Thread: global color histogram

hey
i can't understand this line,plz tell me what is the meaning of 64 color value and on which base it classify/covert RGB in 0 t0 63 integer??
"the global color histogram, method returns 64 color values represent the probability of pixels in the sample image of a particular color."

below the line code return integer values from 0 to 63 for any RGB value . image.getRGB(x,y) return RGB value of pixel at x,y position.
(image.getRGB(x,y)>>18 & 0x30) | (image.getRGB(x,y)>>12 & 0xc) | (image.getRGB(x,y)>>6 & 0x3)

but on which base ,for different RGB value it return same integer y??

okk i got it.will it reduce the quality of image color or the accuracy of histogram??
if i use this same technique for 8 bit 0-255,because java use 8 bit to represent color code like
(image.getRGB(x,y)>> 16 & 0xff) | (image.getRGB(x,y) >> 8 & 0xff) | (image.getRGB(x,y)& 0xff)
which is better ,6 bit or 8 bit ??

thanks for your time