Manual image to icon
From RealWorld Wiki
RealWorld Icon Editor can open raster images and modify them to be better suited for conversion to icon. If the source images are already suitable for conversion, consider using the batch conversion operation for higher speed or the wizard for simpler user interface. How to spot an image that needs adjustments before conversion.
First, open the source image in the application. Common and specialized drawing tools and image filters stand at your disposal. Typical actions include:
Once your image is ready, open the Operation menu and click one of the Create icon commands.
There is a couple of predefined commands and also two interactive commands. The difference between them is only in configuration. All of them are based on the Icon - From Image transformation followed by a operation generating 8-bit and 4-bit versions of images.