我正在将 pdf 文件转换为 png 图像,这样我就可以将文本添加到 png,然后再转换回 pdf。我正在使用下面的代码转换为 png。这导致外观质量显着下降。是否可以采取任何措施来防止或最大程度地减少质量损失?
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];
最佳答案
您可以尝试增加要渲染的图像上下文的大小:
UIGraphicsBeginImageContext(CGSizeMake(1224,1584));
...
CGContextTranslateCTM(currentContext, 10, 1584);
但你真的可能应该使用 PDF context像这样:
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);
// Create URL for PDF file
NSString *filename = @"sample-out.pdf";
NSURL *outputURL = [NSURL fileURLWithPathComponents:[NSArray arrayWithObjects:documentsDirectory, filename, nil]];
// Create PDF context
CGContextRef pdfContext = CGPDFContextCreateWithURL((CFURLRef)outputURL, NULL, NULL);
CGPDFContextBeginPage(pdfContext, NULL);
UIGraphicsPushContext(pdfContext);
// Flip coordinate system
CGRect bounds = CGContextGetClipBoundingBox(pdfContext);
CGContextScaleCTM(pdfContext, 1.0, -1.0);
CGContextTranslateCTM(pdfContext, 0.0, -bounds.size.height);
CGContextDrawPDFPage (UIGraphicsGetCurrentContext(), CGPDFDocumentGetPage (myDocument, 1));
// Drawing commands
[@"Hello World!" drawAtPoint:CGPointMake(0, 0) withFont:[UIFont boldSystemFontOfSize:72.0f]];
// Clean up
UIGraphicsPopContext();
CGPDFContextEndPage(pdfContext);
CGPDFContextClose(pdfContext);
关于ios - 在 iOS 中将 pdf 转换为 png 会导致外观质量大幅降低,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/15455151/