A Hybrid-Binarization Approach for Degraded Document Enhancement

Images get degraded because of unbalanced enlightenment including text-smearing, ink-bleeding, degradation of ink over time, manuscript characters from background coming out and blended with the characters of the main side etc. So, degraded-document enhancement is a challenging issue. In recent years, several binarization approaches are proposed to enhance these images. These techniques have focused on finding a suitable global threshold value or a local threshold value for every region to eliminate the degradations. A hybrid approach can be a good solution to deal with all these matters to-gether. This paper proposes a hybrid approach of binarization for degraded documents to produce better quality result. Then, the performance of the proposed technique is evaluated using DIBCO 2010 to DIBCO 2018 databases and compared with the existing methods which confirmed that the proposed method is robust, efficient. Finally, a direction towards future works and challenges is stated.


Introduction
There are numerous old and historical documents and manuscripts which are stored in libraries and archives. These documents have essential information about the heritage of human. Different ecological issues, inappropriate management and bad-quality materials of the paper degraded these documents [1] [2] [3]. So, the analysis on the degradation of manuscripts is a challenging area for researchers nowadays.

Journal of Computer and Communications
Binarization is the primary step of analyzing documents. It is a technique of conversion from grayscale or into a binary image. The consequent steps are vastly reliant on the accomplishment of binarization and the success of binarization can affect the preservation of the significant information of the degraded documents.
There are different types of binarization approaches which contain several advantages and drawbacks. So, it is very demandable to develop a quick, ideal and appropriate method for every degraded document [4].
The core principle of this research is to offer an image binarization technique to satisfy different purposes. It attempts to unite the benefits of local and global thresholding.
Our paper is structured as follows: In Section 2 we have illustrated literature review. Section 3 presented our proposed binarization technique briefly. In Section 4, the performance evaluation is briefly described. We have discussed the advantages of the proposed method in Section 5 and conversed about the future works and challenges in Section 6. Finally, in Section 7, we have concluded the paper along with some future research directions.

Literature Review
In recent years, many researchers worked on binarization techniques. A complete evaluation on image binarization along with some noble and benchmarked binarization methods are presented below: Lu et al. [4] presented a contrast-enhancement based thresholding technique.
They focused on the difference of the contrast of grayscale image in different regions of input image.
Mollah et al. [5] presented a binarization method for the images of business cards. Based on intensity-variance, a card image is separated into small blocks which can be extracted from background. The areas without text are removed and the texts are exacted and thresholded by applying a local adaptive method.
Darek Bradley et al. [6] proposed a vigorous and simple binarization technique which depends on spatial variation in illumination.
Badekas et al. [7] presented a binarization technique for color pictures where texts are mixed with the background.
Otsu [8] presented a global thresholding technique. It can convert grayscale images to bi-level images and can divide the pixels into background and foreground divisions. The Otsu's technique works well with the images with bi-modal model.
Sauvola [9] presented another procedure which uses standard deviation to find out the threshold value. It is an upgraded version of Niblack's technique.
Nick et al. [10] presented local thresholding technique. In this process, the value of thresholding is moved downward to eliminate noise and to lessen the contrast problem.

Proposed Methodology
The binarization method is used as the main part in different analyses of documents. On the other side, the method must be simple and suitable for every document analysis. Figure 1 shows

Inputting Image
Inputting image is the initial step of this procedure. Images are captured by camera or obtained by using secondary sources such as scanner.

Converting to Gray-Scale Image
After completing the above step, we need to verify the image to know the format of the image. When the inputted image is in RGB format then the image will be transferred into grayscale format. But, if the image is in grayscale, then it will be preprocessed in the next stage.

Preprocessing
The preprocessing step is the next stage for the grayscale image. Generally, preprocessing is required to eliminate the imperfections of the input-image. This

Post-Processing
The binary image will go through post-processing. We have done noise removal operation for the enhancement of the document.

Experimental Results
For evaluating the performance of our technique, we have done some simula-    Table 1. We have applied the following method to compute the accuracy A:

Future Works and Challenges
We have presented a technique that combines the advantages of different binarization techniques such as global and local binarization. So, future researchers can focus on parameter tuning, noise removing, post-processing for qualitative binarization. The post-processing can reduce the performance by increasing the execution time but it can develop the quality of the manuscripts. Several filters could be used for noise problems and these filters could reduce black spots from the final image. In this way, we can preserve the important information of the degraded documents.

Conclusion
Historical documents hold important information of ancient times.