2.1 Pixels superposition: black and white (left) and colored (right) 33
2.2 Electromagnetic spectrum 33
2.3 Additive color model with primaries red, green, and blue 34
2.4 Subtractive color model with primaries cyan, magenta, and yellow 35
2.5 Examples of pixels superposition 37
2.6 More examples of pixels superposition 37
2.7 Lattice for the RGB and CMY color models 38
2.9 The VV trick for the case of 4 colors. Subpixels with different colors are never superposed 45
3.6 Elementary blocks for circle share A for sharing 3 secrets: (a) 71
3.9 Absolute location of block [1, j], [2, j], and [3, j] 73
3.10 Elementary blocks of share B for sharing 3 secrets: 74
3.11 Instances of the first three pixels of the three strips in (a) P1, (b) P2, and (c) P3 75
3.15 Results of (a) A ⊗ B, (b) A120° ⊗ B, and (c) A240° ⊗ B 79
3.16 Elementary block for x secrets 80
3.19 Stacking results of the chosen visual patterns for Feng et al.’s scheme. 84
3.23 Transforming circle shares (a) and (b) into cylinder counterparts (c) and (d), respectively 90
4.1 Six possible patterns of subpixel arrangements with 50% gray. 97
4.2 An example of visual secret sharing scheme (VSSS) 98
4.3 An example of extended visual cryptography scheme (EVCS). 101
4.4 An example of random grid (RG) 102
4.5 Samples of ordered dither matrices 104
4.6 Point process and error diffusion 105
4.7 Error filters for error diffusion 106
4.8 Iterative and search-based method 106
4.9 Dither matrices for similar shadow scheme proposed in [32] 112
4.10 The conjugate error diffusion algorithm proposed in [9] 113
4.11 Examples of subpixel arrangements with enhanced misalignment tolerance 116
4.12 Variation of subpixel arrangement having the same transparency 117
4.13 An example of difference maximization 118
4.14 The possible pattern combinations of subpixel arrangements 118
4.15 Physical implementation of the concentric subpixel arrangements using square patterns 119
4.17 Examples of resulting images 121
4.18 Examples of the output with density pattern using 3 × 3 122
5.1 A construction for (2,n) Boolean probabilistic VCS 148
5.2 Ulutas et al. [18] construction for (2,n) Boolean probabilistic VCS 149
5.3 A construction for (n, n) Boolean probabilistic VCS 149
7.3 Binary image B in Experiment 1 208
7.4 Implementation results of Algorithm 4 for VCRG-3 with respect to B: 209
7.5 Implementation results of Algorithm 5 for VCRG-3 with respect to 210
7.6 Implementation results of Algorithm 6 for VCRG-3 with respect to 211
7.8 Reconstructed results of VCRG-3 with respect to 213
8.1 Example of encoding a visual cryptography scheme 224
9.1 A construction for almost ideal contrast (ΓQual, ΓForb)-VCS with reversing 263
9.2 A construction for ideal contrast VCS with reversing using a BSS 267
9.3 Cimato, De Santis, Ferrara, and Masucci’s ideal contrast VCS with reversing 269
9.4 Hu and Tzeng’s ideal contrast VCS with reversing 272
9.5 Yang, Wang, and Chen’s ideal contrast VCS with reversing 274
9.6 Ideal contrast VCS with reversing starting from any VCS 277
10.2 The concept of 2-out-of-2 VC 284
10.3 A 2-out-of-3 visual secret sharing scheme 284
10.4 Cheating in visual cryptography 286
11.4 The regions of deviation (dx, dy) that can recover the secret image 313
12.2 A man-in-the-middle manipulation attack by a trojan on an online money transfer 331
12.3 The main method is also applicable to mobile banking 332
12.5 Pixel-based (left) versus segment-based (right) visual cryptography 335
12.6 The main method using segment-based visual cryptography in (a) and (b) 336
12.10 For confirmation, the user has to click his PIN using inverted numbers 341
12.16 The voter enters the vote, verifies the image, and separates the slides 347
13.1 Error diffusion process 353
13.2 Original multitone ”Lena” (X) 354
13.3 Halftone image generated by error diffusion with the Steinberg kernel 355
13.4 Halftone image generated by error diffusion with the Jarvis kernel (Y1) 355
13.5 Secret pattern ”UST” to be embedded in the halftone image (W) 358
13.7 Image Y obtained by overlaying Y1 in Figure 13.4 and Y2 in Figure 13.6 359
13.8 The DHCED (Data Hiding by Conjugate Error Diffusion) process 360
13.10 Image Y obtained by overlaying Y1 in Figure 13.4 and Y2 in Figure 13.9 364
13.11 Original multitone ”Pepper” (X2) 364
13.13 Image Y obtained by overlaying Y1 in Figure 13.4 and Y2 in Figure 13.12 365
13.14 Original multitone image ”Ramp” (X) 369
13.15 Secret pattern ”Column” to be embedded in the halftone image (W) 369
13.16 Halftone images generated by error diffusion with the Jarvis kernel (Y1) 370
13.18 Image Y obtained by overlaying Y1 in Figure 13.16 and Y2 in Figure 13.17. 371
13.21 Contrast of Y in Figure 13.18 vs row-wise average intensity of X in Figure 13.14 (Ramp) 373
13.24 Image Y obtained by overlaying Y1 in Figure 13.16 and Y2 in Figure 13.23. 375
13.27 Contrast of Y in Figure 13.24 vs row-wise average intensity of X in Figure 13.14 (Ramp) 377
14.1 Principle of image sharing 383
14.2 Image sharing based on the Lagrange interpolation in (a) and (b) 390
14.3 Experimental results of image sharing based on the Lagrange interpolation in (a) and (b) 391
14.4 The image sharing by using a high degree polynomial interpolation in (a)-(c) 392
14.5 Intersection of two pencils of lines in (a) and (b) 394
14.6 Image sharing scheme based on moving lines 395
14.7 Improved algorithm of image sharing 397
14.8 The experimental results of image sharing by moving lines 397
14.9 The experimental results of image sharing by moving lines 398
14.10 The experimental results of image sharing by moving lines 398
14.11 Breaking the correlation of neighboring blocks in an image 399
15.1 The format of Bij, where xj, wj, υi, and υi are represented as binary pattern 408
15.2 The format of stego-block with the size of 2 × 2 gray-level pixels 409
15.4 Demonstration of steps in RAHA 414
15.8 (a) the target images; (b)–(e) the four cover images; (b′)–(e′) the four stego-images 421
16.1 The ij-th block of the k-th cover 429
16.2 The block of the k-th stego-image in Lin-Tsai’s scheme 430
16.3 The cover blocks used in Yang et al.’s scheme 431
16.4 The block of a stego-image in Yang et al.’s scheme 431
16.5 The block of a stego-image in Chang et al.’s scheme 433
16.6 The flowchart of Chang et al.’s scheme 434
16.7 Error diffusion architecture 435
16.8 The kernel weights of Floyd and Steinberg’s error filter 435
16.9 The positions of pixels located at the border in an image 436
16.10 The “excursion” skill 437
16.11 The neighboring pixels that accepted error diffusion for Case 1 438
16.12 The neighboring pixels that accepted error diffusion for Case 2 438
16.13 The neighboring pixels that accepted error diffusion for Case 3 439
16.15 The flowchart of Chung and Wu’s ELUT scheme 441
16.16 Procedure for generating final grayscale image in Step 4 443
16.17 The flowchart of the work by the sender 446
16.18 The flowchart of the work by the recipient 446
16.19 The z-th block of GI and the corresponding HIz, Pz 447
16.20 The four pixels of each cover block CBi 448
16.21 Hiding the six data bits of F(Xi) 448
16.22 Hiding the check bits p1, p2 449
16.23 The flowchart of Step 4 450
16.24 The four pixels of each stego block CB′j 451
16.25 The 2-bit check bits carried in CB′z when t =2 451
16.26 The bits of Xi and F(Xi) carried in the stego block 452
16.28 The experimental results for comparing the PSNR among the past work and ours 455
16.29 The visual quality of the reconstructed grayscale image 456
18.217.208.72