added maximum contrast bypass mode

The original paper assumes maximum contrast is the goal, thus it embeds synthetic random bits after the payload has been embedded. The maximum contrast bypass mode ensures that the algorithm terminates right after the payload has been embedded.

.gitignore

@@ -0,0 +1,3 @@
+
+main.asv
+*.asv

main.m

@@ -3,18 +3,31 @@
 image=double(imread('Kodak images/Original/kodim01_org.png'));
 
 %Payload
-payload_length=25000; %number of bits to be embedded
+rng(1) %Presets randomness to ensure the results are reproducible
+payload_length=15000; %number of bits to be embedded
 payload=randi([0,1],payload_length,1);
 
-%Embedding
-[rdh_image, ~, ~, ~,embedding_capacity_left]=mbp(image,payload);
+%% Embedding for maximum contrast
+iteration_max=[];
+[rdh_image, ~, ~, ~,embedding_capacity_left]=mbp(image,payload,iteration_max,[]);
 if embedding_capacity_left < 0
-    disp('Failed embedding')
+    disp('Failed embedding, increase iteration_max') % default maximum iteration_max is 300, you can increase it as much as you want, but it may take longer time
 else
     disp(['Can embed ' num2str(embedding_capacity_left) ' bits more (estimated)'])
 end
 
-%Recovery check
+%% Embedding only the payload => does not maximize the contrast
+max_contrast_bypass_mode=1;
+iteration_max=[];
+[rdh_image_non_max_contrast, ~, ~, ~,embedding_capacity_left_non_max_contrast]=mbp(image,payload,iteration_max,max_contrast_bypass_mode);
+if embedding_capacity_left_non_max_contrast < 0
+    disp('Failed embedding, increase iteration_max') % default maximum iteration_max is 300, you can increase it as much as you want, but it may take longer time
+else
+    disp(['Can embed ' num2str(embedding_capacity_left_non_max_contrast) ' bits more (estimated)'])
+end
+
+
+%% Recovery check for maximum contrast case
 [payload_rec, re_image] = mbp_recovery(rdh_image);
 if isequal(re_image,image)
     disp('Original image recovered')
@@ -28,10 +41,41 @@
     disp('Failed to recover the payload')
 end
 
+%% Recovery check for when only the specified payload has been embedded => does not maximize the contrast
+[payload_rec_non_max_contrast, re_image_non_max_contrast] = mbp_recovery(rdh_image_non_max_contrast);
+if isequal(re_image_non_max_contrast,image)
+    disp('Original image recovered')
+else
+    disp('Failed to recover the original image')
+end
+
+if isequal(payload_rec_non_max_contrast,payload)
+    disp('Payload recovered')
+else
+    disp('Failed to recover the payload')
+end
+
+
 %show the image
 close all
 figure(1)
 imshow(uint8(image))
 figure(2)
 imshow(uint8(rdh_image))
+figure(3)
+imshow(uint8(rdh_image_non_max_contrast))
+
+
+
+
+
+
+
+
+
+
+
+
+
+
 end

mbp.m

@@ -1,8 +1,10 @@
-function [rdh_image, iteration_max, EC_list, LM_size_list, embedding_capacy_left]=mbp(image, actual_payload, iteration_max)
-switch nargin
-    case 2
+function [rdh_image, iteration_max, EC_list, LM_size_list, embedding_capacy_left]=mbp(image, actual_payload,iteration_max, max_contrast_bypass_mode)
+if isempty(iteration_max)
         iteration_max = 300;
 end
+if isempty(max_contrast_bypass_mode)
+    max_contrast_bypass_mode = 0;
+end
 %Preprocess Payload (length appended)
 image_size=size(image);
 payload_length_max=2*ceil(log2(image_size(1)*image_size(2)+1));
@@ -46,7 +48,7 @@
     %Embedding capacity + stop condition check
     H_P_s=sum(image_hor==P_s);
 
-    if H_P_s-sum(image_hor(1:16)==P_s) < length(LM)+32 || iteration == iteration_max %Stop condition reached
+    if H_P_s-sum(image_hor(1:16)==P_s) < length(LM)+32 || iteration == iteration_max || (max_contrast_bypass_mode==1 && length(payload_total) > length(actual_payload)) %Stop condition reached
         %no need to update iteration
         P_s=P_s_previous;
         P_c=P_c_previous;