Date of download: 5/27/2016 Copyright © 2016 SPIE. All rights reserved. Results of edge detector for the printed text and the “Lena” image. Figure Legend: From: Visual secret sharing scheme: prioritizing the secret pixels with different pixel expansions to enhance the image contrast Opt. Eng. 2007;46(9): doi: /

Date of download: 5/27/2016 Copyright © 2016 SPIE. All rights reserved. Two-pixel secret image and the colocations of subpixels in the shadows using the fixed and different pixel expansions. Figure Legend: From: Visual secret sharing scheme: prioritizing the secret pixels with different pixel expansions to enhance the image contrast Opt. Eng. 2007;46(9): doi: /

Date of download: 5/27/2016 Copyright © 2016 SPIE. All rights reserved. Overlapping patterns: (a) the arrangement for conventional schemes; (b) the arrangement with the invariant aspect ratio; (c) detailed representations of Fig. ; (d) the arrangement with the arbitrary aspect ratio. Figure Legend: From: Visual secret sharing scheme: prioritizing the secret pixels with different pixel expansions to enhance the image contrast Opt. Eng. 2007;46(9): doi: /

Date of download: 5/27/2016 Copyright © 2016 SPIE. All rights reserved. Mapping Pattern M, shadow images, and the recovered image for the (2,3) VSS scheme using the secret image “T”: (a) the 20×20- pixel secret image with 66 important pixels, (b) the 30×30-pixel mapping pattern M produced by using the proposed mapping algorithm, (c) three shadows by using the encoding algorithm, and (d) the recovered image produced by stacking any two out of three shadows. Figure Legend: From: Visual secret sharing scheme: prioritizing the secret pixels with different pixel expansions to enhance the image contrast Opt. Eng. 2007;46(9): doi: /

Date of download: 5/27/2016 Copyright © 2016 SPIE. All rights reserved. Recovered images for different shadow sizes. Figure Legend: From: Visual secret sharing scheme: prioritizing the secret pixels with different pixel expansions to enhance the image contrast Opt. Eng. 2007;46(9): doi: /

Date of download: 5/27/2016 Copyright © 2016 SPIE. All rights reserved. (a) to (h) obtained from Figs. by adjusting and rescaling. Figure Legend: From: Visual secret sharing scheme: prioritizing the secret pixels with different pixel expansions to enhance the image contrast Opt. Eng. 2007;46(9): doi: /

Date of download: 5/27/2016 Copyright © 2016 SPIE. All rights reserved. Diagram for Table : (a) the values of N2 for different mA and (b) the values of R for different mA. Figure Legend: From: Visual secret sharing scheme: prioritizing the secret pixels with different pixel expansions to enhance the image contrast Opt. Eng. 2007;46(9): doi: /

Date of download: 5/27/2016 Copyright © 2016 SPIE. All rights reserved. Important pixels in “House,” i.e., the edges in “House” obtained from the Sobel edge detector with different thresholds. Figure Legend: From: Visual secret sharing scheme: prioritizing the secret pixels with different pixel expansions to enhance the image contrast Opt. Eng. 2007;46(9): doi: /

Date of download: 5/27/2016 Copyright © 2016 SPIE. All rights reserved. Average pixel expansion mI for different thresholds: the maximum value is mI=2.407 when λ=0.04. Figure Legend: From: Visual secret sharing scheme: prioritizing the secret pixels with different pixel expansions to enhance the image contrast Opt. Eng. 2007;46(9): doi: /

Date of download: 5/27/2016 Copyright © 2016 SPIE. All rights reserved. Proposed (2,3) VSS scheme: (a) the original gray secret image used for finding the edges, (b) the important pixels in “House” using the threshold λ=0.04(NI=14,250), (c) the binary halftone image “House” used as the secret image, (d) three shadows, and (e) the recovered image by stacking any two out of three shadows. Figure Legend: From: Visual secret sharing scheme: prioritizing the secret pixels with different pixel expansions to enhance the image contrast Opt. Eng. 2007;46(9): doi: /

Date of download: 5/27/2016 Copyright © 2016 SPIE. All rights reserved. Hou-Tu color VSS scheme using our method: (a-1) the original color secret image “Baboon” (a-2) the “Baboon” with eight quantization colors used as the secret image, (a-3) the gray-scale image for the ”Baboon” used for finding the edges, (a-4) the important pixels in “Baboon” using the threshold λ=0.07(NI=15948), (b) the yellow shadow image, (c) the magenta shadow image, (d) the cyan shadow image, (e) the black shadow image, and (f) the recovered image by stacking four shadows (Color online only). Figure Legend: From: Visual secret sharing scheme: prioritizing the secret pixels with different pixel expansions to enhance the image contrast Opt. Eng. 2007;46(9): doi: /

Date of download: 5/27/2016 Copyright © 2016 SPIE. All rights reserved. New VSS-based automated visual authentication system. Figure Legend: From: Visual secret sharing scheme: prioritizing the secret pixels with different pixel expansions to enhance the image contrast Opt. Eng. 2007;46(9): doi: /

Date of download: 5/27/2016 Copyright © 2016 SPIE. All rights reserved. Simulated human visual system. Figure Legend: From: Visual secret sharing scheme: prioritizing the secret pixels with different pixel expansions to enhance the image contrast Opt. Eng. 2007;46(9): doi: /

Date of download: 5/27/2016 Copyright © 2016 SPIE. All rights reserved. Overlap between subpixels and secret pixels for the pattern of Fig. –1. Figure Legend: From: Visual secret sharing scheme: prioritizing the secret pixels with different pixel expansions to enhance the image contrast Opt. Eng. 2007;46(9): doi: /

Date of download: 5/27/2016 Copyright © 2016 SPIE. All rights reserved. Overlap between the subpixel and the secret pixel in the pattern Ma,b: (a) the (a×a)-size secret pixel block, (b) the (b×b)-size subpixel block, and (c) the overlap of a subpixel located at the coordinate (u,v) relative to a secret pixel located at the coordinate (x,y). Figure Legend: From: Visual secret sharing scheme: prioritizing the secret pixels with different pixel expansions to enhance the image contrast Opt. Eng. 2007;46(9): doi: /