Sunday Reads

Laura Currie
20th November 2022

Vive la Résolution…

Oversampling, pixel binning and line skipping are often mentioned when discussing video. You may have a basic grasp of the meanings, but it can be really useful to jump in and learn more about the technical explanations. We hope that by the end of this piece you will feel confident knowing how they differ from each other, and which is most suitable for you!

When you shoot video with a hybrid photo and video camera such as a mirrorless or DSLR, ­the resulting files aren’t always the correct aspect ratio or resolution for capturing 4K UHD footage. The majority of their sensors offer an aspect ratio of 3:2 but 4K UHD needs a ratio of 16:9, because of this, the footage needs to be adjusted to suit the requirements of 4K UHD.

There are various different methods available to you when it comes to converting the footage to 4K, but as with most things, there are pros and cons to be considered. The quickest options will save you time and be kinder to the camera’s processor, but you will lose detail and you may end up with strange distortion issues.

Cropping

The most basic method for turning your footage into correctly shaped 4K is cropping. If your camera has a 6K sensor, it will take what it needs from the centre of the sensor so that it captures 4K at the correct aspect ratio of 16:9.

It’s the quickest and easiest method, but by doing this you’re using only a small portion of the sensor. This means you are collecting the minimum amount of data possible to produce 4K footage, which can lead to a lack of detail. It’s a similar principle to using a cropped lens on a full-frame camera.

Line skipping 

Line skipping is where the camera discards rows of pixels as it shoots in order to reduce the readout to 4K.

Like cropping, this method is quite destructive as you are reducing the concentration of data recorded, leading to less detail and sometimes, odd visual artefacts such as aliasing, which we’ll touch on shortly. The image above is a simplified illustration of line skipping, but you get the idea!

Pixel binning

To explain pixel binning, first we need to understand the Bayer filter mosaic. It is a mosaic of miniscule colour filters that are placed over the megapixels of a sensor, made up of red, green and blue, and each one absorbs light matching its own colour. Interestingly, it’s made up of twice as many greens than blues or reds, as the human eye sees far more shade variations in green than the other two.

Pixel binning reduces the footage down to 4K by grouping matching pixels and combining them into one big pixel, so a 48mp image becomes a 12mp image, thus reducing your file size.

Pixel binning is by far the best method we’ve discussed so far when it comes to retaining as much image quality as possible, but that’s not to say it’s without faults. As the pixels effectively become much larger units, they become more clumsy and less ‘supple’, meaning when you look closely, you’ll notice courser, almost jagged edges – which is known as aliasing. Low pass filters are designed to reduce this effect in-camera, but it can lead to soft images.

Oversampling

Finally, we come to oversampling, by far the kindest way to reduce your file to 4K with the correct resolution and aspect ratio. Using a camera with a higher resolution than 4K, you capture super-high resolution footage and then reduce it down to a beautifully detailed 4K file. These images offer less noise because, contrary to popular opinion, smaller pixels render less visible noise detail, resulting in clearer images. Another benefit of this more natural approach is that it results in fewer distortion effects such as moiré and aliasing. This process is of course a lot more power hungry and will demand a lot from the camera’s CPU, but if you have the time and camera power to oversample, this is the best way to go for the best possible image quality.

So, there you have it! We hope you enjoyed taking this rather nerdy journey with us. Next week, resetting your Wi-Fi router.

(Not really.)