feature: Optional OCR-Assisted Draft Pre-Fill

2026-06-28 01:28:54 +08:00
parent 5039dbb979
commit c160c5f912
42 changed files with 3592 additions and 33 deletions
@@ -0,0 +1,66 @@
+using Docnet.Core;
+using Docnet.Core.Models;
+using SixLabors.ImageSharp;
+using SixLabors.ImageSharp.PixelFormats;
+using SixLabors.ImageSharp.Processing;
+
+public class ImagePreprocessor
+{
+    // US Letter at 300 DPI — sufficient for Tesseract on clinical scans.
+    private const int PdfRenderWidth = 2550;
+    private const int PdfRenderHeight = 3300;
+
+    public Stream Preprocess(Stream input, string contentType)
+    {
+        Stream? pdfRenderStream = null;
+        try
+        {
+            if (contentType == "application/pdf")
+            {
+                pdfRenderStream = RenderPdfFirstPage(input);
+                input = pdfRenderStream;
+            }
+
+            using var image = Image.Load(input);
+
+            image.Mutate(ctx => ctx
+                .Grayscale()
+                .GaussianSharpen(1.5f)
+                .BinaryThreshold(0.5f));
+
+            var output = new MemoryStream();
+            image.SaveAsPng(output);
+            output.Position = 0;
+            return output;
+        }
+        finally
+        {
+            pdfRenderStream?.Dispose();
+        }
+    }
+
+    private static Stream RenderPdfFirstPage(Stream pdfStream)
+    {
+        using var buffer = new MemoryStream();
+        pdfStream.CopyTo(buffer);
+        var pdfBytes = buffer.ToArray();
+
+        using var docReader = DocLib.Instance.GetDocReader(
+            pdfBytes,
+            new PageDimensions(PdfRenderWidth, PdfRenderHeight));
+
+        if (docReader.GetPageCount() == 0)
+            throw new InvalidOperationException("PDF contains no pages.");
+
+        using var pageReader = docReader.GetPageReader(0);
+        var rawBytes = pageReader.GetImage();
+        var width = pageReader.GetPageWidth();
+        var height = pageReader.GetPageHeight();
+
+        using var image = Image.LoadPixelData<Bgra32>(rawBytes, width, height);
+        var output = new MemoryStream();
+        image.SaveAsPng(output);
+        output.Position = 0;
+        return output;
+    }
+}