What is OCR? – Optical Character Recognition Explained – AWS

The OCR engine or OCR software works by using the following steps:

Image acquisition

A scanner reads documents and converts them to binary data. The OCR software analyzes the scanned image and classifies the light areas as background and the dark areas as text.

Preprocessing

The OCR software first cleans the image and removes errors to prepare it for reading. These are some of its cleaning techniques:

• Deskewing or tilting the scanned document slightly to fix alignment issues during the scan.
• Despeckling or removing any digital image spots or smoothing the edges of text images.
• Cleaning up boxes and lines in the image.
• Script recognition for multi-language OCR technology

Text recognition

The two main types of OCR algorithms or software processes that an OCR software uses for text recognition are called pattern matching and feature extraction.

Pattern matching

Pattern matching works by isolating a character image, called a glyph, and comparing it with a similarly stored glyph. Pattern recognition works only if the stored glyph has a similar font and scale to the input glyph. This method works well with scanned images of documents that have been typed in a known font.

Feature extraction

Feature extraction breaks down or decomposes the glyphs into features such as lines, closed loops, line direction, and line intersections. It then uses these features to find the best match or the nearest neighbor among its various stored glyphs.

Postprocessing

After analysis, the system converts the extracted text data into a computerized file. Some OCR systems can create annotated PDF files that include both the before and after versions of the scanned document.