Have you ever wondered what the ‘p’ stands for in 720p? What about the ‘i’ in 1080i? They stand for progressive scan and interlaced respectively, but what do those terms actually mean? We’ll be defining both as well as weighing which is better and why. Let’s get started by comparing the definitions.
Interlaced vs progressive scan
Progressive vs interlaced explained
To see how these two terms compare and contrast, we’ll start by defining them individually. If you encounter any other unfamiliar terms, be sure to check out our guide to filmmaking vocabulary and our glossary of cinematography terms to learn more.
PROESSIVE AND INTERLACED DEFINITIONs
First, what is progressive?
Progressive is one of two primary scanning methods used in the transmission of broadcast television signals. Progressive scan indicates the specific pattern that lines of visual information are displayed across the viewer’s TV screen. With progressive scanning, all of the lines that make up a single frame are transmitted at once.
Second, what is interlaced?
Interlaced is the alternative scanning method to progressive scan. With interlaced scanning, lines of visual information are alternated as odds and evens. Only half of a frame’s visual information is broadcast at a time (i.e., the even lines will be displayed on a viewer’s screen, THEN the odd lines will be displayed; not simultaneously).
Difference Between Interlaced and Progressive Scan:
- Two different methods for broadcast scanning
- Progressive-scan displays all lines at once
- Interlaced-scan displays half of the lines at a time
Interlaced Refresh Rate
Image scanning over the years
The distinction between these two scanning methods was more important during the days of CRT TVs and the height of broadcast television. Interlacing images began as something of a compromise to the high demands of television broadcasting of the time. In the digital age, interlaced scanning is a thing of the past in all but a few select areas.
Progressive scan became the standard in the 1990s after decades where both scanning methods found consistent use on television screens. As technology improved and standard definition broadcasts were phased out, so too was interlaced scanning.
Interlaced vs Progressive Refresh Rate
The case for interlaced
Broadcasting interlaced video was cheaper than broadcasting progressive-scan images but also resulted in lower quality images with a higher risk of artifacting, flickering, and other visual imperfections.
With only 50% of the broadcast lines visible at any given time, the transitions between the odd and even lines often resulted in inferior images. But, the switching back and forth between odd and even lines happened so quickly — about 60 times per second — that the human eye perceives a full image rather than two half-images in close proximity.
Interlacing also conserved bandwidth at a time where it could be in short supply. The technical savings were so significant that a station may have been able to broadcast interlaced footage at a 1080i resolution while only being capable of broadcasting progressive-scan footage at a 720p resolution. Interlaced scanning represented a compromise between accessibility, visual fidelity, and image quality.
It often came down to a case-by-case basis whether or not individuals considered the savings of interlaced scanning worth the drawbacks. Certain types of programs like soap operas and news broadcasts were considered worth the costs of interlaced broadcast. While other types of programs like major television shows or films broadcast on television may have opted for progressive scan to retain the highest visual fidelity possible at the time.
Is Progressive Scan Better than Interlaced
The case for progressive-scan
Progressive scanning ate up more bandwidth and was more costly but also resulted in a much higher quality image presented for each individual frame. Progressive-scan broadcasts were the clear choice for anyone prioritizing quality and visual fidelity.
In the modern age, it’s not much of a choice between the two scanning methods. Interlaced scanning is best to be avoided whenever possible, and that’s pretty easy to do these days.
What is the 4:3 Aspect Ratio?
You now know what the ‘p’ and ‘i’ stand for in TV displays. Even though the distinction between progressive scan and interlaced has become a bit moot over the years, not every television technical limitation of old has become obsolete. Learn why some filmmakers choose to continue using the 4:3 aspect ratio formerly required by television screens despite the widespread adoption of widescreen televisions, up next