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Tektronix provides test and measurement instruments, solutions and services for the computer, semiconductor, military/aerospace, consumer electronics and education industries worldwide.
The international standard CCIR-601-1 specifies eight-bit digital coding for component video, with black at luma code 16 and white at luma code 235, and chroma in eight-bit two's complement form centred on 128 with a peak at code 224. This coding has a slightly smaller excursion for luma than for chroma: luma has 219 risers compared to 224 for Cb and Cr. The notation CbCr distinguishes this set from PbPr where the luma and chroma excursions are identical. For Rec. 601-1 coding in eight bits per component, Y_8b = 16 + 219 * Y Cb_8b = 128 + 112 * (0.5/0.886) * (Bgamma - Y) Cr_8b = 128 + 112 * (0.5/0.701) * (Rgamma - Y) Some computer applications place black at luma code 0 and white at luma code 255. In this case, the scaling and offsets above can be changed accordingly, although broadcast-quality video requires the accommodation for headroom and footroom provided in the CCIR-601-1 equations. CCIR-601-1 Rec. calls for two-to-one horizontal subsampling of Cb and Cr, to achieve 2/3 the data rate of RGB with virtually no perceptible penalty. This is denoted 4:2:2. A few digital video systems have utilized horizontal subsampling by a factor of four, denoted 4:1:1. JPEG and mpeg normally subsample Cb and Cr two-to-one horizontally and also two-to-one vertically, to get 1/2 the data rate of RGB. No standard nomenclature has been adopted to describe vertical subsampling. To get good results using subsampling you should not just drop and replicate pixels, but implement proper decimation and interpolation filters. YCbCr coding is employed by D-1 component digital video equipment.
Industry:Entertainment
Kodak's PhotoYCC colour space (for PhotoCD) is similar to YCbCr, except that Y is coded with lots of headroom and no footroom, and the scaling of Cb and Cr is different from that of Rec. 601-1 in order to accommodate a wider colour gamut: Y_8bit = (255/1.402) * Y C1_8bit = 156 + 111.40 * (Bgamma - Y) C2_8bit = 137 + 135.64 * (Rgamma - Y) The C1 and C2 components are subsequently subsampled by factors of two horizontally and vertically, but that subsampling should be considered a feature of the compression process and not of the colour space.
Industry:Entertainment
The U and V signals above must be carried with equal bandwidth, albeit less than that of luma. However, the human visual system has less spatial acuity for magenta-green transitions than it does for red-cyan. Thus, if signals I and Q are formed from a 123 degree rotation of U and V respectively (sic), the Q signal can be more severely filtered than I (to about 600 kHz, compared to about 1.3 MHz) without being perceptible to a viewer at typical TV viewing distance. YIQ is equivalent to YUV with a 33 degree rotation and an axis flip in the UV plane. The first edition of W.K. Pratt "Digital Image Processing", and presumably other authors that follow that bible, has a matrix that erroneously omits the axis flip; the second edition corrects the error. Since an analog NTSC decoder has no way of knowing whether the encoder was encoding yuv or YIQ, it cannot detect whether the encoder was running at 0 degree or 33 degree phase. In analog usage the terms YUV and YIQ are often used somewhat interchangeably. YIQ was important in the early days of NTSC but most broadcasting equipment now encodes equiband U and V. The D-2 composite digital DVTR (and the associated interface standard) conveys ntsc modulated on the YIQ axes in the 525-line version and pal modulated on the YUV axes in the 625-line version.
Industry:Entertainment
If three components are to be conveyed in three separate channels with identical unity excursions, then the Pb and Pr colour difference components are used: Pb = (0.5/0.886) * (Bgamma - Y) Pr = (0.5/0.701) * (Rgamma - Y) These scale factors limit the excursion of EACH colour difference component to -0.5 .. +0.5 with respect to unity Y excursion: 0.886 is just unity less the luma coefficient of blue. In the analog domain Y is usually 0 mV (black) to 700 mV (white), and Pb and Pr are usually +- 350 mV. YPbPr is part of the CCIR Rec. 709 HDTV standard, although different luma coefficients are used, and it is denoted E'Pb and E'Pr with subscript arrangement too complicated to be written here. YPbPr is employed by component analog video equipment such as M-II and BetaCam; Pb and Pr bandwidth is half that of luma.
Industry:Entertainment
In composite NTSC, PAL or S-video systems, it is necessary to scale (B-Y) and (R-Y) so that the composite ntsc or pal signal (luma plus modulated chroma) is contained within the range -1/3 to +4/3. These limits reflect the capability of composite signal recording or transmission channel.
The scale factors are obtained by two simultaneous equations involving both B-Y and R-Y, because the limits of the composite excursion are reached at combinations of B-Y and R-Y that are intermediate to primary colours. The scale factors are as follows: U = 0.493 * (B - Y) V = 0.877 * (R - Y) U and V components are typically modulated into a chroma component: C = U*cos(t) + V*sin(t) where t represents the ~3.58 MHz NTSC colour sub-carrier.
PAL coding is similar, except that the V component switches Phase on Alternate Lines (+-1), and the sub-carrier is at a different frequency, about 4.43 MHz. It is conventional for an NTSC luma signal in a composite environment (ntsc or S-video) to have 7.5% setup: Y_setup = (3/40) + (37/40) * Y A pal signal has zero setup. The two signals Y (or Y_setup) and C can be conveyed separately across an S-video interface, or Y and C can be combined (encoded) into composite NTSC or PAL: NTSC = Y_setup + C PAL = Y + C U and V are only appropriate for composite transmission as 1-wire NTSC or PAL, or 2-wire S-video. The UV scaling (or the IQ set, described below) is incorrect when the signal is conveyed as three separate components. Certain component video equipment has connectors labelled YUV that in fact convey ypbpr signals.
Industry:Entertainment
When a roll of 16mm film, perforated along one edge, is held so that the outside end of the film leaves the roll at the top and toward the right, winding "A" should have the perforations on the edge of the film toward the observer, and winding "B" should have the perforations on the edge away from the observer. In both cases, the emulsion surface should face inward on the roll.
Industry:Entertainment
The human visual system has much less acuity for spatial variation of colour than for brightness. Rather than conveying RGB, it is advantageous to convey luma in one channel, and colour information that has had luma removed in the two other channels. In an analog system, the two colour channels can have less bandwidth, typically one-third that of luma. In a digital system each of the two colour channels can have considerably less data rate (or data capacity) than luma. Green dominates the luma channel: about 59% of the luma signal comprises green information. Therefore it is sensible, and advantageous for signal-to-noise reasons, to base the two colour channels on blue and 1red. The simplest way to remove luma from each of these is to subtract it to form the difference between a primary colour and luma. Hence, the basic video colour-difference pair is (B-Y), (R-Y) (pronounced "B minus Y, R minus Y"). The (B-Y) signal reaches its extreme values at blue (R=0, G=0, B=1; Y=0.114; B-Y=+0.886) and at yellow (R=1, G=1, B=0; Y=0.886; B-Y=-0.886). Similarly, the extrema of (R-Y), +-0.701, occur at red and cyan. These are inconvenient values for both digital and analog systems. The colour spaces YPbPr, YCbCr, PhotoYCC and YUV are simply scaled versions of (Y, B-Y, R-Y) that place the extrema of the colour difference channels at more convenient values.
Industry:Entertainment
A standard platform for mass consumer interactive multimedia applications. So it is more akin to CD-DA, in that it is a full specification for both the data/code and standalone playback hardware: a CD-I player has a CPU, RAM, ROM, OS, and audio/video/(MPEG) decoders built into it. Portable players add an LCD screen and speakers/phonejacks. It has limited motion video and still image compression capabilities. It was announced in 1986, and was in beta test by Spring 1989.
This is a consumer electronics format that uses the optical disc in combination with a computer to provide a home entertainment system that delivers music, graphics, text, animation, and video in the living room. Unlike a CD-ROM drive, a CD-I player is a standalone system that requires no external computer. It plugs directly into a TV and stereo system and comes with a remote control to allow the user to interact with software programs sold on discs. It looks and feels much like a CD player except that you get images as well as music out of it and you can actively control what happens. In fact, it is a CD-DA player and all of your standard music CDs will play on a CD-I player; there is just no video in that case.
For a CD-I disk, there may be as few as 1 or as many as 99 data tracks. The sector size in the data tracks of a CD-I disk is approximately 2 kbytes. Sectors are randomly accessible, and, in the case of CD-I, sectors can be multiplexed in up to 16 channels for audio and 32 channels for all other data types. For audio these channels are equivalent to having 16 parallel audio data channels instantly accessible during the playing of a disk.
Industry:Entertainment
Recognizing the need for providing ubiquitous video services using the Integrated Services Digital Network (ISDN), CCITT (International Telegraph and Telephone Consultative Committee) Study Group XV established a Specialist Group on Coding for Visual Telephony in 1984 with the objective of recommending a video coding standard for transmission at m x 384 kbit/s (m=1,2,..., 5). Later in the study period after new discoveries in video coding techniques, it became clear that a single standard, p x 64 kbit/s (p = 1,2,..., 30), can cover the entire isdn channel capacity. After more than five years of intensive deliberation, CCITT Recommendation H.261, Video Codec for Audiovisual Services at p x 64 kbit/s, was completed and approved in December 1990. A slightly modified version of this Recommendation was also adopted for use in North America. The intended applications of this international standard are for videophone and videoconferencing. Therefore, the recommended video coding algorithm has to be able to operate in real time with minimum delay. For p = 1 or 2, due to severely limited available bit rate, only desktop face-to-face visual communication (often referred to as videophone) is appropriate. For p>=6, due to the additional available bit rate, more complex pictures can be transmitted with better quality. This is, therefore, more suitable for videoconferencing.
Industry:Entertainment
A defect of photographic films and plates. Light forming an image on the film is scattered by passing through the emulsion or by reflection at the emulsion or base surfaces. This scattered light causes a local fog which is especially noticeable around images of light sources or sharply defined highlight areas.
Industry:Entertainment
