Abstract: The descreen methods for color or grayscale images captured by scanner are generally blur arithmetic.But for halftone image generated by RIP the blur arithmetic is useless because the image is bi-level bitmap one so that it is of only 0 and 1 two levels.The descreen method is based on a very different arithmetic,it finds out the center of halftone cell and screen ruling parameters first,and then divides the image into halftone cell.By computing dot area percentage in each halftone cell and converting its value to the grayscale,the halftone dots would be eliminated.The computing results show that the descreening results dependent upon the resolution,screen ruling angle and frequency of the halftone image.The descreen effect of this method is reasonable good and a full color image can be composed from 4 RIPed separation images.The method can be used to digital soft proof based on the RIPed separation images.