SkiaSharp Tiff支架

Question

目前，SkiaSharp不支持tiff图像。(它支持jpg、gif、bmp、png和其他一些。)

如何将tiff图像转换为SKBitmap对象？

有一个想法:也许有一种转换tiff流> png流> SKBitmap对象的有效方法？我不确定System.Drawing能否有效地处理tiff>png流。另一个可能的选择是LibTiff.Net，但是需要一个如何将tiff流转换为png流的示例。

另一个想法:访问tiff像素并将其直接绘制到SKCanvas上？

其他想法？

Answer 1

@DougS

您的实现基本上是正确的，但由于有多个内存分配和副本，所以性能不太好。

我注意到您正在创建3个内存块，每个块的总大小为(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;

我想我创建了一个类似的方法来解码流，只有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;
    }
}

生活在这里的要旨：https://gist.github.com/mattleibow/0a09babdf0dc9d2bc3deedf85f9b57d6

让我解释一下密码..。我基本上是像您一样创建int[]，但随后将其传递给SKBitmap并让它接管。当SKBitmap驻留在非托管内存中时，我会将它固定在一起，GC可能会移动它，但当位图被释放时，我肯定会将它解锁。

下面是一个更详细的步骤：

// 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);

仅对于调试会话中的一些原始统计数据，您的代码对于我的图像大约需要500 my，但是我的代码只需要20 my。

我希望我不要对你的代码太苛刻/否定，我不是那个意思。

Answer 2

我不是专家，所以我欢迎任何能够使代码更高效的专家(或者有完全不同的想法来进入SKBitmap)。

这使用LibTiff.Net

using BitMiracle.LibTiff.Classic;

. . . .

public static void ConvertTiffToSKBitmap(MemoryStream tifImage)
{
    SKColor[] pixels;
    int width, height;
    // open a Tiff stored in the memory stream, and grab its pixels
    using (Tiff tifImg = Tiff.ClientOpen("in-memory", "r", tifImage, new TiffStream()))
    {
        FieldValue[] value = tifImg.GetField(TiffTag.IMAGEWIDTH);
        width = value[0].ToInt();

        value = tifImg.GetField(TiffTag.IMAGELENGTH);
        height = value[0].ToInt();

        // Read the image into the memory buffer 
        int[] raster = new int[width * height];
        if (!tifImg.ReadRGBAImageOriented(width, height, raster, Orientation.TOPLEFT))
        {
            // Not a valid TIF image.
        }
        // store the pixels
        pixels = new SKColor[width * height];
        for (int y = 0; y < height; y++)
        {
            for (int x = 0; x < width; x++)
            {
                int arrayOffset = y * width + x;
                int rgba = raster[arrayOffset];
                pixels[arrayOffset] = new SKColor((byte)Tiff.GetR(rgba), (byte)Tiff.GetG(rgba), (byte)Tiff.GetB(rgba), (byte)Tiff.GetA(rgba));
            }
        }
    }
    using (SKBitmap bitmap = new SKBitmap(width, height))
    {
        bitmap.Pixels = pixels;

        // do something with the SKBitmap
    }
}