NSImage 无法缩放

Question

我正在开发一个快速应用程序，其中我有一种方法可以将@2x 图像重新缩放为常规图像。问题是它没有:(

为什么？

-(BOOL)createNormalImage:(NSString*)inputRetinaImagePath {

    NSImage *inputRetinaImage = [[NSImage alloc] initWithContentsOfFile:inputRetinaImagePath];



    NSSize size = NSZeroSize;
    size.width = inputRetinaImage.size.width*0.5;
    size.height = inputRetinaImage.size.height*0.5;

    [inputRetinaImage setSize:size];


    NSLog(@"%f",inputRetinaImage.size.height);


    NSBitmapImageRep *imgRep = [[inputRetinaImage representations] objectAtIndex: 0];

    NSData *data = [imgRep representationUsingType: NSPNGFileType properties: nil];

    NSString *outputFilePath = [[inputRetinaImagePath substringToIndex:inputRetinaImagePath.length - 7] stringByAppendingString:@".png"];

    NSLog([@"Normal version file path: " stringByAppendingString:outputFilePath]);
    [data writeToFile:outputFilePath atomically: NO];
    return true;
}

Answer 1

你必须非常小心 NSImage 的 size 属性。它不一定指的是 bitmapRepresentation 的像素尺寸，它可以指例如显示的大小。一个 NSImage 可能有许多 bitmapRepresentations 用于不同的输出大小。

同样，改变 NSImage 的 size 属性不会改变 bitmapRepresentations

所以你需要做的是计算出你希望输出图像的大小，然后使用来自源 NSImage 的 bitmapRepresentation 以该大小绘制一个新图像。

获得该尺寸取决于您如何获得输入图像以及您对它的了解。例如，如果您确信您的输入图像只有一个 bitmapImageRep，您可以使用这种类型的东西（作为 NSImage 上的一个类别）

  - (NSSize) pixelSize
{
    NSBitmapImageRep* bitmap = [[self representations] objectAtIndex:0];
    return NSMakeSize(bitmap.pixelsWide,bitmap.pixelsHigh);
}

即使您有多个 bitmapImageRep，第一个也应该是最大的，如果这是创建 Retina 图像的尺寸，那么它应该是您所追求的 Retina 尺寸。

确定最终尺寸后，您可以制作图像：

- (NSImage*) resizeImage:(NSImage*)sourceImage size:(NSSize)size
{

    NSRect targetFrame = NSMakeRect(0, 0, size.width, size.height);     
    NSImage* targetImage = nil;
    NSImageRep *sourceImageRep =
    [sourceImage bestRepresentationForRect:targetFrame
                                   context:nil
                                     hints:nil];

    targetImage = [[NSImage alloc] initWithSize:size];

    [targetImage lockFocus];
    [sourceImageRep drawInRect: targetFrame];
    [targetImage unlockFocus];

return targetImage; 

}

更新

这里是 NSImage 上像素大小获取类别的更详细版本...让我们假设图像没有什么，它有多少 imageReps，它是否有 any bitmapImageReps...这将返回它可以找到的最大像素尺寸。如果它找不到 bitMapImageRep 像素尺寸，它将使用它可以得到的任何其他东西，这很可能是边界框尺寸（由 eps 和 pdf 使用）。

NSImage+PixelSize.h

#import <Cocoa/Cocoa.h>
#import <QuartzCore/QuartzCore.h>

@interface NSImage (PixelSize)

- (NSInteger) pixelsWide;
- (NSInteger) pixelsHigh;
- (NSSize) pixelSize;

@end

NSImage+PixelSize.m

#import "NSImage+PixelSize.h"

@implementation NSImage (Extensions)

- (NSInteger) pixelsWide
{
    /*
     returns the pixel width of NSImage.
     Selects the largest bitmapRep by preference
     If there is no bitmapRep returns largest size reported by any imageRep.
     */
    NSInteger result = 0;
    NSInteger bitmapResult = 0;

    for (NSImageRep* imageRep in [self representations]) {
        if ([imageRep isKindOfClass:[NSBitmapImageRep class]]) {
            if (imageRep.pixelsWide > bitmapResult)
                bitmapResult = imageRep.pixelsWide;
        } else {
            if (imageRep.pixelsWide > result)
                result = imageRep.pixelsWide;
        }
    }
    if (bitmapResult) result = bitmapResult;
    return result;

}

- (NSInteger) pixelsHigh
{
    /*
     returns the pixel height of NSImage.
     Selects the largest bitmapRep by preference
     If there is no bitmapRep returns largest size reported by any imageRep.
     */
    NSInteger result = 0;
    NSInteger bitmapResult = 0;

    for (NSImageRep* imageRep in [self representations]) {
        if ([imageRep isKindOfClass:[NSBitmapImageRep class]]) {
            if (imageRep.pixelsHigh > bitmapResult)
                bitmapResult = imageRep.pixelsHigh;
        } else {
            if (imageRep.pixelsHigh > result)
                result = imageRep.pixelsHigh;
        }
    }
    if (bitmapResult) result = bitmapResult;
    return result;
}

- (NSSize) pixelSize
{
    return NSMakeSize(self.pixelsWide,self.pixelsHigh);
}

@end

您可以在当前文件中#import "NSImage+PixelSize.h" 以使其可访问。

使用此图像类别和 resize: 方法，您可以这样修改您的方法：

//size.width = inputRetinaImage.size.width*0.5;
//size.height = inputRetinaImage.size.height*0.5;
size.width  = inputRetinaImage.pixelsWide*0.5;
size.height = inputRetinaImage.pixelsHigh*0.5;

//[inputRetinaImage setSize:size];
NSImage* outputImage = [self resizeImage:inputRetinaImage size:size];

//NSBitmapImageRep *imgRep = [[inputRetinaImage representations] objectAtIndex: 0];
NSBitmapImageRep *imgRep = [[outputImage representations] objectAtIndex: 0];

应该为你解决问题（附带条件：我没有在你的代码上测试过）

Answer 2

我修改了我用来为你缩小图像的脚本:)

-(BOOL)createNormalImage:(NSString*)inputRetinaImagePath {

    NSImage *inputRetinaImage = [[NSImage alloc] initWithContentsOfFile:inputRetinaImagePath];

    //determine new size
    NSBitmapImageRep* bitmapImageRep = [[inputRetinaImage representations] objectAtIndex:0];
    NSSize size = NSMakeSize(bitmapImageRep.pixelsWide * 0.5,bitmapImageRep.pixelsHigh * 0.5);

    NSLog(@"size = %@", NSStringFromSize(size));

    //get CGImageRef
    CGImageSourceRef source = CGImageSourceCreateWithData((__bridge CFDataRef)[inputRetinaImage TIFFRepresentation], NULL);
    CGImageRef oldImageRef =  CGImageSourceCreateImageAtIndex(source, 0, NULL);
    CGImageAlphaInfo alphaInfo = CGImageGetAlphaInfo(oldImageRef);
    if (alphaInfo == kCGImageAlphaNone) alphaInfo = kCGImageAlphaNoneSkipLast;

    // Build a bitmap context
    CGContextRef bitmap = CGBitmapContextCreate(NULL, size.width, size.height, 8, 4 * size.width, CGImageGetColorSpace(oldImageRef), alphaInfo);

    // Draw into the context, this scales the image
    CGContextDrawImage(bitmap, CGRectMake(0, 0, size.width, size.height), oldImageRef);

    // Get an image from the context
    CGImageRef newImageRef = CGBitmapContextCreateImage(bitmap);

    //this does not work in my test.
    NSString *outputFilePath = [[inputRetinaImagePath substringToIndex:inputRetinaImagePath.length - 7] stringByAppendingString:@".png"];

    //but this does!
    NSArray* paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString* docsDirectory = [paths objectAtIndex:0];
    NSString *newfileName = [docsDirectory stringByAppendingFormat:@"/%@", [outputFilePath lastPathComponent]];

    CFURLRef url = (__bridge CFURLRef)[NSURL fileURLWithPath:newfileName];
    CGImageDestinationRef destination = CGImageDestinationCreateWithURL(url, kUTTypePNG, 1, NULL);
    CGImageDestinationAddImage(destination, newImageRef, nil);

    if (!CGImageDestinationFinalize(destination)) {
        NSLog(@"Failed to write image to %@", newfileName);
    }

    CFRelease(destination);

    return true;
}