Image processing

Improving the quality of scanned images can serve two different purposes:

  • enhance the visual appearance of images when viewed by humans,
  • enhance the quality for post-processing steps such as OCR and layout analysis.

Depending on the use case, different tools or settings have to be applied to optimize the image processing result for a particular purpose or material.

Common software tools used to enhance the visual appearance of images are tools for deskewing, contrast enhancement or border adjustment. The overall goal is to transform scanned images in a way that results in sharp and readable text, clear images and a white background. Additionally, borders and page sizes are usually adjusted to be the same size for every page to improve the viewing experience for a set of pages. These requirements can result in different processing parameters applied to different regions of an image in order to have letters rendered with very high contrast compared to images or photos which require much less contrast.

Image enhancement for post-processing purposes usually involves tools for deskewing, noise removal and binarisation. However, the parameters used for such tools depend very much on the intended use case. For example if the goal is to improve OCR results by applying image enhancement tools, the optimal parameters might vary for different OCR engines. Additionally, parameters might have to be adjusted for different data sets or even individual pages within a given data set.

We have prepared training materials for the following tools: