Question

我知道有一种方法可以将PDF页面保存到NSImage，然后像这样输出到JPG：

NSData *pdfData = [NSData dataWithContentsOfFile:pathToUrPDF];    
NSPDFImageRep *pdfImg = [NSPDFImageRep imageRepWithData:pdfData];
NSFileManager *fileManager = [NSFileManager defaultManager];
NSInteger pageCount = [pdfImg pageCount];
for(int i = 0 ; i < pageCount ; i++) {
    [pdfImg setCurrentPage:i];
    NSImage *temp = [[NSImage alloc] init];
    [temp addRepresentation:pdfImg];
    NSBitmapImageRep *rep = [NSBitmapImageRep imageRepWithData:[temp TIFFRepresentation]];
    NSData *finalData = [rep representationUsingType:NSJPEGFileType properties:nil];
    NSString *pageName = [NSString stringWithFormat:@"Page_%ld.jpg", (long)[pdfImg currentPage]];
    [fileManager createFileAtPath:[NSString stringWithFormat:@"%@/%@", @"pathWrUWantToSave", pageName] contents:finalData attributes:nil];
}

但是“TIFFRepresetation”只能输出最高72 DPI。所以我认为从PDF获取高DPI图像的最佳方法是在Mac OS X上使用CGImage。如何做到这一点？我的目标应用程序适用于Mac OS X，而非iOS ...

非常感谢

Answer 1

最后我得到了解决方案：

自OS X 10.8起，NSImage有一个基于块的初始化器，用于将基于矢量的内容绘制到位图中。我们的想法是提供一个绘图处理程序，只要请求图像的表示就会调用它。点和像素之间的关系通过将NSSize（以点为单位）传递给初始化器并显式设置表示的像素尺寸来表示：

NSString* localDocuments = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,NSUserDomainMask, YES) objectAtIndex:0];
NSString* pdfPath = [localDocuments stringByAppendingPathComponent:@"1.pdf"];
NSData* pdfData = [NSData dataWithContentsOfFile:pdfPath];
NSPDFImageRep* pdfImageRep = [NSPDFImageRep imageRepWithData:pdfData];
CGFloat factor = 300/72;
NSInteger pageCount = [pdfImageRep pageCount];
for(int i = 0 ; i < pageCount ; i++) {
    [pdfImageRep setCurrentPage:i];
    NSImage* scaledImage = [NSImage imageWithSize:pdfImageRep.size flipped:NO drawingHandler:^BOOL(NSRect dstRect) {
        [pdfImageRep drawInRect:dstRect];
        return YES;
    }];
    NSImageRep* scaledImageRep = [[scaledImage representations] firstObject];
    /*
     * The sizes of the PDF Image Rep and the [NSImage  imageWithSize: drawingHandler:]-context
     * are define in terms of points.
     * By explicitly setting the size of the scaled representation in in Pixels, you 
     * define the relation between ponts & pixels.
     */
    scaledImageRep.pixelsWide = pdfImageRep.size.width * factor;
    scaledImageRep.pixelsHigh = pdfImageRep.size.height * factor;
    NSBitmapImageRep* pngImageRep = [NSBitmapImageRep imageRepWithData:[scaledImage TIFFRepresentation]];
    NSData* finalData = [pngImageRep representationUsingType:NSJPEGFileType properties:nil];
    NSString* pageName = [NSString stringWithFormat:@"Page_%ld.jpg", (long)[pdfImageRep currentPage]];
    [[NSFileManager defaultManager] createFileAtPath:[NSString stringWithFormat:@"%@%@", pdfPath, pageName] contents:finalData attributes:nil];
}

如何将PDF转换为CGImage，然后保存为高DPI JPG图像？

1 个答案: