This document summarizes the results of experiments examining the effect of scanning parameters like color, resolution, and binarization method on OCR accuracy. The experiments found that bitonal images produced the best OCR results on average but the optimal method varied between images. Higher resolution images did not necessarily improve OCR accuracy. The quality of archival images was also found to affect OCR performance. The document concludes different scanning choices may be suitable depending on the document type and quality.

1. The Effect of Scanning Parameters on OCR Results A Case Study Apostolos Antonacopoulos PRImA Lab, The University of Salford, United Kingdom www.primaresearch.org

2. Outline Background Image selection Methods and procedures Experiments Experiment 1: Colour Vs. greyscale Vs. bitonal Experiment 2: Effects of resolution Experiment 3: Comparison with NLNZ images Conclusions

3. Background Cost of storage is a real issue for Content Holders Study by Tracy Powell and Gordon Paynter of the National Library of New Zealand (DLIB 2009) opened a number of questions Aims: Examine the effects of colour in addition to greyscale and bitonal Examine the effects of producing bitonal images in different ways Examine the effects of different resolutions Study the results by image rather than average

4. Image Selection Qualitative selection Parts of newspaper articles (no layout issues) Variety of newspapers from British Library collection Quality of overall page taken into account Regions of different quality selected from same page Only text regions selected (no graphics present) No additional artefacts (e.g. warping) present

5. Methods and Procedures Regions marked using Aletheia and extracted from the main image as separate PAGE files Text was keyed and represented in PAGE files Selected ( “ standard ” ) colour reduction and binarisation methods were applied ABBYY FineReader Engine 9 used for OCR IMPACT OCR evaluation tool used

6. Experiment 1: Colour/Grey/Bitonal

7. Accuracy Variation per Image

8. Bitonal: Best Algorithm Vs. Scanner

9. Original with Large Bitonal Variation BL9_r0

10. Experiment 2: Effects of Resolution

11. Experiment 3: Examine NLNZ Images

12. Variations in Quality and Accuracy Other bitonal algorithm better NLNZ1_r1 Scanner bitonal better NLNZ4_r0

13. Conclusions Averages do not give an accurate picture. Different decisions should be taken for different document types Better quality images leave room for improvement (re-OCR), especially when accuracy is far from high 90s% Current OCR systems are not taking advantage of extra quality? Higher quality (at least greyscale) is an investment Perhaps not so high resolution for “routine” material “ Lossy ” compression is a real option Better to have a high quality image with an imperceptible “loss” than a perfect low quality image!

14. Further Information PRImA http://www.primaresearch.org IMPACT http://www.impact-project.eu