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

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"];

Answer 2

Make sure you have the latest tessdata file from Google code
http://code.google.com/p/tesseract-ocr/downloads/list
This will provide you with a list of tessdata files that you need to download and include in your app if you haven't already. In your case you will need tesseract-ocr-3.02.eng.tar.gz as you are looking for the English language files
The following article will show you where you need to install it. I read through this tutorial when I built my first Tesseract project and found it really useful
http://lois.di-qual.net/blog/install-and-use-tesseract-on-ios-with-tesseract-ios/

Answer 3

Like Adam said, if you want good results, you'll have to do some image processing and configure some settings (white-listing certain characters, etc).
For anyone else stumbling upon this question, I've put together a sample project here that does some white-listing and image processing:https://github.com/mstrchrstphr/OCR-iOS-Example

Answer 4

and my output is
Solution :
tesseract.language = #"eng+fra";
tesseract.pageSegmentationMode = G8PageSegmentationModeAuto;
tesseract.engineMode = G8OCREngineModeTesseractCubeCombined;
tesseract.image = [image.image g8_blackAndWhite];
tesseract.maximumRecognitionTime = 60.0;
[tesseract recognize];
NSLog(#"%#", tesseract.recognizedText);
reco_area.text = [tesseract recognizedText];
for tessdata
click here

Answer 5

whatever # Adam Richardson explained is correct along with that add this 1) scaleimage method for increase size of the image(dimensions increase)
func scaleImage(image: UIImage, maxDimension: CGFloat) -> UIImage {
var scaledSize = CGSize(width: maxDimension, height: maxDimension)
var scaleFactor: CGFloat
if image.size.width > image.size.height {
scaleFactor = image.size.height / image.size.width
scaledSize.width = maxDimension
scaledSize.height = scaledSize.width * scaleFactor
} else {
scaleFactor = image.size.width / image.size.height
scaledSize.height = maxDimension
scaledSize.width = scaledSize.height * scaleFactor
}
UIGraphicsBeginImageContext(scaledSize)
image.draw(in: CGRect(x: 0, y: 0, width: scaledSize.width, height: scaledSize.height))
let scaledImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
return scaledImage!
}
2) store this eng.traineddata language file in filemanager
func storeLanguageFile() throws{
var fileManager: FileManager = FileManager.default
let nsDocumentDirectory = FileManager.SearchPathDirectory.documentDirectory
let nsUserDomainMask = FileManager.SearchPathDomainMask.userDomainMask
let docDirectory = NSSearchPathForDirectoriesInDomains(nsDocumentDirectory, nsUserDomainMask, true)[0] as NSString
let path: String = docDirectory.appendingPathComponent("/tessdata/eng.traineddata")
if fileManager.fileExists(atPath: path){
var data: NSData = NSData.dataWithContentsOfMappedFile((Bundle.main.resourcePath?.appending("/tessdata/eng.traineddata"))!)! as! NSData
var error: NSError
try FileManager.default.createDirectory(atPath: docDirectory.appendingPathComponent("/tessdata"), withIntermediateDirectories: true, attributes: nil)
data.write(toFile: path, atomically: true)
}
}
3) after that you can use https://github.com/BradLarson/GPUImage for increase clarity of the image
you can use this
func preprocessedImage(for tesseract: G8Tesseract!, sourceImage: UIImage!) -> UIImage! {
var stillImageFilter: GPUImageAdaptiveThresholdFilter = GPUImageAdaptiveThresholdFilter()
stillImageFilter.blurRadiusInPixels = 4.0
var filterImage: UIImage = stillImageFilter.image(byFilteringImage: sourceImage)
return filterImage
}
these 3 steps will help you to increase the accuracy of the tesseract upto 60 ~ 70 %