gdImagePtr gdImageNeuQuant( gdImagePtr im, const int max_color, int sample_factor ) 
Creates a new palette image from a truecolor image
This is the same as calling gdImageCreatePaletteFromTrueColor with the quantization method GD_QUANT_NEUQUANT.
| im | The image. | 
| max_color | The number of desired palette entries. | 
| sample_factor | The quantization precision between 1 (highest quality) and 10 (fastest). | 
A newly create palette image; NULL on failure.
Creates a new palette image from a truecolor image
gdImagePtr gdImageCreatePaletteFromTrueColor ( gdImagePtr im, int dither, int colorsWanted )