This way all pixels will be considered in the Learning Phase of NeuQuant.
See: https://scientificgems.wordpress.com/stuff/neuquant-fast-high-quality-image-quantization/
I encountered the problem when converting black text on white background. Sometimes the black color was not gathered because of the sampling phase of NeuQuant. This might be worth a try for other color problems too.
This way all pixels will be considered in the Learning Phase of NeuQuant. See: https://scientificgems.wordpress.com/stuff/neuquant-fast-high-quality-image-quantization/ I encountered the problem when converting black text on white background. Sometimes the black color was not gathered because of the sampling phase of NeuQuant. This might be worth a try for other color problems too.