Image Sharing with Steganography and Authentication - Visual Cryptography and Secret Image Sharing - page 433

the height of the ridge falls below T 2 . The Canny edge detector is more likely
to detect true weak edges and less likely than the others to be fooled by noise.

16.3.4 Edge Lookup Inverse Halftoning Technique
The inverse halftoning technique is used to reconstruct a gray-scale image from
an input halftone image. Based on the lookup table (LUT) [10,16] technique,
in 2005 Chung and Wu [11] proposed a new edge-based lookup table (LUT)
scheme that improves the quality of the reconstructed grayscale image. In
the following paragraphs we call Chung and Wu's scheme ELUT for short.
The ELUT scheme first applies the LUT-based inverse halftoning scheme as a
preprocessing step to transform the input halftone image to a base grayscale
image, and then the edges are extracted and classified from the base grayscale
image. According to these classified edges, a novel edge-based LUT is built up
to reconstruct the grayscale image, i.e., the ELUT scheme. Figure 16.15 is a
owchart of Chung and Wu's ELUT scheme.

FIGURE 16.15
The owchart of Chung and Wu's ELUT scheme.

Input: A set of n training image pairs GIi i ;HI i ), where GI i and HI i are

denoted as the i-th grayscale image and its corresponding halftone