The proposed method partially and completely encrypts the gray scale Document images. The complete image encryption is also performed to compare the performance with the existing encryption methods. The partial encryption is carried out by segmenting the image using the Quad-tree decomposition method based on the variance of the image block. The image blocks with uniform pixel levels are considered insignificant blocks and others the significant blocks. The pixels in the significant blocks are permuted by using 1D Skew tent chaotic map. The partially encrypted image blocks are further permuted using 2D Henon map to increase the security level and fed as input to complete encryption. The complete encryption is carried out by diffusing the partially encrypted image. Two levels of diffusion are performed. The first level simply modifies the pixels in the partially encrypted image with the Bernoulli's chaotic map. The second level establishes the interdependency between rows and columns of the first level diffused image. The experiment is conducted for both partial and complete image encryption on the Document images. The proposed scheme yields better results for both partial and complete encryption on Speed, statistical and dynamical attacks. The results ensure better security when compared to existing encryption schemes.A new partial image encryption method for document images using variance based quad ... (C R Revanna) 787In [2], the authors proposed a bit-level scrambling algorithms to scramble bit positions. It is also said that the proposed algorithm provides flexibility to select any image as the input source image, any decomposition technique for obtaining the bit plane, any decomposed bit plane as the security key bit plane and any scrambling technique for the bit-level permutation. In [3], a chaotic system based partial image encryption is proposed. The proposed scheme includes bit plane decomposition of source image. After decomposing, the significant bit plane are selected for encryption. Encryption is achieved by generating the pseudorandom number sequence using chaotic system.In [4], a chaotic based partial grey sale image encryption is proposed. It is observed that the authors proposed a bit plane decomposing method for encryption. The various bit planes (significant and insignificant) are identified based on autocorrelation threshold of different binary planes. The key sequence obtained by chaotic map is used to encrypt the correlated bit planes. In [5], both selective and complete image encryption using the sequence of chaotic map. At first the chaotic map is used to generate a key to completely encrypt the plain image. Second, for the same input image selective portion is encrypted. Finally the complete and selective encrypted results are combined by XOR operation to achieve better security. A new technique called graph coloring problem (GCP) for partial encryption of medical image is proposed in [6]. The GCP technique is used to select the optimal positions of the pixels from the input medical imag...