Question

I’ve started a simple project in which it must get an image containing text with superscripts and then by using OCR (currently I’m using tesseract) it has to recognize the superscript characters + the normal ones.

For example, we have a chemical equation such as Cl², but when I use the tesseract to recognize it, it gives me Cl2 (all in one line).

So, what is the solution for this problem? Is there any other OCR API that has the ability to read superscripts?

Answer 1

Very good question that touches more advanced features of any OCR system.

First of all, to make sure you are NOT overlooking the functionality even though it may be there on an OCR system. Make sure to look at your result test not in plain TXT format, but in some kind of rich text capable viewer. TXT viewers, such as Notepad on Windows, often do not support superscript/subscript characters, so even if OCR were to give you correct characters, your viewer could have converted it to display it. If you are accessing text result programatically, that is less of an issue because you are supposed to get a proper subscript character value when accessing it directly. Just note that viewers must support it for you to actually see it. If you eliminated this possible post-processing conversion and made sure that no subscript is returned from OCR, then it probably does not support it.

Just like in this text box, in your original question you tried to give us a superscript character example, but this text box did not accept it even though you could copy/paste it from elsewhere.

Many OCR will see subscript as any other normal character, if they can see it at all. OCR of your use needs to have technical capability to actually produce superscripts/subscripts, and many of them do, but they tend to be commercial OCR systems not surprisingly.

I made a small testcase before answering this letter. I generated an image with a few superscript/subscript examples for my testing (of course EMC2 was the first example that came to mind 🙂 .
You can find my test image here:
http://www.ocr-it.com/documents/superscript_subscript_test_page.tif

And processed this image through OCR-IT OCR Cloud 2.0 API using all default settings, but exporting to a rich text format, such as MS Word .DOC.

You can find my test image here:
http://www.ocr-it.com/documents/superscript_subscript_test_page_result.doc

Also note: When you are interested to extract superscript/subscript characters, pay separate attention to your image quality, more than you would with a typical text. Those characters are tiny and you need sufficient details and resolution to achieve descent OCR quality. Even scanned at 300 dpi images sometimes have issues with tiny characters due to too few pixels. If you are considering mobile and digital cameras, that becomes even more important.

DISCLOSURE: My specialty is implementing internal OCR solutions for companies of different sizes. My company is WiseTREND. Contact me directly if I can assist with anything further.