Comparisons of the camera OECF, the ISO speed, and the SFR of digital still-picture cameras

摘要

In this paper, the techniques as well as the measurement results of the performnace of commercial digital still-picture cameras are presented. The key parameters such as the camera Opto-Electronic Conversion Function (OECF), the noise based ISO speed, and the spatial frequency response (SFR) are reported. The camera OECF is defined as the relationship between the input luminance and the grayscale or digital output from the camera, which was measured by using a test chart with twelve squares of various luminances. The ISO speed was calculated from the exposure time, the effective f-number,a nd the fluminance at different incremental signal-to-noise ratios. In general, the exposure time is not obtainable from a commercial digital camera unless a destructive measurement is undergoing. In this study, a device was setup to obtain the exposure time when the OECF test chart was recording. A modified slanted-edge method was employed to estimate the SFR by imaging a pattern witha black-to-white edge tilted at an arbitrary angle. There are seven digital still picture cameras as our test samples whose CCD sensor contains VGA-size and million pixels. The camera OECF of these cameras did not show significant difference under a large range of illumination. However, the ISO speed and the SFR were of great variation.