SAR DAR PAR = Mind blown

[Cheech]

I've tried really hard to figure this out on my own, because it seems like a common question, but I cannot wrap my head around this concept.

I have a 16/9 DVD source, no cropping, no resizing, the actual pixels are 720x480.

So I fire up MeGUI which I recently am trying to learn and I see they have preset AR's with ratios out of left field, where the heck did 1.822784 for NTSC come from, and why does PAL have a different one? How can you call something 16/9 when WxH != 1.777777 or in my case a DAR of 1.18519 if I'm doing the calculation right.

If I take MeGUI's weird ratio it thinks is right and do the math:
720*1.822784 = 1312.40
1312.40/480 = 2.734! That nowhere near 16/9

What am I doing wrong?

[allanon019]

I just use resize and use 720x400, which is perfect widescreen. Also, if you don't want any black borders at all, then try resizing to 720x408

[dat720]

DAR is the display aspect ratio, 1312x480 is what the image is stretched to by the player, the video is not actually 1300 pixels wide, it is still 720 or what ever it started at, the DAR is what the player will stretch the video to to maintain the PAR (pixel aspect ratio) someone with more knowledge correct me if im wrong.

[mikeytown2]

This is a good start
http://avisynth.org/mediawiki/Aspect_ratios

[J_Darnley]

If I take MeGUI's weird ratio it thinks is right and do the math:
720*1.822784 = 1312.40
1312.40/480 = 2.734! That nowhere near 16/9
It should be obvious that you are multiplying the the wrong thing by the aspect ratio you are getting from MeGUI. The Display AR is obtained by dividing the width by the height.
E.g. 1920 / 1080 = 16/9 therefore 1080 * 16/9 = 1920 and that means that 480 * 1.822784 = 874.93632 which is your display width.

If you want to know why a 16:9 video is not exactly 16:9 look at the ITU specs and docs. The link that mikeytown2 posted is a very good place to start. In short it is all very complicated and and comes from analogue transmission of video

[Keiyakusha]

Sorry that I write here, my question is very simple (I hope so) and slightly relates to the topic.

Tell me please, in how many times resolution 1280x720 is bigger than 640x360?
-- 2 times, if it is considered on diagonal?
-- 4 times, if it is considered on number of pixels?
In what cases, how I should calculate?

Thanks!

[J_Darnley]

Sorry that I write here, my question is very simple (I hope so) and slightly relates to the topic.

Tell me please, in how many times resolution 1280x720 is bigger than 640x360?
-- 2 times, if it is considered on diagonal?
-- 4 times, if it is considered on number of pixels?
In what cases, how I should calculate?

Thanks!

1280/640 = 2 <-- the horizontal scale factor is 2
720/360 = 2 <-- the vertical scale factor is 2
The diagonal is also twice as long

(1280*720)/(640*360) = 2*2 = 4 <-- the image has 4 times as many pixels, the area is 4 times greater.

What do you mean by "In what cases, how I should calculate"?

[Gavino]

Tell me please, in how many times resolution 1280x720 is bigger than 640x360?
-- 2 times, if it is considered on diagonal?
-- 4 times, if it is considered on number of pixels?
You are correct on both counts...

There is no 'right' answer to the 'how many times' question.
Before we can tell you the answer is 'x', we need to know the context of your question and what you are going to do with that number 'x' once you have it.

However, I think when people talk about resizing by a factor of 2, they usually mean doubling the width and height, giving 4 times as many pixels.

[Keiyakusha]

J_Darnley
It is hard for me to write in English, sorry. Just forget about last question.
However, I think when people talk about resizing by a factor of 2, they usually mean doubling the width and height, giving 4 times as many pixels.Ok, I think this enough for me. :thanks: