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1 These codes use the DCT,Hartley and Subband DCT
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2 Transforms for watermarking purposes.All schemes
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3 are blind,no original image is used for detection.
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4 Each casting module is accompanied by a testing
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5 module.Supposing that the watermark key that you
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6 select during casting is in the range 1-1000,the
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7 testing module will test all the keys in this range
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8 to produce the well known similarity diagrams used
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9 by Cox, Piva and many more with the peak being the
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10 proof of the watermark existence.
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11
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12 I do not include a detection module because this implies
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13 the use of certain thresholds. Although the casting
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14 methods are almost standardized (multiplicative formula)
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15 there are still questions about this thresholding but
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16 the testing modules can be easily changed to fit this
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17 purpose.
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18
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19 The DCT scheme does not use the visual masking improvement
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20 that Barni and his team suggest in one of their later works.
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21 In all casting programs we assume that the coefficients are
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22 diagonaly scanned,and ordered as shown in the following example.
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23
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24 ----------------------
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25 | 1| 3| 6|10|15|...
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26 ----------------------
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27 | 2| 5| 9|14|...
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28 ----------------------
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29 | 4| 8|13|...
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30 ----------------------
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31 | 7|12|...
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32 ----------------------
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33 |11|...
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34 ----------------------
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35
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36 which is quite simple comparing to the zig zag scanning
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37 pattern that we know from the JPEG standard but does not
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38 affect at all the idea that we have of the middle
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39 frequencies.Also the user should take care that
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40
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41 starting_coefficient+number_of_coeffs_to_change<(N*N)/2
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42
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43 which means that we shouldn't exceed the matrix diagonal.
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44 To do so the scanning scheme should be changed accordingly
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45 but this doesn't seem important because in all of the
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46 schemes we don't get out of the middle frequencies coefs.
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47 With correctly selected parameters,the schemes perform in
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48 the same way as if the coeffs were zig zag scanned.
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49
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50 In the Subband DCT version,the first set of questions
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51 about starting coefficient,number of coefficients to
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52 alter and alpha parameter, refer to the LH,HL and HH
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53 band while the second set of questions sets the parameters
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54 about the LL band only.
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55
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56 All schemes should not be used with the same set of parameters
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57 because each of the transforms, possess certain specific
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58 properties. This should be kept in mind for testing purposes.
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59 To use the right set of parameters please refer to corresponding
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60 bibliography.
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61 All code has been tested in Visual C++ v6.0
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62
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63 Have some nice tests...
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64 Vassilis Fotopoulos
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65
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66 for more info,ideas or points of discussion
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67 email vfotop1@physics.upatras.gr
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