Brightness method shows "Out of memory" exception

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C#

C#4.0

image-processing

To change brightness of an image in c#.net 4 i have used the following method.

public void SetBrightness(int brightness)
       {
           imageHandler.RestorePrevious();
           if (brightness < -255) brightness = -255;
           if (brightness > 255) brightness = 255;
           ColorMatrix cMatrix = new ColorMatrix(CurrentColorMatrix.Array);
           cMatrix.Matrix40 = cMatrix.Matrix41 = cMatrix.Matrix42 = brightness / 255.0F;
           imageHandler.ProcessBitmap(cMatrix);
       }

         internal void ProcessBitmap(ColorMatrix colorMatrix)
             {
               Bitmap bmap = new Bitmap(_currentBitmap.Width, _currentBitmap.Height)

               ImageAttributes imgAttributes = new ImageAttributes();
               imgAttributes.SetColorMatrix(colorMatrix);
               Graphics g = Graphics.FromImage(bmap);
               g.InterpolationMode = InterpolationMode.NearestNeighbor;
               g.DrawImage(_currentBitmap, new Rectangle(0, 0, _currentBitmap.Width,
               _currentBitmap.Height), 0, 0, _currentBitmap.Width,
               _currentBitmap.Height,  GraphicsUnit.Pixel, imgAttributes);
               _currentBitmap = (Bitmap)bmap.Clone();


           }

If brightness is changed several times then "Out of memory" exception is shown. I have tried to use "Using block" but went in vein.

Any ideas?

please see the link
Image Processing Using Matrices in C#
and suggest if any types of optimization is possible in the methods (Rotation, brightness, crop and undo).