Pixel Shape - square versus rectangle

[jjkilleen]

Are there HDTVs whose pixel shape is non-square or which change pixel shape as a function of signal type or TV settings?

[Richard]

All digital video systems are based on a pixel matrix that uses square pixels from capture to delivery and presentation.

All FPD's, fixed pixel display, are stuck with what they are and cannot change so no, they cannot change shape based on content/source.

The two HD pixel matrix are 1280x720 - 720p and 1920X1080 - 1080i/p. Best performance comes from having a display that is native to one of those and even then the best response will come from sources that also match. Native 720p is very difficult to find if not impossible in a flat panel display.

For various reasons there are numerous displays that are not native to either one. The worst offenders are those that clearly do not use square pixels such as 1024X1024, 1024X768 or 1280X1080 ect. yet still retain a 16:9 aspect. 1024X1024 is a square, 1:1, if using square pixels so at 16:9 they have to be rectangular. Either way all of these have one thing in common; any video source has to be scaled to the oddball matrix the display uses and you cannot bypass it with an HD source because it simply does not match.

This is a sheer videophile performance concern only as many have been satisfied with a non-conforming pixel matrix.

Viewing HDTV on a Computer Monitor
viewtopic.php?t=8486

[jjkilleen]

Thanks-I thought that was the answer. My post was triggered by what I thought was an error in another forum. I'm just getting into HDTV, and there's an incredible amount of misinformation out there.

[eliwhitney]

jjkileen-

In your surfing, here are (3) that might help some -

http://practical-home-theater-guide.com ... ratio.html deals with rather uselessness of all the popular huge numerical numbers, ratios, etc., which are rampant but have little meaning...

http://www.htguys.com/archive/2006/November142006.html offers an in-depth article about 720p Vs 1080p... when / why / etc..

http://hdguru.com/?p=107 see 30 July article about possible Throwaway HDTV by Brands due to no Service at all after 365th day or No Parts, or Costly prepaid round trip Freight, etc..

Good Luck !
eli whitney

[jrben1]

Any discussion about pixel ratios should also include the ratio of the pixel itself. Photographic pixels are actually square and have a pixel ratio of 1.0. In other words the height is the same as the width. The pixel ratio for NTSC TV is 0.9, or height greater than width. The pixel ratio for widescreen (16X9) is 1.2. When you do video editing and import photographic stills you have to adjust the pixel ratio in order to avoid distortion.

[Richard]

I'm scratching my head here... HD is based on square pixels... do the math - they have to be square.

When you do video editing and import photographic stills you have to adjust the pixel ratio in order to avoid distortion.

To maintain the clarity of the original it has to be bit mapped to the display. Any other method would require scaling - forcing one pixel depth into another in which they do not match. This must be what you are referring to...

If you capture in 1920X1080 then in a perfect world a 1920X1080 display will reproduce that flawlessly. This isn't a perfect world so you would have to find a display that meets video standards first - they exist.

If you capture in anything other than 1920X1080 it will have to be scaled. 1920X1080 into a 1280X720 would have to have flaws and 4000X2000 into a 1920X1080 would have to have flaws.

There are all kinds of variables with this but trying to keep it simple at this point...

[jrben1]

Open Adobe Premiere Pro and import a widescreen clip, then check it's properties. You will find that the pixel ratio is 1.2. If you import a still image from Photoshop the pixel ratio will be 1.0. This must be adjusted to 1.2 to prevent distortion of the still image.

[akirby]

Understanding aspect ratios

[quote]Frame aspect ratio

Frame aspect ratio describes the ratio of width to height in the dimensions of an image. For example, DV NTSC has a frame aspect ratio of 4:3 (or 4.0 width by 3.0 height). For comparison, a typical widescreen frame has a frame aspect ratio of 16:9; many camcorders that have a widescreen mode can record using this aspect ratio. Many films are shot using even wider aspect ratios.
A 4:3 frame aspect ratio (left), and a wider 16:9 frame aspect ratio (right)

When you add clips into a project with a different frame aspect ratio, you must decide how to reconcile the different values. For example, there are two common techniques for showing a widescreen movie with a 16:9 frame aspect ratio on a standard TV with a 4:3 frame aspect ratio. You can fit the entire width of the 16:9 frame into a black 4:3 frame, a technique called letterboxing, which results in black bands above and below the widescreen frame. Or, you can fill the 4:3 frame with only a selected area of the 16:9 frame, a technique called pan and scan. Though this technique eliminates the black bars, it also eliminates part of the action. Adobe Premiere Elements automatically letterboxes any 16:9 footage that you add into a 4:3 aspect ratio project.
Pixel aspect ratio

Pixel aspect ratio describes the ratio of width to height in a single pixel of a frame. Pixel aspect ratios vary because different video systems make different assumptions about the number of pixels required to fill a frame. For example, many computer video standards define a frame that has a 4:3 aspect ratio as 640 x 480 pixels. Pixels that are square, which have an aspect ratio themselves of 1:1, perfectly fill the horizontal and vertical space defined by that frame. However, video standards such as DV NTSC, which is the standard followed by most consumer DV camcorders (sold in the U.S.), define a 4:3 aspect ratio frame as 720 x 480 pixels. Consequently, in order to fit all of these pixels in the frame, the pixels must be narrower than the square pixels. These narrow pixels are called rectangular pixels, and they have an aspect ratio of 0.9:1, or 0.9 as they are commonly called. DV pixels are vertically oriented in systems producing NTSC video and horizontally oriented in systems producing PAL video. Adobe Premiere Elements displays a clip

[Richard]

However, video standards such as DV NTSC, which is the standard followed by most consumer DV camcorders (sold in the U.S.), define a 4:3 aspect ratio frame as 720 x 480 pixels. Consequently, in order to fit all of these pixels in the frame, the pixels must be narrower than the square pixels.

Yep, NTSC video is a mess... glad it is going away...