In case you haven’t heard the News: The word pixel is a short hand term for “picture element” and pixels of various shapes create a video display.
If This Is It?
Not all pixels are created equal, in shape that is. Confusion arises because some pixels are square in shape, while others are rectangular. Computer displays always employ square pixels, but video (such as on a TV or a DVD) usually employs rectangular shaped pixels. The ratio between the width and height of the rectangle is called the pixel aspect ratio. Square pixels are said to have a 1:1 pixel aspect ratio, that is the height and width are equal. However, there are many video standards with different pixel shapes, both in the rapidly diminishing analog world and the new frontier of digital video. For example, one commonly used standard definition acquisition format – known as D1 or DV format, can represent either full screen (4:3) video or widescreen (16:9) using the same screen pixel dimensions (720x480). The pixel aspect ratio for 4:3 video is 0.9, which creates a tall, skinny pixel; with a slight change of heart, the same pixels interpreted with a 1.2 aspect ratio makes a short fat rectangle that is used for a widescreen video (called anamorphic). In order to see the forest for the trees, the device onto which the video is displayed must be set properly to know how to interpret these pixels. The terms full screen and widescreen are common consumer electronics formats that relate to the aspect ratio of a television screen, which brings me to an important point.
Sometimes Bad is Bad
Another perplexing factor is that the “frame aspect ratio” of a display is really independent of the pixel aspect ratio of a particular piece of video. The frame aspect ratio of a television, no matter what kind, is either full screen 4:3 ratio, or widescreen 16:9 ratio. Nearly all modern LCD and plasma flat panel TVs are widescreen, having a 16:9 frame aspect ratio. Widescreen ratio is the same or similar to the origination formats for high definition video and film, and really makes for a superior viewing experience (great for Sports IMHO), but, not everyone has a widescreen TV yet. Computer displays are still available in 4:3 formats, but most manufacturers are moving aggressively into widescreen (actually most computer widescreens have a 16:10 ratio…I can hear your collective groans of confusion and frustration, you need a couple days off to digest this right?).
Walkin’ on a Thick Line
Actually more like bars than lines…I’m talking black bars around the edges of a video. Everyone has probably viewed a program where black bars were added to the top and bottom of the picture (letterboxed), or to the sides (pillar boxed). This is necessary when displaying video in an (frame) aspect ratio that is different than the source aspect ratio. If you are showing a widescreen video on a fullscreen display, the total size is reduced, leaving empty black nothingness at the top and bottom. Conversely, when fullscreen video is displayed on a widescreen display, black bars appear on the sides, as the smaller picture is centered on the larger screen. And then there is the most awesome situation where a letterbox has already been imbedded into a 4:3 video and when you put it into a widescreen display, you get a black box around the whole video – it’s like watching a TV at the end of a long dark hallway!
Of course, different manufacturers have come up with other ways to deal with ratio conversion, including a number of zooming and stretching algorithms that distort the video in different ways so as to get rid of the bars. Take away the keys because this drives me crazy, especially when a fullscreen video is stretched side-to-side and everybody looks fat (or at least much fatter than they are in real life!). The opposite is true when squeezing widescreen video onto a 4:3 screen and everything is squished. It frequently looks similar to how things (reportedly) look after ingesting certain hallucinogenic compounds, leading me to conclude that I want a new drug!
Picture This
When viewing video on a computer, there are some different considerations. Since computers always display square pixels, everything should always look correct right? First, I have seen many a computer screen that has been forced into the wrong aspect ratio. There are a number of reasons this might happen, but most computer graphics cards should be able to display both widescreen and fullscreen ratios, you just have to set your resolution correctly. Also, video that originated in a non-square aspect ratio needs to be properly converted to a square pixel ratio (which requires changing the video dimensions) or it will not display correctly. You don’t have look too hard on the Internet to find video that is improperly formatted, crappy video is especially prolific on the web! But me, I believe in love and pristine video, do you? Even if you are hard at play, take some time to figure this just take some time to figure this stuff out and you too will have faith in the power of pristine video.
Here is a handy guide showing how various aspect ratios look on different displays.
Jeff Maslouski is manager of post production and is truly capable of putting a room into a hypnotic trance with his excruciatingly precise explanations of all things technical.
