def METHOD_NAME(RGB_true, RGB_pred, alpha_mask):
    """Computes the L1 reconstruction loss, weighting the inverted alpha
        mask values in the predicted RGB image by beta.
    # Arguments
        RGB_true: Tensor [batch, H, W, 3]. True RGB label values.
        RGB_pred: Tensor [batch, H, W, 3]. Predicted RGB values.
        alpha_mask: Tensor [batch, H, W, 1]. True normalized alpha mask values.
    # Returns
        Tensor [batch, H, W, 3] with background loss values.
    """
    background_true = RGB_true * (1.0 - alpha_mask)
    background_pred = RGB_pred * (1.0 - alpha_mask)
    background_loss = tf.abs(background_true - background_pred)
    return background_loss