Brightness method shows "Out of memory" exception

Question

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
http://www.codeproject.com/Articles/227016/Image-Processing-using-Matrices-in-Csharp
and suggest if any types of optimization is possible in the methods (Rotation, brightness, crop and undo).