Moreover, there are still DVD players around that only carry support for up to 480p or 480i, meaning a viewer cannot get the full experience of any high-definition DVD they insert into the player. Regular DVD quality can vary considerably, with some displaying content at a resolution lower than 720p, such as 480p.
HD DVDs contain 720p content and sometimes 1080p, while all Blu-ray discs contain 1080p content. New TVs may attempt to automatically change settings to whatever is most appropriate, but they may fail to do so in some cases. Those who want the best picture quality need to change their TV's settings to accommodate changing video feeds.
When watching digital TV, video quality can vary wildly. Some video content is filmed or trimmed to a smaller vertical resolution than 1080 pixels-or it's interlaced, rather than progressively scanned-but it is still considered HD. The FCC defines high-definition (HD) quality video as 720p, 1080p, and 1080i, and all modern TVs carry support for at least 720p resolution, with many supporting 1080p. The video below offers a summary of the differences between 1080p and 720p in terms of picture quality.
Image smoothness is affected by many other factors, including how big a TV is, how close one sits to it, what DVD player is in use, what a TV's refresh rate is or what its aspect ratio is set to, and even what the frame rate of the video or game content is. Not everything comes down to resolution, however. Retrieved April 16, 2013.Comparing the visual quality of different resolutions and standards.
^ "Toxic dust adds to WTC death toll".: Cite journal requires |journal= ( help) National Institute of Standards and Technology. Design, Construction, and Maintenance of Structural and Life Safety Systems (NCSTAR 1-1). In addition, there is at least one secondary death – one person was ruled by a medical examiner to have died from lung disease due to exposure to dust from the World Trade Center's collapse. The overwhelming majority of casualties were civilians, including nationals of over 70 countries. The death toll of the attacks was 2,973, including the 19 hijackers. There were no survivors from any of the flights. in an attempted attack on the United States Capitol Building. The fourth plane crashed into a field near Shanksville in rural Pennsylvania after some of its passengers and flight crew attempted to retake control of the plane, which the hijackers had redirected toward Washington, D.C. The hijackers crashed a third airliner into the Pentagon in Arlington, Virginia, just outside Washington, D.C. Both buildings collapsed within two hours, destroying nearby buildings and damaging others. The hijackers intentionally crashed two of the airliners into the Twin Towers of the World Trade Center in New York City, killing everyone on board and many others working in the buildings. On that morning, 19 al-Qaeda terrorists hijacked four commercial passenger jet airliners.
The September 11 attacks (often referred to as September 11th or 9/11) were a series of coordinated suicide attacks by al-Qaeda. According to a presiding judge, the conspirators' chief aim at the time of the attack was to destabilize the north tower and send it crashing into the south tower, toppling both landmarks. Four others had been convicted in May 1994 for their involvement in the 1993 bombing. Yousef and Eyad Ismoil were convicted in November 1997 for their carrying out the bombing. Sheikh Omar Abdel Rahman was convicted in 1996 for involvement in the bombing and other plots.
Yousef fled to Pakistan after the bombing but was arrested in Islamabad in February 1995, and was extradited back to the United States to face trial. Many people inside the North Tower were forced to walk down darkened stairwells that contained no emergency lighting, some taking two hours or more to reach safety. Six people were killed, over 1,000 were injured and 50,000 other workers and visitors were left gasping for air within the 110 story towers. The blast opened a 100-foot (30 m) hole through five sublevels with the greatest damage occurring on levels B1 and B2 and significant structural damage on level B3. On February 26, 1993, at 12:17 p.m., a Ryder truck filled with 1,500 pounds (680 kg) of explosives, planted by Ramzi Yousef, detonated in the underground garage of the North Tower in Lower Manhattan, New York City, United States. Main article: 1993 World Trade Center bombing