Question

In following code, I am getting an error on the line bitmap = newBitmap, saying it can’t assign bitmap since it’s a using variable. How can i resize the Bitmap?

public static Bitmap ResizeBitmap(Bitmap b, int nWidth, int nHeight)
{
            Bitmap result = new Bitmap(nWidth, nHeight);
            using (Graphics g = Graphics.FromImage((Image)result))
                g.DrawImage(b, 0, 0, nWidth, nHeight);
            return result;
}

....

using (var bitmap = new Bitmap(_width, _height, _width * 3, PixelFormat.Format24bppRgb, pBuffer))
{
    if (!this.Secondpass)
    {
        long[] HistogramValues = Form1.GetHistogram(bitmap);
        Form1.Histograms.Add(HistogramValues);
        long t = Form1.GetTopLumAmount(HistogramValues, 1000);
        Form1.averagesTest.Add(t);                            
    }
    else
    {                    
        if (_frameId > 0)
        {
            double t = Form1.averagesTest[_frameId] / 1000.0 - Form1.averagesTest[_frameId - 1] / 1000.0;
            w.WriteLine("averagesTest >>>  " + t);
            double tt = framesCounts();
            if (_frameId == framesCounts())
            {
                w.Close();
            }
            if (Form1.averagesTest[_frameId] / 1000.0 - Form1.averagesTest[_frameId - 1] / 1000.0 > 0.0) 
            {
                count = 6;
            }

            if (count > 0)
            {
                Bitmap newBitmap = ResizeBitmap(bitmap, 10, 10);
                bitmap.Dispose();
                bitmap = newBitmap;
                bitmap.RotateFlip(RotateFlipType.Rotate180FlipX);
                bitmap.Save(Path.Combine(_outFolder, _frameId.ToString("D6") + ".bmp"),ImageFormat.Bmp);
                count --;
            }
        }
    }
}

Answer 1

You’re attempting to re-assign the variable bitmap which was defined in the using statement. According to the C# Specification, that is an error:

Local variables declared in a resource-acquisition are read-only, and must include an initializer. A compile-time error occurs if the embedded statement attempts to modify these local variables (by assignment or the ++ and — operators) or pass them as ref or out parameters.