您可以执行多种操作来实现较小的文件大小。让我来引导你通过它。

首先，你可以add custom image sizes 并将尺寸调整到最小。将以下内容放入函数文件中：

function my_insert_custom_image_sizes( $sizes ) {
    // get the custom image sizes
    global $_wp_additional_image_sizes;
    // if there are none, just return the built-in sizes
    if ( empty( $_wp_additional_image_sizes ) )
        return $sizes;

    // add all the custom sizes to the built-in sizes
    foreach ( $_wp_additional_image_sizes as $id => $data ) {
        // take the size ID (e.g., \'my-name\'), replace hyphens with spaces,
        // and capitalise the first letter of each word
        if ( !isset($sizes[$id]) )
            $sizes[$id] = ucfirst( str_replace( \'-\', \' \', $id ) );
    }

    return $sizes;
}


function custom_image_setup () {
    add_theme_support( \'post-thumbnails\' );
    add_image_size( \'small\', 160, 9999 ); //  small
    add_image_size( \'medium\', 300, 9999 ); //  medium
    add_image_size( \'large-cropped\', 578, 200, true ); //  cropped
    add_filter( \'image_size_names_choose\', \'my_insert_custom_image_sizes\' );
}

add_action( \'after_setup_theme\', \'custom_image_setup\' );

所以，my_insert_custom_image_sizes 将自定义图像添加到Media uploader窗口，我在custom_image_setup.

接下来，我们需要为每个尺寸设置JPEG压缩值。遵守以下规定：

add_filter(\'jpeg_quality\', create_function(\'$quality\', \'return 100;\'));

add_action(\'added_post_meta\', \'ad_update_jpeg_quality\', 10, 4);

function ad_update_jpeg_quality($meta_id, $attach_id, $meta_key, $attach_meta) {

    if ($meta_key == \'_wp_attachment_metadata\') {

        $post = get_post($attach_id);

        if ($post->post_mime_type == \'image/jpeg\' && is_array($attach_meta[\'sizes\'])) {

            $pathinfo = pathinfo($attach_meta[\'file\']);
            $uploads = wp_upload_dir();
            $dir = $uploads[\'basedir\'] . \'/\' . $pathinfo[\'dirname\'];

            foreach ($attach_meta[\'sizes\'] as $size => $value) {

                $image = $dir . \'/\' . $value[\'file\'];
                $resource = imagecreatefromjpeg($image);

                if ($size == \'large\') {
                    // set the jpeg quality for \'large\' size
                    imagejpeg($resource, $image, 35);
                } elseif ($size == \'medium\') {
                    // set the jpeg quality for the \'medium\' size
                    imagejpeg($resource, $image, 40);
                } elseif ($size == \'small\') {
                    // set the jpeg quality for the \'small\' size
                    imagejpeg($resource, $image, 40);
                } elseif ($size == \'large-cropped\') {
                    // set the jpeg quality for the \'large-cropped\' size
                    imagejpeg($resource, $image, 45);
                } else {
                    // set the jpeg quality for the rest of sizes
                    imagejpeg($resource, $image, 60);
                }

                // or you can skip a particular image size
                // and set the quality for the rest:
                // if ($size == \'splash\') continue;

                imagedestroy($resource);
            }
        }
    }
}

如注释所示，本部分设置压缩值：imagejpeg($resource, $image, VALUE). 您将需要仔细研究一下，找出哪个值最适合哪个图像大小。我为其余的图像设置了60%的压缩。

上述代码仅影响新更新的图像。如果您希望运行一个脚本来更改现有图像，请在插件文件夹中添加一个新文件夹并创建一个新的php文件，其中包含以下代码：

<?php
/*
Plugin Name: Compression JPEG Quality
Plugin URI: http://domain.com
Description: This plugin will change the jpeg image quality according to its size.
Author: Christine
Version: 1.0
Author URI: http://domain.com
*/

register_activation_hook(__FILE__, \'ad_modify_jpeg_quality\');

function ad_modify_jpeg_quality() {

    $attachments = get_posts(array(
        \'numberposts\' => -1,
        \'post_type\' => \'attachment\',
        \'post_mime_type\' => \'image/jpeg\'
    ));

    if (empty($attachments)) return;

    $uploads = wp_upload_dir();

    foreach ($attachments as $attachment) {

        $attach_meta = wp_get_attachment_metadata($attachment->ID);
        if (!is_array($attach_meta[\'sizes\'])) break;

        $pathinfo = pathinfo($attach_meta[\'file\']);
        $dir = $uploads[\'basedir\'] . \'/\' . $pathinfo[\'dirname\'];

        foreach ($attach_meta[\'sizes\'] as $size => $value) {

            $image = $dir . \'/\' . $value[\'file\'];
            $resource = imagecreatefromjpeg($image);

                    if ($size == \'large\') {
                        // set the jpeg quality for \'large\' size
                        imagejpeg($resource, $image, 35);
                    } elseif ($size == \'medium\') {
                        // set the jpeg quality for the \'medium\' size
                        imagejpeg($resource, $image, 40);
                    } elseif ($size == \'small\') {
                        // set the jpeg quality for the \'small\' size
                        imagejpeg($resource, $image, 40);
                    } elseif ($size == \'large-cropped\') {
                        // set the jpeg quality for the \'large-cropped\' size
                        imagejpeg($resource, $image, 45);
                    } else {
                        // set the jpeg quality for the rest of sizes
                        imagejpeg($resource, $image, 60);
                    }

            imagedestroy($resource);
        }
    }
}
?>

最后，添加WP Smush.it 插件将进一步降低文件大小。

需要考虑的几个注意事项：

所有这些都不会影响PNG文件的上载。使用此文件格式的唯一选项是添加一个插件，该插件将PNG转换为JPEG，但这意味着透明度将无法工作。另一个绝望的解决方案是将所有PNG文件转换为PNG 8位文件格式，该格式限制为256色。但是，这将使您的上载回到90年代。压缩不会影响Full size 大小选项。这是原始文件上载。如果您运行的是多作者网站，并且希望避免作者添加此文件大小，则可以添加筛选器以从下拉列表中删除此文件大小