QR barcode decoder problem.

[C# Programming]

my decoder cannot detect picture of webcam. i change the brightness and contrast. some time can detect but some times cannot. i know thats picture problem. now i edit the image but its useless. can i change webcam setting or do any changes to my code..here is my code....

private void btnDecode_Click_1(object sender, EventArgs e)
{
try
{


DeviceManager manager = new DeviceManagerClass();
Device d = null;
foreach (DeviceInfo info in manager.DeviceInfos)
{
d = info.Connect();

}

Item item = d.ExecuteCommand(CommandID.wiaCommandTakePicture);

foreach (string format in item.Formats)
{

WIA.ImageFile imagefile = item.Transfer(format) as WIA.ImageFile;
// if (File.Exists("d:\\test.jpg"))
{
// picDecode.Image = null;
// File.Delete("d:\\test.jpg");
}
imagefile.SaveFile("d:\\4.jpg");
Bitmap image = new Bitmap("d:\\4.jpg");
Bitmap bm = new Bitmap(image, 200, 150);

System.Drawing.Bitmap TempBitmap = bm;
float brightness = 0.6f;
float constrast = 6f;
System.Drawing.Bitmap NewBitmap = new System.Drawing.Bitmap(TempBitmap.Width, TempBitmap.Height);
System.Drawing.Graphics NewGraphics = System.Drawing.Graphics.FromImage(NewBitmap);
float[][] FloatColorMatrix ={
new float[] {constrast, 0, 0, 0, 0},
new float[] {0, constrast, 0, 0, 0},
new float[] {0, 0, constrast, 0, 0},
new float[] {0, 0, 0, constrast, 0},
new float[] {brightness, brightness, brightness, 1, 1}
};

System.Drawing.Imaging.ColorMatrix NewColorMatrix = new System.Drawing.Imaging.ColorMatrix(FloatColorMatrix);
System.Drawing.Imaging.ImageAttributes Attributes = new System.Drawing.Imaging.ImageAttributes();
Attributes.SetColorMatrix(NewColorMatrix);
NewGraphics.DrawImage(TempBitmap, new System.Drawing.Rectangle(0, 0, TempBitmap.Width, TempBitmap.Height), 0, 0, TempBitmap.Width, TempBitmap.Height, System.Drawing.GraphicsUnit.Pixel, Attributes);
Attributes.Dispose();
NewGraphics.Dispose();

picDecode.Image = NewBitmap;
break;

}

QRCodeDecoder decoder = new QRCodeDecoder();
String decodedString = decoder.decode(new QRCodeBitmapImage(new Bitmap(picDecode.Image)));
txtDecodedData.Text = decodedString;

}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
}
}

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