1. An image conversion method for converting a digital image obtained by a scanning unit into a converted digital image, comprising the steps of: acquiring statistics for at least some pixels of the digital image; extracting characteristic values of a background color using the acquired statistics; selecting pixels in the digital image; and converting the selected pixels, wherein each pixel in the digital image is sequentially set as a target pixel, and the selection of a target pixel depends on a representative color distance determined between a number of pixels located in a vicinity of the target pixel and the background color.