NDE flaw detectability is given by flaw size such as crack length. Flaw size parameters or flaw response parameters are used to assess crack detectability. Normalized exposure is used to calculate the flaw size parameter in x-ray radiography. Detector response is used to calculate more complex flaw response parameters. The flaw size parameter provides crack indication width and crack indication amplitude parameter such as void path length ratio parameter. X-ray flaw size parameter model, given here, uses ray tracing model in two dimensions to compute flaw size parameters such as the indication width and the void path length ratio parameter. Results from an analytical model previously published by the author were compared with the ray tracing model. Two runs of ray tracing model are provided. These runs include normal and oblique incident angle x-ray. Since the revised analytical model provides better agreement with the ray tracing model for indication width and normalized exposure, it was used to provide flaw detectability assessments using contrast-to-noise ratio and net unsharpness. Film and digital detector responses are modeled in the analytical model. Modulation transfer function (MTF) is also modeled in the analytical model based on measured basic detector resolution SRb as given in ASTM E2033. Using the detector response and detector MTF, flaw response parameters are computed. Several runs of analytical model were conducted. These runs included zero and oblique incident angle x-ray; simulated film detector, simulated digital detector, micro-focus source and conventional (0.4 mm focal spot) source. Part thickness was also varied. Surface plots with crack depth on x-axis and flaw width on y-axis are provided for MTF. These runs provide plots of MTF, flaw size parameter width, void path length amplitudes, MTF accounted amplitude parameter, simulated detector signal, revealing effect of various quantities on the flaw detection parameters and crack detectability using ASTM E2698 contrast sensitivity, contrast-to-noise ratio and net unsharpness. The paper provides a method to assess and optimize capability of x-ray technique to detect cracks or cracklike flaws reliably through simulation and analysis.