I’ve developed a reputation for having the longest blogs of anyone at Action Camera. This one is going to bring my average length way down because that answers to the questions above, though asked over and over since the specs of the 7S III we’re leaked, are quite simple.
Why only 12 megapixels?
Simply put ,more megapixels than you need only leads to smaller photosites which leads to less light and more noise. Typical 4K resolution is 3840 x 2160 pixels ie. 2160p. Do the math and you’ll find that you only need 8.3 megapixels to arrive at true 4K resolution. So, the question is not why 12MP but why not 8.3? The answer that is also quite simple. Movies shot in standard 4K are shot in a 16:9 aspect ratio like most modern TV’s and computer monitors, and 35mm or full frame sensors are 3:2 aspect. What it boils down to is that Sony would rather have “extra” pixels top and bottom for those may want to use the 7S III as a hybrid camera; stills and video. What all that means is that the 7S III has 12MP because that is the optimum number of MP for shooting 4K video if your sensor is 3:2 aspect ratio.
One more downside of a superfluous megapixel count is that it causes unnecessary strain on the processor which can lead to heat issues. I’m lookin’ at you Canon… Further it causes a camera to jump through hoops to arrive at your final resolution. If your goal is 4K footage but your sensor has a megapixel count that is too large than your camera must do one of several things to output 4K.
Oversampling, or down-resing from say a 6K or even 8K capture down to 4K is the best way to achieve this and gives you the best over all image detail but again takes massive processing power. To avoid this most cameras will employ pixel binning or line skipping. Rather than go into the details of what these mean let’s suffice it to say the both save processing power at the expense of image quality and detail. The final method is a simple crop. This means using a portion of the sensor equivalent to 8.3MP. This not only cripples the sensors ability to gather light but also adjusts the “crop” of your lenses resulting in a change in the field of view of your lens. Simply starting with a sensor of the appropriate size and MP avoids all these issues.
Is 12MP enough?
Well, through the course of answering the first question I pretty much answered this one. Not only is it enough it’s optimal. But in case you still needed more evidence; evidence that is less confusing and more in your face, and conclusive… here goes.
Blade Runner 2049, A Star is Born (2018), Green Book, Solo: A Star Wars Story, and Game of Thrones; No, these films were not shot on the Sony A7S III, nor we’re they shot a 12MP camera. They we’re all however shot using the Arri Alexa Mini. The Arri Alexa Mini has a max resolution of 3424×2202. 7.5MP. Need more convincing? The Arri Alexa SXT has a movie credit list nearly as impress as the Alexa Mini, including; The Black Panther, Marry Poppins and Bohemian Rhapsody. Yep… also 7.5MP max resolution.
Bottom line: If video is your thing and you we’re wondering if 12MP was going to an issue; stop worrying. See… pretty short for one of my blogs.