Question

In Xcode, I am trying to pre process an image prior to sending it to OCR’ing. The OCR engine, Tesseract, handles images based on the Leptonica library.

As an example:
The Leptonica feature pixConvertTo8(“image.tif”)… is there a way to “transfer” the image raw data from UIImage -> PIX (see pix.h from the leptonica library) -> perform the pixConvertTo8() and back from PIX -> UImage – and this preferably without saving it to a file for transition – all in memory.

- (void) processImage:(UIImage *) uiImage
{
 NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

// preprocess UIImage here with fx: pixConvertTo8();

CGSize imageSize = [uiImage size];
int bytes_per_line  = (int)CGImageGetBytesPerRow([uiImage CGImage]);
int bytes_per_pixel = (int)CGImageGetBitsPerPixel([uiImage CGImage]) / 8.0;

CFDataRef data = CGDataProviderCopyData(CGImageGetDataProvider([uiImage CGImage]));
const UInt8 *imageData = CFDataGetBytePtr(data);

// this could take a while.
char* text = tess->TesseractRect(imageData,
                                 bytes_per_pixel,
                                 bytes_per_line,
                                 0, 0,
                                 imageSize.width, imageSize.height);

Answer 1

these two functions will do the trick….

- (void) startTesseract
{
//code from http://robertcarlsen.net/2009/12/06/ocr-on-iphone-demo-1043

NSString *dataPath = 
    [[self applicationDocumentsDirectory]stringByAppendingPathComponent:@"tessdata"];
/*
 Set up the data in the docs dir
 want to copy the data to the documents folder if it doesn't already exist
 */
NSFileManager *fileManager = [NSFileManager defaultManager];
// If the expected store doesn't exist, copy the default store.
if (![fileManager fileExistsAtPath:dataPath]) {
    // get the path to the app bundle (with the tessdata dir)
    NSString *bundlePath = [[NSBundle mainBundle] bundlePath];
    NSString *tessdataPath = [bundlePath stringByAppendingPathComponent:@"tessdata"];
    if (tessdataPath) {
        [fileManager copyItemAtPath:tessdataPath toPath:dataPath error:NULL];
    }
}

NSString *dataPathWithSlash = [[self applicationDocumentsDirectory] stringByAppendingString:@"/"];
setenv("TESSDATA_PREFIX", [dataPathWithSlash UTF8String], 1);

// init the tesseract engine.
tess = new  tesseract::TessBaseAPI();
tess->Init([dataPath cStringUsingEncoding:NSUTF8StringEncoding], "eng");

}

- (NSString *) ocrImage: (UIImage *) uiImage
{

//code from http://robertcarlsen.net/2009/12/06/ocr-on-iphone-demo-1043
    CGSize imageSize = [uiImage size];
double bytes_per_line   = CGImageGetBytesPerRow([uiImage CGImage]);
double bytes_per_pixel  = CGImageGetBitsPerPixel([uiImage CGImage]) / 8.0;

CFDataRef data = CGDataProviderCopyData(CGImageGetDataProvider([uiImage CGImage]));
const UInt8 *imageData = CFDataGetBytePtr(data);
imageThresholder = new tesseract::ImageThresholder();       

imageThresholder->SetImage(imageData,(int) imageSize.width,(int) imageSize.height,(int)bytes_per_pixel,(int)bytes_per_line);



// this could take a while. maybe needs to happen asynchronously.
tess->SetImage(imageThresholder->GetPixRect());

char* text = tess->GetUTF8Text();
// Do something useful with the text!
NSLog(@"Converted text: %@",[NSString stringWithCString:text encoding:NSUTF8StringEncoding]);

return [NSString stringWithCString:text encoding:NSUTF8StringEncoding]
}

You will have to declare both tess and imageThresholder in the .h file

tesseract::TestBaseApi *tess;
tesseract::ImageThresholder *imageThresholder;