阿里云OCR图片转换成文字识别调用

using Newtonsoft.Json;
using System;
using System.Collections.Generic;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;
using System.Linq;
using System.Net;
using System.Net.Security;
using System.Security.Cryptography.X509Certificates;
using System.Text;

namespace Common.Utils
{
    public static class OCRUtil
    {
        private const String Host = "https://ocrapi-document.taobao.com";
        private const String Path = "/ocrservice/document";
        private const String Method = "POST";
        private const String Appcode = "************";
        private static readonly IList<string> ImageExList = new List<string>()
        {
            ".jpg",
            ".png",
            ".bmp"
        };

        /// <summary>
        /// 确保图片可用
        /// </summary>
        /// <param name="fileName"></param>
        private static void EnsureImageCanUse(string fileName)
        {
            if (string.IsNullOrWhiteSpace(fileName))
            {
                throw new ArgumentNullException(nameof(fileName), "文件名为空");
            }
            if (!File.Exists(fileName))
            {
                throw new FileNotFoundException("文件不存在", fileName);
            }
            string ex = System.IO.Path.GetExtension(fileName);
            if (ImageExList.IndexOf(ex.ToLower()) == -1)
            {
                throw new FileFormatException("图片格式需为jpg，png，bmp");
            }
            FileInfo fileInfo = new FileInfo(fileName);
            if (fileInfo.Length > 1204 * 1204 * 4)
            {
                throw new Exception("文件不能大于4M");
            }
        }

        /// <summary>
        /// 将图片转换为Base64字符串
        /// </summary>
        /// <param name="fileName"></param>
        /// <returns></returns>
        private static string ImageToBase64String(string fileName)
        {
            Bitmap bitmap = new Bitmap(fileName);
            string ex = System.IO.Path.GetExtension(fileName).ToLower();
            using (MemoryStream ms = new MemoryStream())
            {
                ImageFormat format;
                switch (ex)
                {
                    case ".png":
                        format = ImageFormat.Png;
                        break;
                    case ".jpg":
                        format = ImageFormat.Jpeg;
                        break;
                    default:
                        format = ImageFormat.Bmp;
                        break;
                }
                bitmap.Save(ms, format);
                byte[] arr = new byte[ms.Length];
                ms.Position = 0;
                ms.Read(arr, 0, (int)ms.Length);
                ms.Close();
                return Convert.ToBase64String(arr);
            }
        }

        /// <summary>
        /// 阿里云OCR图片转文字
        /// </summary>
        /// <param name="fileName"></param>
        /// <returns></returns>
        public static string ImageToText(string fileName)
        {
            EnsureImageCanUse(fileName);

            String querys = "";
            String bodys = "{\"img\":\"" + ImageToBase64String(fileName) + "\",\"url\":\"\",\"prob\":false}";
            String url = Host + Path;
            HttpWebRequest httpRequest = null;
            HttpWebResponse httpResponse = null;

            if (0 < querys.Length)
            {
                url = url + "?" + querys;
            }

            if (Host.Contains("https://"))
            {
                ServicePointManager.ServerCertificateValidationCallback = new RemoteCertificateValidationCallback(CheckValidationResult);
                httpRequest = (HttpWebRequest)WebRequest.CreateDefault(new Uri(url));
            }
            else
            {
                httpRequest = (HttpWebRequest)WebRequest.Create(url);
            }
            httpRequest.Method = Method;
            httpRequest.Headers.Add("Authorization", "APPCODE " + Appcode);
            //根据API的要求，定义相对应的Content-Type
            httpRequest.ContentType = "application/json; charset=UTF-8";
            if (0 < bodys.Length)
            {
                byte[] data = Encoding.UTF8.GetBytes(bodys);
                using (Stream stream = httpRequest.GetRequestStream())
                {
                    stream.Write(data, 0, data.Length);
                }
            }

            httpResponse = (HttpWebResponse)httpRequest.GetResponse();
            if (httpResponse.StatusCode != HttpStatusCode.OK)
            {
                throw new WebException("阿里云OCR接口调用识别失败");
            }

            Stream st = httpResponse.GetResponseStream();
            StreamReader reader = new StreamReader(st, Encoding.GetEncoding("utf-8"));
            string responseStr = reader.ReadToEnd();

            OcrResult ocrResult = JsonConvert.DeserializeObject<OcrResult>(responseStr);
            return OcrResultToString(ocrResult);
        }

        private static string OcrResultToString(OcrResult ocrResult)
        {
            StringBuilder sb = new StringBuilder(500);
            var wordList = ocrResult.prism_wordsInfo;
            foreach (var item in wordList)
            {
                int leftX = item.pos[0].x;
                int blankSpaceCount = (int)Math.Floor((double)leftX / 60);
                if (blankSpaceCount > 0)
                {
                    sb.Append(' ', blankSpaceCount*2);
                }
                sb.AppendLine(item.word);
            }
            return sb.ToString();
        }

        public static bool CheckValidationResult(object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors errors)
        {
            return true;
        }
    }


    /// <summary>
    /// OCR识别结果
    /// </summary>
    public class OcrResult
    {
        public string sid { get; set; }
        public string prism_version { get; set; }
        public int prism_wnum { get; set; }
        public List<Prism_Wordsinfo> prism_wordsInfo { get; set; }
        public int height { get; set; }
        public int width { get; set; }
        public int orgHeight { get; set; }
        public int orgWidth { get; set; }
    }

    public class Prism_Wordsinfo
    {
        public string word { get; set; }
        public IList<Pos> pos { get; set; }
    }

    public class Pos
    {
        public int x { get; set; }
        public int y { get; set; }
    }

}