Degradation modeling

"Knowing the problem is half way to meeting the solution."

Degradation modeling is a key step in development of restoration and enhancement method for document images. For document images which suffer imaging degradation, there are many well-developed models which can be used to generate datasets of text in the form of a single character, a single word, or even a whole page. In contrast, very old documents and ancient texts usually suffer physical degradation of several types as a result of their age. Much of the degradation suffered by document images that stems from physical processes is the result of some type of ink diffusion. Such defects are common in very old documents, as well as in media and documents made of poor-quality materials.

Recto and verso sides of a document image showing a thin stroke on the verso side and its nonlinear pattern on the recto side. The nonlinear nature of ink seepage can easily be seen from the interference patterns of the verso side that show through onto the recto side.


Seepage of ink through a paper is a complex physical phenomenon in which many parameters, such as thickness, the characteristics of the paper, the distribution of the paper fibers, and ink quality, are involved. From the fluid mechanics point of view, seepage is the flow of liquid through a porous medium that actually is a collection of numerous of tiny cells. The first and fastest approach to simulate these phenomena is macro-scale modeling. There are different models for studying liquid seepage in porous media. The final macro-scale equation of all these models is usually a diffusion-like equation. This is a common to many other fluid-solid systems as well, for example soil-water and soil-oil systems.

Recently, we developed a diffusion-based defect model for generating the physical defects in the documents is proposed. The model can be used for inserting defects, such as aging and ink seepage. Using this defect model, the datasets of physically degraded document images can be generated to develop, train, compare, and evaluate restoration methods. Also, the model can be cascaded with other well-developed defect models which simulate defects originating from imaging processes.

A schematic diagram of the defect model is presented below. The handwriting plate is an example of the possibility of having multiple sources for the recto side.

Defect modelDefect model

For more information, please refer to [1].


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