Question

I am using tesseract library in my application for the image scanning. I have read somewhere that library gives good performance for image that over 100 DPIs.I am capturing the photo with iPhone 4 and iPad and giving it as input of tesseract library.But still library giving unreadable output .What is the DPIs for the iPhone or iPad camera?How can i improve the performance of tesseract library?

Answer 1

Get a 12 inch ruler and a tape measure. Put the ruler on the table. Hold the phone above the ruler, pointing the camera at the ruler. Use the tape measure to measure the distance from the ruler to the camera. Take a photo of the ruler.

Open the photo in an image viewer or editor. (You can use Preview on the Mac, for example.) Use the image viewer/editor to measure the size of the ruler in pixels.

Divide the size (in pixels) of the ruler by 12. That is the pixels per inch (aka dots per inch or DPI) of a picture of the ruler, when taken from the distance you measured with the tape measure.

The point about needing 100 DPI is that the OCR library needs sufficient resolution to recognize letters. It probably wants the letters to be 15-20 pixels tall (I’m guessing). If the letters are too small, the image may just not have enough information for the OCR library to work. And the letters could also be too big – the library is probably not programmed to look for letters that are 100 pixels tall. And if the letters are the right size, but blurry, the OCR library will probably not be able to recognize them.

It may simply be that you are trying to take a picture of text that is too small, so when you hold the camera close enough to make the letters the right size, the camera cannot focus and the picture is blurry. In that case, there is probably nothing you can do to fix it (except get a phone with a better camera).