ImageUtil.cs

namespace TensorFlow
{
    using System.IO;

    // Taken and adapted from: https://github.com/migueldeicaza/TensorFlowSharp/blob/master/Examples/ExampleCommon/ImageUtil.cs
    public static class ImageUtil
	{
		// Convert the image in filename to a Tensor suitable as input to the Inception model.
		public static TFTensor CreateTensorFromImageFile (string file, TFDataType destinationDataType = TFDataType.Float)
		{
			var contents = File.ReadAllBytes (file);

			// DecodeJpeg uses a scalar String-valued tensor as input.
			var tensor = TFTensor.CreateString (contents);

            // Construct a graph to normalize the image
            using (var graph = ConstructGraphToNormalizeImage(out TFOutput input, out TFOutput output, destinationDataType))
            {
                // Execute that graph to normalize this one image
                using (var session = new TFSession(graph))
                {
                    var normalized = session.Run(
                        inputs: new[] { input },
                        inputValues: new[] { tensor },
                        outputs: new[] { output });

                    return normalized[0];
                }
            }
        }

        // Additional pointers for using TensorFlow & CustomVision together
        // Python: https://github.com/tensorflow/tensorflow/blob/master/tensorflow/examples/label_image/label_image.py
        // C++: https://github.com/tensorflow/tensorflow/blob/master/tensorflow/examples/label_image/main.cc
        // Java: https://github.com/Azure-Samples/cognitive-services-android-customvision-sample/blob/master/app/src/main/java/demo/tensorflow/org/customvision_sample/MSCognitiveServicesClassifier.java
        private static TFGraph ConstructGraphToNormalizeImage (out TFOutput input, out TFOutput output, TFDataType destinationDataType = TFDataType.Float)
		{
			const int W = 227;
			const int H = 227;
            const float Scale = 1;

            // Depending on your CustomVision.ai Domain - set appropriate Mean Values (RGB)
            // https://github.com/Azure-Samples/cognitive-services-android-customvision-sample for RGB values (in BGR order)
            var bgrValues = new TFTensor(new float[] { 104.0f, 117.0f, 123.0f }); // General (Compact) & Landmark (Compact)
            //var bgrValues = new TFTensor(0f); // Retail (Compact)

            var graph = new TFGraph ();
            input = graph.Placeholder (TFDataType.String);

            var caster = graph.Cast(graph.DecodeJpeg(contents: input, channels: 3), DstT: TFDataType.Float);
            var dims_expander = graph.ExpandDims(caster, graph.Const(0, "batch"));
            var resized = graph.ResizeBilinear(dims_expander, graph.Const(new int[] { H, W }, "size"));
            var resized_mean = graph.Sub(resized, graph.Const(bgrValues, "mean"));
            var normalised = graph.Div(resized_mean, graph.Const(Scale));
            output = normalised;
            return graph;
		}
	}
}