本研究提出空間域的最低位元取代法與像素差值之資訊隱藏技術，利用人體視覺系統觀察能力有限的情況下於灰階影像中隱藏秘密訊息。本研究是以Jung學者於2018年所提出混合LSB／PVD藏密法為基礎而改良的資訊隱藏方法，其方法是將掩護影像切割成1×3個像素區塊進行運算，選定區塊中間像素為基底像素。其次，基底像素採用採用LSB及OPAP藏密法嵌入4位元的秘密訊息，其餘像素與藏密後的基底像素作差值計算，採用改良混合LSB／PVD法進行藏密，以LSB藏密法為基礎將像素區分高位元組及低位元組，在低位元採用2-bit LSB藏密法及高位元中6位元採用新式PVD藏密法。二種藏密法結合以提高影像嵌入容量，並保持低失真的影像品質。實驗以Lena等8張灰階影像進行測試，實驗結果本研究的平均藏密量為1,075,071位元，與混合LSB／PVD藏密法相較，藏密量可提升約略2.3％（約24,219位元），本研究因具有較高的藏密量，當嵌入率達4.1 bpp，影像品質可維持約30.82 dB，證明本研究藏密法可有效提升藏密量，同時能維持人眼難以察覺的範圍內。

This research proposes the least-significant-bit (LSB) substitution combined with the pixel-value differencing (PVD) steganography in the spatial domain, which hides secret information in grayscale images when the observation ability of the human visual system is limited. This research is an improved information hiding method based on the hybrid LSB/PVD method proposed by Jung et al. in 2018, which divides the original cover image into three consecutive non-overlapping blocks and selects the second pixel in each block as a base pixel. Next, the 4-bits secret data are embedded into the base pixels through LSB substitution and the Optimal Pixel Adjustment Process (OPAP).The difference values between the base pixels and their left and right counterparts will then indicate the quantity of information that can be embedded. The improved hybrid LSB/PVD method is used to embed the secret data, and the pixels are divided into high-byte and low-byte groups based on the LSB method. The 2 bits LSB method is used in the low-byte area and the new PVD method is used in the 6 bits in the high-byte area. The least-significant-bit (LSB) substitution combined with the new pixel-value differencing (PVD) steganography increases the image embedding capacity and maintains a low-distortion image quality. The experiments are tested with 8 grayscale images such as Lena. The experimental results show that the average embedded capacity is 1,075,071 bits. Compared with the original hybrid LSB/PVD method, it can be increased by about 2.3% (about 24,219 bits).When the embedded capacity is up to 4.1 bpp, the image quality can be maintained at about 30.82 dB. The experimental results show that the proposed method not only increases the embedded capacity, but also maintains the acceptable of the human eye image quality.