Structure Integral transform (SIT) is a mathematical tool for invariant shape recognition. SIT has a superior ability to capture the interior structure information by integrating the shape image function over 2D dissecting structure, but the details on the dissecting structure are discarded. In this paper, for the first time, we propose a novel multi-scale piecewise line integral strategy for SIT which introduces the grayscale information. At a higher scale, the integral line on dissecting structure will be equally divided more times, which brings to a coarse to fine description for each integral line. The proposed multi-scale piecewise integral strategy has been validated to extend SIT from binary shape to grayscale shape successfully through experiments on Leeds' Butterflies dataset and Ponce Group's Butterflies dataset.