COMPARING LIGHT SENSITIVITY, LINEARITY AND STEP RESPONSE OF ELECTRONIC CAMERAS FOR OPHTHALMOLOGY

PURPOSE: To develop and test a procedure to measure and compare light sensitivity, linearity and step response of electronic cameras. METHODS: The pixel value (PV) of digitized images as a function of light intensity (I) was measured. The sensitivity was calculated from the slope of the P(I) function, the linearity was estimated from the correlation coefficient of this function. To measure the step response, a short sequence of images was acquired. During acquisition, a light source was switched on and off using a fast shutter. The resulting PV was calculated for each video field of the sequence. RESULTS: A CCD camera optimized for the near-infrared (IR) spectrum showed the highest sensitivity for both, visible and IR light. There are little differences in linearity. The step response depends on the procedure of integration and read out.