使用PHP将图像转换为WordPress中的灰度

Question

I'm trying to customize a WordPress plugin which has a function that I wish to add the action to convert colored images to grayscale. I learned that imagefilter($image, IMG_FILTER_GRAYSCALE)does the trick. But I can't seem to get it to work.

public function stream_photo( $image_path, $src, $key, $user_id, $coord, $crop ) {
    $image = wp_get_image_editor( $image_path ); // Return an implementation that extends WP_Image_Editor

    //DEBUG
    imagefilter($image, IMG_FILTER_GRAYSCALE);

    $quality = UM()->options()->get( 'image_compression' );

    if ( ! is_wp_error( $image ) ) {
        if ( ! empty( $crop ) ) {

            if( ! is_array( $crop ) ) {
                $crop = explode(",", $crop );
            }

            $src_x = $crop[0];
            $src_y = $crop[1];
            $src_w = $crop[2];
            $src_h = $crop[3];

            $image->crop( $src_x, $src_y, $src_w, $src_h );

            $max_w = UM()->options()->get('image_max_width');
            if ( $src_w > $max_w ) {
                $image->resize( $max_w, $src_h );
            }
        }

        //DEBUG
        //echo "Image path is: " . $image_path;
        //$image = wp_load_image($image_path);
        //imagefilter($image_path, IMG_FILTER_GRAYSCALE);

        $image->save( $image_path );

        //DEBUG
        //imagefilter($image, IMG_FILTER_GRAYSCALE);

        $image->set_quality( $quality );

        //DEBUG
        //echo "Image path is: " . $image_path;
        //$image2 = wp_load_image($image_path);
        //imagefilter($image2, IMG_FILTER_GRAYSCALE);
    } else {
        wp_send_json_error( esc_js( __( "Unable to crop stream image file: {$image_path}", 'ultimate-member' ) ) );
    }
}

Answer 1

The problem is this lines of code:

$image = wp_get_image_editor( $image_path ); // Return an implementation that extends WP_Image_Editor

//DEBUG
imagefilter($image, IMG_FILTER_GRAYSCALE);

wp_get_image_editor return a WP_Image_Editor object, but imagefilter require only 'image resource'. The change below should work.

$image = wp_get_image_editor( $image_path ); // Return an implementation that extends WP_Image_Editor

$im = imagecreatefrompng($image_path);
if($im && imagefilter($im, IMG_FILTER_GRAYSCALE)){
    // Convert to grayscale
    imagefilter(imagecreatefrompng($image_path), IMG_FILTER_GRAYSCALE);
    // Save image
    imagepng($im, $image_path);
    imagedestroy($im);
}

That's for PNG, should you catch all image extension instead of PNG only.