Why Tesseract OCR library (iOS) cannot recognize text at all?

Question

I'm trying to use Tesseract OCR library in my iOS application. I downloaded tesseract-ios library from github and when I tried to recognize a simple text image I got garbage instead. Here is an image of what I tried to recognize:

I got unreadable text:

T0I1101T0W KIR1 H1I1101T0W KIR1 H1I1101T0W CIBEPS H1 ES PBHY P306 EHH11 133I R1 11335 11I1H1 19 13S SYIL 3B19 M H300H1911 H1113 AIR1 J1 OIII 3I9SH5H133IS 13V9 I1 Q1H211 E015 19 W331 H1 111SW

Why Tesseract can't recognise even simple image? Here is code which I used to instantiate Tesseract:

Tesseract* tesseractObject = [[Tesseract alloc] initWithDataPath:@"tessdata" language:@"eng"];
[tesseractObject setVariableValue:@"0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ" forKey:@"tessedit_char_whitelist"];
[tesseractObject setImage:image];
[tesseractObject recognize];
NSLog(@"RECOGNISED= %@" , [tesseractObject recognizedText]);

Here is my project structure:

I added English testdata folder by reference. So what am I doing wrong? How can I fix this?

Answer 1

You are using the option tessedit_char_whitelist with the value "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ" which limits the character recognition to this list only. However the image that you want to process contains lower case characters, if you want to use this option you will have to include lower cases char too.

[tesseractObject setVariableValue:@"0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ" forKey:@"tessedit_char_whitelist"];