An inexpensive measurement system for characterizing digital still cameras is described. The method adopted involves performing mathematical analyses directly on the images of test charts obtained from the DSC. These charts comprise of squarewave patterns with selected spatial frequencies, the phases of which with respect to the CCD sensors cover most or all of the phase domain. By working on the final images generated by DSCs, we can include the effects of the digital signal processing on the performance of the DSC. Slightly rotated optical patterns of squarewaves with different spatial frequencies were projected on the CCD to determine the phase-dependent CTF. These phase-dependent data were then statistically analyzed to obtain average CTF values that better describe the characteristics of the DSC. The low cost system developed in our laboratory is very suitable for evaluating and designing digital signal processing algorithms when developing digital still cameras.
KEYWORDS: Charge-coupled devices, Imaging systems, Modulation transfer functions, Cameras, Digital cameras, CCD image sensors, Signal to noise ratio, Optical filters, Contrast transfer function, Light sources
We describe in this paper an evaluation system for completely characterizing a digital still camera developed at our laboratory. The CCD sensor array of the camera was first used to assess the modulation transfer function of the lens system, the calibrated lens was then used to measure the single-chip color CCD sensor array. Accordingly, performance of the complete camera system can be evaluated as a whole. Measurements performed on this imaging system include dynamic range, signal to noise ratio, modulation transfer function and contrast transfer function of the lens as well as the CCD. With the help of a standard color test plate and prior knowledge about the spectral distributions, spectral response of the color filters coated on the CCD were computed approximately. The results of our experiments were compared with the data sheet provided and the theoretical calculation. The apparatuses needed for measuring the entire imaging system include only calibrated light source and standard test patterns, while the data access subsystem was part of the digital camera and the mathematical analyzing tools are developed on a personal computer. Consequently, system design was simplified and the evaluation process was made more efficient and cost effective.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.