Evaluating & Comparing Camera Performance
With cameras being used in applications ranging from consumer products such as PDA’s, automotive rear viewing systems, and medical devices to military applications including thermal imaging and ranging systems, how does one rationally compare the performance of these cameras? No single metric can fully describe the performance of an imager and no short article can thoroughly treat the complexities of testing the performance of an imaging camera. Instead, this page is intended to describe some of the more important evaluation metrics that are used to assess overall camera performance.
One of the reasons that the application areas for imaging have exploded is that camera technologies themselves are changing. It is helpful to divide cameras into those that rely on reflected light (visible, near, and short wave infrared, 350 nm – 2.5 microns wavelength) and those that rely on imaging the thermal emissions of the object itself (3-14 microns wavelength). Cameras working in the visible and near infrared use silicon based devices, near short wave infrared-red cameras use InGaAs, and thermal infrared imagers (both cooled and uncooled) use MCT and InSb.
The past few years have seen the widespread adoption of a number of digital high speed serial camera output formats: USB 2.0, IEEE-1394 (“FireWire”), CameraLink, and gigabit Ethernet (“GigE”), greatly expanding the transmission and interfacing of video signals. At the same time proprietary parallel digital camera LVDS outputs (parallel data is particularly well suited to non-standard formats and line scan cameras) and standard analog video remain popular. With camera manufacturers adhering to standard data formats (such as the DCAM standard for FireWire) to varying extents, the challenge for camera test equipment is to seamlessly interface with all of these formats.
How can I verify my camera’s performance? Is comparing the resolutions (number of pixels) and responsivities of two cameras sufficient to make an appropriate choice? What do I need to measure at incoming inspection to make sure my cameras will perform as they should?
Listed below is a sampling of camera performance metrics:
• Pixel size (the actual area that is sensitive to light)
• Cell size (the spacing of pixels in the imager)
• Number of pixels (horizontal and vertical)
• Signal Transfer Function (SiTF), Modulation Transfer Function (MTF)
• Responsivity and Linearity
• Noise
• Spectral sensitivity
For more information on the camera performance metrics, click here.