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Digital Video, its main features

Digital Video, its main features

digital video

Until recently, few people could have imagined that with an ordinary home computer it would be possible not only to watch your favorite movies, but also to create your own video library, digitize the content of old videotapes, edit family videos, and even create your own. movie masterpieces.

DIGITAL VIDEO

It all started in 1992, when IBM and Intel developed the Indeo software technology (short for Intel Video). With its help, users have the opportunity to digitize video and create video files on a PC, with subsequent playback on the monitor screen.

Initially, digital video was an analog signal converted to digital format. Furthermore, the conversion procedure itself inevitably led to a certain loss of quality. Today, VCRs and old VHS cameras are a thing of the past, and modern digital video cameras, DVD and Blu-Ray players, which allow you to receive a signal immediately in digital form, rule the ball. And analog television is gradually giving way to more progressive digital.

Key features of digital video
Digital video has five main characteristics: screen resolution, frame rate, color depth, bit rate (video transmission width), and image quality.

Screen resolution (resolution): indicates the number of dots (pixels) horizontally and vertically that make up the image (video frame) on the screen. When recording resolution, the value of the number of dots per line (horizontal resolution) is indicated first and then the number of lines involved in the image (vertical resolution). For example, for the European PAL video standard, the frame size is 720×576 pixels, for the North American NTSC standard – 720×480, for high definition video (HD 720p) – 1280×720, and for the new HDTV standard (Full HD) – 1920×1080 pixels. As you probably understand, the higher the screen resolution, the better the video quality.

The frame rate is a value that indicates how many frames are changed per second. The standard video playback speed is considered a value equal to 30 frames / s. For cinema, this figure is slightly lower and amounts to 24 frames / s.

Color depth (color resolution) is a characteristic that indicates the number of colors that can participate in the formation of a video image. The number of colors in digital video is measured in bits. So 1 bit can take two different values ​​(0 or 1) and it only allows encoding two colors (usually black and white), respectively. With two bits, you can encode 4 colors (2 2 = 4), with three bits – 8 colors (2 3), four – 16 (2 4) and so on.

Typically, color resolution is described by special color models. In computer technology, the RGB (red-green-blue) model is used, which can be represented by the following most common color depth modes: 8-bit (256 colors), 16-bit (65,536 colors), and 24-bit (16,777 .216 colors). By the way, the human eye, according to various opinions, can perceive 5-10 million shades of color.

Bit rate (video stream width): Shows the number of video bits processed per second of time. In other words, this is the video transmission speed, which is measured in megabits per second (Mbps). The higher it is, the better the quality. For example, for the DVD video standard, the bit rate is about 5 Mbps and for the HDTV format, it is already 10 Mbps. By the way, most of the time the bit rate value is used to evaluate the quality of the video transmitted over the Internet.

Image quality is a characteristic designed to evaluate the quality of processed video compared to the original and is determined by a set of values ​​for resolution, color depth, and video transmission speed.

Compression standards
One minute of pure, uncompressed and digitized sound takes up about 10MB on a computer’s hard drive, as a result of which, for the vast majority, music files are stored in a compressed form to save space. How long does a minute of uncompressed video take? For example, to place a 60-second video with a rate of 30 frames per second, a resolution of 720×576 pixels, and a color depth of 16-bit, you will need approximately one and a half gigabytes of free disk space. And this without taking into account the audio track. After these numbers, it is probably not necessary to explain why digital video is stored on our computers exclusively in compressed form.

There are several dozen popular compression formats that use different compression algorithms.

Digital Video

Digital video

Digital Video

Little by little, all the equipment for the production of television and video programs in the world is going digital. Why is this happening? Not at all due to the fact that digital methods are admired by all and that the image quality is radically improving, the reasons for such a transition are mainly economic, because now both the price and the cost of operating a digital complex are less than a traditional analog one with the same functions. Now that digital technology has reached a certain maturity, analog equipment is suddenly less efficient, less reliable, and much less profitable.

DIGITAL VIDEO

EN The very foundations of video production and delivery of images to the viewer are currently being revised, and the dynamics of change in the current age – digital – is much higher than in analog. Today, for example, the 4: 3 aspect ratio is gradually being replaced by the 16: 9 aspect ratio, interlaced-progressive (non-interlaced) scanning and changing encoding standards increase image quality. The economy also dictates the need to compress video information. Naturally, any compression degrades the quality of the rendering and is applied not for a good life, but out of necessity.

Do not think that video compression was not used before and that it only appeared with the advent of digital technologies. No, compression has always been used, but only before it was analog, and today it is necessary to make it completely digital, getting rid, as much as possible, of double compression, that is, both analog and digital.

Modern digital compression methods, which have replaced analog, especially when combined with computer technology, can not only improve the quality of the video itself, but also expand the possibilities of video production and optimize the display of audiovisual products.

Basic concepts of digital transformation
P Essentially, the digital representation, or digitization, is a partition of the domain of a continuous function in some intervals and the representation of this function as a set of values ​​at the end of these intervals. So, for a digital sound signal, the second interval on the time scale is divided into 32, 44 or 48 intervals, in each sample the sound is measured and its value is stored with a certain representation precision, generally from 14 to 20 bits. These operations are called sampling processes, that is, the representation of any continuous quantity (in this case, sound) through periodic discrete measurements. After that, they say that the sound is digitized with a sample rate of 32 to 48 kHz, respectively, and a bit depth of 14 to 20 bits. Therefore, the digital current

In digital video, the process of sampling a value is simply generalized to a multivalued function that has an area of ​​value, not a number, but an image (that is, it becomes three-dimensional) in order to break the solid lines of an image (scanning beam) in so-called pixels, or image elements, our three-dimensional. the space will be because when the image is presented at each moment of time, it is not a value, as in sound, but the whole image: a frame. As a result, the video signal is also represented as a sequence of integers, in other words, as a stream of data.

In the case of (separate) component analog video signals, each channel must simultaneously transmit three color components (red – red, green – green and blue – blue, i.e. RGB) or a luminance signal together with signals of color difference (YUV). The conversion of RGB color components into YUV components is one by one, but the latter method allows to emphasize the change in the brightness of the signal, for which the human eye provides a separate perception mechanism, with the help of the rods. in the retina, in contrast to the perception of color made by the cells of the cone. Rods are more sensitive than cones, so in systems with separate component coding (e.g.

Sampling theory, in turn, requires that the sampling frequency be at least twice the bandwidth of the signal to be digitized. In the case of a broadband signal (for sound, that is, for example, the simultaneous reproduction of several octaves of frequencies), the sampling frequency must be at least twice the highest frequency of the input signal analog