High quality UIImage from PDF

问题:

I'm converting a PDF page into a UIImage. While doing so, I lose the image quality. Need help in getting high quality images.

Code to generate UIImage

-(UIImage *)imageForPage:(int)pageNumber {     CGPDFPageRef pdfPageRef = [self pdfReferenceForPage:pageNumber];      CGSize pageSize = [self sizeOfPage:pageNumber];      //UIGraphicsBeginImageContext(pageSize);      UIGraphicsBeginImageContextWithOptions(pageSize, NO, 0.0);      CGContextRef context = UIGraphicsGetCurrentContext();     CGContextSetInterpolationQuality(context, kCGInterpolationHigh);      CGContextTranslateCTM(context, 0.0, pageSize.height);     CGContextScaleCTM(context, 1.0, -1.0);     CGContextSaveGState(context);      CGAffineTransform pdfTransform = CGPDFPageGetDrawingTransform(pdfPageRef, kCGPDFCropBox, CGRectMake(0, 0, pageSize.width, pageSize.height), 0, true);     CGContextConcatCTM(context, pdfTransform);      CGContextDrawPDFPage(context, pdfPageRef);     CGContextRestoreGState(context);      UIImage *resultingImage = UIGraphicsGetImageFromCurrentImageContext();     UIGraphicsEndImageContext();      return resultingImage; }   - (void)saveImage {        UIImage *image = [self imageForPage:1];        [UIImageJPEGRepresentation(image, 1.0) writeToFile:filePath atomically:YES]; } 

Image comparison

Original PDF

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Image from PDF

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EDIT: CODE WITH CHANGES

float dpi = 100.0 / 72.0;  CGPDFPageRef pdfPageRef = [self pdfReferenceForPage:pageNumber];  CGSize pageSize = [self sizeOfPage:pageNumber]; pageSize.width = pageSize.width * dpi; pageSize.height = pageSize.height * dpi;  UIGraphicsBeginImageContext(pageSize);  CGContextRef context = UIGraphicsGetCurrentContext(); CGContextSetInterpolationQuality(context, kCGInterpolationHigh); CGContextTranslateCTM(context, 0.0, pageSize.height); CGContextScaleCTM(context, dpi, -dpi); CGContextSaveGState(context); //CGAffineTransform pdfTransform = CGPDFPageGetDrawingTransform(pdfPageRef, kCGPDFCropBox, CGRectMake(0, 0, pageSize.width, pageSize.height), 0, true); //CGContextConcatCTM(context, pdfTransform); CGContextDrawPDFPage(context, pdfPageRef); CGContextRestoreGState(context);  UIImage *resultingImage = UIGraphicsGetImageFromCurrentImageContext(); UIGraphicsEndImageContext();  return resultingImage; 

回答1:

When you ask the PDF for it's page size, you're getting a width/height for 72 PPI. You might try creating a context that's scaled up using a scale transform. For example, if you wanted to render at 300 dpi, add a scale transform to scale by 300.0/72.0.

If you export as TIFF, you will be able to encapsulate the final PPI (300) of the generated image.

回答2:

Try this code for Swift 3 :

func drawPDFfromURL(url: URL) -> UIImage? {     guard let document = CGPDFDocument(url as CFURL) else { return nil }     guard let page = document.page(at: 1) else { return nil }      let pageRect = page.getBoxRect(.mediaBox)     let renderer = UIGraphicsImageRenderer(size: pageRect.size)     let img1 = renderer.jpegData(withCompressionQuality: 1.0, actions: { cnv in         UIColor.white.set()         cnv.fill(pageRect)         cnv.cgContext.translateBy(x: 0.0, y: pageRect.size.height);         cnv.cgContext.scaleBy(x: 1.0, y: -1.0);         cnv.cgContext.drawPDFPage(page);     })     let img2 = UIImage(data: img1)     return img2 } 

This gives much higher resolution

回答3:

This one gives the best quality... if you need another quality just change dpi.

    func drawPDFfromURL(url: URL) -> UIImage? {     guard let document = CGPDFDocument(url as CFURL) else { return nil }     guard let page = document.page(at: 1) else { return nil }     let dpi: CGFloat = 300.0 / 72.0     let pageRect = page.getBoxRect(.mediaBox)      let renderer = UIGraphicsImageRenderer(size: CGSize(width: pageRect.size.width * dpi, height: pageRect.size.height * dpi))      let img1 = renderer.jpegData(withCompressionQuality: 1.0, actions: { cnv in           UIColor.white.set()           cnv.fill(pageRect)           cnv.cgContext.translateBy(x: 0.0, y: pageRect.size.height * dpi);           cnv.cgContext.scaleBy(x: dpi, y: -dpi);           cnv.cgContext.drawPDFPage(page);          })     let img2 = UIImage(data: img1)     return img2 } 

回答4:

I've written a handy UIImage PDF renderer category that you may find helpful. It also caches all rendered results for high performance.

https://github.com/mindbrix/UIImage-PDF

文章来源: High quality UIImage from PDF