31

我正在对图像进行一些操作，完成后，我想将图像保存为磁盘上的 PNG。我正在执行以下操作：

+ (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];
}

此代码有效，但问题出在视网膜 mac，如果我打印 NSBitmapImageRep 对象，我会得到不同的大小和像素矩形，当我的图像保存在磁盘上时，它的大小是原来的两倍：

$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>

我绑定强制像素大小不关心视网膜比例，因为我想保留原始大小：

imageRepresentation.pixelsWide = image.size.width;
imageRepresentation.pixelsHigh = image.size.height;

这一次，当我打印 NSBitmapImageRep 对象时，我得到了正确的大小，但是当我保存我的文件时，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>

知道如何解决这个问题并保留原始像素大小吗？

4

6 回答 6

49

如果你有一个NSImage并且想将它作为图像文件保存到文件系统，你不应该使用lockFocus! lockFocus创建一个新图像，该图像被确定为显示在屏幕上，仅此而已。因此lockFocus使用屏幕的属性：普通屏幕为 72 dpi，视网膜屏幕为 144 dpi 。对于您想要的，我建议使用以下代码：

+ (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];
}
于 2013-07-07T08:58:11.077 回答
16

NSImagelockFocus当您在带有视网膜屏幕的系统上时，它可以感知分辨率并使用 HiDPI 图形上下文。
您传递给NSBitmapImageRep初始化程序的图像尺寸以点（而不是像素）为单位。因此，一个 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类别来创建具有明确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
于 2013-07-07T08:00:40.730 回答
5

我在 web 上找到了这段代码，它适用于视网膜。贴在这里，希望能帮到人。

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];
于 2015-03-20T08:44:57.317 回答
4

以防万一有人偶然发现这个线程。这肯定是有缺陷的解决方案，它可以将图像保存为 1x 大小（image.size），而不管设备在 swift 中如何

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
    }
}
于 2015-08-19T21:41:12.263 回答
3

这是基于Heinrich Giesen 的回答的 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)")
    }
}
于 2019-05-06T00:06:11.460 回答
0

我的 2 美分 OS X 包括处理扩展的写入 + 屏幕外图像绘制（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)
        }
    }
}
于 2016-09-13T14:04:10.733 回答