It is shown that the effect of sensor noise in displacement and strain maps obtained with the grid method can be accurately predicted. Analytical expressions linking resolution and spatial resolution in these maps on the one hand, and standard deviation of sensor noise on the other hand are first given. These expressions are then experimentally evidenced. It is shown that a grid image preprocessing step must be performed to reach this goal in order to account for heteroscedasticity of sensor noise and micro-vibrations that corrupt grid images.