State of Imaging (page 2)

With image sensor technology making incremental improvements every year, both CCDs and CMOS sensors will continue to get better while becoming even more affordable, which will lead to higher resolution, low-cost camcorders.

Heath McKnight is a filmmaker and writer. He recently co-wrote HDV: What You NEED to Know, Volume 2, from VASST. He would like to thank Graeme Nattress for research help with this article.

CCD: Charge-Coupled Device that is used to detect light, but not color, in video and digital still cameras. On their own, most sensors would detect only black-and-white images. To achieve full color, filters are used on the chips, either spread out evenly (three-CCD Red, Blue and Green, using dichroic filters in a prism) or on each pixel (one-CCD via colored filters).

CMOS: Complementary Metal-Oxide-Semiconductor. You may be familiar with it from digital still cameras. This more affordable chip consumes less power and contains electronics that convert the analog information from the pixels to a digital form. This conversion must be performed off-chip in CCD sensors.

SNR: Signal-to-Noise Ratio. The higher the SNR, the cleaner the image; the lower the SNR, the more noise. Smaller pixels, relatively speaking, have a lower SNR than bigger pixels.

DIFFRACTION: This occurs as light travels through an aperture, especially one that is closed due to increased light. The resolution of the image will actually decrease with diffraction; to avoid it, control the light going into the lens with neutral density filters or with filters, diffusion, etc. on the lights themselves. Keep the aperture as open as possible with smaller-chip cameras.

BAYER PATTERN: Named after inventor Dr. Bryce Bayer, it is used with one-chip camera systems to allow the chip to "see" color. It's broken down as RGBG - 50% green, 25% blue and 25% red.

CCD vs. CMOS: CCDs have traditionally provided a "cleaner" image via a higher SNR than CMOS, but recent and ongoing developments in CMOS technology have closed this gap, especially in the case of large, high-resolution, high-frame-rate chips.With CMOS, less vertical smear is an advantage; vertical smear is very common when shooting with a very bright object, such as a light, that is in the shot. The effect shows up as "points" coming off a bright spot, which CMOS helps to reduce.

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