For many decades television resolution and broadcast standards were defined by vertical resolution. This is the number of alternating black and white horizontal lines that could be clearly seen during broadcast.
NTSC traditionally was 525 lines, and PAL 576 lines.
720p & 1080p
Fast forward to mainstream flat panel HD displays, and they are advertised as 720p (early HD - a resolution of 1280 x 720 pixels), and 1080p (full HD - a resolution of 1920 x 1080 pixels).
The advertised 720p and 1080p continue to reference the number of vertical rows that were being squeezed into the screen.
Why 4K is deceiving
The name 4K gives the impression that there are four times more vertical lines on screen than 1080p.
However, this is not so.
The true screen resolution of 4K is 3840 x 2160. If you apply the same naming convention used on 720p and 1080p, we’d not call a screen 4K, but instead “2160p”.
Instead, of using the vertical number of rows as had previously been done in 720p and 1080p naming, 4K adopts the horizontal number of rows for its name.
The marketing term 4K refers therefore to the horizontal resolution (the number of vertical rows lined up side-by-side on screen) - which is close to 4000.
The 8K monitor also derives its name from its horizontal number of pixels 7680 x 4230 resolution.
It certainly is clever to use 4K and 8K for naming, it sounds better than 2106p and 4230p.
However, exactly how deceptive this marketing strategy remains a bit unclear.
The history of television display resolutions and computer display resolutions is actually far more complicated the more one looks into it. ('Why did television CRT advertise vertical resolution, vs computer CRTs? Was it always the same? Did this shift at some point? What really is the display resolution? How does it differ from frame size? and from pixel size? What is a ‘pixel’?)
Furthermore, now that televisions displays and computer displays actually overlap in many ways, this just adds to the complexity given that computer displays typically advertise their horizontal pixels.
Because computer monitors had a higher resolution than that of traditional television (For instance a 1280 x 1024 monitor has 1024 vertical rows of pixels), NTSC 525 line broadcast was converted into an equivalent frame size of about 720 horizontal x 486 vertical pixels (known as the D1 standard). If anyone recorded digital video footage in the early 2000s or made NTSC DVDs the frame size used was 720 x 480.
The number 720 at this time was a bit confusing, because 720 in NTSC DVD frame size was the horizontal number of rows on standard NTSC DVD…but the term 720 was then also being used around then for 720p HD display…but at that time using the vertical rows….not the frame size.
Consider also reading in this series:
- Part 1 : UI/UX: Writing X vs Y dimensions
- Part 2: Why are phone dimensions backwards: Height x Width ?
- Part 3: Why 4K is misleading (this article)
- Part 4: When is a pixel not a pixel? pixels, points, dps
Some background reading
For an excellent background on 720p and 1080p
History of NTSC and PAL Video Standards
4K Resolution (source of cover image)
Hid Definition Television
Cathode-ray tube (first invented in 1890s and improved in 1920s)
History of computer monitor (first touch screen built in 1965!)
Comparison of computer display standards
Technical overview of vertical and horizontal screen resolution on TVs