nsimage 转 png ，jpg的nsdata 类型

NSImage * image = ..........;

NSData *imageData = [image TIFFRepresentation];NSBitmapImageRep *imageRep = [NSBitmapImageRep imageRepWithData:imageData];[imageRep setSize:[[_imageView image] size]];

// pngNSData * imageData1 = [imageRep representationUsingType:NSPNGFileType properties:nil];// jpgNSDictionary *imageProps = nil;NSNumber *quality = [NSNumber numberWithFloat:.85];imageProps = [NSDictionary dictionaryWithObject:quality forKey:NSImageCompressionFactor];NSData * imageData1 = [imageRep representationUsingType:NSJPEGFileType properties:imageProps];