Tesseract OCR Camera

Question

I'm using Tesseract OCR 3.01 in my iOS application, it shows 90% accuracy for my data when I pick an image from my phone’s library. But if I use the same image from the camera, it is showing jumbled letters. I followed this tutorial, kindly guide me if something can be done to make sure it works from camera as it works for gallery images.

Answer 1

Yup, There are three things to be specific, First of all, OCR works well with black and white images rather than colored, So If you could try to convert your image to B&W, it would increase accuracy.

The second thing is the size and orientation, You need to force the image to be of 640*480 or 320 size, this would increase both the speed of recognition and the accuracy as well, For orientation , there are a lot of ways to manage.

Finally, If some how you can allow the user to specify Exactly where or on which part of the image he wants to perform the OCR, this greatly increases the accuracy and time since the library does not need to check the entire image for text, rather you already specify the part to be searched for.

PS:I have been working on creating an OCR app for the past few weeks.

Answer 2

Almost for sure the problem is "orientation". Apple tends to create images in one bit map form - the image bits are laid out as if the camera was on its side with the volume buttons top and right. Images that you see which appear taller than wider are still laid out as above, but there is an "orientation" in the EXIF object included with the image.

I'm going to guess that tesseract does not look at the EXIF, but expects the image in a "standard" format so that text is in the position it would be for a person reading the text.

You can test my hypothesis by using camera images taken with volume button top right.

If they work, then what you will need to do is process the image yourself, and re-arrange the bits per the orientation setting. This is not all that hard to do but will require you to read up on vImage and/or bit map contexts.