Display specifications can be complicated, considering there are multiple factors to consider – like resolution, refresh rates, contrast ratio, aspect ratio, display size, and HDR capabilities. When looking at TVs and the source signals they receive, a point of contention is the difference between 1080p and 1080i, and what it means for the average TV owner. Below is a simple explanation of what the differences are and what you need to know about the standards.
Progressive and Interlaced
1080p and 1080i refer to a display resolution of 1,920 x 1,080 pixels, and it is the suffixes attached to the resolution number that you must pay attention to.
The “p” in 1080p stands for “progressive”, while the “i” in 1080i means “interlaced”. These terms refer to the scanning technique used to display, store, and transmit images. Progressive scanning is a common method for displaying video, with entire images displayed a certain amount of times per second.
This depends on the frames per second of the source video and the refresh rate of the TV. Interlaced scanning is different, and involves a technique in which alternating halves of an image are displayed per interlacing “field”. A single frame of interlaced 1080i video consists of two sequential 1920 x 540 images, with the first field consisting of all odd-numbered vertical pixel lines and the second all even-numbered pixel lines.
Both these half-images together create a frame every 30th of a second. This means if a second of 1080i video consists of 30 “1,920 x 1,080” frames, it includes 60 “1,920 x 540 fields”. An important note is that when the source video is 1080i/60, there are in fact no full images – as each of the 60 interlaced fields occupy a different point in time and 30 interlaced frames are displayed per second.
Due to the fidelity and fully-displayed frames, a 1080p video delivers a sharper and more refined image which can provide better quality during scenes with lots of motion. Interlaced video suffers in scenes with lots of motion, as it only displays half an image at a single point in time.
This makes it difficult to display fast movement. Compared to progressive scan, interlaced video has more jagged edges and motion artifacts. Visual quality of 1080i video can also depend on your TV, as some video processors are better at deinterlacing video than others.
Broadcast and Decoding
Currently, DStv broadcasts in 1080i and 720p, and does not offer Full HD quality.
Users who use a 1080p TV to watch DStv are in fact watching deinterlaced 1080i video or a 720p broadcast.
A major reason for 1080i broadcasts is reduced bandwidth requirements and infrastructure limitations.
DStv said in 2016 it would not offer Full HD broadcasts any time soon, as their implementation would require changes to broadcast infrastructure and use more bandwidth than the current broadcast resolutions.
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MultiChoice is focused on expanding its high definition offering on DStv, but currently has no plans to switch to the 1080p standard. DStv currently broadcasts its high definition channels in 1080i, which MultiChoice said offers good-quality viewing to its customers. While both standards have the same number of horizontal lines on screen (1,080), they use different scan types to broadcast and display video.
The “i” in 1080i refers to interlaced scan, which first draws the odd lines of a frame on screen, followed by the even lines. Progressive scan, which is what 1080p uses, draws the lines in sequence. MultiChoice explained that 1080p uses roughly twice the bandwidth of 1080i.
This means that for every one 1080p channel DStv brings on air, it could possibly have launched two 1080i channels instead.
“In the average household, the size of the screen and the positioning of the viewer from that screen means that changing to 1080p won’t make a significant difference in quality of viewing,” said MultiChoice.
Potentially upgrading two channels from standard definition, which in PAL countries like South Africa has 576 lines of resolution, to 1080i therefore has a greater benefit to more DStv subscribers than adopting 1080p.