C#

[SecurityPermission(SecurityAction.LinkDemand, Flags = SecurityPermissionFlag.UnmanagedCode)]
public class MessageFilter : IMessageFilter
{
    private const int WM_ACTIVATE = 0x006;
    private const int WM_NCACTIVATE = 0x086;

    public bool PreFilterMessage(ref Message m)
    {
        if(m.Msg == WM_NCACTIVATE)
            return true;
        return false;
    }
}

MessageFilter mf = new MessageFilter();
Application.AddMessageFilter(mf);

Bitmap previewimage = null;
int brightness_value = 0;
int contrast_value = 0;

public PicPreviewForm(string filename) 
{
	previewimage = new Bitmap(Image.FromFile(filename));
	pictureBox1.Image = previewimage;
}
public void ApplyFilter()
{
      Bitmap bit;
      bit = new Bitmap(previewimage);
	
if(brightness had been changed)
{
	BrightnessFilter(bit, brightness_value);
}
If(contrast had been changed)
{
	ContrastFilter(bit, contrast_value);            
}
PictureBox.Image = bit;               
                
        
}