Conversion of two bit to one bit

Like Vulpes said, a 2-bit image can contain up to 4 colors for each pixel. Such images usually have a palette to specify what the 4 possible colors are for the whole image. On the other hand, 1-bit images can have only 2 colors, and may or may not contain a palette. If they don't have a palette, such as CCITT Fax formats, the 2 possible color would be pure white and pure black. Also, there are other issues when doing the conversion, such as whether you want to perform dithering during color reduction. Dithering uses patterns such as dots to mimic shades and colors in the reduced image. If you don't have a need to control any of these parameters, you can try to use the .NET System.Drawing.Bitmap.Clone() method and use the Format1bppIndexed value for the PixelFormat parameter. However, if you need more advanced options such as controlling the palette or dithering options, you can to use a specialized imaging toolkit like Lead Tools.