HD videotape

For SD, refer to Composite NTSC and PAL: Legacy Video Systems.

Since publication of the first edition of this book there has been a dramatic decline in the use of videotape. Much legacy SD videotape equipment is still in use, but SD requirements are now fairly easily met by hard drive and flash media. Videotape is still in fairly wide use for HD, and still retains a few advantages over hard drive and flash media. Also, several compression systems originally devised for videotape have successfully made the transition into hard drive and flash media.

Table 43.1 summarizes digital videotape formats for HD.

Malvar, Henrique S. (1992), Signal Processing with Lapped Transforms

(Norwood, Mass.: Artech House).

Downsampling of 1920× 1080 to 1440× 1080 means that luma sample aspect ratio is effectively 4⁄3 (and chroma subsampling is equivalent to 4:1:1) relative to the original luma array.

Downsampling of 1920× 1080 to 1280× 1080 means that luma sample aspect ratio is effectively 3⁄2 (and chroma subsampling is equivalent to 3:1:1) relative to the original 1920× 1080 luma array.

D-5 HD (HD-D5, D-15)

The SMPTE D-5 standard defined recording of uncompressed SD at 270 Mb/s. Panasonic adapted the D-5 format to HD by equipping it with a motion-JPEG codec having a compression ratio of about 5:1; the coding is quite similar to that of DV. This variant of the D-5 VTR is denoted D-5 HD or HD-D5; after its introduction, it was standardized by SMPTE as D-15.

The D-5 HD system records 720p or 1080i video at either 59.94 Hz or 60.00 Hz, with 4:2:2 chroma subsampling.

One difference from DV is that D-5 HD compression uses a lapped (overlapped) transform, where the rightmost column of samples in an 8× 8 block overlaps the leftmost column of the next block to the right. Upon decoding, the redundantly coded columns are reconstructed by averaging appropriate samples from two neighboring blocks. This scheme reduces blocking artifacts compared to the nonlapped transform used in DV.

D-6

SMPTE D-6 defined a videotape format for uncompressed, 8-bit, 4:2:2 HD, at a bit rate of 1.188 Gb/s. This equipment had superb performance and was very expensive; it is now obsolete.

HDCAM (D-11)

HDCAM was developed and commercialized by Sony. Interlaced or progressive HD video at any of several frame rates is downsampled to 1440× 1080 image format and subject to 3:1:1 chroma subsampling. Compression is M-JPEG-style, comparable to that of DV, using a lapped (overlapped) transform (like

D-5 HD), coded at about 135 Mb/s. HDCAM uses a tape cassette derived from Betacam, with 1⁄2-inch tape. The videotape recording scheme was standardized as SMPTE D-11.

DVCPRO HD (D-12)

The DV25/DV50 standards were adapted to 100 Mb/s to accommodate 1080i30 HD signals downsampled to 1280× 1080 image format (or 720p60 downsampled to 960× 720), with 4:2:2 chroma subsampling in the

EIA/CEA-770.3, High Definition TV

Analog Component Video Interface.

coincident with each other, and with sync, within 1⁄4 of a sample clock – for 720p60 and 1080i30, time-coinci- dent within ±3.4 ns.

EIA/CEA has standardized the 720p60 and 1080i30 systems as described here, including these Y’PBPR levels, for use in consumer HD electronics devices.

Preand postfiltering characteristics

Component Y’, R’, G’, or B’ signals in 720p59.94 or 720p60 – and for that mattter, 1080i30 – have

a nominal passband of 30 MHz; colour difference components have a nominal passband of 15 MHz.

Figure 44.3 overleaf, Filter template for Y’ and R’G’B’ components, depicts filter characteristics for preand postfiltering of R’, G’, B’, and Y’ component signals. Analog PB and PR colour difference component signals are preand postfiltered using the same template scaled by a factor of two on the frequency axis. The characteristics are frequency-scaled from the template included in BT.601, with a few modifications.

Amplitude ripple tolerance in the passband is ±0.05 dB with respect to insertion loss at 100 kHz. Insertion loss is 6 dB or more at half the sampling rate of the Y’, R’, G’, and B’ components.

SMPTE ST 274 includes luma and colour difference templates in “Annex B (Informative).” In standards lingo, the word informative signals that the information is distributed with the standard, but compliance with the annex is not required to claim conformance with the standard.

Passband insertion gain [dB]

Stopband insertion gain [dB]

+0.050

+0.025

0

-0.025

-0.050

-10

-20

-30

-40

-50

-60

-6 dB

-40 dB

-50 dB

ISO/IEC 10918, Information Technology – Digital compression and coding of continuous-tone still images.

This chapter describes JPEG, a standard for lossy compression of still images. JPEG is based upon the discrete cosine transform (DCT). JPEG is rarely used directly in video, but it forms the basis of M-JPEG (used in desktop video editing) and DV compression. Also, JPEG techniques form the core of MPEG.

Motion-JPEG (M-JPEG) refers to the use of a JPEGlike algorithm to compress each field or frame in

a sequence of video fields or frames. M-JPEG systems use the methods of JPEG, but rarely (if ever) conform to the ISO/IEC JPEG standard. DV is a specific type of M-JPEG, which is well standardized; it is described in the following chapter, DV compression, on page 505. The I-frame-only variant of MPEG-2 is conceptually equivalent to M-JPEG, but again has a well-respected standard; see MPEG-2 video compression, on page 513.

The JPEG standard, cited in the margin, defines four modes: sequential, hierarchical, progressive, and lossless. The JPEG standard accommodates DCT coefficients having from 2 to 16 bits, and accommodates two different entropy coders (Huffman and arithmetic). Baseline refers to a defined subset of JPEG’s sequential mode that is restricted to 8-bit coefficients and restricted to Huffman coding. Only baseline JPEG is commercially important; JPEG’s other modes are mainly of academic interest, and won’t be discussed here.