title: Converting pdf to png in iOS results in substantially lower appearance quality
body: <p>I am converting a pdf file to png image so I can add text to the png then convert back to a pdf. I am using the code below to convert to the png. This is resulting in a substantial decrease in the quality of the appearance. Is there anything that can be done to prevent or minimize the loss of quality? </p>
  
  <pre><code>NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
  NSString *documentsDirectory = [paths objectAtIndex:0];
  NSString *writeableDBPath = [documentsDirectory stringByAppendingPathComponent:@"sample.pdf"];
  
  CFStringRef path;
  CFURLRef url;
  
  path = CFStringCreateWithCString (NULL, [writeableDBPath UTF8String], kCFStringEncodingUTF8);
  url = CFURLCreateWithFileSystemPath (NULL, path, kCFURLPOSIXPathStyle, 0);
  
  CGPDFDocumentRef myDocument;
  
  myDocument = CGPDFDocumentCreateWithURL(url);
  
  UIGraphicsBeginImageContext(CGSizeMake(612,792));
  CGContextRef currentContext = UIGraphicsGetCurrentContext();
  
  CGContextTranslateCTM(currentContext, 10, 792); //596,842 //640x960, 
  CGContextScaleCTM(currentContext, 1.0, -1.0); // make sure the page is the right way up
  
  CGPDFPageRef page = CGPDFDocumentGetPage (myDocument, 1); // first page of PDF is page 1 (not zero)
  CGContextDrawPDFPage (currentContext, page);  // draws the page in the graphics context
  
  UIImage* image = UIGraphicsGetImageFromCurrentImageContext();
  UIGraphicsEndImageContext();
  
  NSString* imagePath = [documentsDirectory stringByAppendingPathComponent: @"test.png"];
  [UIImagePNGRepresentation(image) writeToFile: imagePath atomically:YES];
  </code></pre>