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Visual cryptography for color images

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This is a presentation made in SIL765 class, IIT Delhi

This is a presentation made in SIL765 class, IIT Delhi

Published in: Engineering, Technology, Education

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• 1. Young-Chang Hou Department of Information Management National Central University, 2002 Mukesh Kumar(2010CS50288) Khaleeque Ansari (2010CS10222)
• 2. • General Idea • Introduction • Visual Cryptography on binary images • Visual Cryptography on gray-level images • Visual Cryptography on color images
• 3. • Traditional Cryptography • Encryption and decryption process need high computation costs • Need secret key for decoding • Visual Cryptography • less computation • Easy and fast decoding • No need of secret key
• 4. • Encrypt the secret image in n parts. • All n part can get together and recover secret image. • Less than n parts cannot recover secret image. • Example- • S1 and S2 individually have no information About secret number • S1 XOR S2 = Secret number Secret: 1011 S1:0110 S2:1101
• 5. • Naor and Shamir proposed the visual cryptography in 1994. • Used to encrypt written materials like printed text, pictures, handwritten text etc.
• 6. • Naor and Shamir proposed a scheme • take a pixel from secret image • extend it onto 2x2 subpixel • Randomly choose 1 out of 2 share.
• 7. • Transform the gray-level image into black-and white halftone image • Halftone technology uses the density of black dots to simulate the content of grayscale image • White area: low density of black dots • Black area: high density of black dots
• 8. • Basic principles of color • Additive model- primary colors (red, blue and green) are mixed to obtain the desired color.(eg. Computer screen ). • Subtractive model- color is represented by combinations of color lights reflected from the surface of an object.(eg apple absorb green and blue part of natural light and reflect red light)
• 9. • Rijmen and Preneel’s method • Each color pixel is expanded into a 2x2 block • Each 2x2 block is filled with red,green,blue and white • 24 possible combination (permutation of 4 colors) • Human eye cant detect color of tiny subpixel • Will treat as an average color • Disadvantage- • In additive model, any color mixed with white color gives white.
• 10.
• 11. • Method 1 • 1 secret image is converted to 4 shares C,M,Y & Mask
• 12. • Method 1 • 50% lost in contrast • Two level security control
• 13. • Method 2
• 14. • Method 2 • 25% contrast of Original Image
• 15. • Method 3
• 16. • Method 3 • 50% Contrast Loss • 2 Shares
• 17. • First paper to exploit color decomposition and halftone technology to generate visual cryptography for both gray-level and color images
• 18. • Shyong jian Shyu, Efficient visual secret sharing scheme for color images, Pattern Recognition Volume 39, Issue 5, May 2006 • Wikipedia page on Visual Cryptograpy http://en.wikipedia.org/wiki/Visual_cryptography
• 19. Questions ?