This photo as you see it on this web page comes to about a fifth of a megapixel

Do you need a 20-megapixel camera?

You probably do if you’re working on extreme high-quality professional print jobs and/or for some of the serious high-end photo agencies. You’ll know if that’s you. And most likely it isn’t.

Professional photographers have some reasons for monster megapixel counts, which I talk about later. But most people would rarely need to go beyond about 6 or 8 megapixels, even if they want to print nice big photos to a high standard on their home ink-jet printer.

So, what’s a megapixel?

A megapixel is a million pixels. So if your camera takes a 1-megapixel photo then the resulting image would measure something like 1,200 pixels wide by 900 pixels deep.

1,200 × 900 = 1,080,000. There’s your million.

That might sound like a lot of pixels, but how many do you need to print that photo? The answer depends on how tightly you pack those little pixels together when you print.

Your typical newspaper photo gets between 150 and 200 rows of dots (pixels) per inch — measured horizontally and also vertically — into its photos.

Glossy magazines tend to work at higher resolutions to get that really nice quality, printing their pics at between 240 and 360 dots per inch.

From now on, I’ll refer to dots per inch as ‘dpi’.

What’s the best-quality print resolution for glossy magazines?

Many experts say that once you go beyond 300 dpi, the dots start becoming so tiny that the human eye can’t see any difference. However we already know that some printers work at 360 dpi. I’m pretty sure no one has eyes good enough to see any difference beyond 360 dpi.

How big would your 1-megapixel photo print?

Let’s imagine we print your 1 megapixel photo in a newspaper.

At 200 dpi your 1,200 × 900 pixel photo would be:

(1,200 divided by 200) inches wide and
(900 divided by 200) inches deep.

Which comes to 6 inches wide by 4 and a half inches deep.

That’s okay for a smallish pic, but if you wanted to stretch that photo across the whole front page you’d quickly see its limitations. It would look fuzzy and, well, just plain awful.

And if it was printed in a glossy magazine?

Let’s take the high-end example of 360 dpi.

Your 1,200 × 900 pixel photo would be:

(1,200 divided by 360) inches wide and
(900 divided by 360) inches deep.

Which comes to 3 and a bit inches wide by 2 and a half inches deep.

In other words, a typical small magazine photo.

Printing your photos at home

Modern inkjet printers boast about printing your stuff at resolutions of thousands of dots per inch. Wow, that sure does sound good, and true enough, the output quality from those printers is very good indeed. But not as freakishly good as the numbers might make you think.

You see, they use a different sort of technology which results in a way of measuring dots per inch that creates very big numbers. So an inkjet printer working at 4,800 × 2,400 dpi resolution does NOT require a 4,800 × 2,400 pixels-per-inch photo to print properly. In fact, if you tried to push a photo at that resolution through your home printer I have a hunch it would either take forever to print or crash your computer (and I won’t even start contemplating the bit about having a different resolution vertically and horizontally). Instead, you could save your pic at 360 dpi and print it at the very highest settings. Assuming you used the right inks and paper and so on, it would come out looking fantastic.

That’s enough talk about 1 megapixel. What about your typical camera today?

Your average digital SLR camera now will probably exceed 10 megapixels in its image resolution. Let’s look at the numbers to see how big that kind of photo would print. And don’t worry: I’ll do all the maths for you.

A typical 10 megapixel photo might be 3,888 × 2,592 pixels.

3,888 multiplied by 2,592 equals 10,077,696. There’s your ten megapixels.

Using the same formula as above we can see it’s more than enough pixels to print your photos.

In a newspaper, it would print about 19 and a half inches wide by 13 inches deep. Which is wider than a full broadsheet newspaper page.

In a glossy magazine at the high end of the scale (360 dpi) that same photo would print at about 11 inches by 7 inches. Almost enough to fill an A4 page. And don’t forget this was at the high end of resolution settings. At 300 dpi your image will print slighter bigger than an A4 page.

And printing at home, you could save your 10 megapixel file at a very reasonable 200 dpi and it would easily be big enough to fill an A3 page, and look great too. Now, personally I don’t even know anyone who has an A3 printer at home, so suddenly your file is looking bigger than it needs to be.

Okay, but what if you want to chop off half the photo and still print it big?

Hah! That’s the key point! Most pro photographers don’t need to print photos much bigger than about 10 megapixels unless they’re doing high-resolution glossy posters or something fancy (expensive) like that. But sometimes a portion of their photo isn’t needed. They want to chop off parts of it (crop the photo) and still have enough pixels left over to print it nice and big. So they might start with a 12 megapixel photo, for example. Then discard a sixth of those pixels when they crop it. And they’re still left with a 10 megapixel photo.

That’s the main reason why you’d want to go higher than about 10 megapixels.

So more megapixels is good then, is it?

Well yes, and no.

The ‘yes’ reasons

More pixels means that you have the luxury of having more to throw away if you need to crop the photo, while still having enough pixels left over for your printing needs. And of course, for the pros working towards large-format high-quality printing, they just might need big pixel counts.

The ‘no’ reasons.

The ‘no’ reasons can be broken up into a few categories:

FILE SIZE

More pixels means bigger files sizes, and that means:

• slowing down your camera
• clogging up your camera’s buffer more quickly during fast-burst shooting
• filling up your camera’s storage card more quickly
• slowing down image transfers to your computer
• filling up your computer’s hard drive more quickly
• the need for bigger archiving backup-facilities
• Bigger files take more memory and are more cumbersome to work on in your image-editing software.

LIMITS IN WHAT YOUR LENS CAN DO

Even under ideal conditions, most lenses struggle to capture enough detail to exceed what 10-15 megapixels can hold. This is one reason why the professionals with their high-end cameras spend several thousands of dollars more on high-end lenses.

LIMITS IN WHAT YOUR SENSOR CAN DO

I’ll use some rough numbers here. The geeks and purists might take offense and say rude things about me, but they’ll probably agree with my overall message.

A 10-megapixel camera will require close enough to 10 million pixels on its sensor. Now, since the sensor in your typical digital SLR is only about a square inch in size, that means each pixel on its surface must be about a ten-millionth of a square inch in size! In fact, if you take into account the way they build them, there’s usually a tiny gap between each pixel. Which makes them even smaller.

Try to imagine how small a ten-millionth of a square inch is. No, don’t bother. It’s crazy-small. In fact, using current limits of technology, it’s barely enough area for capturing enough photons to get a useful sample of light.

So when a pixel in your sensor gets too small, it might get things wrong. Instead of registering a green pixel for an area of grass, it might not capture enough of that green light, and so it bungles things and records a red pixel instead. Or a white pixel in an area that was supposed to be in shadow. Your photo starts getting speckled with pixels of the wrong tone. That speckling is called noise and too much noise will greatly reduce the image quality in your photos.

Can you see now, how too high a megapixel count can result in lower image quality?

This is why compact cameras, which have very small sensors combined with unrealistically high megapixel counts, tend to produce noisy photos, especially in the shadow areas and weak-light situations where there just aren’t enough photons landing on those miniscule sensor pixels.

Now, the clever boffins who make the cameras’ sensors are getting better at their job all the time, and the sizes down to which they shrink those pixels are getting smaller and smaller. Also, I think it is fair to say that some brands of camera appear to perform better than others. But some of those marketing types all too often push for megapixel counts in excess of what even those smart boffins can handle. And for what benefit? In my opinion it is just for some sort of shallow advertising claims.

And a bit of yes and no

When you reduce your image size in your image-editing software, some of the noise tends to go away. Shrink your images down enough and noise pretty much disappears altogether. So, a large photo with a bit of noise can be shrunk, and sometimes end up with the same image quality as a less-noisy photo taken at lower resolution.

For this reason, some people argue that more pixels are better, because in good light you get great pics. And in low light you just sacrifice some image size later on. The question is, how much you have to reduce your images to make them usable.

How much noise is okay?

If you print your photo and it looks great, then obviously the amount of noise in your photo is acceptable. Too much noise though, and you will notice colours starting to look wrong and details disappearing.

But the good news: the camera manufacturers are well aware of these issues and have some great people working on sensor design, which means cameras should keep getting better.

So is it yes, or no?

Perhaps the maths at the beginning of this article was a bit boring. But it doesn’t take much number-crunching to see there are more ‘no’ reasons than ‘yes’. In other words, there are more problems than benefits with giant megapixel counts.

So how many megapixels do you need?

Professional photographers do sometimes need to capture very high resolution images. But for everyone else, my personal opinion is that you needn’t worry about giant numbers of megapixels. Chances are your camera will have more than you need already. Unless you plan on doing high-end large-format printing or heavy cropping of your images, you probably won’t need much more than about 10 or perhaps 15 megapixels. That will let you crop your photo down to about 6 megapixels, which is quite a bit of cropping when you think about it, and it can still look great in print and be more than enough to look great on screen. With the really big megapixel counts your lens might not capture enough detail to make any difference anyway.

On those occasions when you need super-high resolution, consider the option of taking a few photos in a panorama and stitching them together in your image-editing software.

Instead of looking for super-high megapixel counts, in my opinion most people would be better off looking into camera performance. That doesn’t mean examining every pixel of your photos on screen. It means looking at how well the camera works in all sorts of conditions and all sorts of light, including low light. If you’re a wildlife photographer you’ll really appreciate a camera that works well in low light, in those times close to sunset and sunrise when many animals come out of hiding. Low light (high ISO) photography is becoming more of an issue with digital camera manufacturers and in the coming years I hope to see them putting more emphasis on that, rather than on squeezing in ever more millions of pixels.

Copyright © Mark David. All rights reserved