Convert PDF to UIImageView - ios

Question

I've found some code which gives me a UIImage out of a PDF-File. It works, but I have two questions:
Is there a possibility to achieve a better quality of the UIImage? (See Screenshot)
I only see the first page in my UIImageView. Do I have to embed the file in a UIScrollView to be complete?
Or is it better to render just one page and use buttons to navigate through the pages?
P.S. I know that UIWebView can display PDF-Pages with some functionalities but I need it as a UIImage or at least in a UIView.
Bad quality Image:
Code:
-(UIImage *)image {
UIGraphicsBeginImageContext(CGSizeMake(280, 320));
CGContextRef context = UIGraphicsGetCurrentContext();
CFURLRef pdfURL = CFBundleCopyResourceURL(CFBundleGetMainBundle(), CFSTR("ls.pdf"), NULL, NULL);
CGPDFDocumentRef pdf = CGPDFDocumentCreateWithURL((CFURLRef)pdfURL);
CGContextTranslateCTM(context, 0.0, 320);
CGContextScaleCTM(context, 1.0, -1.0);
CGPDFPageRef page = CGPDFDocumentGetPage(pdf, 4);
CGContextSaveGState(context);
CGAffineTransform pdfTransform = CGPDFPageGetDrawingTransform(page, kCGPDFCropBox, CGRectMake(0, 0, 280, 320), 0, true);
CGContextConcatCTM(context, pdfTransform);
CGContextDrawPDFPage(context, page);
CGContextRestoreGState(context);
UIImage *resultingImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return resultingImage;
}

Answer 1

I know i'm a little late here, but i hope i can help someone else looking for an answer.
As to the questions asked:
I'm afraid the only way to achieve a better image quality is to render a bigger image, and letting the UIImageView resize it for you. I don't think you can set the resolution, but using a bigger image may be a good choice. It won't take too long for the page to render, and the image will have a better quality. PDF files are rendered on demand depending on the zoom level, that's why they seem to have "better quality".
As to rendering all the pages, you can get the number of pages in the document calling CGPDFDocumentGetNumberOfPages( pdf ) and using a simple for loop you can concat all the images generated in one single image. For displaying it, use the UIScrollVIew.
In my opinion, this approach is better than the above, but you should try to optimize it, for example rendering always the current, the previous and the next page. For nice scrolling transition effects, why not use a horizontal UIScrollView.
For more generic rendering code, i always do the rotation like this:
int rotation = CGPDFPageGetRotationAngle(page);
CGContextTranslateCTM(context, 0, imageSize.height);//moves up Height
CGContextScaleCTM(context, 1.0, -1.0);//flips horizontally down
CGContextRotateCTM(context, -rotation*M_PI/180);//rotates the pdf
CGRect placement = CGContextGetClipBoundingBox(context);//get the flip's placement
CGContextTranslateCTM(context, placement.origin.x, placement.origin.y);//moves the the correct place
//do all your drawings
CGContextDrawPDFPage(context, page);
//undo the rotations/scaling/translations
CGContextTranslateCTM(context, -placement.origin.x, -placement.origin.y);
CGContextRotateCTM(context, rotation*M_PI/180);
CGContextScaleCTM(context, 1.0, -1.0);
CGContextTranslateCTM(context, 0, -imageSize.height);
Steipete already mentioned setting the white background:
CGContextSetRGBFillColor(context, 1, 1, 1, 1);
CGContextFillRect(context, CGRectMake(0, 0, imageSize.width, imageSize.height));
So the last thing to keep in mind is when exporting an image, set the quality to the maximum. For example:
UIImageJPEGRepresentation(image, 1);

Answer 2

What are you doing with the CGContextTranslateCTM(context, 0.0, 320); call?
You should extract the proper metrics form the pdf, with code like this:
cropBox = CGPDFPageGetBoxRect(page, kCGPDFCropBox);
rotate = CGPDFPageGetRotationAngle(page);
Also, as you see, the pdf might has rotation info, so you need to use the CGContextTranslateCTM/CGContextRotateCTM/CGContextScaleCTM depending on the angle.
You also might wanna clip any content that is outside of the CropBox area, as pdf has various viewPorts that you usually don't wanna display (e.g. for printers so that seamless printing is possible) -> use CGContextClip.
Next, you're forgetting that the pdf reference defines a white background color. There are a lot of documents out there that don't define any background color at all - you'll get weird results if you don't draw a white background on your own --> CGContextSetRGBFillColor & CGContextFillRect.