understanding resolution and aspect ratios

[Andy in NY]

Let me preface by saying that i just spent all damn day reading the "black bars" thread, and this certainly isn't what i'm asking about.

But recently I bought an apple tv and am transfering all my dvds onto it. Im using handbrake to encode them. I notice that there are 2 things when it comes to the picture... aspect ratio and then theres another number... usually 8** x 5** or 1028 x 720 (those are just random numbers, not specifics). what do those numbers mean? I suspect something to do with resolution, but i'm not sure. if they are having to do with resolution, can i change them to "upconvert" the picture quality? i notice a difference between viewing them from an upconverting dvd player and watching them on the apple tv.

[nmycon]

an aspect ratio is a ratio

as in, comparing 2 numbers such as 4:3 or 16:9

basically, this means:

4:3

for every 4 "units" the picture is wide, it is 3 "units" high

16:9

for every 16 "units" the picture is wide, it is 9 "units" high

1.78:1 is full screen on a 768p/1080p screen

it means every 1.78 units wide = 1 unit high

We can prove this:

1080p resolution is 1920x1080

1920 divided by 1080 = 1.77777778, rounded to 1.78

You may think "what about 4:3 or 16:9? Thats more complicated!"

not really, does 1.33:1 sound familiar? That is pan and scan full screen to a ratio of 1.

4:3 = 4 divided by 3 = 1.333continued

Do the same with 16:9 and you'll find that it is the same as 1.78:1

SO TO SUMMARIZE EVERYTHING!

the numbers 1920x1080 is a resolution, a measurement of how large the video actually is on your screen (measured in pixels, just like cm or inches in the real world)

an aspect ratio shows how the length/height of the video (in pixels) are related

for example, a film with a resolution of 1366x768 and 1920x1080 both have an aspect ratio of 16:9 or 1.78:1 but are different sizes

I hope I explained it so that you were able to understand!

[U4K61]

Originally Posted by Andy in NY

Let me preface by saying that i just spent all damn day reading the "black bars" thread, and this certainly isn't what i'm asking about.

But recently I bought an apple tv and am transfering all my dvds onto it. Im using handbrake to encode them. I notice that there are 2 things when it comes to the picture... aspect ratio and then theres another number... usually 8** x 5** or 1028 x 720 (those are just random numbers, not specifics). what do those numbers mean? I suspect something to do with resolution, but i'm not sure. if they are having to do with resolution, can i change them to "upconvert" the picture quality? i notice a difference between viewing them from an upconverting dvd player and watching them on the apple tv.

"resolution"
The number of pixels a fixed-pixel-array display such as LCD/Plasma has. For a CRT, it is the number of scan lines (and how many pixles it has per line). If the source and the sets native resolution are different, a scaling engine is used to match the incoming picture format to the display such as converting a 480p DVD image to 1080p. The 1080p PQ, however, will probably be lower then the origional 480p, as the mapping is not 1:1 as it would have been on a native 480p set. See The fallacy of upconversion: 4x4 Image upscaled to 7x7. Obviously the 7x7 image is not what the director intended.

Some common video resolutions:
480p = 720 x 480
576p = 720 x 576
720p = 1280 x 720
768p = 1366 x 768
1080p = 1920 x 1080
What we see advertised in the store or printed on the box is the set's vertical resolution, which is the number of horizontal 'lines' it has. Just multiply the horizontal and the vertical to find out how many pixles the sets native resolution is. 1920 x 1080 = 2,073,600 pixels.

"aspect ratio"
A ratio such as 4:3 or 16:9 (incorrectly written as 4x3 or 16x9) is just an equivalence class: 4(n):3(n) and 16(n):9(n).

4:3 = 1.33. 8:6, 12:9, 16:12 are all really the same as 4 'over' 3. We know this by dividing both the top(numerator) and bottom(denominator) of a fraction until you can't go any further or by using Greatest Common Factor. 8:6 = 4(2):3(2).

Ditto for 16:9 = 1.78. 720p and 1080p sets are both 1.78 even though they have different numbers of square 1:1 pixels. 16/9 = 1.78, 1280/720 = 1.78, 1920/1080 = 1.78

Pixel Aspect Ratio 3:41
Finding the Greatest Common Factor, GCF 10:21
Prime Numbers 5:15
Prime Numbers - The Sieve of Eratosthenes 2:55