4K Is The Current Sweet Spot

You probably think I'm going to add to the headline the appendage "for video." 

Nope. 

4K is the sweet spot for still photography. 

Just as a reminder, 4K is 3840 x 2160 pixels (at the 16:9 video ratio). If we normalize that out to the 3:2 aspect ratio, we get essentially 4000 x 2640, or 10.5mp. The 12mp Nikon D3—which will come up again in this discussion—is 12mp, or 4256 x 2832 pixels. Yes, the D3 is still in the sweet spot for photography.

You might have noticed that we blew past 10-12mp quite some time ago with our dedicated cameras. In the past decade we first snuck up on 24mp (10, 12, 16, 24), then just kept going (36, 45, 61). We left the sweet spot behind quite some time ago.

Why do I say the sweet spot is 4K? Because we went from printing images to viewing images. It's the result of what happened with social networking. No longer do we look at 4x6 prints from a photo lab when sharing images with friends, we instead look at them on our smartphones. 

The maximum resolution of an iPhone (Max model) is 2778 x 1284, or 3.5mp. A current iPad Pro is 2732 x 2048, or 5.6mp. Your TV is likely 3840 x 2160 pixels (8.3mp), but not a lot of you are viewing your images on TVs. You might be looking at them on a TV-like monitor when you edit your images; a 5K iMac is 5120 x 2880, or 14.7mp, though once you add your software's windowing and controls, you're probably looking at the actual image being observed back down near 4K. 

So how many pixels do you need? ;~)

This is usually where the "but I crop a lot" discussion comes up. I'm going to set that aside for this article and assume that you're using the right lens with your feet in the right place for your subject; you're using all the pixels in your camera. Here's the number of pixels you need:

  • If you're mostly social sharing you need 4mp, maybe 6mp max.
  • If you're showing images in presentations on screens, you need 8mp, maybe 12mp max.

Which makes that 12mp D3 and D3s look pretty darned good 15 years later, doesn't it? Remember, that camera opened up new territory in low light, had an excellent focus system, featured an all-day battery life, and it could photograph at 11 fps. Do you really need more pixels and more camera today? 

Apparently not, because I still see some pros using their D3s bodies. A D3s still matches up pretty well with a D6 when normalized for output size. And if your output size is social media or even journalism (newspaper, magazine, etc.), 12mp works out to be just fine.

So how many pixels do you need?

I'm going to temper things a little bit and make you feel a little better about buying that 45mp camera. The Bayer mosaic that is in virtually all of our cameras really needs about 1.5x the pixels to account for the interpolation that it has to do to get RGB values for each position. For a 4K display output that would be...wait for it...12.5mp. Dang, there's that D3 again. 

Some believe that you really should have 4x the pixels (the binners) to really pull out everything you can out of a Bayer-based camera. That puts us at 33mp, but I'd say that's it's a rare person that could see any significant difference between a 33mp and 12mp image at 4K output resolution. 33mp is also 8K (;~), which maybe buys you some future proofing for on-screen viewing, though I think we're still quite a ways from 8K screens being affordable, let alone prevalent. (It will happen; never bet against tech's relentless downsizing.)

So how many pixels do you need?

For me, the answer has long been 24mp. Far more than I absolutely need for images that end up on screens, but still capable of making an excellent 13x19" print on a desktop inkjet printer, such as the common Canon and Epson photo printer models. 24mp on a full frame sensor also has some auxiliary benefits over chasing higher pixel counts: mirrorless autofocus in low light benefits from the larger pixel sizes, and I have to worry far less about diffraction impacting my results (and potential acuity gains). Couple that with smaller file sizes (than 45mp), and it's a win, win, win. 

But note what I wrote about the binners and the eventual 8K presence: there's a reason why the Sony A7 Mark IV is 33mp (or the recently announced 33mp Canon R7, for that matter). Coupled with allowing more liberal cropping in the near term, 33mp is probably the new 24mp, because it's 8K friendly. But frankly, I'd be perfectly happy with either 24mp or 33mp right now.

"Okay then, Thom, why are you using a 45mp Z9 and 50mp A1?" Not because of the pixels. It's more because the overall camera is simply better for what I need. That's true of the autofocus systems, frame rates, buffers, and more. All those extra pixels? It worries me that I'll get lazy and start cropping instead of trying to get it right in the camera. That has an impact on perspective. If I'm lazy and don't get closer to the animals/athletes, I'm not getting the perspective that's made my best work, well, my best work. No one ever wants to talk about perspective, but I'm pretty sure that all the images you think are great were driven in some way by perspective choice (or happenstance of perspective in some cases). Perspective is also the reason why I didn't opt to buy an 800mm lens, by the way. I don't like the perspective I'd be using it at (and then there's the issue of heat waves, too; more distance between you and the subject means more heat waves that can influence the results).

All of which brings us to two last subjects regarding how many pixels you actually need.

First, why are the camera makers pursuing more pixels, more pixels, and even more pixels? Iteration, basically. It's what they know how to do. 100mp on a full frame sensor looks a lot different (better) at the micro level than 100mp on a smartphone sensor, too, so the camera companies believe that this is an advantage. The problem, of course, is that this is putting the camera companies further and further away from the primary photography needs of most people, which is sharing images with others. 

Nikon, for instance, realized this when they came up with SnapBridge. Sure, your expensive 45mp camera can talk to your phone. But guess what? By default SnapBridge sends that phone a 2mp image! Exactly what did you need all those extra pixels for? Unfortunately, Nikon hasn't budged from that 2mp marker since the D500 first appeared using it, yet the smartphone resolution has gone up since then. Note what I said was the correct number for social sharing, above (4mp, maybe 6mp). Can't set that using SnapBridge. If the iPad I'm showing my photos on needs 5.6mp and I'm sending it 2mp, just how good do those images actually look? Back when the D500 came out, sure, the best smartphones were typically 1334 x 750 pixels, or 1mp), but that has rapidly moved upscale. Is there anyone in Tokyo that has a clue? Apparently not.

In essence, the camera makers are simply doing what they've always done. We had pixel pushing before smartphones took over the photo market. We went from 2.7mp (D1) to 6mp to 11mp (1Ds) pretty darned fast. Long before the smartphones really took over we were at 12mp. Bigger numbers are easy marketing ("now with twice the pixels!"). And cramming more on a semiconductor is what tech is all about in the first place, so win, win, right? 

Not if it doesn't solve a user problem.

Our last subject about how many pixels you might require is "but I need to print big." 

Hmm. I question the word "need" in that sentence, but let's assume you do. The other word that's important is "big." If both words are true for you, why aren't you using a 100mp GFX or better? ;~)

The current 45/50mp cameras net you a 28" print (300 dpi), and if you use my rule of thumb about how far you can push your pixels in print, you should be able to easily top 40" with a good looking print. Do you really need bigger? And again, there's that "need" word. 

I'm sure there are folk that would still say, yes, this is what they do and what they need (print big). Thing is, those folks are in the minority—really, how many of you made 28" print or larger last year?—and shouldn't really be dictating the mainstream of what's happening in the primary camera market. What's important is that the sweet spot cameras are well designed and perfectly optimized.

So, the final current sweet spots as I currently see them:

  • Screen output: 4K max (8.3mp)
  • Print output: 6K for desktop printers (24mp)
  • Camera input: 6K to 8K max (24mp to 33mp)

Bonus credit: Did you know that the Z6 can take 4K still images at 30 fps with autofocus? (Page 691 of my Z6/Z7 Guide.) 

Just to be complete and clear: more sampling is always better than less sampling. Sampling, as in how many digital pixels per fixed unit of analog size. So technically, higher pixel counts are always better than lower pixel counts. The problem with more sampling, though, is the diminishing returns it brings due to things like diffraction, shot noise, and more. It's almost like an exponential drag we're encountering these days as we increase pixel counts beyond our presentation needs. I eventually sold my 61mp Sony A7R Mark IV because I just didn't see the real world benefit it provided over my 45mp D850, Z7 II, Z9, and 50mp A1. Was there a benefit? Maybe, but it was smaller than expected, wasn't tangible to my work, and probably not to yours, either. 


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