Process compressed pixel data.

[ifpiero]

First I should thank you all for providing me great help of processing uncompressed pixel data.
Now I want to process compressed pixel data , My application is that ,I want to add watermark to the image embedded in the dicom file . I need to do the following steps ,
(1) read out the pixel data
(2) decode the compressed pixel data
(3) add watermark
(4) encode the pixel data again
(5) write the pixel data back to the dicom file ,update the meta file informtion
(6) save the dicom file.

My question is that ,which functions can I use for the above steps? And Any suggestion is greatly appreciated !
thanks in advance !

[ifpiero]

Anyone can give me some hints ?
Thanks in advance.