Sky modelling and subtraction process in the NASIM pipeline, illustrated for the IC 2000 galaxy. This figure shows the main steps within the sky subtraction loop implemented via the loopflow.mk Makefile. Top-left: Final stack image produced by the NASIM pipeline prior to additional sky modelling. Top-middle: Masked final stack, created by applying a strong mask with NOISECHISEL to isolate background regions. Top-right: Examples of masked images, showing individual masked, resampled frames. Bottom-right: Examples of sky modelling, based on fits with a second-order polynomial function. Bottom-middle: Examples of sky-subtracted images, following subtraction of the sky model. Bottom-left: Final stack after sky subtraction, demonstrating improved background uniformity and enhanced recovery of LSB features.