An Improved Bidirectional Shift-Based Reversible Data Hiding Scheme Using Double-Way Prediction Strategy

Algorithm 1

Pseudocode of embedding process 1.

	Input: grayscale cover image I, secret si, as one bit of the secret message S, and threshold TH
	Output: stego image I1
	for each pixel I (i, j) (except for the pixels in the last column and the last row)
	Scan in the raster scan order;
	Calculate the prediction error of I (i, j) as Pe (i, j) with equations (1) and (2);
	Generate PEH of I, PK = 2 × TH, PKl = 2 × PK;
	Find out zero bins and denote them as Zrn and Zlm;
	/right expanding and shifting/
	if
	Δbin (i, j) =  + TH + si;
	elseif
	Δbin (i, j) = PK − n, where ;
	else
	Δbin (i, j) = 0;
	endif;
	I1r (i, j) = I (i, j) + Δbin (i, j);
	end;
	/finish right and begin left expanding and shifting/
	for each pixel I1r (i, j)
	Per (i, j) = I1r (i, j) − P (i, j) = I (i, j) + Δbin (i, j) − P (i, j) =  + Δbin (i, j);
	if
	Δbinl (i, j) = Per (i, j) − TH − PK − ;
	elseif Per (i, j) < −TH
	Δbinl (i, j) = −PKl + m, where , ;
	else
	Δbinl (i, j) = 0;
	endif;
	I1 (i, j) = I1r (i, j) + Δbinl (i, j);
	Pel (i, j) =  + Δbin (i, j) + Δbinl (i, j);
	end;
	/finish embedding process 1/