Ask HD Beat: Does 480p and 16:9 Really Match?
By Ben Drawbaugh 
posted April 25th 2006 4:45PM
posted April 25th 2006 4:45PM
Reader Ralph writes in and asks: Does 480p and 16:9 Really Match? If a video game is 640x480 which is
obviously not 16x9 how is the image 16x9? So is it some behind the scenes TV work that is going on to make the image
widescreen? Or is the image stretched slightly?"Yet another great question by an HD Beat reader. This really drove me nuts until I researched it. You sort of already know the answer, the picture is displayed in the appropriate aspect ratio regardless of the actual resolution. The reason is that not all pixels are square. Any image can be made up of any number or shape of pixels. When we watch 640x480 on a 4x3 TV the pixels are square as they are with 1280x720 on an HDTV. When we watch most SD widescreen video like Fox Widescreen or video games which are only capable of displaying a certain number of pixels, they use square pixels so they can produce a 16x9 image.
DVD players do this as well as video game consoles and cable boxes. This is why they all these devices have settings which allow you to set the aspect ratio of your TV. If you turn it to widescreen even though you don't have a widescreen TV the image will be distorted. Some cable boxes will actually add black bars on either side so that the image is not distorted by the TV. The interesting thing is that DVDs are 720x480 which also isn't 16x9, but thanks to anamorphic abilities of your player, your TV scales the image to the native resolution of your TV. All the more reason to go HD on your DVD player.
Fox Widescreen has worked like this for years, Fox was the first to update their infrastructure to digital, but before HD was prevalent, as a result they were reluctant to go HD and ended up the last of the 4 major networks to go HD. They were able to do this because their video was recorded with cameras with 16x9 modes that effectively shrinks the pixels to SD and then stretched them back at the other end. Fox Widescreen still continues to fool many people during promos and shows like Cops; people think they are HD just because they are widescreen. Some people have actually captured images of Fox widescreen in a 4:3 fame due to technical difficulties.
DIRECTV is also known to shave some pixels off in order to save bandwidth. Some call it HD lite, but basically instead of sending out 1920x1080 they will transmit 1280x1080. This is how their HD has some of the lowest bit rates in the business. But regardless of how many pixels they shave off we still see a 16x9 image.
Any info on DirecTV's performance on their MPEG4 feeds?
Another interesting example... Stand-alone TiVo units record shows at 480x480 for SD 4:3 sets - obviously using rectangular pixels.
This has been happening in the UK for a while. We've had digital TV (terrestrial, satalite and cable) since '97, but are only just getting HD. Our digital transmisions are in 720x576, but to save bandwidth quite a few channels shave off pixels but keep the aspect ratio. Channel 4 usually broadcast in 704x576, and I think some of the Sky and shopping channels are lower than that.
Hey I asked that same question just the other day on digg, no one really answered/knew though I guess. Well now I know to ask hdbeat first next time :D
On a relating note, Nintendo with their Revolution still! hasn't said whether or not they are making all their games with widescreen by default. Even worse they have confirmed that its games will not be HD (720 or 1080) but only 480p, but if they end up not supporting widescreen with this machine that'll be around for a good 5 years I really think they're shooting themself in the foot. Sure HD isn't yet a big time average household commodity, but its growing hellishly fast and who knows where we'll be by 2010.
Isn't fox in 720p HD now?
DirecTV's HD Lite is a crime. If consumers continue to accept this treatment we can forget about every having true HD from MSOs.
The two worst things to happen to HD are HD Lite and Multicasting.
So this article is a month old at this point, but I thought I might clear some stuff up anyway. I'm an HD broadcast producer and always find it interesting what people consider HD and not HD.
For starts, what is this 640x480 on SD TV that is being listed? Broadcast SD is 720x486, SD never used square pixels for 16x9 or 4x3. HD is broadcast using non-square pixels as well, but it's also SHOT using non-square pixels. Two main formats for anything shot in HD would be DVCProHD and HDCam. DVCProHD is 1280x1080 in 4:2:2 for 1080i and 960x720 4:2:2 for 720P. HDCam is 1440x1080 in 3:1:1 for 1080i. So, neither will actually give a recorded format of 1920 pixels at all, and chroma will give you far less...chroma resolution would be 640x1080 for DVCProHD and 480x1080 in HDCam.
So yes, not all pixels are square, but also realize that not all resolutions contain full RGB888 resolution, any video broadcast/record format is in a YUV or similar colourspace that subsamples chroma far more than luma.
And to say that HD Lite is a crime is pretty ignorant, since most of the time your HDTV doesn't even have 1920x1080 resolution. Just because it is a 1080i HDTV doesn't mean it has a true effective resolution of 1080i. We were doing some broadcasting at E3 displaying on 42" monitors that were 1024x768 widescreens, no body would have guessed that these were technically "not HD".