How Many Megapixels Do You Actually Need?

A digital camera with a question mark on the screen

Camera resolution in the early 2000s was a space race for better and bigger. Nikon heralded the beginning of the end—with the release of the era-defining 36-megapixel D800—to what had become the resolution stasis.

Nikon’s Z9 is barely upped at 46MP, however, Leica’s version of the 60MP M11 and Fuji going ahead with the 102MP GFX100S belies a renewed charge to the top.

But how many pixels does the photographer have? Really need to?

The role of decision in photography

Working with analog cameras gave rise to a subtle sense of accuracy: everyone started with the same blank canvas and could – so to speak – draw with as much physical detail as possible. In practice, this meant careful selection of the film to be used based on technical considerations (such as grain grade or film speed) that sit alongside a particular “look” you might want to achieve (such as preferring Velvia over Ektachrome). The alchemy magic that led to these results was left to the experts, although with black and white you had a slightly larger field of view in your darkroom.

The change to digital changed the relationship between the photographer, the camera, and the image. Photons are photons and the image sensor simply calculates them: what happens after the fact is post-production, whether that’s in your camera or in your photo-editing software. This innate understanding of color and contrast still resonates with film companies, particularly where they made cameras.

Kodak’s demise meant that Fuji took sole responsibility in this space, something he’s happy to push with a range of movie simulation modes. This was particularly important where processing power and memory storage were more expensive (AKA “should I shoot a JPEG?”), but the proliferation of smartphones, and especially photo filters, led to the expectation of a one-click experiment (which clearly means that the answer to the question The former is “no”).

Separating the physical medium (film) from the physical output (print) naturally resulted in the need to know what resolution the image (or sensor) should actually be, and the starting point for understanding this question is deciding what your final product will be. This is critical because a real physical fingerprint ultimately contains a set of guiding parameters that largely control how it is perceived by the real physical eye.

These parameters vary depending on whether you are shooting for photo book printing, acrylic, magazine cover, or billboard. Variation in size, print media, and printing techniques – and yes resolution – combine to deliver the final product.

Precision Calculation of Printed Images

In some ways, the answer to the resolution question is deceptively simple: how many pixels you want to see. However, there is a more complex background to providing some numbers to indicate “how many you want to see”.

The starting point for this understanding is to remember that we are talking about the human eye and the physical footprint, which means having a basic idea of ​​how far the image will be displayed. Do you print a bulletin board or a picture book? The closer you are, the smaller the image or, conversely, the larger the image, the further away you are. It’s an obvious point, but how often do you pause to look into the viewing distance?

As a general rule, the diameter of the image should be about one-half to two-thirds of the viewing distance. Perhaps the most useful thing is that the viewing distance should be 1.5-2 times the diameter of the image. If you produce an A4 print, the image is about 14 inches in diameter which equates to a viewing distance of 28 inches or about 2.5 feet, which seems very common in galleries.

A man watches a whiteboard in an exhibition
A common rule of thumb is that a diagonal (blue) image should be about one-half to two-thirds of the viewing distance (red).

Of course, this is only half of the equation (image size) and doesn’t tell you how many pixels you need. The second half is to consider the number of pixels per inch (PPI) required; How many pixels should be used to trick the eye into seeing a continuous tone for a given viewing distance? In this case, there is is being An answer to life, the universe and everything. It’s 3438, or more specifically 3438/width distance (in inches).

3438 is the magic number for the PPI calculation

Taking the example above: 3438/28 = 122 PPI. For our A4 print the equivalent of 1500 x 1000 or 1.5 megapixels is surprisingly low. There are two other common edge cases. With a 6 x 4 you can view it at about 12 inches which results in 286 ppi and thus the common recommendation for printing at 300 ppi (and requires a 2 megapixel image). For an A1 canvas viewed 4 feet away, the PPI would be exactly 72 with a minimum image size of 4 megapixels.

The science behind the numbers depends on the visual acuity of the human eye. For someone in good health, the eye’s resolution is one arc minute (0.000290888 radians) from the angle which, after some high school trigonometry, gives us the following general formula:

PPI = 3438 / Viewing distance (in inches)

If you want to calculate viewing distance in the metric system, the magic number is 8595.

PPI = 8595 / viewing distance (in centimeters)

If you stick to this two-step process – estimating your viewing distance and calculating your required PPI – you’ll have a pretty good idea of ​​the accuracy required to achieve the results you want.

Do we need more accuracy?

What is surprising in the above accounts is actually how Little The resolution you really need; If you want an A1 canvas, which measures 23.39 x 33.11 inches (59.4 x 84.1 cm), just take 4-megapixel photos. The obvious conclusion of this number is that you have to shoot at a lower resolution (maybe 6MP), although you can only do this for JPEGs (Nikon cameras have long allowed you to choose FX or DX modes, but this then changes the effective focus height).

However, the decision is important for two main reasons. First, it provides latitude in your workflow. For example, if your image is slightly skewed, straightening it will require cropping, which inevitably means pixels are lost.

Perhaps most importantly, you have the option to crop In itself As part of a post-production workflow. Photographers have always done this, but the advent of high-resolution sensors means that you won’t eventually lose any detail from the printed output. The more pixels you have, the more choices you have in terms of how to crop your creative output or, in fact, multiple perceptions.

The second point is very relevant to the digital age and may be a consequence of it. People Wants To see more details. In an age when we are so used to “pinch and zoom” there seems to be a desire to use that seemingly infinite ability to zoom in to see more and more in a way that reminds me of the famous 1977 movie. Ten Powers.

In the realm of analog photography, this is perhaps best illustrated by the work of German photographer Andreas Gursky who is famous for his incredibly detailed portraits of architecture and landscapes. And to sell expensive pictures too… Rhein II went for $4,338,500 in 2014.

edition of Second Rhine By Andreas Gursky Sold for $4.3 million in 2011.

Produced as a 143 x 73 inch (3.6 x 1.9 m) chromogenic print mounted behind acrylic, it appears flat, possibly dull. However, this is not the point. Gursky continued the picture as “hyper-realistic,” and in that sense, you probably need to see it in the body to appreciate how comprehensive it is. They are undoubtedly designed to overwhelm your senses (Gursky describes his process for Watchman).

Digital Photo Show and Megapixel Wars

As photographers, we can be criticized as pixel photographers, but perhaps this is an innate desire that is reflected in the growth and popularity of gigapans. You just have to see the interest generated by the likes of the 717 GB image of night watch. Likewise, the success of Google Earth rests in part on the same fascination. In the photography space, ZoomHub – the open source successor to Microsoft’s ZoomIt – uses DeepZoom to seamlessly zoom in and out of high-resolution images.

So the next time you’re creating a high-resolution panorama or capturing a 100MP background, try creating a ZoomHub image for online viewing and enjoy your inner pixel-scanning self (and those of others). This indulgence may also indicate a desire for higher-resolution sensors.

I hope the Leica M11 marks the start of a new mega-pixel space race…

Image credits: Stock image licensed by Depositphotos

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