Keep image EXIF info after compressing original image?

Question

After testing I realized that Word Press after image upload will make medium and thumbnail sized images of original image without EXIF/IPTC info

I realized it is because GD image library is used on my host, and that is how GD library works by default, strip out all image info.

After research I found out that if ImageMagick and the Imagick PHP extension is used instead of GD library EXIF info will be retained (with ImageMagick default settings) in generated resized image files.

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UPDATE 1

ImageMagick and the Imagick PHP extension is installed on my host now. Now all generated images keep EXIF/IPTC info (original, medium and thumbnail image, all of them are with EXIF/IPTC data).

I allow visitors to upload hi-res images on site, and in most cases visitors do not optimize/compress images before upload and sometimes image file size is quite big.

For example 12MP image can be 10 MB, but after 85% jpeg compression its file size can be 2-3 times smaller, almost without noticeable loss of quality.

I put this function to functions.php (my theme folder) to compress original image during upload, to save up disk space and speed up loading of hi-res image on page with it.

// Image compression on upload, compress original image
function wt_handle_upload_callback( $data ) {
    $image_quality = 85; // 85% compression
    $file_path = $data['file'];
    $image = false;

    switch ( $data['type'] ) {
        case 'image/jpeg': {
            $image = imagecreatefromjpeg( $file_path );
            imagejpeg( $image, $file_path, $image_quality );
            break;          
        }

        case 'image/png': {
            $image = imagecreatefrompng( $file_path );
            imagepng( $image, $file_path, $image_quality );
            break;          
        }

        case 'image/gif': {         
            // Nothing to do
            break;
        }
    }

    return $data;
}
add_filter( 'wp_handle_upload', 'wt_handle_upload_callback' );

It works fine, original image is compressed, BUT this function removes EXIF/IPTC data on all images (I need to keep EXIT, at least on original image). Without function above, original and all resized images are with EXIF/IPTC data (because ImageMagick is installed), but original image is not compresed than.

How to fix, adjust function above to keep EXIF?

UPDATE 2

WP 4.5 is reseased with some image hadling improvements, and also with option to preserve image EXIF data (in case ImageMagic is used on host, which is in my case). WP 4.5 introduced new filter "image_strip_meta" which can be used to keep or remove EXIF on generated resized images (medium and thumbnails).

Can this filter be used to keep EXIF in original image when function above for compressiong original image (which remove all EXIF data from original and all resized image version) is used?

Or, anything else which will result in compressing original image right after upload and keep EXIF in original image?

Answer 1

The problem is that you are using functions from GD library to manipulate images, not functions from WordPress Image API (WP_Image_Editor class). So, WordPress things doesn't apply to the generated image by your code.

WordPress Image API uses ImageMagick if available, otherwise it uses GD library.

In order to keep EXIF data:

1. If GD library is used, you need to install PHP wih the EXIF exension and configure PHP with --enable-exif flag.
2. If ImageMagick is available, then WordPress will use it and EXIF and other meta data is preserved. Also, you have access to image_strip_meta filter (not availabe if GD library is used).

As you have ImageMagick installed, you could use it instead of GD library. Or, maybe better, use WordPress API:

add_filter( 'wp_handle_upload', 'wt_handle_upload_callback' );
function wt_handle_upload_callback( $data ) {

    // get instance of WP_Image_Editor class
    $image = wp_get_image_editor( $data['file'] );

    if( ! is_wp_error( $image ) ) {
        $image->set_quality( 85 );
        $image->save( $data['file'], $data['type'] );
    }

    return $data;
}

I've not tested the above code and I think you don't need it. If the only prupose of doing all of this is to compress the image, you must know that the image is already compressed by WordPress to 82% quality (90 before WP 4.5). If you need to change the compression quality just use jpeg_quality filter:

add_filter( 'jpeg_quality', 'cyb_set_jpeg_quality' );
function cyb_set_jpeg_quality() {
    return 85;
}

Answer 2

You should not assume that image related metadata survives the wordpress image manipulation. As you found out it depends on the image manipulation library installed on the server, and actually in version 4.5 the aim would be to strip some of it as noted here https://make.wordpress.org/core/2016/03/12/performance-improvements-for-images-in-wordpress-4-5/.

If you need the metadata as part of the thumbnail (and I fail to see why would you need it), you should just directly call the php image manipulation API, and then update the wordpress DB to set the proper fields as if the wordpress API handled it (probably can be done with some filters without changing the overall process too much)