Compression of Steganographed PPG Signal with Guaranteed Reconstruction Quality Based on Optimum Truncation of Singular Values and ASCII Character Encoding.

Extraction and analysis of various clinically significant features of photoplethysmogram (PPG) signals for monitoring several physiological parameters as well as for biometric authentication have become important areas of research in recent years. However, PPG signal compression; particularly quality-guaranteed compression, and steganography of patient's secret information is still lagging behind.This paper presents a robust, reliable and highly-efficient singular value decomposition (SVD) and lossless ASCII character encoding (LL-ACE)-based quality-guaranteed PPG compression algorithm. This algorithm can not only be used to compress PPG signals but also do so for steganographed PPG signals that include the patient information.It is worth mentioning that such an algorithm is being proposed for the first time to compress steganographed PPG signals. The algorithm is tested on PPG signals collected from four different databases, and its performance is assessed using both quantitative and qualitative measures. The proposed steganographed PPG compression algorithm provides a compression ratio that is much higher than that provided by other algorithms that are designed to compress the PPG signals only.(1) the clinical quality of the reconstructed PPG signal can be controlled precisely, (2) the patient's personal information is restored with no errors, (3) high compression ratio, and (4) the PPG signal reconstruction error is neither dependent on the steganographic operation nor on the size of the patient information data.