A wafer-scale linear image sensor chip (WLISC) is proposed with gapless pixel line and signal readout circuit segments. The WLISC converts pixel line image (PLI) of length LPL into line image signal (LIS). The WLISC includes a linear array of sensor segments. Each sensor segment includes a gapless local pixel line segment (LPLSj) of sensing elements. The LPLSj converts portion of the PLI into a raw image segment signal set (RISSj). The LPLSj set forms a gapless global pixel line (GPL) corresponding to PLI. The sensor segment also includes readout circuit segment (RCSj) coupled to LPLSj for processing RISSj into a readout image segment signal set (ROSSj). The RCSj has a set of contact pads (CTPj) for off-chip interconnection. Upon off-chip interconnection of the CTPj set thus composing the ROSSj set into LIS, the WLISC functions as a key part of a linear image sensor system of image length LPL.