Reversible Data Hiding (RDH) is a kind of data hiding technique that allows the embedded
data can be retrieved as needed and can restore the stego image exactly as the original
image after the extraction of embedded data. Recently, RDH has been applied for medical
record management, where any distortion of digital images is not allowed. Many new RDH
techniques have been developed such as Pixel Value Ordering (PVO). This method is very
popular because it has the advantage of reducing the number of pixels shifted, such that
it can improve the stego image quality. However, existing method has a low embedding
capacity (31%). To overcome this problem, this paper proposed a modified Pixel Value Ordering where the difference value is expanded after sorting the pixel values resulting from
the embedding process based on different values of 0 and 1. In this case, the difference
values of -2, 0, 1, and 3 are used to embed the data, instead of only using the difference
values 0 and 1. The proposed method also uses the frequency of bit 0 and 1 in the message
to determine the pixels mapping that can be used to embed the message. The experiments
results show that the proposed method achieved an average embedding capacity (37%) and
obtained a higher PSNR value of 61 dB.
Keywords: Reversible Data Hiding (RDH), medical record, medical images, Pixel Value
Ordering (PVO).