Objective-C Requires Chilkat v11.7.0+

Assess PDF Text Quality Before Extracting

See more PDF Text Extraction Examples

Demonstrates the "assess" operation, which returns only the quality report: whether the text can be trusted, which pages are scanned images that need OCR, and how each page's text was found. Use it to triage documents before extracting. (Chilkat does not perform OCR.) Objective-C

#import <CkoPdf.h>
#import <CkoJsonObject.h>

BOOL success = NO;

//  This example requires the Chilkat API to have been previously unlocked.
//  See Global Unlock Sample for sample code.

//  The PDF used in this example (page 2 is a scanned image with no text) is available at mixed_text_image.pdf

CkoPdf *pdf = [[CkoPdf alloc] init];
success = [pdf LoadFile: @"qa_data/pdf/mixed_text_image.pdf"];
if (success == NO) {
    NSLog(@"%@",pdf.LastErrorText);
    return;
}

CkoJsonObject *json = [[CkoJsonObject alloc] init];
CkoJsonObject *jsonOut = [[CkoJsonObject alloc] init];

//  "assess" computes the quality report without producing any text.
//  It is fast, and it is always allowed, even for an encrypted PDF that forbids copying.
success = [pdf ExtractText: @"assess" jsonIn: json jsonOut: jsonOut];
if (success == NO) {
    NSLog(@"%@",pdf.LastErrorText);
    return;
}

//  The overall rating is the worst rating among the pages that have text:
//  "good", "fair", "poor", or "none" when there is no text at all.
NSLog(@"%@%@",@"Rating: ",[jsonOut StringOf: @"quality.rating"]);

//  Is the PDF tagged (does it have a structure tree)?
NSLog(@"%@%d",@"Tagged: ",[jsonOut BoolOf: @"quality.tagged"]);

//  The pages that are images only and would need OCR, such as "2" or "4,9".
NSLog(@"%@%@",@"Pages needing OCR: ",[jsonOut StringOf: @"quality.pagesNeedingOcr"]);

//  The per-page report.
int j;
int count_j;
int i = 0;
int count_i = [[jsonOut SizeOfArray: @"quality.pages"] intValue];
while (i < count_i) {
    jsonOut.I = [NSNumber numberWithInt: i];
    //  textSource is "text" (real text), "ocrLayer" (invisible text over an image),
    //  "imageOnly" (needs OCR), "mixed", or "empty".
    NSLog(@"%@%d%@%@%@%@",@"Page ",[[jsonOut IntOf: @"quality.pages[i].page"] intValue],@": rating ",[jsonOut StringOf: @"quality.pages[i].rating"],@", textSource "
        ,[jsonOut StringOf: @"quality.pages[i].textSource"]);
    //  Each issue has a machine-readable code and a sentence.
    j = 0;
    count_j = [[jsonOut SizeOfArray: @"quality.pages[i].issues"] intValue];
    while (j < count_j) {
        jsonOut.J = [NSNumber numberWithInt: j];
        NSLog(@"%@%@%@%@",@"    ",[jsonOut StringOf: @"quality.pages[i].issues[j].code"],@": ",[jsonOut StringOf: @"quality.pages[i].issues[j].message"]);
        j = j + 1;
    }

    i = i + 1;
}

//  Decide what to do with the document:
if ([jsonOut StringOf: @"quality.rating"] == @"none") {
    NSLog(@"%@",@"No extractable text; the whole document needs OCR.");
}
else {
    if ([jsonOut StringOf: @"quality.pagesNeedingOcr"] != @"") {
        NSLog(@"%@",@"Some pages need OCR; the remaining pages can be extracted with the text or markdown operation.");
    }
    else {
        NSLog(@"%@",@"All pages can be extracted.");
    }

}

//  Sample output:

//  Rating: good
//  Tagged: false
//  Pages needing OCR: 2
//  Page 1: rating good, textSource text
//  Page 2: rating none, textSource imageOnly
//      imageOnly: No text; page is a scanned image
//  Page 3: rating good, textSource text
//  Some pages need OCR; the remaining pages can be extracted with the text or markdown operation.