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The Megapixel Myth – are more megapixels better?

The Megapixel Myth

There are many reasons why you might want to upgrade your smartphone but should you upgrade your smartphone for extra megapixels?

The importance of the smartphone’s camera

For Smartphone manufactures, the camera is a big deal.  It is one of the most effective ways they can differentiate their product from the hordes of similar looking, similarly specified smartphones produced by their competitors.  Among the easiest ways to boast photographic supremacy is to advertise an increase in megapixels since most consumers understand more megapixels mean better-looking photographs.   But is this true and should you upgrade your smartphone on megapixels alone?

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What is a megapixel?

A megapixel (mp) is one-million pixels and with more pixels you get a larger photo, a bigger file, and the potential to record more detail from the scene.  Megapixels are represented by photo sites which cover the surface of your camera’s sensor.  When a photo site is exposed to photons (light), a small electrical charge is produced and these electronic charges are then interpreted and crafted into a photograph.

More megapixels require more photo sites to be squeezed onto a sensor and it stands to reason that this is easier to accomplish if the sensor is large.  To keep your lens small, your smartphone’s camera features a very small sensor – almost 20 times smaller than one you will find in an entry level digital SLR and more than 50 times smaller than many professional cameras. 

Relative sizes of camera sensors. A large 24mp sensor will vastly outperform a small 40mp sensor

Since a smartphone’s camera sensor has far less space to accommodate photo sites, any increase in megapixels is accomplished by further shrinking each individual photo site and it is here where problems begin.

What is Diffraction?

To stay compact, the smartphone has a small sensor mounted behind a small lens featuring a very small aperture and it is the aperture that determines the amount of light that reaches the sensor in much the same way our iris expands and contracts to control the amount of light entering our eyes.  In many cases the aperture in a smartphone is less than 2mm in diameter and light squeezed through the tiny opening is diffracted.

Because the aperture is so narrow, the light is effectively rerouted from its original course just like a wave hitting a cliff will begin to steer around it.  To make things more difficult, different colours are affected differently so the image is not just redirected but also scrambled and the end result is a photo that appears blurred and stripped of detail.

Diffraction is not limited to photography.  If you have ever looked at the moon on a warm evening you might notice it appears hazy while on a cool winter’s evening, the moon appears sharp and full of detail.  Diffraction will have the same effect on your photos.

Large sensors are usually behind lenses with far larger apertures but even if they were not, their large photo sites offer our wayward light a far larger target to hit.  On small smartphone sensors, the sites are crammed together so densely that the light will likely impact neighbouring photo sites or several different photo sites at once reducing image resolution.

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What is sensor Noise?

In addition to being more susceptible to diffraction, smaller photo sites consume less light before becoming saturated in the same way a small glass captures less water than a bucket. Having less light to work with introduces noise – a grain effect reminiscent of a poorly tuned TV channel. This grain can be removed with software but doing so further reduces the detail within the image.

Google’s Pixel 3 attempts to work around this issue by using a relatively low resolution sensor (12 megapixels) and compensate by taking multiple exposures.  In doing so, the small photo sites are filled up with light before been emptied and filled again and the end result is more light overall. The downside of this approach is that the real world is rarely still and The Pixel 3 must use clever computing algorithms to make sure that once all the images are merged into one photograph, the car caught driving through your shot is frozen in motion and not a long blurred streak across the frame.

Are Megapixels just for Marketing?

Google’s approach, while innovative and sensible, remains a difficult sell to customers who often presume 12 megapixels is not enough especially when making comparisons with other Smartphones.  At this point, the value of megapixels lies not within image quality but its strength as a marketing tool.

Huawei’s P30 Pro is a fine example in that it uses a 40mp sensor to produce 10mp photos in a process known as ‘pixel binning’ where, in the simplest terms, the 40mp image is boiled down to its best bits.  Whilst there is merit in this approach, the P30 pro is marketed as a smartphone with a 40-megapixel camera implying significant resolution and appearing highly favorable when compared against its competitors.  If you have already bought the P30 Pro, rest assured its 10-megapixel output does not affect its position as one of the very best smartphones for photography.

Should you buy a new Smartphone for more Megapixels?

Whilst Smartphone Photography has improved, the number of megapixels is playing a diminished role in the overall quality of your image and future gains are more likely to be facilitated by computer assisted trickery.  If you are considering upgrading your smartphone primarily to improve the quality of your images, megapixels alone cannot be used to determine true resolution or overall image quality. Nor can it be used as a metric to compare one smartphone camera against another.

It would also be a mistake to use a megapixel count to compare a smartphone with a traditional camera since larger sensors offer far superior resolution.  My 2006 Nikon D40 featured a 6-megapixel sensor and produced cleaner, more detailed images than my 2016 16-megapixel iPhone SE.

A far simpler metric to measure image quality is price. As usual, it seems you do get what you pay for and there are various sites across the Internet that assess performance based on the actual image output rather than the manufacturer’s claims and specifications.  It is also worth considering what kind of photos you take since many phones excel over each other in niche areas.  For example, Google’s Pixel 3’s night mode offers excellent low light performance and iPhones are well known for producing desirable colour.

If your end-game is better image quality, buying a low-end smartphone and using the savings to purchase a dedicated camera may prove a cost-effective alternative to top-tier smartphones.  While you have the inconvenience of two separate devices, you gain substantially better image quality, faster performance and the creative flexibility of an optical zoom and/or interchangeable lenses. 

Whether any of this is of importance to you depends on how strongly you value your photography.  Smartphones offer a fantastic and highly convenient platform for casual photography and the pictures look very acceptable when viewed on your device’s screen, posted on social media, and printed small.  If you are using your smartphone to capture once-in-a-lifetime moments, you might prefer to be aware that traditional cameras still offer far more than even the very best smartphone cameras.

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