![]() ![]() Understanding how the HVS works is important for the following reasons: These signals are the same for all neurons, regardless of the information they carry, whether visual, audible, tactile, or other. Study of the enormously complex nervous system is manageable because there are only two types of signals in the nervous system: one for long distances and the other for short distances. Neurons either generate pulses or inhibit existing pulses, and result in a variety of phenomena ranging from Mach bands, band-pass characteristic of the visual frequency response, to the edge-detection mechanism of the eye. The electrochemical communication between the nervous system and the brain is carried out by about 100 billion nerve cells, called neurons. The human visual system (HVS) is part of the human nervous system, which is managed by the brain. Additionally, compression methods and techniques became more refined. Meanwhile, the network capabilities also grew, making it possible to address the needs of today’s industries. However, these parameters are no longer in use, so Part 2 of the specification contains HDTV system parameters with square pixel common image format. For example, the recommendation BT.709, aimed at high-definition television (HDTV), started with defining parameters for the early days of analog high-definition television implementation, as captured in Part 1 of the specification. Over the years these recommendations evolved. One after another, the ITU-R Recommendations BT.601, Footnote 3 BT.709, Footnote 4 and BT.2020 Footnote 5 appeared to support video formats with increasingly higher resolutions. These capabilities fueled the growing demand of ever higher video resolutions and data rates to accommodate diverse video applications with better-quality goals. With increased compute capabilities, video encoding and processing operations became more manageable over the years. ![]() While the format specifies many picture rates (24 Hz, 25 Hz, 30 Hz, 50 Hz, and 60 Hz), with a resolution of 352 × 288 at 30 Hz, the required data rate was brought down to approximately 37 Mbps, which would typically fit into a basic Digital Signal 0 (DS0) circuit, and would be practical for transmission. In order to partially address the data-rate issue, the 15 th specialist group (SGXV) of the CCITT Footnote 2 defined the Common Image Format (CIF)to have common picture parameter values independent of the picture rate. Note that the raw data rate for the ITU-R 601 formats Footnote 1 is ∼165 Mbps (million bits per second), beyond the networks’ capabilities. In the 1990s, transmission of raw digital video data over POTS or ISDN was unproductive and very expensive due to the sheer data rate required. ![]()
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