Using the Microsoft OCR Library for WinRT from a desktop app

Recently I had a need to do some OCR processing from a desktop app. Unfortunately the OCR package from Microsoft is for WinRT apps only. However, by using this excellent NuGet package: https://blogs.msdn.microsoft.com/lucian/2015/10/23/how-to-call-uwp-apis-from-a-desktop-vbc-app/#comment-7985

I was able to get this to work from desktop code.

        private async Task<string> ExtractText(string filename)

        {

            OcrEngine ocrEngine = OcrEngine.TryCreateFromLanguage(new Windows.Globalization.Language("EN-US"));

            SoftwareBitmap softwareBitmap = GetSoftwareBitmap(filename);

            var ocrResult = await ocrEngine.RecognizeAsync(softwareBitmap);

            string extractedText = "";

            if (ocrResult != null)

            {

                foreach (var line in ocrResult.Lines)

                {

                    // Iterate over words in line.

                    foreach (var word in line.Words)

                    {

                        extractedText += word.Text + " ";

                    }

                    extractedText += Environment.NewLine;

                }

            }

            return extractedText;

        }

        private static unsafe SoftwareBitmap GetSoftwareBitmap(string filename)

        {

            WriteableBitmap writeableBitmap = null;

            using (FileStream file = File.Open(filename, FileMode.Open))

            {

                BitmapSource srcImage = BitmapDecoder.Create(file,

                    BitmapCreateOptions.None, BitmapCacheOption.OnLoad).Frames[0];

                if (srcImage.Format != PixelFormats.Bgra32)

                    srcImage = new FormatConvertedBitmap(srcImage, PixelFormats.Bgra32, null, 0);

                writeableBitmap = new WriteableBitmap(srcImage);

            }

            writeableBitmap.Lock();

            var pixels = new byte[writeableBitmap.PixelWidth * writeableBitmap.PixelHeight * 4];

            byte* pBuf = (byte*)writeableBitmap.BackBuffer;

            for (int i = 0; i < pixels.Length; i++)

                pixels[i] = *pBuf++;

            var ibuffer = pixels.AsBuffer();

            writeableBitmap.Unlock();

            SoftwareBitmap softwareBitmap = new SoftwareBitmap(BitmapPixelFormat.Bgra8, writeableBitmap.PixelWidth, writeableBitmap.PixelHeight);

            softwareBitmap.CopyFromBuffer(ibuffer);

            return softwareBitmap;

        }

Here is a sample app that I have prepared, you are free to use this in commercial projects.  https://theuxblog20160710035436.azurewebsites.net/ocrdesktop.zip

Paul Tallett, UX Global Practice, Microsoft UK

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