What is the point of 4k on small display?

I agree with your broad point about the variability of human vision, but printing isn't (usually) a good point of comparison -- at least in the case of continuous tone printing (I'll get to the case of line art below). Printers can't generally produce continuous tones in the way that monitors can, by modulating light output (for OLED) or transmission (or LCD) displays. They can print a dot or not at any given point on that grid.

(That's not entirely true either. Photo printers can generally produce ink of 2 or 3 shades of gray, cyan, and magenta, and often they can generate 2 or 3 different drop sizes, so they may really have a palette of maybe 4-6 different darknesses. But that's a far cry from 256 or 1024.)

The way photo printers generate what looks like continuous tone is by modulating the fraction of dots on that grid that are covered by ink. So when one talks about 2880x1440 DPI, say, that doesn't mean that you can actually reproduce different shades of magenta in the form of lines spaced 1/2880" apart. What higher printed resolution does -- up to a point, depending upon the size of drops you can use -- is allow you to distinguish shades of color in smaller areas, or achieve sharper transitions between areas of a given shade. In practice, above about 200 DPI or so you won't see pixelation even at something like 5760x2880 DPI; there simply aren't enough dots in the grid to resolve colors at anything finer than that.

The exception, as I noted above, is for line art -- true black and white printing, when you're not trying to reproduce shades of gray (black text is line art of a kind). And yes, in some cases you can easily distinguish between line art rendered at 2880 DPI with that rendered at 1440 DPI. Think of a very narrow line at a very shallow angle from vertical or horizontal, or a disk of radial lines spaced 1 degree apart. If the line is a hairline (the narrowest possible line), you'll easily see stair stepping behavior, and in the case of a radial disk, you'll see moire patterns that extend further from the center at lower resolution (and if the resolution is asymmetric, which is very common -- 2880x1440 or 5760x1440 DPI, you'll see asymmetric moire patterns). Remember, you can't anti-alias, because each dot position either contains a dot or it doesn't; we can't lay down a dot at 1/256 darkness. At 2880 DPI we're only using the smallest drops the printer can print.

But this is a special case; text, even though it's typically rendered in pure black and white, just doesn't contain the kind of patterns that are sensitive to this. 600 DPI on a laser printer is usually quite high enough for any text output.

Bottom line, comparisons between printing and light emitting monitors simply aren't very useful in this regard.

 

Point(s) taken.

How sensitive the eyes can be though is what I was trying to convey with that possibly poor example...

I don't believe you're right though with how many shades a (good) printer is capable of. While a single ink is limited to how many shades it can produce, the possibility of mixing them is almost infinite.

See:
http://www.rit-mcsl.org/fairchild/WhyIsColor/Questions/6-7.html


Have a look at that image of a single dark gray dot (R = G = B = 50) in the link above.

Monitors can't touch this. They are much more stair stepped than a fine print can be.

 

Ink can be mixed. Unfortunately it's not a well controlled process (as the irregular shape of the ink patches would hint). There are good reasons printer designers focus on adding more independent colors instead of relying on the mixing. Stabilizing voltage or PWM window at a certain level is much easier.

I do agree with your conclusion, at least in a semi-quantitative sense.

 

A typical Epson inkjet has maybe 8 colors (3 shades of black, 2 each of cyan and magenta, 1 yellow) in 3 drop sizes, any/all of which can be deposited at a given point on the paper. That's 16 bits (adding in the drop size of zero) of color information that can be in any given spot, considerably less than the 24-30 of a monitor. And there's a lot of overlap; printing a small drop of black and a larger drop of light grey at the same spot isn't really all that useful.

Now, a printer may well have a larger gamut than a monitor depending upon the particular colorants and monitor respectively, but an inkjet printer simply can't produce a lot of different colors at a given grid point. But it doesn't actually have to; the grid points can be averaged to allow a very wide range of colors over a broader area. A monitor isn't normally used in that way (although a lot of laptop displays are only 6 bits per primary, and a video driver or panel could in principle dither the colors to achieve something closer to 8 bits/primary, as long as you don't demand the full 8 bits at any one point).

Back to your point about the possibility of mixing the inks, that's right, but only over a coarser grid. If you're looking at a 360x360 subgrid superimposed over a 2880x2880 raster, you have 64 drops per subgrid cell. *That* is what gives you the much wider range of colors.

 

1) You are oversimplifying how printers work and
2) I don't use typical printers.

The overlapping nature of inks w/paper is what gives them a much less 'digital' image look.

Certain images on certain monitors (i.e. a backlit device) do have a certain ethereal beauty to them. Almost all fine prints do too if the artist/photographer/editor and the printer operator (not always the same person) each maximize their respective portions of the job.

Unless a monitor is wall sized (over 10' diagonal), is color corrected for any viewing angle and specific ambient light source and the resolution of that monitor is greater than ~2400 dpi - prints will always look better to human eyes that have been trained properly to see those distinctions.

To take this example to the extreme; it is highly useless to me to have the 'very best' display on a handheld/wrist attached device - even if all those important characteristics were vastly surpassed. Vs. a print at the size the photographer/artist intended that can be viewed not only at normal/ideal distances from a high quality (fine art) printer, but also inspected much closer up too.

I get your point that in some aspects certain monitors may have superior spec's.

But the whole is always more important than just the sum of the parts.

 

What kind of printers do you use?