Show-through occurs when a duplex printed paper is scanned using a scanner or a copy machine. The image of backside printing shows through the paper and mixes with the frontside image. Conventional work to cancel show-through considers this problem as a blind source separation problem. Both corrected images and point spread functions, which express blurring of the back-side image, are estimated by an optimization process using a cost function. The conventional method, however, cannot cancel the show-through well when the front-side printing is thick because the effect of front-side printing on the show-through is not taken into account. We propose an improved cancellation method that can be applied to thick-printed areas. The effectiveness of the method was verified by experiments.