String to byte[] and byte[] to Image in .NET

Question

I am using NITGEN's Fingkey Hamster DX for capturing a finger print.

I have converted the fingerprint data to a text format which gives me a string like the following (string "sr" in below code gives this string):

AQAAABQAAAAEAQAAAQASAAEAZAAAAAAA*AAAAOHbWlAewfLK7kOnScKzeN5HMVcDmjce0KPkeqyeiWEdTnJutHvnhyrnkW9OPbQNQc7/94lnozdd3Zz8RKiRSj8HHdCMZ8XIdaCy0tCxp2wLwRbVrHl14QkJlQMGqeJyzu06h/ZorwN5vVoxuzFDM9dKyqlm85XHuOeoeACxO/xZrE3NdH4aesbYWgy2i5Cru2AHymemLVeu7BX5BRgFkRrx6JzcZpW9Jn0r3GOkdSqGZG85soUxNX4GN*4gJlqjfCg81cDZAi5NqiEosZjJUXwZ2677ll3OCOUaS31/7v7qF9NN1XdlNc1hrI8kQfmtbRNM3EOybwAoFTHG76rqRos

I have tried to convert this string into a byte[] array using following code :

textFIR = new NBioAPI.Type.FIR_TEXTENCODE();
UInt32 r = m_NBioAPI.GetTextFIRFromHandle(hCapturedFIR, out textFIR, true);

string sr = "";
if (textFIR != null)
{
    sr = textFIR.TextFIR;
    byte[] src = new byte[sr.Length*sizeof(char)];

    System.Buffer.BlockCopy(sr.ToCharArray(),0,src,0,src.Length);
    MemoryStream ms = new MemoryStream(src);
    System.Drawing.Image FP = System.Drawing.Image.FromStream(ms);
    FP.Save("G:\\TempFP.Jpeg", ImageFormat.Jpeg);
}

But on Image.FromStream(ms) I am getting "Parameter is not valid." exception.

Also: stackoverflow.com/q/14360257/109702, stackoverflow.com/q/11730373/109702, — slugster
– slugster, Commented Sep 7, 2013 at 4:56
"I have converted the fingerprint data to a text format" - What type was the fingerprint data to begin with? a byte array? — Mitch Wheat
– Mitch Wheat, Commented Sep 7, 2013 at 4:57
No they dont provide a simple byte array. They want users to play with their TYPES only. — Touhid K.
– Touhid K., Commented Sep 7, 2013 at 5:03
I am uising NITGEN's NITGEN.SDK.NBioBSP..And the fingerprint data type is "NBioAPI.Type.HFIR hCapturedFIR". And "m_NBioAPI.Capture(out hCapturedFIR, NBioAPI.Type.TIMEOUT.DEFAULT, m_WinOption)" this line gives hCapturedFIR. — Touhid K.
– Touhid K., Commented Sep 7, 2013 at 5:12

dotNET · Accepted Answer · 2013-09-07 04:57:04Z

1

Though I don't have experience with the particular library you're using, I can see some obvious problems with your code and expect them to be causing the issue. Check these two lines of your code:

string sr = "";
byte[] src = new byte[sr.Length*sizeof(char)];

sr is an empty string at this time, so sr.Length will be zeroand the byte array will also be zero-length, therefore BlockCopy will not be able to write anything to it. You should move this second line inside the if block, after the line sr = textFIR.TextFIR;.

answered Sep 7, 2013 at 4:57

dotNET

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5 Comments

Touhid K. Over a year ago

I tried what you told me to do. But it still gives me the same exception. Parameter is not Valid.

Touhid K. Over a year ago

I am not sure abut that..Because textFIR is an object which encodes actual finger print data (NBioAPI.Type.HFIR) into a text.

dotNET Over a year ago

I just went through their documentation (nitgen.com.br/download/…). Looks like there's more to it than simply converting into a memory stream. Nowhere do they mention the exact image format they are using.

Touhid K. Over a year ago

Any idea on this dotNET? I am stuck on this since last week. I would really appreciate your help.

dotNET Over a year ago

Try Tejas's idea. I don't have either the hardware or the software with me, so it is a bit difficult for me to experiment with it.

Vijay Sirigiri · Accepted Answer · 2013-09-07 06:13:36Z

1

The text in TextFIR member is neither a valid base64 encoded data or an image data. It is a multi-byte text data used to store and verify with other FIR.

Use the API in NImgConv.dll to get an image from the FIR data.

answered Sep 7, 2013 at 6:13

Vijay Sirigiri

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6 Comments

Touhid K. Over a year ago

But NImgConv.dll is written in cpp and delphi. I dont have its c# classes. the version of my Sdk is 3.12. It doe not include c# classes for this. Have u done this in c#? Can u send me an example code if u have done this?

Vijay Sirigiri Over a year ago

If it is a COM component then regsvr32 NImgConv.dll and add ref from COM tab in VS otherwise follow the instructions stackoverflow.com/questions/569603/…

Touhid K. Over a year ago

I am new to .NET and developing field. I tried regsvr32 NImgConv.dll And got following error : The module "NImgConv.dll" was loaded but entry-point DllRegister was not found. Make sure that NImgConv.dll is a valid DLL or OCX file and try again. Any Idea? I did not get the second option.

Vijay Sirigiri Over a year ago

It might not be a COM component; try following the instructions from the url stackoverflow.com/questions/569603/…

Touhid K. Over a year ago

I am sorry but I dont even have an option for creating C++/CLI projects in my VS. I am totally new to this.

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Nilesh Thakkar · Accepted Answer · 2013-09-07 05:31:40Z

0

You should try FromBase64string method to convert it to byte array.

public static  byte[] StringToBytes(string streamString)
{
   return Convert.FromBase64String(streamString);
}

To make sure your base64string is valid, you can check it like

<img alt="" src="data:image/jpeg;base64,**your base 64 string**" />

Check out this link for more info.

answered Sep 7, 2013 at 5:31

Nilesh Thakkar

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1 Comment

Touhid K. Over a year ago

I got following exception on trying to do this : The input is not a valid Base-64 string as it contains a non-base 64 character, more than two padding characters, or a non-white space character among the padding characters.

Tejas Vaishnav · Accepted Answer · 2013-09-07 05:58:14Z

0

I think you got the string is in Base64 format, so you can use this functions to convert your string to Bytes[] and then use another function to convert Bytes[] to image.

    internal bool SaveBytesToFile(string fileFullPath, byte[] stream)
    {
        if (stream.Length == 0) return false;
        try
        { 
            try
            {
                using (FileStream fileStream = System.IO.File.Create(fileFullPath, (int)stream.Length))
                {
                    fileStream.Write(stream, 0, stream.Length);
                }
            }
            catch (Exception ex)
            {
                //Write Error log
                errorhandler.Write(ex);
                return false;
            }

            return true;
        }
        catch (Exception ex)
        {
            //Write Error log
            errorhandler.Write(ex);
            return false;
        }

    }

    internal byte[] StringToBytes(string streamString)
    {
        return Convert.FromBase64String(streamString);
    }

    internal string BytesToString(byte[] stream)
    {
        return Convert.ToBase64String(stream);
    }

answered Sep 7, 2013 at 5:58

Tejas Vaishnav

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1 Comment

Touhid K. Over a year ago

I can not convert this string to byte array. I get following exception on trying to do this : The input is not a valid Base-64 string as it contains a non-base 64 character, more than two padding characters, or a non-white space character among the padding characters

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