如何从NSImage保存PNG文件(视网膜问题)正确的方法？

Question

我试图将数组中的每个图像保存为.PNG文件(也是正确的大小,因为视网膜mac dpi问题没有按比例放大)并且似乎无法找到解决方案.如何从NSImage(视网膜问题)保存PNG文件的解决方案似乎没有为我工作.我已经尝试了每一个,他们每个人仍然会在视网膜.etc中将72x72文件保存为144x144.

更具体地说,我正在寻找一个NSImage类别(是的,我在Mac环境中工作)

我试图让用户选择一个目录来保存它们并执行从数组中保存图像,如下所示:

- (IBAction)saveImages:(id)sender {
    // Prepare Images that are checked and put them in an array
    [self prepareImages];

    if ([preparedImages count] == 0) {
        NSLog(@"We have no preparedImages to save!");
        NSAlert *alert = [[NSAlert alloc] init];
        [alert setAlertStyle:NSInformationalAlertStyle];
        [alert setMessageText:NSLocalizedString(@"Error", @"Save Images Error Text")];
        [alert setInformativeText:NSLocalizedString(@"You have not selected any images to create.", @"Save Images Error Informative Text")];

        [alert beginSheetModalForWindow:self.window
                          modalDelegate:self
                        didEndSelector:@selector(testDatabaseConnectionDidEnd:returnCode:
                                                   contextInfo:)
                            contextInfo:nil];
        return;
    } else {
        NSLog(@"We have prepared %lu images.", (unsigned long)[preparedImages count]);
    }

    // Save Dialog
    // Create a File Open Dialog class.
    //NSOpenPanel* openDlg = [NSOpenPanel openPanel];
    NSSavePanel *panel = [NSSavePanel savePanel];

    // Set array of file types
    NSArray *fileTypesArray;
    fileTypesArray = [NSArray arrayWithObjects:@"jpg", @"gif", @"png", nil];

    // Enable options in the dialog.
    //[openDlg setCanChooseFiles:YES];
    //[openDlg setAllowedFileTypes:fileTypesArray];
    //[openDlg setAllowsMultipleSelection:TRUE];
    [panel setNameFieldStringValue:@"Images.png"];
    [panel setDirectoryURL:directoryPath];


    // Display the dialog box.  If the OK pressed,
    // process the files.
    [panel beginWithCompletionHandler:^(NSInteger result) {

        if (result == NSFileHandlingPanelOKButton) {
            NSLog(@"OK Button!");
            // create a file manager and grab the save panel's returned URL
            NSFileManager *manager = [NSFileManager defaultManager];
            directoryPath = [panel URL];
            [[self directoryLabel] setStringValue:[NSString stringWithFormat:@"%@", directoryPath]];

            // then copy a previous file to the new location

            // copy item at URL was self.myURL
            // copy images that are created from array to this path


            for (NSImage *image in preparedImages) {
#warning Fix Copy Item At URL to copy image from preparedImages array to save each one
                NSString *imageName = image.name;
                NSString *imagePath = [[directoryPath absoluteString] stringByAppendingPathComponent:imageName];

                //[manager copyItemAtURL:nil toURL:directoryPath error:nil];
                NSLog(@"Trying to write IMAGE: %@ to URL: %@", imageName, imagePath);
                //[image writePNGToURL:[NSURL URLWithString:imagePath] outputSizeInPixels:image.size error:nil];
                [self saveImage:image atPath:imagePath];
            }
            //[manager copyItemAtURL:nil toURL:directoryPath error:nil];


        }
    }];

    [preparedImages removeAllObjects];

    return;

}

一个用户试图通过使用此NSImage类别来回答他,但它不会为我生成任何文件或PNG.

@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:[self isFlipped] 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, 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

Answer 1

我在原始帖子中提供的答案也遇到了麻烦.进一步阅读让我看到Erica Sadun关于调试视网膜显示器代码而没有视网膜显示器的帖子.她创建了所需大小的位图,然后将当前绘图上下文(基于显示/视网膜受影响)替换为与新位图关联的通用图形.然后,她将原始图像渲染到位图中(使用通用图形上下文).

我拿了她的代码并在NSImage上做了一个快速的类别,它似乎为我做了这个工作.打电话后

NSBitmapImageRep *myRep = [myImage unscaledBitmapImageRep];

你应该有一个正确(原始)尺寸的位图,无论你开始使用什么类型的物理显示.从这一点开始,您可以调用representationUsingType:properties未缩放的位图来获取您要写出的任何格式.

这是我的类别(标题省略).注意 - 您可能需要公开位图初始化程序的颜色空间部分.这是适用于我的特定情况的价值.

-(NSBitmapImageRep *)unscaledBitmapImageRep {

    NSBitmapImageRep *rep = [[NSBitmapImageRep alloc]
                               initWithBitmapDataPlanes:NULL
                                             pixelsWide:self.size.width
                                             pixelsHigh:self.size.height
                                          bitsPerSample:8
                                        samplesPerPixel:4
                                               hasAlpha:YES
                                               isPlanar:NO
                                         colorSpaceName:NSDeviceRGBColorSpace
                                            bytesPerRow:0
                                           bitsPerPixel:0];
    rep.size = self.size;

   [NSGraphicsContext saveGraphicsState];
   [NSGraphicsContext setCurrentContext:
            [NSGraphicsContext graphicsContextWithBitmapImageRep:rep]];

    [self drawAtPoint:NSMakePoint(0, 0) 
             fromRect:NSZeroRect 
            operation:NSCompositeSourceOver 
             fraction:1.0];

    [NSGraphicsContext restoreGraphicsState];
    return rep;
}

Answer 2

感谢tad和SnowPaddler.

对于不熟悉Cocoa并使用Swift 4的任何人,您可以从编辑历史中查看Swift 2和Swift 3版本:

import Cocoa

func unscaledBitmapImageRep(forImage image: NSImage) -> NSBitmapImageRep {
    guard let rep = NSBitmapImageRep(
        bitmapDataPlanes: nil,
        pixelsWide: Int(image.size.width),
        pixelsHigh: Int(image.size.height),
        bitsPerSample: 8,
        samplesPerPixel: 4,
        hasAlpha: true,
        isPlanar: false,
        colorSpaceName: .deviceRGB,
        bytesPerRow: 0,
        bitsPerPixel: 0
        ) else {
            preconditionFailure()
    }

    NSGraphicsContext.saveGraphicsState()
    NSGraphicsContext.current = NSGraphicsContext(bitmapImageRep: rep)
    image.draw(at: .zero, from: .zero, operation: .sourceOver, fraction: 1.0)
    NSGraphicsContext.restoreGraphicsState()

    return rep
}

func writeImage(
    image: NSImage,
    usingType type: NSBitmapImageRep.FileType,
    withSizeInPixels size: NSSize?,
    to url: URL) throws {
    if let size = size {
        image.size = size
    }
    let rep = unscaledBitmapImageRep(forImage: image)

    guard let data = rep.representation(using: type, properties: [.compressionFactor: 1.0]) else {
        preconditionFailure()
    }

    try data.write(to: url)
}