public static BitmapDrawable getErrorImage(final Resources resources, final boolean nonTransparent) {
        if (nonTransparent) {
            return HtmlUtils.IMAGE_NOT_LOADED;
        }
        return ImageUtils.getTransparent1x1Drawable(resources);
    }
Caches are loaded from disk on a computation scheduler to avoid using more threads than cores while decoding
the image. Downloads happen on downloadScheduler, in parallel with image decoding.
main/src/main/java/cgeo/geocaching/network/HtmlImage.java