@DougS
您的实现大部分是正确的,但由于多个内存分配和副本,它的性能不是很好。
我注意到您正在创建 3 个内存块,每个内存块的总大小为 (w*h*4 字节):
// the int[]
raster = new int[width * height];
// the SKColor[]
pixels = new SKColor[width * height];
// the bitmap
bitmap = new SKBitmap(width, height)
您还多次在内存之间复制像素:
// decode the TIFF (first copy)
tifImg.ReadRGBAImageOriented(width, height, raster, Orientation.TOPLEFT)
// convert to SKColor (second copy)
pixels[arrayOffset] = new SKColor(...);
// set bitmap pixels (third copy)
bitmap.Pixels = pixels;
我想我设法创建了一个类似的方法来解码流,只需要一个副本和内存分配:
public static SKBitmap OpenTiff(Stream tiffStream)
{
// open a TIFF stored in the stream
using (var tifImg = Tiff.ClientOpen("in-memory", "r", tiffStream, new TiffStream()))
{
// read the dimensions
var width = tifImg.GetField(TiffTag.IMAGEWIDTH)[0].ToInt();
var height = tifImg.GetField(TiffTag.IMAGELENGTH)[0].ToInt();
// create the bitmap
var bitmap = new SKBitmap();
var info = new SKImageInfo(width, height);
// create the buffer that will hold the pixels
var raster = new int[width * height];
// get a pointer to the buffer, and give it to the bitmap
var ptr = GCHandle.Alloc(raster, GCHandleType.Pinned);
bitmap.InstallPixels(info, ptr.AddrOfPinnedObject(), info.RowBytes, null, (addr, ctx) => ptr.Free(), null);
// read the image into the memory buffer
if (!tifImg.ReadRGBAImageOriented(width, height, raster, Orientation.TOPLEFT))
{
// not a valid TIF image.
return null;
}
// swap the red and blue because SkiaSharp may differ from the tiff
if (SKImageInfo.PlatformColorType == SKColorType.Bgra8888)
{
SKSwizzle.SwapRedBlue(ptr.AddrOfPinnedObject(), raster.Length);
}
return bitmap;
}
}
这里有一个要点:https://gist.github.com/mattleibow/0a09babdf0dc9d2bc3deedf85f9b57d6
让我解释一下代码...我基本上正在创建int[]
就像你一样,但然后将其传递给SKBitmap
并让它接管。我将其固定为SKBitmap
存在于非托管内存中,GC 可能会移动它,但我确信在释放位图时会取消固定它。
以下是更详细的步骤:
// this does not actually allocate anything
// - the size is 0x0 / 0 bytes of pixels
var bitmap = new SKBitmap();
// I create the only buffer for pixel data
var raster = new int[width * height];
// pin the managed array so it can be passed to unmanaged memory
var ptr = GCHandle.Alloc(raster, GCHandleType.Pinned);
// pass the pointer of the array to the bitmap
// making sure to free the pinned memory in the dispose delegate
// - this is also not an allocation, as the memory already exists
bitmap.InstallPixels(info, ptr.AddrOfPinnedObject(), info.RowBytes, null, (addr, ctx) => ptr.Free(), null);
// the first and only copy from the TIFF stream into memory
tifImg.ReadRGBAImageOriented(width, height, raster, Orientation.TOPLEFT)
// an unfortunate extra memory operation for some platforms
// - this is usually just for Windows as it uses a BGR color format
// - Linux, macOS, iOS, Android all are RGB, so no swizzle is needed
SKSwizzle.SwapRedBlue(ptr.AddrOfPinnedObject(), raster.Length);
仅就调试会话中的一些原始统计数据而言,您的代码对于我的一张图像大约需要 500 毫秒,但我的代码只需要 20 毫秒。
我希望我对你的代码听起来不会太严厉/消极,我并不是这个意思。