Bitmap Image from Hex string - extra bytes being added

Question

I have a Hex string that's coming from postscript file.

<< /ImageType 1
/Width 986 /Height 1
/BitsPerComponent 8
/Decode [0 1 0 1 0 1]
/ImageMatrix [986 0 0 -1 0 1]
/DataSource <
803fe0503824160d0784426150b864361d0f8844625138a4562d178c466351b8e4763d1f904864523924964d27944a6552b964b65d2f984c665339a4d66d379c4e6753b9e4f67d3fa05068543a25168d47a4526954ba648202
> /LZWDecode filter >> image } def

Below are the methods that I am using. I have commented out the method for updating color.

public static void ProcessImageColourMapping()
{
    string imageDataSource = "803fe0503824160d0784426150b864361d0f8844625138a4562d178c466351b8e4763d1f904864523924964d27944a6552b964b65d2f984c665339a4d66d379c4e6753b9e4f67d3fa05068543a25168d47a4526954ba648202";
    string imageDataSourceUpdated = GetUpdatedImage(imageDataSource);
}

public static string GetUpdatedImage(string strImageDataSource)
{
    string imageDataSourceUpdated = "";

    byte[] imageBytes = StringToByteArray(strImageDataSource);
    Bitmap bitmapImage = ByteArrayToBitmap(imageBytes);
    //UpdateColour(bitmapImage);
    byte[] imageBytesUpdated = BitmapToByteArray(bitmapImage);
    imageDataSourceUpdated = ByteArrayToString(imageBytesUpdated);

    return imageDataSourceUpdated;
}

public static byte[] StringToByteArray(String imageHexString)
{
    int numberOfChars = imageHexString.Length / 2;
    byte[] byteArray = new byte[numberOfChars];
    using (var sr = new StringReader(imageHexString))
    {
        for (int i = 0; i < numberOfChars; i++)
            byteArray[i] = Convert.ToByte(new string(new char[2] { (char)sr.Read(), (char)sr.Read() }), 16);
    }
    return byteArray;
}

public static Bitmap ByteArrayToBitmap(byte[] byteArray)
{
    int width = 986; //width and height are taken from postscript file for testing a single hex string.
    int height = 1; 
    Bitmap bitmapImage = new Bitmap(width, height, PixelFormat.Format32bppPArgb);
    BitmapData bmpData = bitmapImage.LockBits(new Rectangle(0, 0, width, height), ImageLockMode.ReadWrite, PixelFormat.Format32bppPArgb);            
    try
    {                
        Marshal.Copy(byteArray, 0, bmpData.Scan0, byteArray.Length);
    }
    finally
    {
        bitmapImage.UnlockBits(bmpData);                
    }
    return bitmapImage;
}

public static byte[] BitmapToByteArray(Bitmap bitmap)
{
    BitmapData bmpdata = bitmap.LockBits(new Rectangle(0, 0, bitmap.Width, bitmap.Height), ImageLockMode.ReadOnly, bitmap.PixelFormat);
    int numbytes = bmpdata.Stride * bitmap.Height;
    byte[] bytedata = new byte[numbytes];
    try
    {
        Marshal.Copy(bmpdata.Scan0, bytedata, 0, numbytes);            
    }
    finally
    {
        bitmap.UnlockBits(bmpdata);
    }
    return bytedata;
}

public static string ByteArrayToString(byte[] byteArray)
{
    StringBuilder hex = new StringBuilder(byteArray.Length * 2);
    foreach (byte b in byteArray)
    {
        hex.AppendFormat("{0:x2}", b);
    }
    return hex.ToString();
}

Issue:
In below code, I am not updating anything for incoming Hex string imageDataSource.
Converting it to byte[] - then to Bitmap - Back to byte[] - and finally back to Hex string.

So, imageDataSourceUpdated should have same value as imageDataSource.
However, when I finally check the value for imageDataSourceUpdated, it comes out as:

803fe0503824160d0784426150b864361d0f8844625138a4562d178c466351b8e4763d1f904864523924964d27944a6552b964b65d2f984c665339a4d66d379c4e6753b9e4f67d3fa05068543a25168d47a4526954ba64820200000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000.....
So many zeros being appended.

Can please guide what I am missing here.

Answer 1

You are passing some input string, but the width of the image (and so 1/4 of the size of the byte array) is set to 986 in your sample, which would yield the behaviour you observe - you're not actually passing 986 * 4 bytes of data, but the Bitmap does have that many. So you'll get the first X bytes you actually copied to the bitmap, and then all zeros. In other words, it seems your issue is with your sample data, not with the methods themselves - those work just fine.