1080i

1080i is a term used in high-definition television (HDTV) and video display technology. It means a video mode with 1080 lines of vertical resolution. The "i" stands for interlaced scanning method. This format was once a standard in HDTV. It was particularly used for broadcast television. This is because it can deliver high-resolution images without needing excessive bandwidth.

Definition

The number "1080" in 1080i refers to the number of horizontal lines that make up the vertical resolution of the display. Each of these lines contributes to the overall detail and clarity of the image. The letter "i" stands for interlaced. This is a technique where the image is not displayed all at once. Instead, the frame is split into two fields. One field contains the odd-numbered lines, and the other field contains the even-numbered lines. These fields are displayed in rapid succession, giving the appearance of a full image to the human eye. The interlacing technique was developed to improve the motion portrayal of images without doubling the required bandwidth. This is particularly useful in broadcasting, where bandwidth efficiency is crucial. The frame rate is typically 50 or 60 fields per second, depending on the region. This effectively means 25 or 30 frames per second when the fields are combined.

Comparison with 1080p

A key difference between 1080i and 1080p is how the lines of resolution are displayed. Both offer 1920x1080 pixels, but the display method is different. In 1080p, the "p" stands for progressive scan. Each frame is drawn line by line, from top to bottom, creating a complete image in a single pass. This results in a sharper and more stable picture, especially in fast-moving scenes. On the other hand, 1080i uses an interlaced method. The two fields that make up a frame are captured at slightly different times, leading to a misalignment in fast-moving parts of the image. This can cause artifacts like "combing," where fast-moving objects appear to have a serrated edge. However, 1080i has been preferred in broadcast television due to its lower bandwidth requirements, making it more efficient for over-the-air or cable transmission.

Historical context

The origins of 1080i can be traced back to the late 1990s and early 2000s. This was a time when the world was transitioning from standard-definition television (SDTV) to high-definition television (HDTV). Consumers wanted better image quality. They began to purchase larger televisions and expected more detailed and immersive viewing experiences. In this context, 1080i emerged as a leading standard for HDTV broadcasts. Many broadcasters worldwide adopted it. This was particularly true in regions using the ATSC (Advanced Television Systems Committee) standard in North America and the DVB (Digital Video Broadcasting) standard in Europe. These standards allowed for the transmission of 1080i video signals. This made it possible for viewers to enjoy high-definition content on their HDTVs. The adoption of 1080i was particularly significant in sports broadcasting. The higher resolution allowed for more detail and clarity, especially in large stadium shots and fast-paced action. The format's efficiency in utilizing available bandwidth made it a practical choice for broadcasters. However, it required more complex processing on the receiving end to deinterlace the image for display on progressive-scan screens. Overall, 1080i played a crucial role in the early days of HDTV. It bridged the gap between standard-definition broadcasts and the high-definition future that would soon become the norm. While its use has diminished with the rise of 1080p and 4K resolutions, 1080i remains an important milestone in the evolution of television technology.

Technical overview

1080i is a high-definition video mode. It offers a detailed and efficient way to display video content, especially in broadcast television. This section will discuss the technical aspects of 1080i, such as its resolution, the interlacing process, common frame rates, and signal transmission standards.

Resolution

The core of 1080i is its resolution. The resolution is 1920x1080 pixels. This means that each video frame has 1,920 pixels horizontally and 1,080 pixels vertically. This results in over two million individual pixels per frame. This high resolution is why 1080i is called "high-definition". It offers a significant improvement over standard-definition formats, which typically have much lower pixel counts. The 1920x1080 resolution allows for greater detail and clarity in images. This makes it ideal for larger screens where higher pixel density is essential to maintain image quality. The increased resolution is particularly noticeable in fine details such as textures, text, and intricate patterns. These can be rendered with much greater accuracy than in lower-resolution formats.

Interlacing

The "i" in 1080i stands for interlaced. This refers to how each video frame is displayed. Instead of showing the entire frame at once, the interlacing technique divides each frame into two separate fields. The first field contains all the odd-numbered lines (1, 3, 5, etc.), and the second field contains all the even-numbered lines (2, 4, 6, etc.). These two fields are displayed one after the other. The odd lines are shown first, followed by the even lines. This happens very quickly, around 50 or 60 fields per second. The human eye sees these two fields as a single, continuous image. The main advantage of interlacing is that it allows for a higher frame rate without needing more bandwidth. This results in smoother motion, especially for content with moderate to fast movement, like sports broadcasts.

An example frame of poorly deinterlaced video. Despite the fact that most TV transmissions are interlaced, plasma and LCD display technologies are progressively scanned. Consequently, flat-panel TVs convert an interlaced source to progressive scan for display, which can have an adverse impact on motion portrayal.

However, interlacing also has some drawbacks. Since the two fields are captured at slightly different times, fast-moving objects can appear misaligned between the two fields. This creates a visual artifact called "combing." This can reduce image quality, especially in scenes with a lot of motion. Modern display devices often use deinterlacing algorithms to combine the two fields into a single progressive image before displaying it.

Frame rate

The frame rate of 1080i is usually 50 or 60 Hz. It depends on the region. In areas using the PAL or SECAM standards, like Europe and parts of Asia, the frame rate is 50 Hz. In regions using NTSC, like North America and Japan, the frame rate is 60 Hz. The frame rate refers to how often a new field is shown per second. At 50 Hz, 50 fields are shown each second. This results in 25 full frames per second when the odd and even fields are combined. At 60 Hz, 60 fields are shown per second. This results in 30 full frames per second. Interlacing affects how motion is perceived in 1080i. Since each field represents a slightly different moment in time, motion can appear smoother compared to lower frame rate progressive scans. However, this also means 1080i can struggle with fast-moving scenes. The interlaced fields might not perfectly align, leading to motion artifacts.

Signal transmission

The 1080i video signals are governed by broadcasting standards like ATSC in North America and DVB in Europe and other parts of the world. These standards define how digital TV signals are encoded, transmitted, and decoded, ensuring efficient broadcast and reception of 1080i content. ATSC is used primarily in the US, Canada, Mexico, and South Korea. It specifies the digital transmission of high-definition video, including 1080i, over the airwaves. This standard replaced the older NTSC analog system and brought HDTV to a wide audience, with 1080i being one of the main formats supported. DVB is a family of standards used in Europe, Australia, and other regions. DVB-T (terrestrial) and DVB-S (satellite) are the most common implementations, both supporting 1080i as a broadcast format. These standards ensure efficient transmission of 1080i content, enabling the delivery of HD content to millions of households using existing infrastructure. In both ATSC and DVB systems, the 1080i signal is compressed using codecs like MPEG-2 or H.264 to reduce the bandwidth required for transmission. The signal is then transmitted to viewers' homes, where it is decoded by television sets or set-top boxes, which then display the interlaced video on the screen.

See also

• Field (video)
• High-definition television in the United States
• Interlaced video
• List of common resolutions
• Sony HDVS Wideband Analog Video
• Telecine
• Other common resolutions: 4320p  • 2160p  • 1080p  • 720p  • 576p  • 576i  • 480p  • 480i  • 360p  • 288p  • 240p

External links

• High Definition (HD) Image Formats for Television Production (EBU technical publication)