Table 4 A comparison between the three proposed methods
From: Progressive sharing of multiple images with sensitivity-controlled decoding
Methods | Characteristic | Suitable environment | Advantage | Disadvantage |
|---|---|---|---|---|
Method 1 | a) Basic form of our progressive sharing/viewing. | All participants, i.e., all holders of stegos, must be of equal importance. | a) Simple and stable. | Shadow size is larger than that of method 3. |
b) Every stego image is of the same significance. | b) Every stego image hides the same amount of secrets. Therefore, there is no need to worry about which cover image should hide more. | |||
Method 2 | a) The recovered versions of the secret images are identical to that of method 1. | The owners of some stegos are more important than the owners of other stegos. | a) Method 1 is just a special case of method 2. | a) Shadow size is larger than that of method 3. |
b) However, the stego images have different weights in method 2. | b) Hence, compared to method 1, method 2 has more possible ways to control the unveiling of secret images. | b) The hiding capacity of some covers might be insufficient (or a severe impact on some cover images might exist), if a weight value is much larger than other weight values. | ||
c) The stego images' quality is less stable than that of methods 1 and 3. | ||||
d) Therefore, a careful matching between weights and covers might be needed. (In general, assign larger weights to the cover groups of larger size.) | ||||
Method 3 | a) Using the so-called guardian stegos. | a) Suitable for a company which is controlled by a committee (the committee cannot allow any unveiling of secrets without the approval of a certain percentage of the committee members). | a) Some stegos are guardian stegos, and they form the committee to guard the disclosure of secrets (the unveiling of secrets cannot happen if many guardian stegos disapprove it). | a) The social rank of non-guardian stegos is very low. If the number of received guardian stegos is less than the minimal threshold value, then the secret images has no chance to be unveiled (even if ‘every’ non-guardian stego's holder wants to unveil the secret images). |
b) Keys are used in method 3. | b) Also suitable for the protection of images which are very sensitive. | b) The committee has the absolute rights to turn down the disclosure of a secret. | b) Some values of parameter r make the number of progressive levels reduced from the assigned value to a smaller value. | |
c) Smaller shadow size. | ||||
d) Better security than methods 1 and 2. |