While some scanners have the potential to scan at 6000 dpi (dots per inch), industry experts agree that when it comes to scanning for OCR (optical character resolution) 300 dpi is the optimum resolution.
Kevin Neal, Senior Product Marketing Manager at Fujitsu Computer Products believes, “scanning at 300 dpi is not officially a standard for OCR but it is considered the gold standard.”
While some people choose to scan at a lower resolution and then use scanner software to increase the dpi later, this does little to improve the OCR.
“Most leading OCR software companies recommend scanning at a minimum resolution of 300 dpi for effective data extraction. In fact many have 300 dpi as their default setting,” says Mr Neal.
“In other words, for every square inch of paper, the scanner is capturing 300 dots horizontally and 300 dots vertically or 90,000 total dots (300 X 300 = 90,000 dots per square inch). If you use a 200 dpi setting instead of 300 dpi, you’ll only see 40,000 dots per square inch as opposed to 90,000. That’s a significant difference when you think about it.”
Chris Riley, OCR expert and founder of LivingAnalytics Inc, agrees.
“The improvement gap between 200 DPI scan and 300 DPI scan will be at least 2 times the improvement gap of any other resolutions.”
However, this does not mean that bigger is always better. Just because you have a scanner that scans to 1200 dpi or more, doesn’t mean you should.
According to Mr Riley, scanning the same document at 300 dpi and 400 dpi will only create a larger document file and offer little improvement to the image.
“300 DPI is that magic number where you gain the most accuracy without sacrificing speed and file size,” he says.
A test by Adobe showed a 78 page document scanned at 300dpi with OCR resulted in a file size of 1.24MB while the same document at 600 dpi, came in at 3.52MB, almost three times as large.
At Grace Information Management, we specialise in OCR technology to ensure you get optimum results for your scanning projects.