如何将PDF转换为NSImage并更改DPI? [英] How to Convert PDF to NSImage and change the DPI?
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问题描述
我试图将PDF页面转换为NSImage并成功保存为JPG文件.但是,输出结果是正常的72 DPI.我想将DPI更改为300 DPI,但失败了.下面是代码:
I have tried to convert PDF Pages to NSImage and save to JPG files successfully. However the output result is as normal 72 DPI. I want to change the DPI to 300 DPI but failed. Below is the code:
- (IBAction)TestButton:(id)sender {
NSString* localDocuments = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,NSUserDomainMask, YES) objectAtIndex:0];
NSString* pdfPath = [localDocuments stringByAppendingPathComponent:@"1.pdf"];
NSData *pdfData = [NSData dataWithContentsOfFile:pdfPath];
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];
CGFloat factor = 300/72; // Scale from 72 DPI to 300 DPI
//NSImage *img; // Source image
NSSize newSize = NSMakeSize(temp.size.width*factor, temp.size.height*factor);
NSImage *scaledImg = [[NSImage alloc] initWithSize:newSize];
[scaledImg lockFocus];
[[NSColor whiteColor] set];
[NSBezierPath fillRect:NSMakeRect(0, 0, newSize.width, newSize.height)];
NSAffineTransform *transform = [NSAffineTransform transform];
[transform scaleBy:factor];
[transform concat];
[temp drawAtPoint:NSZeroPoint fromRect:NSZeroRect operation:NSCompositeSourceOver fraction:1.0];
[scaledImg unlockFocus];
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:@"%@%@", pdfPath, pageName] contents:finalData attributes:nil];
}
}
推荐答案
Since OS X 10.8, NSImage has a block based initialiser to draw vector based content into a bitmap.
The idea is to provide a drawing handler that is called whenever a representation of the image is requested.
The relation between points and pixels is expressed by passing a NSSize (in points) to the initialiser and to explicitly set the pixel dimensions for the representation:
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 defined in terms of points.
* By explicitly setting the size of the scaled representation in Pixels, you
* define the relation between points & 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];
}
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