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PDF data extraction in Obj-C (images, text, paths)

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Sample Obj-C code for using PDFTron SDK to extract text, paths, and images from a PDF. The sample also shows how to do color conversion, image normalization, and process changes in the graphics state. Learn more about our Obj-C PDF Library and PDF Parsing & Content Extraction Library.

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//---------------------------------------------------------------------------------------
// Copyright (c) 2001-2021 by PDFTron Systems Inc. All Rights Reserved.
// Consult legal.txt regarding legal and license information.
//---------------------------------------------------------------------------------------

#import <OBJC/PDFNetOBJC.h>
#import <Foundation/Foundation.h>

char m_buf[4000];

void ProcessElements(PTElementReader *reader);

void ProcessPath(PTElementReader *reader, PTElement *path)
{
    if ([path IsClippingPath])
    {
        NSLog(@"This is a clipping path");
    }

    PTPathData* pathData = [path GetPathData];
    NSMutableArray* data = [pathData GetPoints];
    NSData* opr = [pathData GetOperators];

    NSUInteger opr_index = 0;
    NSUInteger opr_end = opr.length;
    NSUInteger data_index = 0;
    NSUInteger data_end = data.count;
    
    double x1, y1, x2, y2, x3, y3;
    NSString *str = @"";
    
    // Use path.GetCTM() if you are interested in CTM (current transformation matrix).

    unsigned char* opr_data = (unsigned char*)opr.bytes;
    str = [str stringByAppendingFormat: @" Path Data Points := \""];
    for (; opr_index<opr_end; opr_index = opr_index + 1)
    {
        switch(opr_data[opr_index])
        {
        case e_ptmoveto:
            x1 = [data[data_index] doubleValue]; ++data_index;
            y1 = [data[data_index] doubleValue]; ++data_index;
            sprintf(m_buf, "M%.5g %.5g", x1, y1);
            str = [str stringByAppendingFormat: @"%s", m_buf];
            break;
        case e_ptlineto:
            x1 = [data[data_index] doubleValue]; ++data_index;
            y1 = [data[data_index] doubleValue]; ++data_index;
            sprintf(m_buf, " L%.5g %.5g", x1, y1);
            str = [str stringByAppendingFormat: @"%s", m_buf];
            break;
        case e_ptcubicto:
            x1 = [data[data_index] doubleValue]; ++data_index;
            y1 = [data[data_index] doubleValue]; ++data_index;
            x2 = [data[data_index] doubleValue]; ++data_index;
            y2 = [data[data_index] doubleValue]; ++data_index;
            x3 = [data[data_index] doubleValue]; ++data_index;
            y3 = [data[data_index] doubleValue]; ++data_index;
            sprintf(m_buf, " C%.5g %.5g %.5g %.5g %.5g %.5g", x1, y1, x2, y2, x3, y3);
            str = [str stringByAppendingFormat: @"%s", m_buf];
            break;
        case e_ptrect:
            {
                x1 = [data[data_index] doubleValue]; ++data_index;
                y1 = [data[data_index] doubleValue]; ++data_index;
                double w = [data[data_index] doubleValue]; ++data_index;
                double h = [data[data_index] doubleValue]; ++data_index;
                x2 = x1 + w;
                y2 = y1;
                x3 = x2;
                y3 = y1 + h;
                double x4 = x1; 
                double y4 = y3;
                sprintf(m_buf, "M%.5g %.5g L%.5g %.5g L%.5g %.5g L%.5g %.5g Z", 
                    x1, y1, x2, y2, x3, y3, x4, y4);
                str = [str stringByAppendingFormat: @"%s", m_buf];
            }
            break;
        case e_ptclosepath:
            str = [str stringByAppendingString: @" Close Path"];
            break;
        default: 
            assert(false);
            break;
        }    
    }

    str = [str stringByAppendingString: @"\" "];

    PTGState *gs = [path GetGState];

    // Set Path State 0 (stroke, fill, fill-rule) -----------------------------------
    if ([path IsStroked]) 
    {
        str = [str stringByAppendingString: @"Stroke path\n"]; 

        if ([[gs GetStrokeColorSpace] GetType] == e_ptpattern)
        {
            str = [str stringByAppendingString: @"Path has associated pattern"]; 
        }
        else
        {
            // Get stroke color (you can use PDFNet color conversion facilities)
            // ColorPt rgb;
            // gs.GetStrokeColorSpace().Convert2RGB(gs.GetStrokeColor(), rgb);
        }
    }
    else 
    {
        // Do not stroke path
    }

    if ([path IsFilled])
    {
        str = [str stringByAppendingString: @"Fill path"]; 

        if ([[gs GetFillColorSpace] GetType] == e_ptpattern)
        {        
            str = [str stringByAppendingString: @"Path has associated pattern"]; 
        }
        else
        {
            // PTColorPt *rgb = [[[PTColorPt alloc] init] autorelease];
            // [[gs GetFillColorSpace] Convert2RGB: [gs GetFillColorWithColorPt: rgb]];
        }        
    }
    else 
    {
        // Do not fill path
    }

    // Process any changes in graphics state  ---------------------------------

    PTGSChangesIterator *gs_itr = [reader GetChangesIterator];
    for (; [gs_itr HasNext]; [gs_itr Next]) 
    {
        switch([gs_itr Current])
        {
        case e_pttransform :
            // Get transform matrix for this element. Unlike path.GetCTM() 
            // that return full transformation matrix gs.GetTransform() return 
            // only the transformation matrix that was installed for this element.
            //
            // gs.GetTransform();
            break;
        case e_ptline_width :
            // gs.GetLineWidth();
            break;
        case e_ptline_cap :
            // gs.GetLineCap();
            break;
        case e_ptline_join :
            // gs.GetLineJoin();
            break;
        case e_ptflatness :
            break;
        case e_ptmiter_limit :
            // gs.GetMiterLimit();
            break;
        case e_ptdash_pattern :
            {
                // std::vector<double> dashes;
                // gs.GetDashes(dashes);
                // gs.GetPhase()
            }
            break;
        case e_ptfill_color:
            {
                if ( [[gs GetFillColorSpace] GetType] == e_ptpattern &&
                     [[gs GetFillPattern] GetType] != e_ptshading )
                {    
                    //process the pattern data
                    [reader PatternBegin: YES reset_ctm_tfm: NO];
                    ProcessElements(reader);
                    [reader End];
                }
            }
            break;
        default:
            break;
        }
    }
    [reader ClearChangeList];
    NSLog(@"%@", str);
}

void ProcessText(PTElementReader* page_reader) 
{
    // Begin text element
    NSLog(@"Begin Text Block:");

    PTElement *element; 
    while ((element = [page_reader Next]) != NULL) 
    {
        switch ([element GetType])
        {
            case e_pttext_end:
                // Finish the text block
                //str = [str stringByAppendingString: @"End Text Block.\n"];
                    NSLog(@"End Text Block.");
                return;

            case e_pttext_obj:
            {
                PTGState *gs = [element GetGState];

                PTColorSpace *cs_fill = [gs GetFillColorSpace];
                PTColorPt *fill = [gs GetFillColor];
                
                PTColorPt *outColor = [cs_fill Convert2RGB: fill];

                PTColorSpace *cs_stroke = [gs GetStrokeColorSpace];
                PTColorPt *stroke = [gs GetStrokeColor];

                PTFont *font = [gs GetFont];

                NSLog(@"Font Name: %@\n", [font GetName]);
                
                // font.IsFixedWidth();
                // font.IsSerif();
                // font.IsSymbolic();
                // font.IsItalic();
                // ... 

                // double font_size = gs.GetFontSize();
                // double word_spacing = gs.GetWordSpacing();
                // double char_spacing = gs.GetCharSpacing();
                // const UString* txt = element.GetTextString();

                if ( [font GetType] == e_ptType3 )
                {
                    //type 3 font, process its data
                    PTCharIterator *itr;
                    for (itr = [element GetCharIterator]; [itr HasNext]; [itr Next]) 
                    {
                        [page_reader Type3FontBegin: [itr Current] resource_dict: 0];
                        ProcessElements(page_reader);
                        [page_reader End];
                    }
                }

                else
                {    
                    PTMatrix2D *text_mtx = [element GetTextMatrix];
                    double x, y;
                    unsigned int char_code;

                    PTCharIterator *itr;
                    NSString* str = @"";
                    for (itr = [element GetCharIterator]; [itr HasNext]; [itr Next]) 
                    {
                        char_code = [[itr Current] getChar_code];
                        if (char_code>=32 || char_code<=255) { // Print if in ASCII range...
                            str = [str stringByAppendingFormat: @"%c", char_code];
                        }

                        x = [[itr Current] getX];        // character positioning information
                        y = [[itr Current] getY];

                        // Use element.GetCTM() if you are interested in the CTM 
                        // (current transformation matrix).
                        PTMatrix2D *ctm = [element GetCTM];

                        // To get the exact character positioning information you need to 
                        // concatenate current text matrix with CTM and then multiply 
                        // relative positioning coordinates with the resulting matrix.
                        PTMatrix2D *mtx = text_mtx;
                        [mtx Concat: [ctm getM_a] b: [ctm getM_b] c: [ctm getM_c] d: [ctm getM_d] h: [ctm getM_h] v: [ctm getM_v]];
                        [mtx Mult: [[PTPDFPoint alloc] initWithPx: x py: y]];

                        // Get glyph path...
                        //vector<UChar> oprs;
                        //vector<double> glyph_data;
                        //font.GetGlyphPath(char_code, oprs, glyph_data, false, 0);
                    }
                    NSLog(@"%@", str);
                }

                //str = [str stringByAppendingString: @"\n"];
            }
                break;
            default:
                break;
        }
    }
}

void ProcessImage(PTElement *image)  
{
    bool image_mask = [image IsImageMask];
    bool interpolate = [image IsImageInterpolate];
    int width = [image GetImageWidth];
    int height = [image GetImageHeight];
    int out_data_sz = width * height * 3;

    NSLog(@"Image:  width=\"%d\" height=\"%d\"", width, height);

    // Matrix2D& mtx = image->GetCTM(); // image matrix (page positioning info)

    // You can use GetImageData to read the raw (decoded) image data
    //image->GetBitsPerComponent();    
    //image->GetImageData();    // get raw image data
    // .... or use Image2RGB filter that converts every image to RGB format,
    // This should save you time since you don't need to deal with color conversions, 
    // image up-sampling, decoding etc.

    PTImage2RGB *img_conv = [[PTImage2RGB alloc] initWithImage_element: image];    // Extract and convert image to RGB 8-bpc format
    PTFilterReader *reader = [[PTFilterReader alloc] initWithFilter: img_conv];

    // A buffer used to keep image data.
    NSData *image_data_out = [reader Read: out_data_sz];
    // &image_data_out.front() contains RGB image data.

    // Note that you don't need to read a whole image at a time. Alternatively
    // you can read a chuck at a time by repeatedly calling reader.Read(buf, buf_sz) 
    // until the function returns 0. 
}

void ProcessElements(PTElementReader *reader) 
{
    PTElement *element;
    while ((element = [reader Next]) != NULL)     // Read page contents
    {
        switch ([element GetType])
        {
        case e_ptpath:                        // Process path data...
            {
                ProcessPath(reader, element);
            }
            break; 
        case e_pttext_begin:                 // Process text block...
            {
                ProcessText(reader);
            }
            break;
        case e_ptform:                        // Process form XObjects
            {
                [reader FormBegin]; 
                ProcessElements(reader);
                [reader End];
            }
            break; 
        case e_ptimage:                        // Process Images
            {
                ProcessImage(element);
            }    
            break;
                
        default:
            break;
        }

    }
}

int main(int argc, char *argv[])
{
    @autoreleasepool {
        int ret = 0;
        [PTPDFNet Initialize: 0];

        @try    // Extract text data from all pages in the document
        {
            NSLog(@"__________________________________________________");
            NSLog(@"Extract page element information from all ");
            NSLog(@"pages in the document.");

            PTPDFDoc *doc = [[PTPDFDoc alloc] initWithFilepath: @"../../TestFiles/newsletter.pdf"];
            [doc InitSecurityHandler];

            int pgnum = [doc GetPageCount];
            PTPageIterator *page_begin = [doc GetPageIterator: 1];

            PTElementReader *page_reader = [[PTElementReader alloc] init];

            PTPageIterator *itr;
            for (itr = page_begin; [itr HasNext]; [itr Next])        //  Read every page
            {                
                NSLog(@"Page %d----------------------------------------", [[itr Current] GetIndex]);
                [page_reader Begin: [itr Current]];
                ProcessElements(page_reader);
                [page_reader End];
            }

            NSLog(@"Done.");
        }
        @catch(NSException *e)
        {
            NSLog(@"%@", e.reason);
            ret = 1;
        }
        [PTPDFNet Terminate: 0];
        return ret;
    }
    
}

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