Objective measurements of imaging system sharpness (Modulation Transfer Function; MTF) are typically derived from test chart images. It is generally assumed that if testing recommendations are followed, test chart sharpness (which we also call “chart quality”) will have
little impact on overall measurements. Standards such as ISO 12233  ignore test chart sharpness.
Situations where this assumption is not valid are becoming increasingly frequent, in part because extremely high-resolution cameras (over 30 megapixels) are becoming more common and
in part because manufacturing test stations, which have limited space, often use charts that are smaller than optimum. Inconsistent MTF measurements caused by limited chart sharpness can be problematic in manufacturing supply chains that require consistency in measurements taken at different
We describe how to measure test chart sharpness, fit the measurement to a model, quantify the effects of chart sharpness on camera system MTF measurements, then compensate for these effects using deconvolution–by dividing measured system MTF by a model of the chart
MTF projected on the image sensor. We use results of measurements with and without MTF compensation to develop a set of empirical guidelines to determine when chart quality is
• good enough so that no compensation is needed, and
• too low to be reliably compensated.