Quantification of the image sensor signal and noise is essential to derive key image quality performance indicators. Image sensors in automotive cameras are predominately activated in high dynamic range (HDR) mode, however, legacy procedures to quantify image sensor noise were optimized for operation in standard dynamic range mode. This work discusses the theoretical background and the workflow of the photon-transfer curve (PTC) test. Afterwards, it presents example implementations of the PTC test and its derivatives according to legacy procedures and according to procedures that were optimized for image sensors in HDR mode.