In this paper, we present a new protocol for achieving lower noise and consequently a higher dynamic range in optical encryption. This protocol allows for the securing and optimal recovery of any arbitrary grayscale images encrypted using an experimental double random phase mask encoding (DPRE) cryptosystem. The protocol takes advantage of recent advances that help reduce the noise due to the correlation of random phase mask in the decryption procedure and introduces the use of a "reference mask" as a reference object used to eliminate the noise due to the complex nature of the masks used in experimental DRPE setups. This noise reduction increases the dynamic range of the decrypted data, retaining the grayscale values to a higher extent and opening new possible applications. We detailed the procedure, and we present the experimental results, including an actual experimental video of a grayscale scene, confirming the validity of our proposal.