Originally Posted by DaleDe
Obviously the tool you used to convert to grayscale was inferior to the internal tool. This means you used the wrong tool. I use IrfanView, a free download, and first reduce the colors and then convert to gray scale. It works very well.
IrfanView is not cross-plateform and does not propose library for programing picture tools. At the beginning, I used ImageMagick, then GraphicsMagick, but I had problems to include them in an embeded application with the language that I am using (I want a program who does not need to install something else).