Incorrect output: maximum ISO value = 65535

Resolved kasiel
(@kasiel)

4 months ago

Hello!

I run a members’ area for amateur photographers. The EXIF data for the ISO value isn’t displayed correctly in the lightbox. The maximum value shown is ISO 65535. As some older IT professionals have told me, this is due to a limitation of 2 bits or 16 bytes for the value.

The members can correctly read the ISO values in image editing software. For example, Lightroom displays 80000, while the value shown in the members’ area is 65535.

Would it be possible to fix this? Or is this a limitation that isn’t related to the plugin, but rather to some EXIF specification?

Karsten

Viewing 2 replies - 1 through 2 (of 2 total)

Plugin Support

Val Meow

(@valwa)

3 months, 4 weeks ago

Hey @kasiel! 👋

The EXIF data is taken directly from the attachment metadata that is saved in WordPress when you upload a media.

You can use the mwl_img_iso( $iso, $id, $meta ) filter to check if the ISO is capped at 65535 and, if that is the case, get the actual file to extract the EXIF data from the file directly to get the raw value and return it instead.

Hope this helps!

Thread Starter

kasiel

(@kasiel)

3 months, 4 weeks ago

Thank you, that was helpful! 🙂

The problem: The very high iso values are to find in EXIF[‘UndefinedTag:0x8832’], not in the EXIF[‘ISOSpeedRatings’] as I expected.

I created an new folder in wp-content/plugins: meow-lightbox-iso-fix
I created a new file: meow-lightbox-iso-fix.php within the folder with this code:

<?php
/**
 * Plugin Name: Meow Lightbox ISO Fix
 * Description: Liest das ISO aus EXIF (Nikon-Tag 0x8832) und gibt es an Meow Lightbox zurück.
 * Version: 4.0
 */

if ( ! defined( 'ABSPATH' ) ) {
    exit;
}

add_filter( 'mwl_img_iso', 'kk_force_exif_iso_from_tag_8832', 10, 3 );

function kk_force_exif_iso_from_tag_8832( $iso, $id, $meta ) {

    // Dateipfad des Attachments holen
    $file_path = get_attached_file( $id );
    if ( ! $file_path || ! file_exists( $file_path ) ) {
        return $iso;
    }

    // EXIF-Funktion vorhanden?
    if ( ! function_exists( 'exif_read_data' ) ) {
        return $iso;
    }

    // EXIF-Daten laden (alle Sektionen)
    $exif = @exif_read_data( $file_path, 0, true );
    if ( ! is_array( $exif ) || ! isset( $exif['EXIF'] ) ) {
        return $iso;
    }

    $exif_exif = $exif['EXIF'];

    // 1. Nikon / hoher ISO-Wert in UndefinedTag:0x8832
    if ( isset( $exif_exif['UndefinedTag:0x8832'] ) ) {

        $val = $exif_exif['UndefinedTag:0x8832'];

        // Kann theoretisch auch ein Array sein
        if ( is_array( $val ) ) {
            $val = reset( $val );
        }

        $new_iso = (int) $val;

        if ( $new_iso > 0 && $new_iso < 1000000 ) {
            return $new_iso; // z.B. 80000
        }
    }

    // 2. Fallback: normale ISO-Felder versuchen

    if ( isset( $exif_exif['ISOSpeedRatings'] ) ) {
        $val = $exif_exif['ISOSpeedRatings'];
        if ( is_array( $val ) ) {
            $val = reset( $val );
        }
        $fallback_iso = (int) $val;
        if ( $fallback_iso > 0 && $fallback_iso < 1000000 ) {
            return $fallback_iso;
        }
    }

    if ( isset( $exif_exif['PhotographicSensitivity'] ) ) {
        $fallback_iso = (int) $exif_exif['PhotographicSensitivity'];
        if ( $fallback_iso > 0 && $fallback_iso < 1000000 ) {
            return $fallback_iso;
        }
    }

    // 3. Wenn alles nichts bringt → ursprünglichen Wert von Meow zurückgeben
    return $iso;
}

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