您好，感谢您的阅读！我正在尝试将NSImage对象写入磁盘上的文件，但由于从原始NSImage中提取NSData对象时某些“图像属性”丢失，因此遇到了问题。
为了说明问题，我有以下代码。原始的NSImage对象被称为'image'，我将其传递给imageDump（最后输出），然后我从中提取NSData对象，以便将其写入文件，但这样做似乎删除了一些图像属性。我再次调用imageDump（最后再次输出），但这次注意了一些属性是如何被删除的。例如CGImageGetBitsPerPixel：从32开始，但在第二次调用imageDump时它现在是24？
在将NSData对象写入磁盘之前提取NSData对象时，如何防止删除这些图像属性？
NSLog(@"/n PRINTING THE IMAGE PASSED TO THIS METHOD\n");
[self imageDump:[image CGImageForProposedRect:NULL context:NULL hints:NULL]];
NSData *imageData = [image TIFFRepresentation];
NSImage *montysImage = [[NSImage alloc ] initWithData:imageData];
NSLog(@"/n PRINTING THE IMAGE THAT WAS FIRST CONVERTED TO NSDATA AND THEN BACK\n");
[self imageDump:[montysImage CGImageForProposedRect:NULL context:NULL hints:NULL]];
-(void)imageDump:(CGImageRef)cgimage {
size_t width = CGImageGetWidth(cgimage);
size_t height = CGImageGetHeight(cgimage);
size_t bpr = CGImageGetBytesPerRow(cgimage);
size_t bpp = CGImageGetBitsPerPixel(cgimage);
size_t bpc = CGImageGetBitsPerComponent(cgimage);
size_t bytes_per_pixel = bpp / bpc;
CGBitmapInfo info = CGImageGetBitmapInfo(cgimage);
NSString *file = @"file";
NSLog(
@"\n"
"===== %@ =====\n"
"CGImageGetHeight: %d\n"
"CGImageGetWidth: %d\n"
"CGImageGetColorSpace: %@\n"
"CGImageGetBitsPerPixel: %d\n"
"CGImageGetBitsPerComponent: %d\n"
"CGImageGetBytesPerRow: %d\n"
"CGImageGetBitmapInfo: 0x%.8X\n"
" kCGBitmapAlphaInfoMask = %s\n"
" kCGBitmapFloatComponents = %s\n"
" kCGBitmapByteOrderMask = %s\n"
" kCGBitmapByteOrderDefault = %s\n"
" kCGBitmapByteOrder16Little = %s\n"
" kCGBitmapByteOrder32Little = %s\n"
" kCGBitmapByteOrder16Big = %s\n"
" kCGBitmapByteOrder32Big = %s\n",
file,
(int)width,
(int)height,
CGImageGetColorSpace(cgimage),
(int)bpp,
(int)bpc,
(int)bpr,
(unsigned)info,
(info & kCGBitmapAlphaInfoMask) ? "YES" : "NO",
(info & kCGBitmapFloatComponents) ? "YES" : "NO",
(info & kCGBitmapByteOrderMask) ? "YES" : "NO",
(info & kCGBitmapByteOrderDefault) ? "YES" : "NO",
(info & kCGBitmapByteOrder16Little) ? "YES" : "NO",
(info & kCGBitmapByteOrder32Little) ? "YES" : "NO",
(info & kCGBitmapByteOrder16Big) ? "YES" : "NO",
(info & kCGBitmapByteOrder32Big) ? "YES" : "NO" );
CGDataProviderRef provider = CGImageGetDataProvider(cgimage);
NSData* data = (__bridge id)CGDataProviderCopyData(provider);
//[data autorelease];
const uint8_t* bytes = [data bytes];
printf("Pixel Data:\n");
for(size_t row = 0; row < height; row++)
{
for(size_t col = 0; col < width; col++)
{
const uint8_t* pixel = &bytes[row * bpr + col * bytes_per_pixel];
printf("(");
for(size_t x = 0; x < 3; x++) // 3 WAS -> bytes_per_pixel - changed to remove the alpha component.
{
printf("%.2X", pixel[x]);
if( x < 3 - 1 ) // 3 WAS -> bytes_per_pixel - changed to remove the alpha component.
printf(",");
}
printf(")");
if( col < width - 1 )
printf(", ");
}
printf("\n");
}
}
控制台输出：
2013-11-06 22:52:01.082 LibraryBuilder[20792:303] /n PRINTING THE IMAGE PASSED TO THIS METHOD 2013-11-06 22:52:01.082 LibraryBuilder[20792:303] ===== file ===== CGImageGetHeight: 6 CGImageGetWidth: 7 CGImageGetColorSpace: <CGColorSpace 0x60000003b840> (kCGColorSpaceICCBased; kCGColorSpaceModelRGB; Color LCD) CGImageGetBitsPerPixel: 32 CGImageGetBitsPerComponent: 8 CGImageGetBytesPerRow: 64 CGImageGetBitmapInfo: 0x00002006 kCGBitmapAlphaInfoMask = YES kCGBitmapFloatComponents = NO kCGBitmapByteOrderMask = YES kCGBitmapByteOrderDefault = NO kCGBitmapByteOrder16Little = NO kCGBitmapByteOrder32Little = YES kCGBitmapByteOrder16Big = YES kCGBitmapByteOrder32Big = NO Pixel Data: (F7,F7,F7), (F7,F7,F7), (F7,F7,F7), (F7,F7,F7), (F7,F7,F7), (EA,D9,C2) (F7,F7,F7), (F7,F7,F7), (F7,F7,F7), (F7,F7,F7), (F7,F7,F7), (F7,F7,F7) (F7,F7,F7), (F7,F7,F7), (F7,F7,F7), (F7,F7,F7), (F7,F7,F7), (F7,F7,F7) (F7,F7,F7), (F7,F7,F7), (F7,F7,F7), (F7,F7,F7), (F7,F7,F7), (F7,F7,F7) (B3,B3,B3), (B3,B3,B3), (B3,B3,B3), (B3,B3,B3), (B3,B3,B3), (B3,B3,B3) (F7,F7,F7), (F7,F7,F7), (F7,F7,F7), (F7,F7,F7), (F7,F7,F7), (F7,F7,F7) (F7,F7,F7), (F7,F7,F7), (F7,F7,F7), (F7,F7,F7), (F7,F7,F7), (F7,F7,F7) 2013-11-06 22:52:01.122 LibraryBuilder[20792:303] /n PRINTING THE IMAGE THAT WAS FIRST CONVERTED TO NSDATA AND THEN BACK 2013-11-06 22:52:01.122 LibraryBuilder[20792:303] ===== file ===== CGImageGetHeight: 6 CGImageGetWidth: 7 CGImageGetColorSpace: <CGColorSpace 0x618000032f40> (kCGColorSpaceICCBased; kCGColorSpaceModelRGB; Color LCD) CGImageGetBitsPerPixel: 24 CGImageGetBitsPerComponent: 8 CGImageGetBytesPerRow: 18 CGImageGetBitmapInfo: 0x00000000 kCGBitmapAlphaInfoMask = NO kCGBitmapFloatComponents = NO kCGBitmapByteOrderMask = NO kCGBitmapByteOrderDefault = NO kCGBitmapByteOrder16Little = NO kCGBitmapByteOrder32Little = NO kCGBitmapByteOrder16Big = NO kCGBitmapByteOrder32Big = NO Pixel Data: (F7,F7,F7), (F7,F7,F7), (F7,F7,F7), (F7,F7,F7), (F7,F7,F7), (C2,D9,EA) (F7,F7,F7), (F7,F7,F7), (F7,F7,F7), (F7,F7,F7), (F7,F7,F7), (F7,F7,F7) (F7,F7,F7), (F7,F7,F7), (F7,F7,F7), (F7,F7,F7), (F7,F7,F7), (F7,F7,F7) (F7,F7,F7), (F7,F7,F7), (F7,F7,F7), (F7,F7,F7), (F7,F7,F7), (F7,F7,F7) (B3,B3,B3), (B3,B3,B3), (B3,B3,B3), (B3,B3,B3), (B3,B3,B3), (B3,B3,B3) (F7,F7,F7), (F7,F7,F7), (F7,F7,F7), (F7,F7,F7), (F7,F7,F7), (F7,F7,F7) (F7,F7,F7), (F7,F7,F7), (F7,F7,F7), (F7,F7,F7), (F7,F7,F7), (F7,F7,F7)
答案 0 :(得分：0)
目前尚不清楚任何数据是否真的丢失了。有很多方法可以表示完全相同的图像，并且您正在做一堆扭曲来转储可能修改其格式的数据（不改变它的绘制方式）。比如，如果图像存储BRG或RGB或BGR并不重要，但这些将修改转储的外观。
在您的实例中，如果您的原始图像具有透明度通道但它始终是100％不透明的，则-TIFFRepresentation调用可能（合理地）决定不写出透明度通道，因此当您在其中读取它时走了但这并没有改变图像的绘制方式。
您不会在转储中显示Alpha通道，因此不清楚您是否丢失了任何数据，但其他一切看起来都很正常。