What is an aspect ratio? Put simply, an aspect ratio refers to the proportions of the width in relation to the height of an image. The aspect ratio is primarily determined by the sensor on the camera you are using.
For the following examples, I have used the rear camera on an iPhone 7 Plus. The native resolution on the iPhone 7 plus rear camera is 4032 x 3024 pixels. This equates to a 4:3 aspect ratio. The image below is an example of a full resolution image taken in the native 4:3 aspect ratio.
As you you can see, the image above is 4032 pixels wide and 3024 pixels high. If you multiply 4032 x 3024, you get 12,192,768. This equates to approximately 12.1 megapixels. Apple advertises the iPhone 7 Plus as having a 12MP rear camera, where in actual fact, it is slightly higher.
The native resolution of the iPhone screen is 1920 x 1080 pixels. This is a 16:9 aspect ratio. What this means when you are looking at an image taken in the camera’s native 4:3 aspect ratio is that you will see black bars on either side of the image, as per the example below.
There are many camera apps available that let you choose different aspect ratios. It is important to know that choosing any other aspect ratio, other than 4:3, will result in cropping of the image, as per the example below.
In the above example, I have chosen a 16:9 aspect ratio. As you can see, there is a loss of 757 pixels in the height, going from 3024px to 2267px.
If you view an image taken in a 16:9 aspect ratio, it will fill the screen of the iPhone, with no black bars present, as per the image below.
Other common aspect ratios are 1:1 and 3:2. As you can see from the below image, when using a 1:1 aspect ratio, there is a loss of 1008 pixels in the width, going from 4032px to 3024px.
Again, because the iPhone screen is a 16:9 aspect ratio, you will see black bars on either side of the image when viewing any image taken with any other aspect ratio.
A 3:2 aspect ratio is used for printing standard size 4x6” photos. As you can see from the below image, when using a 3:2 aspect ratio, there is a loss of 336 pixels in the height, going from 3024px to 2688px.
The most important thing to remember is that using any aspect ratio other than 4:3 will result in less data being captured by the camera’s sensor. This means that you won’t be using the camera’s full 12.1 megapixels.
If your sole purpose in taking photos with your iPhone is to upload them to Instagram, then using a 1:1 aspect ratio is fine, the loss in data in the image won’t matter. If you are only ever going to display your photos on the iPhone itself, then using a 16:9 aspect ratio is fine.
For those of you that are serious about your iPhone photography, I would recommend only using the native 4:3 aspect ratio, which by the way is the only aspect ratio that I use to capture images using my iPhone. Remember, you can always crop the image later if needed, using either the standard Photos app or a 3rd party app whilst still retaining the full 12.1 megapixel resolution.