Alexa, Canon, Sony F65/55 and RED.
Charge Coupled Device (CCD), either assembled as a linear or two-dimensional array of light sensitive elements. Light is converted to an electrical charge in a linear fashion – proportional to the brightness impinging on each cell. The cells are coupled to a scanning system which, after analog to digital conversion, presents the image as a series of binary digits.
Typically the charge created on each cell is shuffled along to the end of its line where it is measured by an ADC that outputs a digital number corresponding to the charge, and hence, the brightness. This handling of the charge exposes it to noise and early CCD arrays were unable to work over a wide range of brightness. Now they offer low noise, high resolution imaging for television and digital cinematography.
See also: CMOS
The process of overlaying one video picture, or part of, over another. The areas of overlay are defined by a specific range of color, or chrominance, on the background video signal that is used to create a key signal for a chroma keyer. For this to work reliably, the chrominance must have sufficient resolution, or bandwidth. PAL or NTSC analog coding systems significantly restrict chroma bandwidth and so are of very limited use for making a chroma key which, for many years, was restricted to using live, RGB camera feeds.
An objective of the ITU-R BT.601 and 709 digital sampling standards was to allow high quality chroma keying in post production. The 4:2:2 sampling system allows far greater bandwidth for chroma than PAL or NTSC and helped chroma keying, and the whole business of layering, to thrive in post production. High signal quality is still important to derive good keys so some high-end operations favor using RGB (4:4:4) for keying – despite the additional storage requirements. Certainly anything but very mild compression tends to result in keying errors appearing – especially at DCT block boundaries.
Chroma keying techniques have continued to advance and use many refinements, to the point where totally convincing composite images can be easily created. You can no longer see the join and it may no longer be possible to distinguish between what is real and what is keyed.
The normal interpretation of a component video signal is one in which the luminance and chrominance remain as separate components, e.g. analog components in Betacam VTRs, digital components Y, Cr, Cb in ITU-R BT.601 and 709. RGB is also a component signal.
Component video signals retain maximum luminance and chrominance bandwidth and the frames are independent of each other and so can be edited at any frame boundary.
See also: Cut (edit)
Luminance and chrominance are combined along with the timing reference sync and color burst information using one of the color coding standards – NTSC, PAL or SECAM – to make composite video. The process, which is an analog form of video compression, restricts the bandwidths (image detail) of the color components. In the composite result color is literally added to the monochrome (luminance or Y) information using a visually acceptable technique. As our eyes have far more luminance resolving power than for color, the sharpness (bandwidth) of the coded color signal is reduced to well below that of the luminance.
This provides a good solution for transmission and viewing but it becomes difficult, if not impossible, to accurately reverse the process (decode) back into pure luminance and chrominance. This limits its use in post production as repetitive decode, recode cycles severely impair the pictures. Deriving keys from composite video gives poor results.
A film-style digital camera from Arri that is highly modular and uses a single Super35mm-sized image CMOS sensor with a Bayer filter and producing the same field of view and depth of field as that of traditional 35mm film motion picture cameras. Like real film cameras it uses a detachable optical viewfinder that is widely preferred to electronic versions on other cameras. It is capable of 1-60Hz frame rates and produces 1080-line images in 4:2:2 or 4: