I read (yet another… ;-) megapixel rant somewhere online yesterday, and it got me thinking again about the fixation on megapixels as a measure of camera “value,” and the odd and sometimes irrational ways that people respond to this issue. It is well known that over the past decade or more, as digital photography technologies have become more and more prevalent (displacing film in many areas), camera technology has continued to advance in many ways. Among these advances is the ability to increase the number of photosites on sensors of a given size – e.g. give us “more megapixels.”

The responses to this tend to fall into three broad categories:

“Whatever” – Some folks, for, uh, whatever reason, don’t seem to be too concerned about increases in photosite density. More on this a bit later.

“Terrible! Stop!” – There are those who argue – often vociferously – against increases in “megapixels.” While their position may include a bit of the “whatever” reaction (as in, “things are good enough already”), their major issues seem to be that a) it is something foisted on us by camera companies merely to sell more cameras, and b) given the limitations of our technology, increasing the number of photosites can only degrade the quality of photographs.

Regarding a), there might be some truth to this, though I think the objection is over-blown. Camera (and other technology) companies do work continuously to improve and perfect their products so that they can better compete with other companies and sustain their businesses. There is probably some combination of simply trying to differentiate the products from those of competitors, trying to make sure that they keep up with developments from their competitors, and a genuine interest in pushing technology in ways that have the potential to improve photography.

Issue b) seems a bit more complex. I do think that there are some “limits” beyond which adding more photosites may produce diminishing returns. There are two ways in which this could occur.

First, at some point (which will vary) adding more photosites to a sensor may simply not result in any improvement that will be visible in photographs. It is certainly reasonable to argue that putting 16 megapixels on a point and shoot camera doesn’t result in any meaningful improvement to image quality. It is also unlikely that a typical casual photographer using a cropped sensor camera to produce shared jpgs won’t see any improvement from “more megapixels.” However, in general, I don’t think we want camera manufacturers to design cameras for the average user – doing so would result in cameras that fail to meet the needs of half of the users! In other words, it is better to exceed the typical needs of users as long as this can be done without otherwise degrading performance or inordinately increasing cost. For example (and using made-up numbers) if we think that 8 megapixels is plenty for a point and shoot camera, but find 10 or 12 megapixel sensors can be used without any negative effects and at minimal (and always decreasing) cost, why not?

Second, and more interesting to me, is the idea that increasing the number of photosites will make the cameras worse. There is a whole lot of stuff wrapped up in this notion, so let me see if I can tease some of the elements apart. First, it is a fact that when you make a photosite smaller with a given type of technology that you decrease the signal to noise ratio (“increase noise”) and so forth at the individual photosite level. This sort of thing is often cited by those who believe the whatever iteration of camera technology they currently use is the “best of all possible worlds,” and that anything beyond that must diminish camera performance by way of increased noise and/or decreased dynamic range.

I won’t go into the consumer psychology issues that may be at work here – instead, let me try thinking about history a bit. This argument – that the next or the newest technology will be a step backwards – has been made, as far as I can tell, every time that sensor photosite density has increased. In fact, some of the cameras held up by commenters today as the “best” were the very cameras that earlier commenters claimed would be a step backwards! We currently hear folks who are certain that the next DSLR developments (upper 20MP+? 30MP+?) will certainly create major problems with noise and so forth. And we still hear a few who complain that moving from, say, 12MP full frame sensors to 20MP+ full frame sensors was a bad thing. Before that there were those who were utterly convinced that going from 8MP to 12MP would create unsolvable IQ issues. And before that the 6MP shooters railed against the certainly diminished IQ of the upcoming 8MP sensors. This is about where I came into the DSLR world, but I’m pretty certain that somewhere back there we could find a user of a 2MP camera loudly pronouncing that 2MP was “perfection,” and that 3MP would certainly only be a step backwards! (Come to think of it, we do regularly read some person proclaiming, more or less, “Eh! I have great, Great, I tell you, 30″ x 40″ prints from my 3MP camera hanging on my wall. Who needs them new-fangled megapixels, eh!”)

I like to imagine how it would be if these folks were actually right. I suppose that DSLRs (and other digital cameras) would have continually gotten worse and worse over the past decade or so. Whatever IQ quality level was obtainable in, say, 2002, it would have been worse in 2003, worse than that in 2004… and by now new cameras should have become pretty much unusable! I don’t have to point out that nothing like this has happened. While you will find a few people who claim that their older camera is somehow better than the newer ones with more photosites, a) they are a distinct minority, and b) the logical prediction of their point of view has not panned out over time. Most would agree that, in fact, the opposite has occurred.

“Must have more megapixels!” – At the opposite end of the spectrum are what we might call “MP-aholics.” These folks believe that every increase in photosites provides a significant improvement in their photography and that they must have it! They will sell a 15MP camera when an 18MP camera comes out, or they will put off buying the 21MP camera they “need” now because a 28MP camera might come out next year. It has “more megapixels!” It must be better!

Maybe and maybe not. It is always good to start by considering just how significant sensor resolution is or is not to ones own photography. Let’s say that the photographer usually shoots handheld, perhaps in jpg mode, doesn’t generally do much, if anything, to the photographs in post,  and typically shares photographs as jpgs or occasionally makes a letter size or slightly large print. Basically, any of the current DSLR sensors have image resolution that is more than sufficient to produce excellent results in this context. It is difficult to argue that even a large increase in the number of photosites will produce real improvements that are visible in the final photographic output.

Let’s consider a more critical and careful photographer. Such a photographer might work critically and carefully to maximize image quality and sometimes make quite large prints. Even here, pixel density is rarely the limiting factor when it comes to print size. When shooting with DSLR equipment especially, a range of other factors often come into play first – camera stability, perfect focus, lens quality, aperture selection, subject motion, and so forth. In those rare cases where photosite density is the deciding factor… small increases make little or no sensible difference. While one might think that going from 15MP to 18MP would be significant, in terms of the increase in pixel dimensions of the image the change is very, very tiny. (My general rule of thumb is that a doubling of photosites is potentially significant for those photographers whose prints are currently limited by photosite density.)

So, is there a point to all of this? Yes, but it may not be what some hope for. I’m not buying into either of the extreme positions. There is little or no evidence that increases in photosite density have resulted in steadily declining image quality from digital sensor cameras – worst case, it is at least as good now as before, and there are darned good arguments that it has continued to improve overall. But it is also a fantasy to think that every increase in the number of photosites will improve ones photography – in many cases the increases won’t make any visible difference and in others the difference will be quite small unless the increase in photosite density is quite large.

All of this brings me more or less back to that first “whatever” reaction. For most people buying DSLR cameras, while incremental increases in photosite density will likely not bring a significant improvement in the quality of their photographs, neither will these increases make their photographs worse. In general, camera manufacturers have produced a continuous improvement in the capabilities of their cameras over time, and increasing photosite densities have not produced diminished photographic quality – if anything, the opposite is true.

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