iphone - 来自 PDF 的高质量 UIImage

Question

我正在将 PDF 页面转换为 UIImage。这样做时，我会失去图像质量。在获得高质量图像方面需要帮助。

生成 UIImage 的代码

-(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];
}

图像比较

原始 PDF

图片来自 PDF

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编辑：有变化的代码

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;

score 6 · Accepted Answer

当您询问 PDF 的页面大小时，您会得到 72 PPI 的宽度/高度。您可以尝试创建一个使用比例变换放大的上下文。例如，如果您想以 300 dpi 进行渲染，请添加缩放变换以按300.0/72.0.

如果导出为 TIFF，您将能够封装生成图像的最终 PPI (300)。

score 6 · Accepted Answer

这个提供最好的质量......如果您需要另一种质量，只需更改 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
}

score 3 · Accepted Answer

为 Swift 3 试试这个代码：

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
}

这提供了更高的分辨率

score 2 · Accepted Answer

我编写了一个方便的 UIImage PDF 渲染器类别，您可能会发现它很有帮助。它还缓存所有渲染结果以实现高性能。

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

score 2 · Accepted Answer

import PDFKit

let pdfDocument = PDFDocument(url: pdfUrl)!
let thumb = pdfDocument.page(at: pageIndex)?.thumbnail(of: size, for: .mediaBox)

score 2 · Accepted Answer

2

从 iOS 11.0、macOS 10.13、Mac Catalyst 13.0 开始，您可以使用thumbnailOfSize:forBox：

于 2019-10-09T13:26:22.387 回答

iphone - 来自 PDF 的高质量 UIImage

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6 回答 6

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