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Hello
I am working in the field of Digital Image Watermarking for = colored
images
Attached to this email are two programs
In order to process colored images as in the 1st = program
-I first separated the three RGB components from one = another
-then I performed a DWT on the Bule image component
-and then I tried to multiply all the coefficients by a = constant
number (100)
-Then performed an IDWT on the modified blue image = component
-and Finally, I combined the RG and modified blue = components back
together and wrote the modified image
In the 2nd program
I read the modified RGB image, separated the three = components
and then performed a DWT on the blue modified image = component
Then I divided all the coefficients by the same constant
used in the 1st stage (100)
Then I performed an IDWT on the modified blue image = component
and finall combined the RG and B all together and wrote the
processed image
matter of fact, there is a difference between both images, = the
original Monalisa Image and the processed image.
The precision have been doubled for all variables.
When the value of the constant change the difference = between the
original and processed images change
when the mul;tiplication and division are changed into = addition and
subtraction, for values below 100, there is a slight = modifications, for
values below 1000 , they are more, and so on
so I want to ask why is the process not reversible?
In other meanings
the subtraction should cancel the effect of addition
and the division should cancel the effect of the
multiplication,
but this is not what happens
This problem doesn't appear in gray-level images; and a = colored
image is supposed to be a three stacks of gray level images, = so I
really cannot explain why this happens and I would = truly
appreciate a further assistance to solve it.
Also, if you can direct me for further readings in the area = of
watermarking colored images, I would truly appreciate it. As a = matter of
fact, I could only find 3 papers on the internet and the three = adds PN
sequences while I would like to add a picture which involves = multiplying
and dividing by the weighing factor (ALPHA)
Thanks in Advance
===========================
Eng. Dahlia R.
ElShafie
Teaching Assistant = and M.Sc.
Student
Electronics and
communications
College of = Engineering and
Technology
Arab Academy for = Science and
Technology
Alexandria-Egypt
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