iPad retina display is there a way to reduce filesize of PDF created with CGContextBeginPage?

Question

I'm creating PDF files from UIViews using full screen iPad with Retina Display 2048x1536 resolution (2x scale). The resulting files are very large, I'm getting 6-10 mb files for 2 pages of fairly simple views. Ideally I would get to 4-5 pages per document, but the current approach would make the PDF size prohibitively large.

Is there a way to make the PDFs created this way smaller? Like creating a screenshot of view, converting it to JPG, then writing that to PDF context? Or is there some quality option that I'm missing?

Here's the code to create a PDF from a single view:

+(NSMutableData *)createPDFDatafromUIView:(UIView*)aView 
{
    // Creates a mutable data object for updating with binary data, like a byte array
    NSMutableData *pdfData = [NSMutableData data];

    // Points the pdf converter to the mutable data object and to the UIView to be converted
    UIGraphicsBeginPDFContextToData(pdfData, aView.bounds, nil);
    UIGraphicsBeginPDFPage();
    CGContextRef pdfContext = UIGraphicsGetCurrentContext();


    // draws rect to the view and thus this is captured by UIGraphicsBeginPDFContextToData

    [aView.layer renderInContext:pdfContext];

    // remove PDF rendering context
    UIGraphicsEndPDFContext();

    return pdfData;
}

+(NSString*)createPDFfromUIView:(UIView*)aView saveToFilepath:(NSString*)filepath
{
    // Creates a mutable data object for updating with binary data, like a byte array
    NSMutableData *pdfData = [AppGraphics createPDFDatafromUIView:aView];


    // instructs the mutable data object to write its context to a file on disk
    [pdfData writeToFile:filepath atomically:YES];
    DLog(@"saving PDF to: %@",filepath);
    DLog(@"file exists: %@",[[NSFileManager defaultManager] fileExistsAtPath:filepath]?@"YES":@"NO");
    return filepath;
}

Here's what I'm using to join multiple PDFs together

+ (NSString *)joinPDF:(NSArray *)listOfPaths saveToPath:(NSString*)path
{


    CFURLRef pdfURLOutput = (  CFURLRef)CFBridgingRetain([NSURL fileURLWithPath:path]);

    NSInteger numberOfPages = 0;
    // Create the output context
    CGContextRef writeContext = CGPDFContextCreateWithURL(pdfURLOutput, NULL, NULL);

    for (NSString *source in listOfPaths) {
        CFURLRef pdfURL = (  CFURLRef)CFBridgingRetain([[NSURL alloc] initFileURLWithPath:source]);

        //file ref
        CGPDFDocumentRef pdfRef = CGPDFDocumentCreateWithURL((CFURLRef) pdfURL);
        numberOfPages = CGPDFDocumentGetNumberOfPages(pdfRef);

        // Loop variables
        CGPDFPageRef page;
        CGRect mediaBox;

        // Read the first PDF and generate the output pages
        DLog(@"GENERATING PAGES FROM PDF 1 (%@)...", source);
        for (int i=1; i<=numberOfPages; i++) {
            page = CGPDFDocumentGetPage(pdfRef, i);
            mediaBox = CGPDFPageGetBoxRect(page, kCGPDFMediaBox);
            CGContextBeginPage(writeContext, &mediaBox);
            CGContextDrawPDFPage(writeContext, page);
            CGContextEndPage(writeContext);
        }

        CGPDFDocumentRelease(pdfRef);
        CFRelease(pdfURL);
    }
    CFRelease(pdfURLOutput);

    // Finalize the output file
    CGPDFContextClose(writeContext);
    CGContextRelease(writeContext);

    return path;
}

Answer 1

The solution was indeed to render the image as JPG within the PDF context. The resulting compressed PDF size is smaller - around 300-400kb per page!

//aView is used for its bounds property
//screenshot is the screenshot of the view within its bounds
//compression quality 0.55 is 380kb/page 0.66 is 450kb/page
+(NSString*)createPDFDataFromUIView:(UIView*)aView withScreenshot:(UIImage*)screenshot compressionQuality:(float)compression writeToFile:(NSString*)filepath
{

    //prepare JPEG data for rendering into PDF content
    NSData *jpegData = UIImageJPEGRepresentation(screenshot, compression);
    CGDataProviderRef dp = CGDataProviderCreateWithCFData((__bridge CFDataRef)jpegData);
    CGImageRef cgImage = CGImageCreateWithJPEGDataProvider(dp, NULL, true, kCGRenderingIntentDefault);


    NSMutableData *pdfData = [NSMutableData data];

    // Points the pdf converter to the mutable data object and to the UIView to be converted
    UIGraphicsBeginPDFContextToData(pdfData, aView.bounds, nil);
    UIGraphicsBeginPDFPage();
    CGContextRef pdfContext = UIGraphicsGetCurrentContext();


    // draws rect to the view and thus this is captured by UIGraphicsBeginPDFContextToData


    //we need to change the coordinate system, otherwise the image is drawn upside down
    CGContextTranslateCTM(pdfContext, 0, aView.bounds.size.height);
    CGContextScaleCTM(pdfContext, 1.0, -1.0);

    //this creates pixels within PDF context
    CGContextDrawImage(pdfContext, aView.bounds, cgImage);

    // remove PDF rendering context
    UIGraphicsEndPDFContext();

    [pdfData writeToFile:filepath atomically:YES];

    //memory cleanup
    CGDataProviderRelease(dp);
    CGImageRelease(cgImage);
    return filepath;

}