Aspect Ratios and Sensor Sizes for Video Beginners
Back in the film days, the most commonly used aspect ratio for 35mm films was 4:3. When the audio track was introduced for “talkies”, it was slightly adjusted to 1:17:1. As time went by, cinema film usually remained wider than television.
What is DAR, PAR, and SAR?
Today, digital video aspect ratios have caused a little bit of confusion among filmmakers. There are different types of aspect ratios in digital video, not just one. The one that most people are familiar with is Display Aspect Ratio (DAR). DAR is the ratio of the width-to-the-height of the display frame for any video and, in general, is the aspect ratio of what we see. We commonly know this as 16:9, which is widescreen, and 4:3, which is full screen. Cinema has two leading standards: a normal 1:85 widescreen and anamorphic 2:39 (we’ll get into that a bit later). The other two aspect ratios are Storage Aspect Ratio (SAR) and Pixel Aspect Ratio (PAR) and they all coincide with each other. When a video project is stored onto a disc, it’s outputted with a certain aspect ratio, the SAR. Whoever is placing this info on the disc usually has a set aspect ratio already in place for the project and, therefor, the video is already proportionally scaled to the correct size for viewing. This is when SAR and DAR are equal. For example, a video project chosen to be displayed at 16:9 shows the stored footage at 1280 x 720p. They are the same aspect ratio.
However, there are times when the storage (SAR) does not match the output display. This is when the image becomes distorted or cut off. If the 16:9 display is stored with footage that is set to 720 x 480p, then the SAR will not match and is essentially 720:480= 3:2, which is not 16:9. This would be considered “anamorphic” video and this is where PAR (Pixel Aspect Ratio) comes into play. The pixels of stored video are considered to be either square or non-square and here is the basic equation of how it all comes together:
Display Aspect Ratio = Pixel Aspect Ratio x Storage Aspect Radio
Standard Video and High Definition Video
Sticking to the basics, standard television channels and older televisions are set to the 4:3 aspect ratio. For High Definition (HD) videos, the DAR is fixed to 16:9. A lot of gear is currently made with formats that include HDCAM, DVC-PRO, and XDCAM. These formats may not necessarily store the footage in the native 16:9 sizing but it does use “squeezed” anamorphic formats to keep high quality. However, most HD formats, such as BluRay and PRoRes422, are all stored in native HD frame size. As a result, DAR and SAR are the same and the PAR is 1:1 making the image look super crisp and pristine.
In the universe of image sensors in video, bigger is better when it comes to image quality. Many of the newer cameras, editing workflows, and software are able to work with this new technology. There are those who opt to shoot with GoPro’s 4k Black Edition Camera and then there are those who shoot with the Blackmagic Production 4k Camera. While they’re not able to shoot the same frame rate, they still shoot at the same sensor with 4k, right? Essentially, yes. They can both shoot images that are captured at 3840 x 2160 pixels or better and while they are performing the same function, they’re pretty different. Basically, an image sensor takes light and converts it to a digital format which the camera then wrangles into an image. The bigger the sensor, the more megapixels it takes in equaling a high quality image. This means that each pixel is able to capture more light information, which then leads to better color depth, much more accurate definition in light and dark, producing a cleaner image.
What’s all that Digital Noise?
Have you ever seen that grainy look you get in your images when you crank up the ISO or gain in your camera? That occurs when we try to get more of an image in a low light scenario. This is indicating that the sensor doesn’t have the capability to deliver more light to the actual image, or more of a signal than noise. If you have a larger sensor, then it has more opportunity to send a greater signal, hence not receiving “noise” in lower lit situations.
When working with cameras, it’s important to know your sensor’s size, which includes the crop factor. Crop factor is the field of view for an image when compared to smaller sensors against a full frame sensor. The actual calculation for figuring out the crop factor on a camera body relates to the surface area of the sensors. For example, the APS-C image sensors found in cameras such as the Canon 60D is 22.3 x 14.9mm whereas the full frame image sensor in a Canon 5D Mark III is 36 x 24mm. That means the Canon 5D III is approximately 1.6 times the surface of the 60D, making the crop factor for the 60D 1.6x. To break it down, if you were to use a 50mm prime lens on the 60D body, the focal length will be equivalent to a lens 1.6 times the length, making that 50mm sit like an 80mm on the 60D.
Full frame cameras have a sensor size that is the same size as a frame of 35mm film. Many times the sensor size measurements are based off of old television cameras. APS-C sensor cameras are called that because their sensor size is the same as classic APS-C format film. Nikon, Pentax, and Sony crop sensors usually measure around 23.6 x 15.7 while Canon crops are 22.2 x 14.8mm. Micro Four Third cameras measure smaller at 17.3 x 13mm. While full frame sensors are usually found in DSLRs, there are a few compact cameras that hold the same punch, like the Sony RX1, and a few larger or “bridge” cameras that have itty bitty sensors like the Panasonic Lumix FZ1000. It’s worth checking out the sensor size and learning about aspect ratio when deciding on what camera to shoot with for your next project. If you’re just starting out with video, you may also find it useful to visit our guide on the best DSLR cameras for video before you select your gear and begin shooting.