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我需要从数据库中获取图像，所以我为它编写了一些代码。问题是在某些图像中出现该错误，而在其他图像中出现无效参数错误。

        OleDbConnection l = new OleDbConnection(builder.ConnectionString);
        List<Image> listaImagens = new List<Image>();
        List<String> listaNomes = new List<string>();
        string nome = "";

        try
        {
            OleDbDataAdapter adapter = new OleDbDataAdapter("SELECT * FROM [Fotografias e Manuais de Equipamentos]  WHERE ID >26 AND ID < 30", l);
            DataSet ds = new DataSet();
            adapter.Fill(ds, "Fotografias e Manuais de Equipamentos");
            //string s = ds.Tables["APP_Equip_Ult_Prox_Calibracao"].Columns[16].ColumnName;
            foreach (DataRow row in ds.Tables["Fotografias e Manuais de Equipamentos"].Rows)
            {
                if (row["Designação Equipamento"].ToString().Equals(""))
                {
                    nome = "semNome";
                }
                else
                {
                    nome = row["Designação Equipamento"].ToString();
                }
                listaNomes.Add(row["ID"].ToString()+"_"+row["MARCA"].ToString() + "_" + row["MODELO"].ToString() + "_" + nome);
                try
                {
                    byte[] b = (byte[])row["FOTO"];
                    byte[] imagebyte = OleImageUnwrap.GetImageBytesFromOLEField(b, 30000);

                    MemoryStream ms = new MemoryStream();
                    ms.Write(imagebyte, 0, imagebyte.Length);

                    listaImagens.Add(Image.FromStream(ms));
                }
                catch (Exception)
                {
                    try
                    {
                        byte[] b = (byte[])row["FOTO"];
                        byte[] imagebyte = OleImageUnwrap.GetImageBytesFromOLEField(b, 100000);

                        MemoryStream ms = new MemoryStream();
                        ms.Write(imagebyte, 0, imagebyte.Length);

                        listaImagens.Add(Image.FromStream(ms));
                    }
                    catch (Exception)
                    {
                        byte[] b = (byte[])row["FOTO"];
                        byte[] imagebyte = OleImageUnwrap.GetImageBytesFromOLEField(b, 600000);

                        MemoryStream ms = new MemoryStream();
                        ms.Write(imagebyte, 0, imagebyte.Length);
                        Image img = Image.FromStream(ms); // INVALID PARAMETER ERROR CAUGHT HERE IN DEBBUG
                        listaImagens.Add(img);
                    }
                }
            }
            for (int i = 0; i < listaImagens.Count; i++)
        {
            listaImagens[i].Save("C:\\Users\\sies4578\\Desktop\\Testes\\Fotos\\" + listaNomes[i] +".png", System.Drawing.Imaging.ImageFormat.Png); //EXTERNAL EXCEPTON IN GDI+ ERROR CAUGHT HERE IN DEBBUG
        }
        }
        catch (Exception ex)
        {
            MessageBox.Show("Deu o berro: "+ex.Message);
        }            
    }

OleImageUnwrap.GetImageBytesFromOLEField用于从作为数据库中图像的 OLE 对象中删除标头，并仅获取图像本身的字节：

    public static byte[] GetImageBytesFromOLEField(byte[] oleFieldBytes, int NumMaximoBytesSearch)
    {
        //ref http://stackoverflow.com/questions/19688641/convert-ole-object-in-datarow-into-byte-c-sharp
        // adapted from http://blogs.msdn.com/b/pranab/archive/2008/07/15/removing-ole-header-from-images-stored-in-ms-access-db-as-ole-object.aspx

        int MaxNumberOfBytesToSearch = NumMaximoBytesSearch;
        byte[] imageBytes;  // return value

        var ImageSignatures = new List<byte[]>();
        // BITMAP_ID_BLOCK = "BM"
        ImageSignatures.Add(new byte[] { 0x42, 0x4D });
        // JPG_ID_BLOCK = "\u00FF\u00D8\u00FF"
        ImageSignatures.Add(new byte[] { 0xFF, 0xD8, 0xFF });
        // PNG_ID_BLOCK = "\u0089PNG\r\n\u001a\n"
        ImageSignatures.Add(new byte[] { 0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A });
        // GIF_ID_BLOCK = "GIF8"
        ImageSignatures.Add(new byte[] { 0x47, 0x49, 0x46, 0x38 });
        // TIFF_ID_BLOCK = "II*\u0000"
        ImageSignatures.Add(new byte[] { 0x49, 0x49, 0x2A, 0x00 });

        int NumberOfBytesToSearch = (oleFieldBytes.Count() < MaxNumberOfBytesToSearch ? oleFieldBytes.Count() : MaxNumberOfBytesToSearch);
        var startingBytes = new byte[NumberOfBytesToSearch];
        Array.Copy(oleFieldBytes, startingBytes, NumberOfBytesToSearch);

        var positions = new List<int>();
        foreach (byte[] BlockSignature in ImageSignatures)
        {
            positions = IndexOfSequence(startingBytes, BlockSignature, 0);
            if (positions.Count > 0)
            {
                break;
            }
        }
        int iPos = -1;
        if (positions.Count > 0)
        {
            iPos = positions[0];
        }

        if (iPos == -1)
            throw new Exception("Unable to determine header size for the OLE Object");

        imageBytes = new byte[oleFieldBytes.LongLength - iPos];
        System.IO.MemoryStream ms = new System.IO.MemoryStream();
        ms.Write(oleFieldBytes, iPos, oleFieldBytes.Length - iPos);
        imageBytes = ms.ToArray();
        ms.Close();
        ms.Dispose();
        return imageBytes;
    }

    private static List<int> IndexOfSequence(this byte[] buffer, byte[] pattern, int startIndex)
    {
        // ref: http://stackoverflow.com/a/332667/2144390
        List<int> positions = new List<int>();
        int i = Array.IndexOf<byte>(buffer, pattern[0], startIndex);
        while (i >= 0 && i <= buffer.Length - pattern.Length)
        {
            byte[] segment = new byte[pattern.Length];
            Buffer.BlockCopy(buffer, i, segment, 0, pattern.Length);
            if (segment.SequenceEqual<byte>(pattern))
                positions.Add(i);
            i = Array.IndexOf<byte>(buffer, pattern[0], i + 1);
        }
        return positions;
    }
}

那么为什么会出现这些错误呢？使用内存流生成图像时，我在保存部分的第 18 和第 26 图像处得到第一个错误，而在第 25 个图像处得到另一个错误。

4

1 回答 1

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GetImageBytesFromOLEField()错误是由搜索图像签名的顺序引起的。它首先搜索 BMP 签名，不幸的是，该签名非常短（“BM”），因此在少数情况下，它会在图像数据中找到一对字节，并提取出它认为是 BMP 数据的内容。

解决方法是从

var ImageSignatures = new List<byte[]>();
// BITMAP_ID_BLOCK = "BM"
ImageSignatures.Add(new byte[] { 0x42, 0x4D });
// JPG_ID_BLOCK = "\u00FF\u00D8\u00FF"
ImageSignatures.Add(new byte[] { 0xFF, 0xD8, 0xFF });
// PNG_ID_BLOCK = "\u0089PNG\r\n\u001a\n"
ImageSignatures.Add(new byte[] { 0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A });
// GIF_ID_BLOCK = "GIF8"
ImageSignatures.Add(new byte[] { 0x47, 0x49, 0x46, 0x38 });
// TIFF_ID_BLOCK = "II*\u0000"
ImageSignatures.Add(new byte[] { 0x49, 0x49, 0x2A, 0x00 });

至

var ImageSignatures = new List<byte[]>();
// JPG_ID_BLOCK = "\u00FF\u00D8\u00FF"
ImageSignatures.Add(new byte[] { 0xFF, 0xD8, 0xFF });
// PNG_ID_BLOCK = "\u0089PNG\r\n\u001a\n"
ImageSignatures.Add(new byte[] { 0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A });
// GIF_ID_BLOCK = "GIF8"
ImageSignatures.Add(new byte[] { 0x47, 0x49, 0x46, 0x38 });
// TIFF_ID_BLOCK = "II*\u0000"
ImageSignatures.Add(new byte[] { 0x49, 0x49, 0x2A, 0x00 });
// BITMAP_ID_BLOCK = "BM"
ImageSignatures.Add(new byte[] { 0x42, 0x4D });

一旦我这样做了，我就可以处理整个文件：

图像转换前 .mdb 的大小：31.8 MB
转换后但压缩和修复之前的 .mdb 大小：37.1 MB
压缩和修复后 .mdb 的大小：8.5 MB

编辑

这是我用来转换图像并将它们写回数据库的代码：

private void btnStart_Click(object sender, EventArgs e)
{
    using (var con = new OleDbConnection())
    {
        con.ConnectionString =
                @"Provider=Microsoft.ACE.OLEDB.12.0;" +
                @"Data Source=C:\__tmp\test\Bd Fotos Equipamentos 2.mdb;";
        con.Open();
        using (OleDbCommand cmdIn = new OleDbCommand(), cmdOut = new OleDbCommand())
        {
            cmdOut.Connection = con;
            cmdOut.CommandText = "UPDATE [Fotografias e Manuais de Equipamentos] SET [FOTO]=? WHERE [ID]=?";
            cmdOut.Parameters.Add("?", OleDbType.VarBinary);
            cmdOut.Parameters.Add("?", OleDbType.Integer);

            cmdIn.Connection = con;
            cmdIn.CommandText = "SELECT [ID], [FOTO] FROM [Fotografias e Manuais de Equipamentos]";
            OleDbDataReader rdr = cmdIn.ExecuteReader();
            while (rdr.Read())
            {
                int i = Convert.ToInt32(rdr["ID"]);
                lblStatus.Text = string.Format("Processing ID {0}...", i);
                lblStatus.Refresh();
                byte[] b = (byte[])rdr["FOTO"];
                byte[] imageBytes = OleImageUnwrap.GetImageBytesFromOLEField(b);
                byte[] pngBytes;
                using (MemoryStream msIn = new MemoryStream(imageBytes), msOut = new MemoryStream())
                {
                    Image img = Image.FromStream(msIn);
                    img.Save(msOut, System.Drawing.Imaging.ImageFormat.Png);
                    img.Dispose();
                    pngBytes = msOut.ToArray();
                }
                cmdOut.Parameters[0].Value = pngBytes;
                cmdOut.Parameters[1].Value = rdr["ID"];
                cmdOut.ExecuteNonQuery();
            }
        }
        con.Close();
    }
    this.Close();
}

该GetImageBytesFromOLEField()代码与我之前使用的相同，带有MaxNumberOfBytesToSearch = 1000000.

于 2013-11-20T15:43:55.243 回答