Around the turn of the millennium when digital cameras were first becoming popular megapixels mattered. The average digital camera back in 1999 had less than 2 megapixels (MP), which wouldn't have been enough pixels if you needed to produce a print ready image that filled an A4 page. A 300 dpi image at A4 size would need to measure 2,480 x 3,508 pixels, which is a total of 8,699,840 pixels, or just over 8MP.

These days some compact cameras boast as many as 16MP, while you can get more than 24MP on an SRL. Phone cameras are also packing in the megapixels. The Samsung Galaxy S4 offers a 13MP camera, and the Galaxy S5 will offer a 16MP camera. The Sony Xperia Z2 has a 20.7MP camera. But the camera on Apple's flagship iPhone – the iPhone 5s – only offers 8MP. Does this mean that Apple's iPhone camera is worst than other phone cameras that offer more megapixels?

The answer is no, and we're going to explain why.

READ: Everything you need to know about Apple's iPhone Camera in iOS 8

Dispelling the megapixel myth

It's wrong to think that the more megapixels your sensor has the better your image will be. Of course that doesn't stop various camera phone and camera manufacturers from promoting their products as superior due to the number of megapixels they have packed in. These manufacturers are hoping to fool you into thinking that the number of pixels has something to do with image quality. People like to see a number that indicates whether something is better so many are being taken in by this ruse.

The number of pixels means nothing if the manufacturer has achieved it by cramming them onto a small sensor, as is the case with many modern camera phones. In some cases, in order to achieve more pixels, manufacturers are making those pixels smaller.

A good camera will have the right amount of pixels for the size of the sensor.

It's the size of the pixels that counts

Rather than make the pixels smaller in order to increase the amount of pixels that can be fitted on the sensor, Apple increased pixel size to 1.5µm (from 1.4µm – those measurements are in micrometers) and kept the pixel count the same by using a 15% larger sensor.

As Apple's Phil Schiller said in the keynote announcing the new iPhone 5s: "Bigger pixels equal better picture". Increasing sensor size and pixel size makes a big difference to low light sensitivity and noise.

Why the camera sensor matters

The sensor is what captures the light and converts what you see into an image, it determines image size, resolution, lo-light performance, depth-of-field, dynamic range, and basically how good your photos look.

The sensor is crucial to image quality - it doesn't matter how many pixels you have if the sensor is inferior.  The quality of the image depends on the size of sensor, the number of pixels on it and the size of those pixels.

The size of the sensor also affects what gets recorded on the frame. Smaller sensors crop and capture less of the scene than full frame sensors. As a guide a full frame is the same as a 35mm film frame (36×24 mm). Apple's sensor in the iPhone 5s is 15% larger than that in the iPhone 5.

There are various type of sensor. The iPhone features a CMOS sensor (CMOS stands for complementary metal-oxide semiconductor). The iPhone camera sensor has been provided by Sony since the iPhone 4s. Some cameras use a CCD image sensor, but CMOS sensors work more efficiently, require less power and handle high-speed burst modes better, which is why they tend to be used in camera phones. The Galaxy S4 also features a CMOS sensor.

[Read about how Apple's iPhone compares to the other phones launched at Mobile World Congress]


Other features in the iPhone 5s camera

As we note above, Apple's flagship iPhone - the iPhone 5s - offers 8MP with each of those measuring 1.5µm pixels, and a larger sensor, but there are other ways in which Apple has improved the camera in the iPhone 5s.  

The iPhone 5s has a ƒ/2.2 aperture, this enables it to capture more light than the iPhone 5 (and iPhone 5c camera) with its f/2.4 aperture camera. The combination of this larger image sensor and the larger aperture is a 33% increase in light sensitivity, according to Apple. Because it is more sensitive to light the iPhone 5s can capture brighter images with less noise. 

Other improvements that add up to better photos are the Sapphire crystal lens cover; True Tone flash; Backside illumination sensor; Five-element lens; Hybrid IR filter; Autofocus; Tap to focus; and Auto image stabilization.

For example, the True Tone Flash includes an amber light that compensates for white balance and helps you get the best colour temperature for the shot and leads to more realistic skin tones.

Read our photo comparision between the iPhone 5s, iPhone 5c and iPhone 5.

When more megapixels are bad

As we've established above, there is no point in having more megapixels in a smartphone if those pixels are small and the sensor is poor, but there are additional reasons why you want to avoid camera phones that boast more megapixels.

The more megapixels in your image the more megabytes of space it will take up. If space is already constrained on your smartphone an image that takes up 5MB will be a problem. To get around this your image might be compressed - which means you are losing that extra 'quality' anyway.

If the image is humongous you will may experience frustration when you try to sharing it on Facebook or another social site it will take longer to upload your picture.

When more megapixels are good

The only time when extra pixels on a smartphone camera might be useful is if you might want to crop in on an image to reveal detail in the distance. The extra megapixels will give you a little extra flexibility when it comes to cropping in on your image.

These extra pixels are even more crucial when the camera zoom is poor. Some compact cameras and all DSLRs have optical zooms, which mean that the focal length of the lens increases. Other compacts, and nearly all smartphones have digital zooms. In that case the camera shoots the photo and them crops it in to create the close up.

The Samsung Galaxy S4 Zoom has a 10x optical zoom – thanks to which it looks more like a compact camera that a smartphone.


How many megapixels do you need?

Ken Rockwell explains how to figure out how many megapixels you really need. If you want a super-sharp print you really need to be able to print at 300 DPI (dots per inch). He explains that you can calculate how many pixels you need this way:

Long print dimension in inches = 4 x (square root of megapixels)

Long print dimension in centimeters = 10 x (square root of megapixels)

For example, the square root of four (megapixels) is two. 4 x 2 is 8in. Thus the biggest print you can make without losing sharpness as seen through a magnifier from a 4MP camera is 6 x 8in (15x20cm). From a 16MP camera you could go to 12 x 16in (30x45cm).

Following Rockwell's calculations, this means the 8MP iPhone 5s can give you a [square route of 8 is 2.8284: 10 x 2.8284 = 28.28427] 28cm long, or [4 x 2.8 = 11.3136] 11in long shot.

In comparison, a 13MP phone camera could give you [square route of 13 is 3.6055: 10 x 3.6055 = 36.055] 36cm long, or [4 x 3.6055 = 14.422] 14in long reproduction of your shot.

As a point of comparison, the length of an A4 page is 29.7cm or 11.692in, a tiny bit longer than the 8MP shot, but smaller than the 13MP shot. We think it's unlikely anyone will want to print camera-phone photos out at a size bigger than an A4 sheet so 8MP seems quite adequate. (US letter sized paper is 27.94cm, suggesting that the 8MP shot is ideal for that market).

Basically if you want a 10x8in print 5MP is enough. If you want a 14x11in print (or anything bigger) you'll be ok with 7MP. If you are only going to view images on a computer screen then those images only need to be 1MP.


What will the camera be like in the iPhone 6?

There are various rumours about the next iPhone (you can read all the iPhone 6 rumours here).

With regards to the new iPhone 6 camera Sony is said to be providing the front-facing as well as the rear-facing camera sensors for the next iPhone. Previously the front facing Facetime camera was provided by Omnivision and was just 1.2 megapixels.

As for the rear-facing camera, there are reports suggesting that Apple may add a 10-megapixel camera with an f/1.8 aperture to the next iPhone.

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