Megapixels in photography: what impact do they have?

Today, I’ve decided to tackle a more technical subject, something I don’t cover that often on the blog but that should interest many of you. I’m talking about megapixels in photography, especially on a camera body. What are they, really? How do they affect our photos? Are they just a marketing number? Why are so many people so interested in these famous figures? In short, I’ll try to answer all these questions in this article. If you want to go further, I invite you to read the articles on the basics of photography.

This is a question many beginners, and even more experienced photographers, ask themselves when buying a new camera: should I choose a sensor with more pixels, or will that affect performance? For many years now, sensor resolution has been a feature heavily promoted by manufacturers, and many true and false ideas circulate about the influence of pixel count, especially when it comes to cameras with more pixels than average.

First of all, what does this number of megapixels (MP) actually represent? Without going into too much technical detail, a sensor contains what are called photosites, which capture light. Digitally, these photosites become pixels, which means that a sensor with 20 million photosites will produce 20MP images. You can think of it like a mosaic: the sensor “paints” each fragment, or each pixel, and once all the fragments are painted, the image is formed. Once your image is saved, you can display it on a screen or print it.

On forums, blogs, YouTube and other platforms, you’ll regularly come across heated discussions, articles or videos explaining everything a high number of megapixels supposedly gives you… and, above all, everything it supposedly takes away! The reality is a little more nuanced than that. Generally, people say that having more pixels allows you to print larger and crop your images more. That part is true. But as you browse the internet, the list of supposed drawbacks often gets longer: lower ISO performance, the need for higher-end lenses, heavier files to transfer, store and process, a more limited burst rate, smaller photosites that capture less light, a greater risk of motion blur, and so on… You should know that, in this list, 4 claims that come up very often are already false!

One thing you should know straight away, and that you’ll soon notice, is that most cameras aimed at beginners and enthusiasts — DSLRs, mirrorless cameras, and even compact or bridge cameras — have very similar resolutions, even with different sensor sizes. For example, a Sony RX100 uses 20MP, and most cameras with a 1-inch sensor, such as the Canon G7X III, Panasonic FZ1000 or Sony RX10 II, usually offer the same resolution, simply because Sony supplies this sensor to other brands. Most recent Micro Four Thirds mirrorless cameras offer 16 or 20MP sensors, such as the Panasonic GX9 or Olympus E-M5 II. Most recent APS-C cameras produce 24MP images, such as the Nikon D5600, Canon 2000D or M50, Sony A6000 or Fuji X-T20. Even with full-frame sensors, most cameras sit between 16 and 30MP. Apart from a few low-megapixel but very expensive full-frame bodies such as the Nikon D5 or Sony A9 II, all the cameras mentioned here are mostly aimed at amateur photographers who either can’t afford or don’t need a more high-end camera.

The cameras that really have significantly more pixels than the others are generally full-frame models, such as the Nikon D800/Z7 line, Canon 5DS, Sony A7R series and Panasonic S1R, or medium format cameras, with sensors ranging from 50 to 100MP. That is already quite a list, but I’ll let you check their prices out of curiosity and see whether these are really the cameras most of you would be interested in, or ready to invest in! If you’re not curious, most of the full-frame bodies mentioned start around €2,500–3,000, and the cheapest medium format camera costs around €6,000. So, for a huge majority of you, these are cameras you won’t even consider, especially if it’s your first one. Good news: all these debates about pixel count will have almost no impact on the camera choice for most of you!

So why talk about it at all? Simply because, if you end up being interested in the subject (otherwise, why would you be reading this, right?), it’s important to know how to separate truth from myth. Besides, many people who tell you “this camera has a sensor packed with pixels, it’s just marketing, it’s useless, get another one!” are actually showing that marketing works well, because they are trying to convince you not to choose a camera based only on its number of pixels, without mentioning any other feature of that camera. It doesn’t matter whether it has the best autofocus, the best ergonomics, or the best features… You shouldn’t buy it because it has too many pixels! Curious, isn’t it? A bit like someone telling you, “there’s an extra spare tire in this car, it’s just marketing, buy another one.”

The first, and perhaps the only thing to remember, is that the more you enlarge an image, the more you accentuate its flaws. Put that way, you might think that if a sensor produces more pixel-dense images, those images will be larger, and you’ll see the flaws more clearly. But you also need to remember that you’re going to view these images on a medium — a screen or paper — that will often not display every pixel of your image at its “real” size. For those who don’t know, a Full HD screen displays only 2MP across its entire surface, while a 4K screen displays 8MP, which is also roughly what an A4 print requires for very high quality. A small clarification: for printing, we talk about resolution because it is not a total number of pixels, but a number of dots per inch, the famous dpi. But with a simple mathematical calculation, we can easily define the image definition needed to print at a very high-quality resolution, generally between 250 and 300dpi.

So, displaying your 24MP image full screen on a Full HD display won’t show you a 24MP image, but a 2MP version of it, which is equivalent to reducing the real size of the image. Now, in relation to the first sentence I highlighted in the previous paragraph, you should know that the reverse is also true. In other words, whether you have a 24MP or 50MP full-frame sensor, the image you display full screen on that monitor will be equivalent to a 2MP full-frame image. Of course, if you zoom into the image, you enlarge it, and the image quality will be affected, especially the perceived detail and digital noise. But the quality will be affected just as much with one sensor as with the other at the same enlargement, at least if they are not separated by several generations. This means that at equal enlargement, the ISO performance and level of detail in the image will be at least equal with both sensors, and you’ll also find that motion blur is not more visible on one than on the other. Likewise, at the same shutter speed and aperture, to get the same exposure, you will need the same ISO sensitivity, which confirms that the 50MP photosites, although smaller, did not capture less light than the 24MP ones.

To keep things simple, as long as you view the images on the same medium and at the same zoom level, the quality between two sensors of the same size will be almost the same, whether one has 10MP and the other 100MP. In the same way, if a lens works well for you on a less pixel-dense sensor, you won’t necessarily need a higher-end lens just because you use a more pixel-dense sensor — as long as the final use doesn’t require more than 10MP, which is the case for Full HD or 4K displays and A4 or smaller prints. On the other hand, if you view your image on a medium that displays more pixels than one of the two sensors can provide, for example an 8K screen (32MP), then you will see a difference, but to the disadvantage of the 10MP sensor, because to display the image full screen, it will have to “invent” pixels that the image doesn’t have. Paper prints always require the same number of pixels: 10 years ago, 8MP was recommended for a very high-quality A4 print, it is still the case today, and it will still be the case in 10 years. Screens, however, are evolving even if their physical size remains the same: their definitions are increasing. This means that a 12MP image will look comfortable on a Full HD or 4K display, but will start to “suffer” on a 5K display, and even more on an 8K display. Choosing a camera with a more pixel-dense sensor can therefore make your images relatively more future-proof.

The example of video

One of the good reasons to choose a sensor with fewer pixels, apart from file size, would be video use, especially if you shoot video fairly intensively. Cameras with high-megapixel sensors can still produce very good video quality, which will be more than enough for “classic” use.

However, to film in 4K, for example, sensors do not need more than about 10MP (8MP, but with the 16:9 video ratio, part of the sensor is not used). In fact, the more pixels a sensor has compared with the definition of the video, the more processing is needed to scale, or sometimes crop, the image. This can reduce quality while also reducing the field of view. It can also increase rolling shutter effects (image distortion during fast panning, for example), make it harder to achieve high frame rates such as 120fps, and make the complex, heavy processing required to scale the image more likely to create overheating risks.

At this stage, you may be asking yourself: “Why choose a sensor with fewer pixels if it doesn’t reduce image quality?” Although some of the ideas mentioned in the first paragraph turned out to be false, others remain true and are mostly related to file weight. More pixels mean heavier files, so they take longer to write, transfer and process.

This means that the camera will generally be more limited in burst shooting, you’ll need larger memory cards, transfer times between the card and the computer will be longer, and processing and export times in editing software will also increase. You can reduce display and processing times with a more powerful computer, but it will be more expensive as a result. And as mentioned above, pixel-packed cameras are rarely the most affordable. So between the camera, the lenses you think you need to match it, and the computer you think you need for “acceptable” processing times, selling a kidney may not always be enough (consider renting out family members if necessary, haha!).

More pixels won’t degrade image quality, but they do impose some constraints, especially financial ones. And if you do what people who spread misconceptions about quality often do — zooming in at 100% without taking into account the difference in enlargement — it will be worse, because you’ll convince yourself that your lenses are no longer good enough. How many times have we read the sentence: “lots of pixels require high-end lenses”? In reality, the principle is simple: people recommend high-end lenses when you buy a high-end camera. With APS-C, for example, you’ll be told to use better lenses on a Nikon D500 than on a D3400, even though the D500 has a less pixel-dense sensor.

Highly pixel-dense sensors simply allow larger enlargements. The more you enlarge an image, the more you accentuate its flaws, and vice versa. Their main drawbacks are therefore file size and, of course, price. Remember, however, that while more pixels can make your images more durable over time, this advantage is not always visible today. And as screens increase their definition, 20–24MP images will remain perfectly acceptable. In fact, 10 years ago, people considered 12MP more than enough and 24MP useless. Today, 24MP is considered sufficient and 50MP unnecessary. What will we think in 10 years?

Finally, don’t forget that cameras with very high-resolution sensors are not accessible to most of you anyway. And whether you can afford them or not, you should first look at all the other features: sensor size, AF performance, build quality, ergonomics, grip, functions… These will very often matter much more.

I hope you liked this article, which I admit is a bit more technical than usual, but I hope you still enjoyed it. Once again, thanks to Alex for his clarifications and corrections. To go further in your learning process, why not read about the benefits of RAW and JPEG in photography?

Written by Sylvain PONS

I've been passionate about photography since 2010, learning as I went along. Today, I dedicate myself to guiding others in their choice of camera gear and sharing a variety of tips to improve their photography skills.

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