NSImage 到 NSBitmapImageRep

如何将 NSImage 转换为 NSBitmapImageRep？我有代码：

- (NSBitmapImageRep *)bitmapImageRepresentation
{
    NSBitmapImageRep *ret = (NSBitmapImageRep *)[self representations];

    if(![ret isKindOfClass:[NSBitmapImageRep class]])
    {
        ret = nil;
        for(NSBitmapImageRep *rep in [self representations])
            if([rep isKindOfClass:[NSBitmapImageRep class]])
            {
                ret = rep;
                break;
            }
    }

    if(ret == nil)
    {
        NSSize size = [self size];

        size_t width         = size.width;
        size_t height        = size.height;
        size_t bitsPerComp   = 32;
        size_t bytesPerPixel = (bitsPerComp / CHAR_BIT) * 4;
        size_t bytesPerRow   = bytesPerPixel * width;
        size_t totalBytes    = height * bytesPerRow;

        NSMutableData *data = [NSMutableData dataWithBytesNoCopy:calloc(totalBytes, 1) length:totalBytes freeWhenDone:YES];

        CGColorSpaceRef space = CGColorSpaceCreateWithName(kCGColorSpaceGenericRGB);

        CGContextRef ctx = CGBitmapContextCreate([data mutableBytes], width, height, bitsPerComp, bytesPerRow, CGColorSpaceCreateWithName(kCGColorSpaceGenericRGB), kCGBitmapFloatComponents | kCGImageAlphaPremultipliedLast);

        if(ctx != NULL)
        {
            [NSGraphicsContext saveGraphicsState];
            [NSGraphicsContext setCurrentContext:[NSGraphicsContext graphicsContextWithGraphicsPort:ctx flipped:[self isFlipped]]];

            [self drawAtPoint:NSZeroPoint fromRect:NSZeroRect operation:NSCompositeCopy fraction:1.0];

            [NSGraphicsContext restoreGraphicsState];

            CGImageRef img = CGBitmapContextCreateImage(ctx);

            ret = [[NSBitmapImageRep alloc] initWithCGImage:img];
            [self addRepresentation:ret];

            CFRelease(img);
            CFRelease(space);

            CGContextRelease(ctx);
        }
    }


    return ret;
}

它可以工作，但会导致内存泄漏。至少当我将它与 ARC 一起使用时是这样。使用initWithData:[nsimagename TIFFRepresentation]它无法正常工作。有些图像的表现效果不好。我认为这取决于图像的格式和色彩空间。还有其他方法可以实现这一目标吗？

结果与mrwalker建议的解决方案：

Original image:

Converted to bitmapimagerep and back to image 1 time:

Converted to bitmapimagerep and back to image 3 times:

如您所见，转换为 NSBitmapImageRep 后图像每次都会变暗

@Julius：您的代码太复杂并且包含多个错误。我将仅对第一行进行更正：

- (NSBitmapImageRep *)bitmapImageRepresentation
{
   for( NSImageRep *rep in [self representations] )
      if( [rep isKindOfClass:[NSBitmapImageRep class]] ) return rep;
   return nil;
}

这将提取第一个NSBitmapImageRep如果它是表示中的成员，或者将返回 nil，如果没有NSBitmapImageRep。我会给你另一个解决方案，它总是有效的NSImageReps在陈述中：NSBitmapImageRep, NSPDFImageRep or NSCGImageSnapshotRep or ...

- (NSBitmapImageRep *)bitmapImageRepresentation
{
   CGImageRef CGImage = [self CGImageForProposedRect:nil context:nil hints:nil];
   return [[[NSBitmapImageRep alloc] initWithCGImage:CGImage] autorelease];
}

或者为了避免 NSImage 的子类化，您可以编写：

NSImage *img = [[[NSImage alloc] initWithContentsOfFile:filename] autorelease];
CGImageRef CGImage = [img CGImageForProposedRect:nil context:nil hints:nil];
NSBitmapImageRep *rep = [[[NSBitmapImageRep alloc] initWithCGImage:CGImage] autorelease];

这只会返回一个NSBitmapImageRep如果图像包含多个表示（例如，很多NSBitmapImageRep来自 TIFF 文件）。但添加一些代码很简单。