编写一个用于裁剪文档图像的ASP.NET Core应用

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文档扫描与图像处理

编写一个用于裁剪文档图像的ASP.NET Core应用

2024年6月4日

分类：文档扫描

ASP.NET Core是一个跨平台、高性能、开源的框架，用于构建支持现代的互联网应用程序。用它来构建Web API或者Web应用程序都非常方便。在本文中，我们将构建一个ASP.NET应用来裁剪文档图像。

主要提供以下API ：

/api/document/detect：上传图像并获取检测到的文档边界
/api/document/crop：依据提供的文档边界裁剪上传的文档图像
/api/document/detectAndCrop：上传图像并获取裁剪后文档图像的ID
/api/document/{ID}：根据ID获取上传的图片
/api/document/cropped/{ID}：根据ID获取裁剪后的图像

还编写了一个前端界面来使用这些接口。

前端截图

新建项目

使用Visual Studio创建新的ASP.NET Core Web App项目。

新项目

添加依赖项

从nuget安装Dynamsoft Document Normalizer。我们将使用它来检测文档边界并获取裁剪的文档图像。

dotnet add package Dynamsoft.DotNet.DocumentNormalizer.Bundle --version 2.2.1000

许可证初始化

在Program.cs中，初始化Dynamsoft Document Normalizer的许可证。可以在这里申请一个许可证。

using Dynamsoft.Core;
using Dynamsoft.License;

string errorMsg;
int errorCode = LicenseManager.InitLicense("DLS2eyJoYW5kc2hha2VDb2RlIjoiMjAwMDAxLTE2NDk4Mjk3OTI2MzUiLCJvcmdhbml6YXRpb25JRCI6IjIwMDAwMSIsInNlc3Npb25QYXNzd29yZCI6IndTcGR6Vm05WDJrcEQ5YUoifQ==", out errorMsg); //use a one-day trial license
if (errorCode != (int)EnumErrorCode.EC_OK)
{
    Console.WriteLine("License initialization error: " + errorMsg);
}
else
{
    Console.WriteLine("License valid.");
}

实现API

添加名为DocumentController.cs的API Controller，并创建一个Capture Vision Router属性以调用Dynamsoft Document Normalizer。

namespace DocumentScanner
{
    [Route("api/[controller]")]
    [ApiController]
    public class DocumentController : ControllerBase
    {
        private CaptureVisionRouter cvr = new CaptureVisionRouter();
    }
}

在Program.cs中，映射控制器。

app.MapControllers();

定义请求相关的类。

表示检测到的文档边界的多边形Polygon和点Point。

public class Polygon
{
    public Point[] Points { get; set; }
    public Polygon() {
        Points = Array.Empty<Point>();
    }
}

public class Point
{
    public int X { get; set; }
    public int Y { get; set; }
    public Point(int x, int y)
    {
        X = x;
        Y = y;
    }
}

用于表示的文档的Document类。它可以包含文档边界、base64编码的图像数据、用于在磁盘上存储图像的ID以及成功状态。

public class Document
{
    public string? Base64 { get; set; }
    public Polygon? Polygon { get; set; }
    public bool? Success { get; set; }
    public long? ID { get; set; }
}

添加检测文档边界的方法。

[HttpPost("detect")]
public ActionResult<Document> DetectDocument(Document document)
{
    Document detectedDocument = new Document();
    if (document.Base64 != null) {
        byte[] bytes = Convert.FromBase64String(document.Base64);
        CapturedResult result = cvr.Capture(bytes, PresetTemplate.PT_DETECT_DOCUMENT_BOUNDARIES);
        DetectedQuadsResult quads = result.GetDetectedQuadsResult();
        if (quads != null && quads.GetItems().Length > 0) {
            Polygon polygon = ConvertToPolygon(quads.GetItems()[0].GetLocation());
            detectedDocument.Polygon = polygon;
        }
        long ID = SaveImage(bytes);
        detectedDocument.ID = ID;
        detectedDocument.Success = true;
    }
    return detectedDocument;
}

private Polygon ConvertToPolygon(Quadrilateral quad) {
    Polygon polygon = new Polygon();
    Point[] points = new Point[4];
    points[0] = new Point(quad.points[0][0], quad.points[0][1]);
    points[1] = new Point(quad.points[1][0], quad.points[1][1]);
    points[2] = new Point(quad.points[2][0], quad.points[2][1]);
    points[3] = new Point(quad.points[3][0], quad.points[3][1]);
    polygon.Points = points;
    return polygon;
}

private long SaveImage(byte[] bytes) {
    if (Directory.Exists("images") == false) {
        Directory.CreateDirectory("images");
    }
    DateTimeOffset dateTimeOffset = DateTimeOffset.UtcNow;
    long ID = dateTimeOffset.ToUnixTimeMilliseconds();
    string filePath;
    filePath = "./images/" + ID + ".jpg";
    using (FileStream fs = new FileStream(filePath, FileMode.Create))
    {
        fs.Write(bytes, 0, bytes.Length);
    }
    return ID;
}

添加根据指定的文档边界裁剪文档图像的方法。

[HttpPost("crop")]
public ActionResult<Document> CropDocument(Document document)
{
    Document croppedDocument = new Document();
    if (document.ID != null && document.Polygon != null)
    {
        string filePath = "./images/" + document.ID + ".jpg";
        SimplifiedCaptureVisionSettings settings;
        cvr.GetSimplifiedSettings(PresetTemplate.PT_NORMALIZE_DOCUMENT, out settings);
        settings.roiMeasuredInPercentage = 0;
        settings.roi = ConvertToQuad(document.Polygon);
        string errorMsg;
        cvr.UpdateSettings(PresetTemplate.PT_NORMALIZE_DOCUMENT, settings, out errorMsg);
        CapturedResult result = cvr.Capture(filePath, PresetTemplate.PT_NORMALIZE_DOCUMENT);
        NormalizedImagesResult normalizedImagesResult = result.GetNormalizedImagesResult();
        if (normalizedImagesResult.GetItems().Length > 0)
        {
            ImageData imageData = normalizedImagesResult.GetItems()[0].GetImageData();
            ImageManager imageManager = new ImageManager();
            if (imageData != null)
            {
                int errorCode = imageManager.SaveToFile(imageData, "./images/" + document.ID + "-cropped.jpg");
                if (errorCode == 0) {
                    croppedDocument.ID = document.ID;
                    croppedDocument.Success = true;
                }
            }
        }
    }
    return croppedDocument;
}

private Quadrilateral ConvertToQuad(Polygon polygon)
{
    Quadrilateral quadrilateral = new Quadrilateral();
    quadrilateral.points[0] = new Dynamsoft.Core.Point(polygon.Points[0].X, polygon.Points[0].Y);
    quadrilateral.points[1] = new Dynamsoft.Core.Point(polygon.Points[1].X, polygon.Points[1].Y);
    quadrilateral.points[2] = new Dynamsoft.Core.Point(polygon.Points[2].X, polygon.Points[2].Y);
    quadrilateral.points[3] = new Dynamsoft.Core.Point(polygon.Points[3].X, polygon.Points[3].Y);
    return quadrilateral;
}

添加检测文档边界和裁剪文档图像的方法。

[HttpPost("detectAndCrop")]
public ActionResult<Document> DetectAndCropDocument(Document document)
{
    Document croppedDocument = new Document();
    if (document.Base64 != null)
    {
        byte[] bytes = Convert.FromBase64String(document.Base64);
        CapturedResult result = cvr.Capture(bytes, PresetTemplate.PT_DETECT_AND_NORMALIZE_DOCUMENT);
        NormalizedImagesResult normalizedImagesResult = result.GetNormalizedImagesResult();
        if (normalizedImagesResult != null && normalizedImagesResult.GetItems().Length > 0)
        {
            DateTimeOffset dateTimeOffset = DateTimeOffset.UtcNow;
            long ID = dateTimeOffset.ToUnixTimeMilliseconds();
            ImageData imageData = normalizedImagesResult.GetItems()[0].GetImageData();
            ImageManager imageManager = new ImageManager();
            if (imageData != null)
            {
                int errorCode = imageManager.SaveToFile(imageData, "./images/" + ID + "-cropped.jpg");
                if (errorCode == 0)
                {
                    croppedDocument.ID = ID;
                    croppedDocument.Success = true;
                }
            }
        }
    }
    return croppedDocument;
}

添加获取上传的和裁剪的图像的方法。

[HttpGet("{ID}")]
public ActionResult<string> GetDocument(long ID)
{
    string filePath = "./images/"+ID+".jpg";
    Response.ContentType = "text/plain";
    if (System.IO.File.Exists(filePath))
    {
        byte[] bytes = System.IO.File.ReadAllBytes(filePath);
        string base64String = Convert.ToBase64String(bytes);
        Response.StatusCode = 200;
        return base64String;
    }
    else {
        Response.StatusCode = 404;
        return "not found";
    }
}

[HttpGet("cropped/{ID}")]
public ActionResult<string> GetCroppedDocument(long ID)
{
    string filePath = "./images/" + ID + "-cropped.jpg";
    Response.ContentType = "text/plain";
    if (System.IO.File.Exists(filePath))
    {
        byte[] bytes = System.IO.File.ReadAllBytes(filePath);
        string base64String = Convert.ToBase64String(bytes);
        Response.StatusCode = 200;
        return base64String;
    }
    else
    {
        Response.StatusCode = 404;
        return "not found";
    }
}

进行测试

然后，我们可以编写一个网页，使用AJAX测试API ：

let url = "/api/document/detectAndCrop";
let dataURL = document.getElementById("original").src; //an image element's dataURL
let base64 = dataURL.substring(dataURL.indexOf(",")+1,dataURL.length);
data = {Base64:base64};
const response = await fetch(url, {
  method: "POST",
  headers: {
    "Content-Type": "application/json",
  },
  body: JSON.stringify(data),
});
let json = await response.json();

let imageID = json.id;
if (json.success == true) {
  let response = await fetch("/api/document/cropped/"+imageID);
  let base64 = await response.text();
  displayCropped(base64);
}else{
  alert("Failed to get the cropped Image.");
}

可以在源码仓库里中找到一个功能更全面的示例，它可以编辑检测到的多边形。

启用CORS

如果需要跨域调用API ，需要启用CORS。

在Program.cs中启用CORS。

builder.Services.AddCors();
app.UseCors(builder =>
{
    builder.AllowAnyOrigin()
           .AllowAnyMethod()
           .AllowAnyHeader();
});

如果我们需要通过局域网访问它，则还需要添加Access-Control-Allow-Private-Network的header。

// Enable PNA preflight requests
app.Use(async (ctx, next) =>
{
    if (ctx.Request.Method.Equals("options", StringComparison.InvariantCultureIgnoreCase) && ctx.Request.Headers.ContainsKey("Access-Control-Request-Private-Network"))
    {
        ctx.Response.Headers.Add("Access-Control-Allow-Private-Network", "true");
    }

    await next();
});

源代码

该项目的源代码可在此处获得：https://github.com/tony-xlh/Capture-Vision-Server-Demos/tree/main/Document-Normalizer/ASP.NET