Abstract: Broken objects or false objects is often seen in a binarized draught line image under complex illumination. The new method decides basic threshold for each image block with OTSU algorithm and defines particular threshold for each section in a block with Bernsen algorithm. The Binarized image digitized by the method displays unbroken characters alongside the draught line, with shadows removed. This method also shows better ability in denoising and keeping details than ordinary methods.