modify this part to your needs:
    if( $size[\'height\'] <= 150  && $size[\'width\'] <= 150 )
        $arguments[2] = 2; // very low quality for easy testing

    return $arguments;
}, 10, 4 );

我们将WP_Image_Editor_GD 类别：

/**
 * Extend the WP_Image_Editor_GD to add the custom wpse_make_image_arguments filter.
 * @see http://wordpress.stackexchange.com/a/165241/26350
 */
add_filter( \'wp_image_editors\', function( $editors ) 
{
    // Note that the WP_Image_Editor_GD and WP_Image_Editor_Imagick classes
    // are included within this filter. So let\'s do the same for our extended class.

    // Our extended class that overrides the WP_Image_Editor_GD::make_image() method

    if( ! class_exists( \'WPSE_Image_Editor_GD\' ) )
    {   
        class WPSE_Image_Editor_GD extends WP_Image_Editor_GD
        {
            protected function make_image( $filename, $function, $arguments ) 
            {
                // Add a custom filter      
                $arguments = apply_filters( \'wpse_make_image_arguments\', $arguments, $filename, $this->size, $function );

                // Parent method
                return parent::make_image( $filename, $function, $arguments );
            }
        }
    }

    // Prepend the extended class to the array of image editors:    
    array_unshift( $editors, \'WPSE_Image_Editor_GD\' );

    return $editors;
} );

我们在那里介绍了这个习俗wpse_make_image_arguments 滤器

这样我们可以修改质量设置，before 将保存中间文件。

下面是一个示例：

PS：我没有检查使用Imagick库时的情况，但我想我们可以通过扩展WP_Image_Editor_Imagick 班

2） 更新-设置每个图像大小名称的jpeg质量这里是另一个版本，我们在其中设置每个图像大小名称的jpeg质量：

/**
 * Extend the WP_Image_Editor_GD to set quality per image size name.
 * 
 * @see http://wordpress.stackexchange.com/a/165241/26350
 */
add_filter( \'wp_image_editors\', function( $editors ) 
{
    // Note that the WP_Image_Editor_GD and WP_Image_Editor_Imagick classes
    // are included within this filter. So let\'s do the same for our extended class.

    // Our extended class that overrides the WP_Image_Editor_GD::_resize() method
    if( ! class_exists( \'WPSE2_Image_Editor_GD\' ) )
    {   
        class WPSE2_Image_Editor_GD extends WP_Image_Editor_GD
        {
            protected function _resize( $max_w, $max_h, $crop = false )
            {
                $qualities = apply_filters( \'wpse_jpeg_qualities\', [] );
                $default_quality = (int) apply_filters( \'wpse_default_jpeg_quality\', 82 );                              
                $sizes = wp_get_additional_image_sizes();
                $this->set_quality( $default_quality );         
                foreach( (array) $qualities as $name => $quality )
                {
                    if( 
                        isset( $sizes[$name] ) 
                        && (int)  $sizes[$name][\'width\']  === (int)  $max_w
                        && (int)  $sizes[$name][\'height\'] === (int)  $max_h
                        && (bool) $sizes[$name][\'crop\']   === (bool) $crop  
                    )   
                        $this->set_quality( $quality );                 
                }

                // Parent method
                return parent::_resize( $max_w, $max_h, $crop );
            }
        }
    }

    // Prepend the extended class to the array of image editors:    
    array_unshift( $editors, \'WPSE2_Image_Editor_GD\' );

    return $editors;
} );

我注意到crop参数可以是0、false或空，所以我们做了一些类型转换来确保。

在此，我们引入了以下新过滤器：

add_filter( \'wpse_jpeg_qualities\', function( $qualities )
{ 
    return [ \'hello-image\' => 2, \'medium\' => 2, \'large\' => 2 ];
} );

以及

add_filter( \'wpse_default_jpeg_quality\', function( $quality )
{ 
    return 82;
} );

希望可以根据您的需要进行调整！