1. An item defect inspection method, adapted to an image processing system, comprising the following steps: receiving a test image and a reference image of a test item; obtaining a test block from the test image and obtaining a reference block corresponding to the test block from the reference image to respectively generate a test block image and a reference block image; partitioning the test block image and the reference block image respectively into a plurality of test sub-blocks and a plurality of reference sub-blocks, wherein each of the test sub-blocks corresponds to each of the reference sub-block; comparing the test sub-blocks and the reference sub-blocks so as to identify any interfering test sub-bock and any interfering reference sub-block respectively from the test sub-blocks and the reference sub-blocks, wherein each of the interfering test sub-blocks is not similar to any of the interfering reference sub-blocks, and wherein each of the interfering reference sub-blocks is not similar to any of the interfering test sub-blocks; filtering out the interfering test sub-blocks and the test sub-blocks corresponding to the interfering reference sub-blocks from the test block image to generate a filtered test block image, and filtering out the interfering reference sub-blocks and the reference sub-blocks corresponding to the interfering test sub-blocks from the reference block image to generate a filtered reference block image; obtaining a shift calibration parameter according to the filtered test block image and the filtered reference block image; calibrating the test block in the test image according to the shift calibration parameter to obtain a calibrated test block image; and comparing the calibrated test block image and the reference block image to obtain defect information of the test item corresponding to the test block.