1080i is a high-definition television signal format. Here, "1080" indicates 1,080 horizontal scan lines in the vertical direction, while "i" stands for interlaced scanning—a method of displaying video by alternating between odd and even scan lines. During playback, it first scans the odd-numbered vertical lines, followed by the even-numbered ones, meaning it requires only half the bandwidth of 1080p. Its introduction has had a significant impact on the evolution of the television industry. When displayed in a 16:9 aspect ratio, its resolution is 1080x608.
Relevant Notes
Television picture clarity is measured in terms of horizontal resolution. Simply put, we can imagine dividing the TV screen horizontally into countless scan lines— the finer the division, the sharper the image will appear. Consequently, the more scan lines there are horizontally, the higher the resolution. The unit of resolution is called "TV Line," or simply "line." Conceptually, this means that if you were to stand up each horizontal scan line and lay them side by side, their total number would correspond to the horizontal resolution, adjusted according to the screen's aspect ratio—either 4:3 or 16:9.
Scan format
D1 is in 480i format, matching the clarity of NTSC analog television—525 vertical scan lines, with 483 visible lines, aspect ratios of 4:3 or 16:9, interlaced/60Hz, and a line frequency of 15.25 kHz.
D2 is in 480P format, identical to the progressive-scan DVD standard: 525 vertical scan lines, with 480 visible vertical scan lines, aspect ratios of 4:3 or 16:9, a resolution of 640×480, and operates at 60Hz progressive scan with a line frequency of 31.5 kHz.
D3 is in 1080i format, a standard digital television display mode featuring 1,125 vertical scan lines, with 1,080 visible vertical scan lines, an aspect ratio of 16:9, and a resolution of 1920×1080. It uses interlaced scanning at 60 Hz, with a line frequency of 33.75 kHz.
D4 is in 720p format, a standard digital television display mode, featuring 750 vertical scan lines, with 720 visible vertical scan lines, an aspect ratio of 16:9, and a resolution of 1280×720. It uses progressive scanning at 60Hz, with a line frequency of 45 kHz.
D5 is in 1080p format, a standard digital television display mode featuring 1,125 vertical scan lines, with 1,080 visible vertical scan lines, an aspect ratio of 16:9, and a resolution of 1920×1080 progressive scan—making it a professional-grade format.
Additionally, there's 576i, the standard PAL television display format—with 625 vertical scan lines, 576 visible vertical scan lines, and an aspect ratio of either 4:3 or 16:9. It uses interlaced scanning at 50 Hz, and is denoted as 576i or 625i.
The "i" in the standards above stands for interlaced, while "P" denotes progressive scanning. HDTV is a high-quality video signal standard that includes formats such as 1080i, 720p, and 1080p—meaning D3, D4, and D5 fall under the HDTV category. However, even devices currently supporting 480p are often loosely referred to as being HDTV-compatible. It’s important to note that the requirements for TV set processing capabilities (such as bandwidth) remain distinct.
480i < 576i < 360p < 720i < 480p < 1080i < 720p.
High-definition television
1080i and 1080p are high-definition standard formats defined by the Society of Motion Picture and Television Engineers in the U.S. Among them, 1080p is currently regarded as the top display format for digital TVs, delivering a resolution of 1920×1080 when using progressive scanning. However, due to limitations imposed by storage media—since a single 1080p movie typically requires over 10GB of space—most 1080p films are now primarily distributed via Blu-ray discs. As Blu-ray players and HD media devices become more widespread, downloading high-definition content from the internet has steadily increased. Meanwhile, the emergence of software like KMPlayer and PotPlayer, along with enhanced HD playback capabilities in popular players such as PowerDVD and WinDV, coupled with the growing availability of domestic HD TV channels, has significantly boosted public awareness of high definition. Indeed, many people have even developed a passionate "HD obsession."
When HDTV is mentioned, many people assume it’s simple—just 720P or 1080i, with 1080P being the most advanced option. But here’s the thing: most folks aren’t actually aware of the distinction between 1080i and 1080P when it comes to flat-panel TVs. And even fewer realize that 720P isn’t a standard used by mainstream broadcasters—only a handful of U.S. TV networks still rely on it. Unfortunately, many misconceptions about high-definition technology have spread by word of mouth, leading to widespread confusion. Even the very definitions of 720P, 1080i, and 1080P are often misunderstood. So let’s dive deep into the origins of these terms, debunk some common myths about HD, and finally uncover what high definition truly means.
Get to know HD
In 720i and 1080i, the "i" stands for "interlace," referring to interlaced scanning; "P" represents "Progressive," indicating progressive scanning. To fully explain these terms, we need to start with traditional CRT televisions. In conventional CRT TVs, images are displayed by an electron beam that scans the screen line by line, causing the phosphors to emit light. However, during signal transmission, TV signals are constrained by bandwidth limitations, so only interlaced signals can be efficiently sent to save bandwidth. For example, in NTSC TVs, a single 525-line image is divided into two fields: the first field, called the odd field, scans only the odd-numbered lines (1, 3, 5, etc.), while the second field, the even field, scans just the even-numbered lines (2, 4, 6, etc.). Together, these two fields complete the full frame of 525 lines. Because the human eye has a phenomenon known as visual persistence, our brain perceives this sequence as a continuous, complete image—this is how interlaced scanning works. NTSC-standard programs feature 525 scan lines and 60 frames per second, typically denoted as 60i or 525i. If the scanning is done progressively—line by line—then it’s referred to as 60P or 525P. Similarly, PAL systems use 625 lines and operate at 50 frames per second, labeled as 50i or 625i for interlaced formats, and 50P or 625P for progressive formats. This explanation specifically applies to CRT-based televisions.       
Method of representation
It represents not only the scanning format of CRT televisions but also the format of images captured by camcorders. Since early television systems all used interlaced scanning, cameras designed to shoot NTSC and PAL TV programs were inherently interlaced as well. In other words, any program filmed with a TV camcorder—whether in NTSC or PAL format—will output an interlaced signal, typically denoted as 525/60i for NTSC and 625/50i for PAL. Keep in mind, though, that this applies specifically to TV camcorders.
For analog TV images, which are represented by scan lines, the PAL system is denoted as 625/50i, while NTSC is represented as 525/60i. In contrast, digital signals are described using pixels or resolution metrics. For instance, a PAL-format program has a resolution of 720×576; when displayed progressively, it’s labeled as 576P, and when interlaced, it’s 576i. Meanwhile, an NTSC program boasts a resolution of 720×480—progressive displays are referred to as 480P, while interlaced displays are 480i. This applies specifically to television images.
"Alright, I’ve said quite a bit here—some of it almost sounds like a tongue twister, and admittedly, it might feel a bit repetitive. But when it comes to understanding the concepts of HD 720P, 1080i, and 1080P, it’s absolutely essential. After all this explanation, you should remember that grasping HD—and specifically the distinctions between 720P, 1080i, and 1080P—involves looking at three key aspects: the TV itself, the camera used to capture the footage, and the actual image format. These three elements are distinct yet interconnected, forming the foundation of how we perceive high-definition video."
High-definition definition
High-definition television, also known as HDTV, is defined by the CCIR International Radio Consultative Committee as having an aspect ratio of 16:9. When viewed from a distance three times the screen's height, the image should appear seamless and closely resemble the actual object being displayed.
According to the definition of the ITU International Telecommunication Union, HDTV offers approximately twice the resolution—both horizontally and vertically—compared to conventional television sets, with an aspect ratio of 16:9. Subjectively, its image quality is comparable to that of interlaced-scan HDTV studio standards.
In terms of image formats: apart from a few individual U.S. television stations that have adopted 1280×720 as the HDTV standard, virtually all other countries worldwide—including China, Europe, Australia, Japan, and South Korea—have embraced the new-generation high-definition optical discs, HD DVD and Blu-ray, both standardized at a resolution of 1920×1080. Surprisingly, no country outside the U.S. has yet adopted the 1280×720 standard. However, this still doesn’t explain how the concepts of 720p, 1080i, and 1080p came into being. So, dear readers, please don’t rush—take your time and keep reading. Nowadays, when people hear “high definition,” they immediately think of flat-panel TVs like LCDs and plasma displays. Yet the origins of today’s HD standards actually date back to the 1980s, with the official U.S. HD standard finally established in the 1990s—more than two decades ago. At that time, flat-panel TVs hadn’t even emerged yet. The standards were initially developed with CRT televisions in mind. That’s precisely why the current terminology of 720p, 1080i, and 1080p carries such a strong legacy tied to the CRT era.
High-Definition Analysis
Considering the technological limitations of CRT TVs at the time, and to align with the computer industry's preference for progressive-scan displays, CRTs used a progressive-scan system when displaying images at 1280×720—commonly referred to as 720p. Meanwhile, for 1920×1080 resolutions, CRTs employed an interlaced system, abbreviated as 1080i. Back then, it was simply not feasible to manufacture CRT TVs capable of displaying 1080p content; such 1080p CRT models didn’t emerge until the 21st century. This is how the concepts of 720p, 1080i, and 1080p came into being.
However, CRTs have now been phased out, replaced entirely by flat-panel TVs. As for LCD and plasma TVs, they are classified as fixed-pixel display devices—meaning they don’t require scanning to show images, and each pixel essentially lights up simultaneously. If we were to draw a parallel with interlaced versus progressive scanning, it’s fair to say that most LCD and plasma TVs actually use progressive scanning. But does this mean that the 720p, 1080i, and 1080p resolutions can be eliminated? The answer is no, because there’s still another crucial factor to consider: the format used by cameras.
Camera angle
While high-definition cameras are digital, their scanning method is inherited from analog cameras. Traditional analog cameras exclusively used interlaced scanning, whereas high-definition cameras not only retain the interlaced format but also introduce an additional progressive-scan option.
High-definition cameras not only retain the distinction between interlaced and progressive scanning but also preserve the differences between the PAL system's 50Hz frequency and the NTSC system's 60Hz frequency. Although HD no longer strictly differentiates between PAL and NTSC, regions like the U.S., Japan, and South Korea—historical NTSC territories—still maintain the 60Hz frequency system, while countries such as China, Australia, and Europe continue to rely on the 50Hz system. Since HD programs are entirely digital signals, they can be described simply by their resolution. When shooting HDTV content, filmmakers typically choose between two scanning methods: interlaced and progressive, each with distinct frame rates (the number of progressive frames displayed per second) or field rates (the number of interlaced fields shown per second).
1280x720 resolution offers five frame rates: 60P, 50P, 30P, 25P, and 24P. These can be abbreviated as 720P, and are also represented individually as follows: 720/60P (used by U.S. broadcaster ABC), 720/50P, 720/30P, 720/24P (adopted by FOX), and 720/25P. Notably, the 720/50P and 720/25P formats were not originally part of the standard—instead, they emerged later when Germany was considering its HD image format standards. Recognizing that Germany traditionally operates on a 50Hz system, some manufacturers introduced cameras supporting 720/50P and 720/25P. However, these formats never gained widespread adoption globally; at most, they remained a topic of discussion rather than a practical standard.
The situation becomes even more complex with 1920×1080 resolution: interlaced formats are denoted as 1080i, while progressive formats are labeled as 1080P. In the U.S. and Japan, where the field rate is 60 Hz, it’s represented as 1080/60i; however, in China, Europe, and Australia, it’s 1080/50i—and both of these formats are commonly referred to as 1080i. But that’s not the end of it. To streamline the production and distribution of high-definition content worldwide, a unified standard of 1080/24P has been adopted. This standard has also become the industry benchmark for digital cinema cameras. Notably, the acclaimed "Star Wars Prequel" trilogy was filmed using 1080/24P cameras, and many popular HD TV series, such as "Da Zhai Men," were also shot in this 1080/24P format.
Resolution
However, plasma displays are a whole different story. The 42-inch plasma models come in four different resolutions: 852×480, 1024×768, 1024×1024, and 1024×1080—none of which meet the national high-definition standards. Only the 50-inch plasma model complies with the HD specifications. Even more confusingly, the 1024×1024 and 1024×1080 plasma panels don’t use progressive scanning; instead, they alternate between interlaced fields. This is precisely why it’s often stated that LCD and most plasma TVs actually employ progressive scanning. But here’s the good news: you don’t need to worry about this at all, as even interlaced display doesn’t significantly affect the viewing experience.
In flat-panel TVs—especially some plasma models that don’t meet the national high-definition standards—advertisements still claim these sets deliver 1080P resolution. However, this "1080P" refers to a different concept than the one we discussed earlier. Take Panasonic’s 42PA60C as an example: while its physical resolution is only 852x480—a specification that falls short of the HD standard—the "1080P" Panasonic touts means the TV can receive 1920x1080i signals and upscale them to display in 1920x1080p format. Yet, since the 42PA60C’s native resolution is limited to 852x480, it can’t fully render all 1920x1080 pixels. As a result, the high-definition image is first downscaled to 852x480 before being displayed on the 42PA60C. In this case, calling it "1080P" isn’t entirely accurate; instead, it should be described more precisely as "compatible with 1080P."