1. A method of extracting text from a document image with a complex background, comprising the steps of: a first edge extracting step of extracting edges from said image which have higher contrast than a first contrast threshold; a searching step of searching for connected edges from said extracted edges; a second edge extracting step of extracting connected edges which have higher contrast than a second contrast threshold and which have a number of pixels larger than a predetermined size, wherein said second contrast threshold is higher than said first contrast threshold, and of determining that connected edges are a text edge in case that the number of pixels of the connected edges is smaller than or equal to said predetermined size; a second connected edge searching step of searching for connected edges from edges extracted in said second edge extracting step; a third edge extracting step of extracting connected edges from the connected edges searched for in the second connected edge searching step which have higher contrast than a third contrast threshold and which have a number of pixels larger than said predetermined size, wherein said third contrast threshold is higher than said second contrast threshold.