I think, the difference between the books digital image processing and digital image processing, is that, digital image processing (DIP) deal with the theoretical foundation of digital image processing, while digital image processing using Matlab for image processing.
Moreover, the DIPUM book covers essentially the same topics as DIP, however, the theoretical treatment is not as detailed. some instructors prefer to fill in the theoretical details in class in favor of having available a book with a strong emphasis on implementation.