iPad视网膜显示是否有一种方法来减少用CGContextBeginPage创建的PDF文件大小

Question

我正在使用Retina显示器2048x1536分辨率(2倍比例)的全屏iPad从UIViews创建PDF文件。生成的文件非常大，对于2页相当简单的视图，我得到了6- 10mb的文件。理想情况下，我希望每个文档有4-5页，但目前的方法会使PDF大小过大。

是否有办法使以这种方式创建的pdf更小?喜欢创建视图的屏幕截图，将其转换为JPG，然后将其写入PDF上下文?还是我遗漏了什么高质量的选择?

下面是从单个视图创建PDF的代码:

+(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;
}

这是我用来连接多个pdf文件的方法

+ (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

解决方案确实是在PDF上下文中将图像呈现为JPG。压缩后的PDF大小更小——每页大约300-400kb !

//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;
}