image processing > how to change the contrast > Error

I want to change the contrast using a TrackBar : ---------------

private void contrast_Scroll(object sender, EventArgs e)
        {

            // create filter
            AForge.Imaging.Filters.ContrastCorrection filter = new ContrastCorrection(TrackBar1.Value);
            // apply the filter

            filter.ApplyInPlace(PictureBox1.Image);
        }

--------------- Error :: cannot convert from System.Drawing.Image to AForge.Imaging.UnmanagedImage How to apply the filter on the source image ?? >> I'm a beginner ! http://www.flickr.com/photos/92380688@N03/8395863084/in/photostream[^]"> here the pic

Tags: C#