C# - How to draw image with Gamma or Threshold effect

var rectDest = new Rectangle( 0, 0, this.m_bitmap_source.Width, this.m_bitmap_source.Height );

using ( var graphics = Graphics.FromImage( this.m_bitmap_dest ) )
 using ( var attr = new ImageAttributes() )
 {
   attr.SetGamma( 0.2f );
   
   graphics.DrawImage( this.m_bitmap_source, rectDest, 
                       0, 0, this.m_bitmap_source.Width, this.m_bitmap_source.Height, 
                       GraphicsUnit.Pixel, attr );
 }

You can use Threshold effect too (replace row with Gamma):

attr.SetThreshold( 0.4f );