private void openImageViewer(final ImageGalleryImageBinding binding) {
        if (activity == null || !allowOpenViewer) {
            return;
        }
        allowOpenViewer = false;

        final int intentPos = this.binding.imagegalleryList.getChildAdapterPosition(binding.getRoot());
        final int contentPos = categorizedImageListHelper.getContentIndexForListIndex(intentPos);

        final List<Image> images = new ArrayList<>();
        for (ImageGalleryEntry item : adapter.getItems()) {
            if (!item.isHeader()) {
                images.add(item.image);
            }
        }

        ImageViewActivity.openImageView(this.activity, geocode, images, contentPos,
                this::getImageViewForContentIndex);
    }
allows the gallery to open a image detail view (again)
main/src/main/java/cgeo/geocaching/ui/ImageGalleryView.java