我正在对图像进行一些操作，在完成后，我想将图像保存为磁盘上的PNG。我正在做以下事情：
+ (void)saveImage:(NSImage *)image atPath:(NSString *)path {
[image lockFocus] ;
NSBitmapImageRep *imageRepresentation = [[NSBitmapImageRep alloc] initWithFocusedViewRect:NSMakeRect(0.0, 0.0, image.size.width, image.size.height)] ;
[image unlockFocus] ;
NSData *data = [imageRepresentation representationUsingType:NSPNGFileType properties:nil];
[data writeToFile:path atomically:YES];
}
此代码正常工作，但问题出在视网膜mac上，如果我打印NSBitmapImageRep对象，我得到一个不同的大小和像素rect，当我的图像保存在磁盘上时，它的大小是它的两倍：
$0 = 0x0000000100413890 NSBitmapImageRep 0x100413890 Size={300, 300} ColorSpace=sRGB IEC61966-2.1 colorspace BPS=8 BPP=32 Pixels=600x600 Alpha=YES Planar=NO Format=0 CurrentBacking=<CGImageRef: 0x100414830>
我强迫像素大小不要关心视网膜比例，因为我想保留原始尺寸：
imageRepresentation.pixelsWide = image.size.width;
imageRepresentation.pixelsHigh = image.size.height;
这次我在打印NSBitmapImageRep对象时得到了正确的大小，但是当我保存文件时，我仍然遇到同样的问题：
$0 = 0x0000000100413890 NSBitmapImageRep 0x100413890 Size={300, 300} ColorSpace=sRGB IEC61966-2.1 colorspace BPS=8 BPP=32 Pixels=300x300 Alpha=YES Planar=NO Format=0 CurrentBacking=<CGImageRef: 0x100414830>
知道如何解决此问题，并保留原始像素大小？
答案 0 :(得分：42)
如果您有NSImage并希望将其作为图像文件保存到文件系统，则永远不会使用lockFocus！ lockFocus创建一个新图像，该图像是为了显示屏幕而确定的。因此lockFocus使用屏幕属性：普通屏幕为72 dpi，视网膜屏幕为144 dpi。对于你想要的，我提出以下代码：
+ (void)saveImage:(NSImage *)image atPath:(NSString *)path {
CGImageRef cgRef = [image CGImageForProposedRect:NULL
context:nil
hints:nil];
NSBitmapImageRep *newRep = [[NSBitmapImageRep alloc] initWithCGImage:cgRef];
[newRep setSize:[image size]]; // if you want the same resolution
NSData *pngData = [newRep representationUsingType:NSPNGFileType properties:nil];
[pngData writeToFile:path atomically:YES];
[newRep autorelease];
}
答案 1 :(得分：15)
NSImage具有分辨率，并且当您在具有视网膜屏幕的系统上lockFocus时使用HiDPI图形上下文。
传递给NSBitmapImageRep初始值设定项的图像尺寸以点（不是像素）为单位。因此，150.0点宽的图像在@ 2x上下文中使用300个水平像素。
您可以使用convertRectToBacking:或backingScaleFactor:来补偿@ 2x上下文。 （我没有尝试过），或者您可以使用以下NSImage类别创建具有显式像素尺寸的绘图上下文：
@interface NSImage (SSWPNGAdditions)
- (BOOL)writePNGToURL:(NSURL*)URL outputSizeInPixels:(NSSize)outputSizePx error:(NSError*__autoreleasing*)error;
@end
@implementation NSImage (SSWPNGAdditions)
- (BOOL)writePNGToURL:(NSURL*)URL outputSizeInPixels:(NSSize)outputSizePx error:(NSError*__autoreleasing*)error
{
BOOL result = YES;
NSImage* scalingImage = [NSImage imageWithSize:[self size] flipped:NO drawingHandler:^BOOL(NSRect dstRect) {
[self drawAtPoint:NSMakePoint(0.0, 0.0) fromRect:dstRect operation:NSCompositeSourceOver fraction:1.0];
return YES;
}];
NSRect proposedRect = NSMakeRect(0.0, 0.0, outputSizePx.width, outputSizePx.height);
CGColorSpaceRef colorSpace = CGColorSpaceCreateWithName(kCGColorSpaceGenericRGB);
CGContextRef cgContext = CGBitmapContextCreate(NULL, proposedRect.size.width, proposedRect.size.height, 8, 4*proposedRect.size.width, colorSpace, kCGBitmapByteOrderDefault|kCGImageAlphaPremultipliedLast);
CGColorSpaceRelease(colorSpace);
NSGraphicsContext* context = [NSGraphicsContext graphicsContextWithGraphicsPort:cgContext flipped:NO];
CGContextRelease(cgContext);
CGImageRef cgImage = [scalingImage CGImageForProposedRect:&proposedRect context:context hints:nil];
CGImageDestinationRef destination = CGImageDestinationCreateWithURL((__bridge CFURLRef)(URL), kUTTypePNG, 1, NULL);
CGImageDestinationAddImage(destination, cgImage, nil);
if(!CGImageDestinationFinalize(destination))
{
NSDictionary* details = @{NSLocalizedDescriptionKey:@"Error writing PNG image"};
[details setValue:@"ran out of money" forKey:NSLocalizedDescriptionKey];
*error = [NSError errorWithDomain:@"SSWPNGAdditionsErrorDomain" code:10 userInfo:details];
result = NO;
}
CFRelease(destination);
return result;
}
@end
答案 2 :(得分：5)
我在网上找到了这个代码，它适用于视网膜。粘贴在这里，希望可以帮助别人。
NSImage *computerImage = [NSImage imageNamed:NSImageNameComputer];
NSInteger size = 256;
NSBitmapImageRep *rep = [[NSBitmapImageRep alloc]
initWithBitmapDataPlanes:NULL
pixelsWide:size
pixelsHigh:size
bitsPerSample:8
samplesPerPixel:4
hasAlpha:YES
isPlanar:NO
colorSpaceName:NSCalibratedRGBColorSpace
bytesPerRow:0
bitsPerPixel:0];
[rep setSize:NSMakeSize(size, size)];
[NSGraphicsContext saveGraphicsState];
[NSGraphicsContext setCurrentContext:[NSGraphicsContext graphicsContextWithBitmapImageRep:rep]];
[computerImage drawInRect:NSMakeRect(0, 0, size, size) fromRect:NSZeroRect operation:NSCompositeCopy fraction:1.0];
[NSGraphicsContext restoreGraphicsState];
NSData *data = [rep representationUsingType:NSPNGFileType properties:nil];
答案 3 :(得分：4)
只是因为任何人在这个线程上绊倒了。这是一个有缺陷的解决方案，可以保存1x大小的图像（image.size），无论swift中的设备如何
public func writeToFile(path: String, atomically: Bool = true) -> Bool{
let bitmap = NSBitmapImageRep(bitmapDataPlanes: nil, pixelsWide: Int(self.size.width), pixelsHigh: Int(self.size.height), bitsPerSample: 8, samplesPerPixel: 4, hasAlpha: true, isPlanar: false, colorSpaceName: NSDeviceRGBColorSpace, bytesPerRow: 0, bitsPerPixel: 0)!
bitmap.size = self.size
NSGraphicsContext.saveGraphicsState()
NSGraphicsContext.setCurrentContext(NSGraphicsContext(bitmapImageRep: bitmap))
self.drawAtPoint(CGPoint.zero, fromRect: NSRect.zero, operation: NSCompositingOperation.CompositeSourceOver, fraction: 1.0)
NSGraphicsContext.restoreGraphicsState()
if let imagePGNData = bitmap.representationUsingType(NSBitmapImageFileType.NSPNGFileType, properties: [NSImageCompressionFactor: 1.0]) {
return imagePGNData.writeToFile((path as NSString).stringByStandardizingPath, atomically: atomically)
} else {
return false
}
}
答案 4 :(得分：1)
以下是基于Heinrich Giesen's answer的Swift 5版本：
static func saveImage(_ image: NSImage, atUrl url: URL) {
guard
let cgImage = image.cgImage(forProposedRect: nil, context: nil, hints: nil)
else { return } // TODO: handle error
let newRep = NSBitmapImageRep(cgImage: cgImage)
newRep.size = image.size // if you want the same size
guard
let pngData = newRep.representation(using: .png, properties: [:])
else { return } // TODO: handle error
do {
try pngData.write(to: url)
}
catch {
print("error saving: \(error)")
}
}
答案 5 :(得分：0)
OS X的2美分，包括处理扩展程序+屏幕外图像绘制的写入（方法2）;可以使用NSGraphicsContext.currentContextDrawingToScreen（）
进行验证func createCGImage() -> CGImage? {
//method 1
let image = NSImage(size: NSSize(width: bounds.width, height: bounds.height), flipped: true, drawingHandler: { rect in
self.drawRect(self.bounds)
return true
})
var rect = CGRectMake(0, 0, bounds.size.width, bounds.size.height)
return image.CGImageForProposedRect(&rect, context: bitmapContext(), hints: nil)
//method 2
if let pdfRep = NSPDFImageRep(data: dataWithPDFInsideRect(bounds)) {
return pdfRep.CGImageForProposedRect(&rect, context: bitmapContext(), hints: nil)
}
return nil
}
func PDFImageData(filter: QuartzFilter?) -> NSData? {
return dataWithPDFInsideRect(bounds)
}
func bitmapContext() -> NSGraphicsContext? {
var context : NSGraphicsContext? = nil
if let imageRep = NSBitmapImageRep(bitmapDataPlanes: nil,
pixelsWide: Int(bounds.size.width),
pixelsHigh: Int(bounds.size.height), bitsPerSample: 8,
samplesPerPixel: 4, hasAlpha: true, isPlanar: false,
colorSpaceName: NSCalibratedRGBColorSpace,
bytesPerRow: Int(bounds.size.width) * 4,
bitsPerPixel: 32) {
imageRep.size = NSSize(width: bounds.size.width, height: bounds.size.height)
context = NSGraphicsContext(bitmapImageRep: imageRep)
}
return context
}
func writeImageData(view: MyView, destination: NSURL) {
if let dest = CGImageDestinationCreateWithURL(destination, imageUTType, 1, nil) {
let properties = imageProperties
let image = view.createCGImage()!
let queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)
dispatch_async(queue) {
CGImageDestinationAddImage(dest, image, properties)
CGImageDestinationFinalize(dest)
}
}
}