Resolutions Explained: Where the Numbers Come From, and How to Use Them

Resolutions Explained: Where the Numbers Come From, and How to Use Them

Every figure on a display spec sheet has an odd history behind it. Here’s where they came from, and how to turn them into the right screen.

1080p. 4K. 1366 × 768. P2.5. These figures get quoted constantly and explained almost never, and because people treat them as shorthand for quality, resolution is one of the easiest things in this industry to overspend on.

Here’s the odd part: hardly any of them were picked because they looked best. They were inherited. The 1,080 is a leftover from Japanese analogue television. The 4K isn’t really 4K at all, but a cinema term the marketing department borrowed. The 1366 × 768 exists because of the size of a memory chip. Only P2.5 means exactly what it says. As we’ll come to, that is what makes it the most useful number of the lot.

What a Resolution Actually Measures

A resolution is just a pixel count, written as width by height. Full HD is 1,920 × 1,080, so a little over two million pixels.

On its own, that figure tells you almost nothing. A resolution only means something once you divide it by a physical size and a viewing distance. Two million pixels on a 24-inch monitor and two million pixels spread across a 100-inch video wall are completely different propositions.

And there’s a hard limit at the end of it. Someone with 20/20 vision can pick out detail down to roughly one arcminute, or a sixtieth of a degree. Past that point the extra pixels are simply invisible, and you’re paying for detail nobody in the room can see.

Where the Numbers Came From

Why 16:9 is a compromise, not a preference

By the mid-1980s, cinema had splintered into a dozen different shapes, from 4:3 television all the way out to 2.35:1 CinemaScope, and any new broadcast standard was going to have to live with all of them. In 1984 Dr Kerns Powers, working with the SMPTE group on high-definition production, tried something refreshingly physical. He cut out rectangles of equal area in each of the competing ratios and stacked them up with their centres aligned.

Every one of them fitted inside a rectangle of about 1.77:1, and every one of them contained one too. That is 16:9. It isn’t the shape of human vision or anything so poetic; it’s the geometric mean of the extremes, the compromise that suits nothing perfectly and everything tolerably.

1,080 lines, left over from analogue Japan

NHK started work on an analogue high-definition system called Hi-Vision back in 1979. It ran on a 1,125-line scan, of which 1,035 lines carried actual picture. When broadcasting went digital in the 1990s, the standards bodies wanted to stay compatible with all that existing kit, and 1,080 was the round number that fitted neatly inside the old structure.

The 1,920 is far less mysterious. Once you have settled on 1,080 lines and a 16:9 frame, square pixels leave you no choice: 1,080 × 16 ÷ 9 comes to exactly 1,920. Run the same sum on 720 lines and you get 1,280, which is where 720p comes from.

How 4K got its name

The “K” comes from digital cinema, where it meant 1,024 in the computing sense, so genuine DCI 4K is 4,096 pixels across. The 4K everyone actually buys isn’t that at all. Ultra HD is 3,840 × 2,160, a number chosen because it is exactly double Full HD in both directions and therefore scales HD content without any messy fractions. Strictly speaking, it’s about 3.8K. The marketing department borrowed the cinema name because it sounded better than “Quad Full HD”, and it stuck.

8K works the same way, doubling again to 7,680 × 4,320. 5K is the odd one out at 5,120 × 2,880, and it came from the professional monitor world rather than broadcast.

1366 × 768, the one nobody planned

This is the purest example of a number with no design logic behind it whatsoever. The 768 was carried over from XGA, the 1,024 × 768 panels manufacturers were already tooled up for, so going widescreen meant widening the panel rather than retooling the line. The trouble is that true 16:9 at 768 lines works out at 1,365.33 pixels, which isn’t a whole number. 1,366 divides cleanly by two and keeps the frame buffer just above 1MB, which mattered a great deal given the memory chips of the day. So 1,366 it was, and it has sat 0.05% off true 16:9 ever since.

What film measures instead of pixels

It is worth understanding where those cinema numbers came from in the first place, because film does not really have a resolution. There are no pixels on a negative. What you get instead is grain, and how much detail a frame can hold depends almost entirely on how large that frame is. Scan a strip of film at higher and higher resolutions and there comes a point where you stop recovering detail and start photographing the grain itself. The figures below are roughly where that happens, which is why they are always quoted as estimates rather than specifications.

The reason IMAX sits so far ahead is not clever engineering. Its 15-perforation frames run through the projector sideways, giving each one close to ten times the area of a standard 35mm frame. More negative, more detail. That relationship between physical area and detail is the same principle this whole article rests on, and it is why a 4K image looks superb on a 43-inch screen and distinctly ordinary stretched across a video wall.

The Three Things People Call “Resolution”

Most disappointing installations come down to muddling three separate figures that all get called resolution. They are not the same thing, and a display is only ever as sharp as the weakest of them.

Native resolution: the panel itself

This is the fixed, physical grid of pixels built into the screen, and it is the one figure you cannot change. Every other resolution has to be scaled to fit it. That scaling is the bit worth understanding, because it is where softness comes from. A 4K panel showing a 1080p image doubles every pixel exactly, which is clean and invisible. Feed the same panel something at 1,366 × 768 and it has to interpolate across awkward fractions, which is why text starts to shimmer and edges go fuzzy.

Signal resolution: what actually reaches the screen

This is what the media player, PC or matrix is genuinely putting down the cable, and it quietly caps everything downstream. A 4K panel fed a 1080p signal is a 1080p display that cost more. It is a surprisingly common problem, because nothing on screen tells you it is happening.

The usual culprits are an underpowered media player, a long or low-grade HDMI run, or a splitter and matrix in the chain that only handles 4K at 30Hz. Worth checking the whole path rather than assuming the panel spec is what you are getting.

Content resolution: the artwork you supply

This is the pixel dimensions of the images, video and web pages actually being shown, and it is nearly always the weak link. It is also the cheapest to get right. An image only 1,280 pixels wide, stretched across a 4K video wall, looks exactly as soft as it sounds, and no amount of processing will put back detail that was never captured.

Build content at the native resolution of the screen it is going on, not at whatever size the source file happened to be. And keep logos, type and flat graphics in vector wherever you can, because vector artwork has no fixed resolution at all and stays crisp at any size, on any panel.

Specifying a beautiful fine-pitch wall and then feeding it images pulled off a website is the most expensive mistake in digital signage, and by some distance the most common.

P2.5: The One Number That Means What It Says

Which brings us back to the figure from the opening line. On an LED display nobody leads with resolution; they quote pixel pitch. And unlike everything else on this page, it carries no history whatsoever. P2.5 is 2.5 millimetres from the centre of one LED to the centre of the next. No committee, no rounding, no borrowed marketing term. Just a measurement.

Resolution then falls out of the pitch and the physical size, so a wall three metres wide at P2.5 works out at 1,200 pixels across. But the pitch is the number to hold on to, because it does something no resolution figure can.

It tells you how close people can stand. Apply that one-arcminute limit and you get a distance of pitch × 3,438, which converts into a rule you can do in your head: the pixel pitch in millimetres is roughly the closest comfortable viewing distance in metres. A P2.5 wall looks flawless from about 2.5 metres. A P10 outdoor screen wants around ten.

What the P numbers actually run to

Pitch runs from well under a millimetre up past ten. Our own LED range covers roughly P0.78 to P6 for indoor work, with outdoor cabinets stretching out to P10.

You’ll notice some oddly specific figures in there: P1.875, P1.59, P3.076. Those aren’t marketing inventions. Pitch is dictated by the cabinet, because a panel has fixed physical dimensions and a fixed grid of LED modules, so the pitch is simply the cabinet width divided by the number of pixels across it. A 600mm cabinet carrying 320 pixels gives you 1.875mm and there is nowhere to round to. Anything below about 2.5mm is generally described as fine pitch.

Worth knowing that halving the pitch roughly quadruples the number of LEDs in the same area, and the price follows. Which is why the useful question is never “what is the finest pitch available?” but “what is the coarsest pitch that still looks perfect from where people actually stand?”

Outdoor is a different specification, not just a bigger pitch

Outdoor screens sit at coarser pitches, and that is entirely appropriate. Nobody stands two metres from a roadside display, so a P8 or P10 cabinet resolves cleanly at the distance it is genuinely viewed from and costs a fraction of what fine pitch would.

But pitch is only part of the story. An outdoor-rated cabinet is a different product, not an indoor one in a box.

• Indoor LED typically runs somewhere between a few hundred and 1,500 nits. Outdoors you are competing with daylight, and anything much under 5,000 nits will wash out. Our outdoor cabinets run from 5,500 up to 12,000 nits, with automatic dimming so the same screen isn’t blinding at midnight.
• Look for a stated IP rating on the rear face as well as the front. Rain, dust and insects all find their way in from behind.
• Temperature and humidity. Proper outdoor cabinets are rated for real weather, typically −20°C to 60°C and in some cases −40°C to 80°C, at 10–90% humidity.
• The LED packages themselves are potted and coated differently for outdoor use. You cannot make an indoor panel outdoor-capable by building an enclosure around it. It will fail, usually in its first winter.

So if a display is going anywhere it can be rained on, sit in direct sun or drop below freezing, it needs to be outdoor rated from the outset, not adapted later.

What to Do With All This

• Start with viewing distance, not the spec sheet. How close can someone realistically get? That answer sets the finest pitch or density worth paying for, and anything beyond it is money spent on detail nobody can see.
• Check the whole chain. The player, the cabling, any matrix or splitter and the software all have to carry the resolution you have bought, at the refresh rate you want.
• Mind the content. This is nearly always the weak link, and the cheapest thing to fix. Build artwork at the screen’s native resolution and keep logos and text in vector.
• Don’t over-buy. On most commercial installations, a well-specified 4K professional display, or an LED wall at the right pitch, will beat a higher-resolution product fed poor content.

None of these figures measure quality. They measure pixel count, and pixel count only turns into quality once you have divided it by size and distance. Which is why the first question is never really “what resolution do I need?” but “how close will people be standing?”

If you need support on a project, or just want to know a bit more, feel free to Contact us.