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Old 11th January 2003, 18:16   #1  |  Link
manono
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Resolutions, Aspect Ratios And The ITU-R BT.601 Standard

Hi-

We often get questions from people with varying degrees of experience, about the three subjects in the title of this thread.

One kind of question might have to do with the appearance of the vob files as they are displayed in DVD2AVI or after the .d2v is opened in GKnot. Sometimes people want to just crop the black bars and encode the vob as is, or even encode without cropping at all. But as most of us know, the vobs show the video as it's stored on the DVD, which is not the correct Aspect Ratio. Your DVD player will resize it depending on whether the Display Aspect Ratio (DAR) of the DVD is 4:3 or 16:9. The easiest way to get the DAR is from DVD2AVI when it creates the .d2v. So, the video should be not only be cropped, but resized to proper AR as well.

When cropping and resizing in GKnot, make sure that you have the proper Input Resolution ticked (PAL or NTSC) and the proper Input Pixel Aspect Ratio ticked (default is 16:9). If you use the Auto Crop, be sure and scroll the .d2v afterwards to make sure it did it correctly and that the Aspect Error is low. Or you can tick Pixel Crop, crop the black bars, and then use Smart Crop Left-Right or Smart Crop All. Personally, I set the horizontal resolution I'm aiming for, and then, using the Pixel Crop only, crop the black bars on all sides, and if necessary, crop more on the left and right sides and sometimes from the top and bottom, in order to get the Aspect Error as low as possible. Although it's been said that the eye can't detect Aspect Error until it's above about 2% (when round things start to appear as slight ovals), it should be pretty easy to get it down below .5%. In addition, I'll always try to make all crop figures as even numbers. Afterwards it's usually a good idea to hit View-Resized on the .d2v picture and scroll around to make sure that the faces look normal, and that round things (balls, sun, moon, clocks, wheels, etc.) look round. GKnot doesn't always give you even number crop values. The reasons for the importance of all even numbers are explained by hakko504:

=============================================================================

There are some restrictions on cropping in AviSynth:

In YUY2:
width mod-2
height no restriction if video is progressive
height mod-2 if video is interlaced

In YV12:
width mod-2
height mod-2 if video is progressive
height mod-4 if video is interlaced


Using other crop-values can create strange artifacts at the end of lines/frames. Crop(3,0,716,480), for example, is NOT acceptable as it means you have split a pixel pair! The values are stored in AVIsynth in pairs (or 2x2 matrixes in the case of YV12), and they should never be separated. The restrictions I mentioned are applicable to both the values you feed to Crop() using the above notation, as well as the final resolution.

The reason interlaced YV12 has mod-4 resolution is that it stores the chroma for line 2 and 4 in the same unit! The chroma for line 1 and 3 is also stored in the same unit.

Consider this, a small progressive picture of 4x4 pixels:
Code:
Luma:             Chroma
AABB              A B      
AABB
CCDD              C D
CCDD
A,B,C& D are pixels that share chroma data.
Now this wouldn't be so bad to cut in half right? But now consider an interlaced picture with the same dimensions:
Code:
Luma:             Chroma
AABB              A B      
CCDD
AABB              C D
CCDD
If you cut this in half, the two bottom lines disappear, and along with them the color information for line 2! Not good.

But lets say that you cut 1 pixel from each side in the 4x4 frame. That should work, right? No, not really, because then you would have to interpolate to get the new chroma value { (A+B)/2 }

This situation will never appear in RGB as every pixel has full data in all channels, but even here it is a good idea to make the fields have the same size, hence mod-2 on height. YUY2 on the other hand stores the data so two pixels next to each other shares the chroma data, and should therefore not be separated.
=============================================================================

We frequently get questions about not being able to hit the desired resolution. Instead of 640x272, you might wind up with 640x256, or 640x288. You have to remember that a 2.35:1 movie (for example) isn't usually exactly 2.35:1. As near as I can tell, it might be between about 2.20:1 and 2.40:1, so you aren't always guaranteed to get the resolution you desire. But if you have followed the previous steps correctly, and have gotten a low Aspect Error, then you have a proper Aspect Ratio, and that's the main thing. But if you used Smart Crop All (which crops from the top and bottom), you might try Smart Crop Left-Right (which crops as the name implies).

And one more thing. Many people insist on messing around with the W-Modul and H-Modul. I highly recommend leaving them at their default values of 32 and 16. There is a case that can be made for setting them both to 32 (better compressibility, although it limits the resolutions available to you). And you can probably get away with setting them both to 16 (but with less compatibility). But for both compressibility and compatibility reasons, you should not set either of them to 8 or lower. TheWEF explains the reasons for this:
=============================================================================

divx is encoded in macroblocks of 16 x 16 pixels.

e.g.:

640 x 272 = 174080 pixels = 680 macroblocks.

640 x 274 = 175360 pixels (0.7% more) = 720 macroblocks (5.9% more).

more macroblocks - more compression overhead.

for compressibility reasons i highly recommend to at least use w-mod and h-mod of 16 pixels.

w-mod 32 is recommended for playback compatibility on older gfx-cards.
=============================================================================

The main reason for this thread though, is to post a reply that TheWEF made recently on the subject of the Pixel Aspect Ratio (PAR) and the ITU-R BT.601 Standard. In the Options Tab of GKnot is an option to check in order to resize to the standard. We often get questions about whether or not to check the box. Here is what he has to say on the subject:
=============================================================================

with gknot you want to create divx-avi-computer-video. the correct pixel aspect ratio for this type of video is 1/1 (square pixels).

most video formats do NOT have square pixels, reasons are historic, most formats are of analog origin.

so we have to stretch the pixels to get correct aspect ratio in our avis.

but how do we know the pixel aspect ratio of the input format? - usually resolution is a good hint. following the link below you find "3. A Conversion Table for Digital Video Formats". every resolution has a certain pixel aspect ratio.

of course, with a computer, you can produce video with "any" resolution and PAR you like. so you could download an avi of 720x480 with a PAR of 1/1. someone just made it that way, it will not fit in the conversion table.
but if the source is any kind of standard video, like broadcast, dvd, vcd, svcd, vhs, hi-8, any capture.avi,...anything, the values in the table are correct.

example:
resolution on most ntsc-dvds is 720x480.
in the table you find 72/79 = 0.911 is the PAR for this resolution.

now there is one more thing: it's possible that a video is stretched even more in a certain standardized way called "anamorphic transfer". the PAR values you find in the table are for "non anamorphic transfer". if you want the anamophic PAR for a certain resolution you have to multiply the value with 4/3 = 1.333

example:
720x480 ntsc anamorphic
PAR = (72/79) x (4/3) = 1.215

in gknot you can always see the currently selected PAR right next to "other..." in the "Input Pixel Aspect Ratio" box.
if you open a video with a resolution of 720x480 gknot will automatically select ntsc anamorphic and you can read a PAR of 1.125

you can enter any PAR you like in the "other..." box. usually that doesn't make much sense. but if you press "select" you can select from all the common PARs in the table, anamorphic or not.

some capture cards use some strange half resolutions, e.g. a common one in the PAL world is "Halfe-D1" (360 x 576), half of 720x576.

example if you want to convert such a capture.avi to divx:
press "select", select "128/117 PAL (720x576),..." and check "double" - press "OK".
new PAR is (128/117) x 2 = 2.188


got all that? - ok.




gknots output PAR always is 1/1. but it's possible to convert to any output format you want, you just have to do some manual calculations.

example - you want to convert an ntsc-dvd-anamorphic to a pal-svcd-non anamorphic:
input res is 720x480 -> input PAR=(72/79) x (4/3)
outut res is 480x576 -> output PAR=(128/78)
in "other..." you enter (input PAR) / (output PAR) =
((72/79) x (4/3)) / (128/78) = 0.7405
move the slider to get a resolution width of 480 and save the avs.
you have to edit it manually and "AddBorders()" to get a output resolution hight of 576.
(read avisynth docs if you don't know how to do that)
then e.g. encode with tmpg...



now what's this ITU checkbox in gknot?

if you leave it checked gknot will simply follow the standards and use the PAR values from the table - highly recommended.
if you enter a custom PAR value in "other..." or use the "select" button the checkbox does not have an effect anyway.

so why uncheck it?

if you resize a full non anamorphic ntsc-dvd frame (720x480) to 640x... according to CORRECT standards you get 640x468 and that is NOT a display aspect ratio of 4/3.
if you watch it on your 4/3 computer monitor using a 4/3 desktop resolution (e.g. 640x480) the frame does NOT fill the screen.
when you watch the dvd with your software dvd player (e.g. powerdvd) the frame DOES fill the screen. why? because the programmers accepted a slight AR-error in order to avoid black bars in full screen. the players do it WRONG, but you can't see it because the difference, the AR-error, is too small. you could see the black bars though, so...
some people prefer to resize like the software dvd players do, so they uncheck itu.



it's quite hard to understand all the stuff you can read in the Quick Guide to Digital Video Resolution and Aspect Ratio Conversions. it's simply too much for most people. that's why doom9 still has the simple explanation in his Aspect Ratios Explained. it's an easy way to look at the problem and enough for most people.



wef.

Last edited by manono; 15th January 2003 at 19:19.
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Old 12th January 2003, 02:12   #2  |  Link
TheWEF
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Quote:
Originally posted by valnar
So my question remains. If I watch a given 4:3 DivX movie in a window, I would want it unchecked to get a correct AR...
leave it checked, leave it checked, leave it checked,...


here are reasons i can think of to uncheck itu:

1) you know for certain that the dvd has not been mastered correctly.

2) you are willing to accept the (slight) ar-error, because...


a) you do NOT crop (keep the complete frame, no autocrop,...) a non anamorphic movie and want to play it on a 4:3 computer monitor (e.g. in 800x600, could be a lcd-video-beamer also or something else with vga-in) WITHOUT black borders. this means the movie will be resized to true 4:3 display aspect ration although technically this is not correct.

b) you do NOT crop (keep the complete frame, no autocrop,...) an anamorphic movie and want to play it on a 16:9 computer monitor (don't know, could be a hdtv video beamer in 1920x1080?) WITHOUT black borders. this means the movie will be resized to true 16:9 display aspect ration although technically this is not correct.

c) ?

...so only if you WANT INCORRECT AR.



here are the correct display aspect ratios for dvds:
display aspect ratio = width / height (square pixels)
Code:
PAL (720x576 not square pixels)
non anamorphic   = 1.367521 (close to 4/3  (1.333333))
anamorphic       = 1.823361 (close to 16/9 (1.777777))
NTSC (720x480 not square pixels)
non anamorphic   = 1.367088 (close to 4/3  (1.333333))
non anamorphic   = 1.822784 (close to 16/9 (1.777777))
note that if you crop off 8 pixels on each side you get 704x..., the resolution used in digital video cameras. this resolution uses the same pixel aspect ratio like 720x...
on a normal tv you never get to see these 8 pixels (usually a lot more than 8) because they lie in the "overscan area" outside the screen.
correct display aspect ratio for digital video camera material:
Code:
PAL (704x576 not square pixels)
non anamorphic   = 1.337132 (almost 4/3  (1.333333))
anamorphic       = 1.782842 (almost 16/9 (1.777777))
NTSC (704x480 not square pixels)
non anamorphic   = 1.336708 (almost 4/3  (1.333333))
non anamorphic   = 1.782278 (almost 16/9 (1.777777))
(so this is a method to fill a 4:3 or 16:9 screen completely keeping correct ar: crop off 8 pixels on each side )


none of these real world display aspect ratios really is 4:3 or 16:9, they are just called that way.
PAL-"4:3" is not even the same as NTSC-"4:3"...

i will remove the ITU checkbox in the next release.

wef

Last edited by TheWEF; 12th January 2003 at 03:13.
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Old 12th January 2003, 02:34   #3  |  Link
valnar
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Got it.
I just see a lot of DivX movies for download on the 'Net and they offer the frequently used resolution of 512x384. It's a perfect 4:3 and I assume with square pixels. It is not possible to achieve 512x384 with the BT.601 box checked, that I can tell.

Robert
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Old 12th January 2003, 02:55   #4  |  Link
TheWEF
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Quote:
Originally posted by manono
...an example of how you would watch a DivX movie on a TV?
...or you can use one of those new DVD-MPEG4 players that are starting to show up...
i've been thinking about devices like the new kiss-dvd-player and if we should adjust our ar-settings if we want to play our movies with such a device.

afaik the kiss-player more or less is a linux-pc, a computer with tv-out.
IMO any tv-out system has to assume that computer-pixels are square and take care of their correct display on tv.
i have no idea how an 800x600 pixel computer display is converted for tv-out on an interlaced PAL-TV e.g.(but i guess it has to be a quite rude conversion), anyhow - the tv-out system has to take care of correct ar.
in case of formats like avi we should provide square pixels and nothing else, let tv-out do the conversion.

of course we would get MUCH BETTER QUALITY if we would provide a format that fits the tv-system, something like a PAL-mpeg4-dvd/svcd (with not square pixels). i guess mpeg4-svcd could be really nice.

does anybody know if any standards like that do exist?

wef.
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Old 12th January 2003, 14:56   #5  |  Link
Chibi Jasmin
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These are the correct values as fractions of integers...

DVD (D1=720)

PAL-anamorphic: 512/351 PAR 640/ 351 DAR
PAL-nonanam.: 128/117 PAR 160/ 117 DAR
NTSC-anam.: 96/ 79 PAR 144/ 79 DAR
NTSC-nonanam.: 72/ 79 PAR 108/ 79 DAR

SVCD (2/3 D1=480)

PAL-anamorphic: 256/117 PAR 640/ 351 DAR
PAL-nonanam.: 64/ 39 PAR 160/ 117 DAR
NTSC-anam.: 144/ 79 PAR 144/ 79 DAR
NTSC-nonanam.: 108/ 79 PAR 108/ 79 DAR

VCD

PAL: 128/117 PAR 1408/1053 DAR
NTSC: 72/ 79 PAR 528/ 395 DAR

---

And here a litte table...will probably look screwed here, but you can try to read it line by line...parts in round brackets will try to explain how values interact with each other...sorry, if it looks weird, if it confuses you, just forget it, and use the values above, which are 100% correct! Note: it's just another way of expressing 1.xxx:1 fractions with integers, so no rounding error.

---

Resizing of MPEG-sources compliant to ITU-R BT.601 standard

PAR=pixel aspect ratio DAR=display aspect ratio

According to ITU-R BT.601:

PAL PAR 117/128 (y/x), x/y=1.094 [128/117] PAR
NTSC PAR 79/72 (y/x), x/y=0.911 [ 72/ 79] PAR

All correct resizing is based on 79/72 and 117/128.

anamorphic -> reduce height 3/4

DVD (D1=720)

PAL-anamorphic: 1.459:1 [512/351] PAR 1.823:1 [ 640/ 351] DAR (720x1.094 PAR=788, /432 (3/4 height) -> 1.823 DAR, 576x1.823=1050, /720=1.459 PAR)
PAL-nonanam.: 1.094:1 [128/117] PAR 1.368:1 [ 160/ 117] DAR (720x1.094 PAR=788, /576 -> 1.368 DAR)
NTSC-anam.: 1.215:1 [ 96/ 79] PAR 1.823:1 [ 144/ 79] DAR (720x0.911 PAR=656, /360 (3/4 height) -> 1.823 DAR, 480x1.823= 875, /720=1.215 PAR)
NTSC-nonanam.: 0.911:1 [ 72/ 79] PAR 1.367:1 [ 108/ 79] DAR (720x0.911 PAR=656, /480 -> 1.367 DAR)

SVCD (2/3 D1=480)

PAL-anamorphic: 2.188:1 [256/117] PAR 1.823:1 [ 640/ 351] DAR (1050x576 (2/3 D1=D1), 1050/480 (width)=2.188 PAR)
PAL-nonanam.: 1.641:1 [ 64/ 39] PAR 1.368:1 [ 160/ 117] DAR ( 788x576 (2/3 D1=D1), 788/480 (width)=1.641 PAR)
NTSC-anam.: 1.823:1 [144/ 79] PAR 1.823:1 [ 144/ 79] DAR ( 875x480 (2/3 D1=D1), 875/480 (width)=1.823 PAR)
NTSC-nonanam.: 1.367:1 [108/ 79] PAR 1.367:1 [ 108/ 79] DAR ( 656x480 (2/3 D1=D1), 656/480 (width)=1.367 PAR)

VCD

PAL: 1.094:1 [128/117] PAR 1.337:1 [1408/1053] DAR (352x1.094 PAR=385, /288=1.337:1 DAR)
NTSC: 0.911:1 [ 72/ 79] PAR 1.337:1 [ 528/ 395] DAR (352x0.911 PAR=321, /240=1.337:1 DAR)
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Old 12th January 2003, 20:06   #6  |  Link
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I just have one or two more things to add:

First, the word anamorphic comes from photographic film, where it means something that isn't stored in the correct way, but is distorted in one way or another. With this definition ALL DVD's are anamorphic.

Secondly, MPEG has defined two more DAR as valid for MPEG-2 streams. These are 20:9 and PAR=1. The later would be the MPEG equivalent of AVI's way of defining aspect ratio as width/height. The former on the other hand is more interesting. We all know that 4:3 and 16:9 is movie formats used on the silver screen long before TV (and DVD) . But 20:9? If you look at IMDB you will find less than 100 DVD's with aspect ratio between 2.00:1 and 2.34:1. Why not use 2.35:1 as this is the most common format? Simply because it should be easy to convert between formats! 20:9 = (16:9) * (5:4) MPEG actually states that these formats are used so it shall be possible to just drop lines and add letterboxing in order to change between formats.
Code:
From\To   4:3   16:9   20:9
4:3       x     1/4V   2/5V
16:9     1/4H    x     1/5V
20:9     2/5H   1/5H    x
x= No change.
k/mV= Drop Vertical lines (k lines dropped out of every m) and add black bars at the sides
k/mH= Drop Horizontal lines (k lines dropped out of every m) and add letterboxing at top/bottom.
__________________
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Old 31st January 2003, 17:50   #7  |  Link
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Quote:
Originally posted by TheWEF
when you watch the dvd with your software dvd player (e.g. powerdvd) the frame DOES fill the screen. why? because the programmers accepted a slight AR-error in order to avoid black bars in full screen.

note that if you crop off 8 pixels on each side you get 704x..., the resolution used in digital video cameras. this resolution uses the same pixel aspect ratio like 720x...
on a normal tv you never get to see these 8 pixels (usually a lot more than 8) because they lie in the "overscan area" outside the screen.
more exactly, the standalone dvd players send to the tv set only the central 704(702-711?) pels, then the tv overscan(that could also be 0, specially in not curved angle tv-set) acts on those 704 pels.
Since a dvd doesnt know by wich player and tv will be played is better to have those 16 pels more.

Now, are you sure that the software dvd players dont crops those 8+8 pels before sending to the computer?
If this is the case sw players are ITU complaint
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Old 1st February 2003, 11:05   #8  |  Link
manono
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Hi-

more exactly, the standalone dvd players send to the tv set only the central 704(702-711?) pels

Are you sure about that? I can enter the service menu of my TV and move the picture to the right or left, up or down, and see the parts of the picture that are getting cut off. As near as I can tell, I'm losing at least 16 pixels from both the right and left. So, when I create SVCDs, I'll put 16 pixels of black along the right and left sides so that I can actually see almost all of the picture. Some DVDs will also have black on the left and right sides to allow for the overscan.
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Old 1st February 2003, 13:30   #9  |  Link
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about what one could be sure??

but if standalone players have to be itu compliant should be so,
should send 702 pels for pal and also fOT ntsc(from 711x486-->702x480)
i read that in a very good article saying that pels over 704 dont belong to the tv frame.
Naturally each player and tv have their own behaviour, so in one tv-player you could see a movie 2/3 pixels shifted respect to other tv-player

I dunno about SVCD, i was talking of DVD.
You do svcd after resize, maybe all the 480 pels are sent, so you should cut 8+8.
Obviously in virtual dub we see all pixels.

our ancient resize method was wrong, but MAYBE sw players were right,just as standalone are, or maybe some was right and some wrong, depends from who made the software.

Last edited by movmasty; 1st February 2003 at 13:47.
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Old 8th February 2003, 02:01   #10  |  Link
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Well guys, I'm totally lost at this.

However one thing is more important to me than the cropping, it's
the aspect ratio.

I would be happy to have extra pixels as long as the aspect ratio isn't harmed !

So could anybody actually do the following test for us (I don't have a standalone dvd player) ?

The idea is quite simple :
1) take a dvd (preferrably not a fullscreen 4/3, widescreen/anamorphic would be best) and play it on your standalone DVD player till you find a nice static shot with an easily measurable shape in the middle of your TV screen.

2) measure the height and the width of this shape (could be an actor, a car, a table, it doesn't matter )

3) Calculate the Width / Height ratio

4) Play the same dvd on you computer with a standard software player. Stop at the same frame. Do a window capture (*) of this shot and paste it in paint (or any better drawing software).

5) Count the height and width in pixels of the same shape

6) Calculate the Width / Heigth ratio

Give us the results !!

The whole question would be to know if the ratio will be quite equal or if there will be that famous ~2.5% difference.

If someone could be so nice to do it, please, pretty please, I'm getting mad reading all those technical guides on that topic.

(*) : to avoid messing with directplay acceleration that will produce a black window to be pasted in paint, before launching your dvd software player, start some video in any multimedia programm and hit pause.
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Old 8th February 2003, 18:16   #11  |  Link
Chibi Jasmin
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The problem will be this will maybe vary between different dvd players, but even more vary between different tv-sets...they all have a service menu, where you can play with picture position, amount of overscanning and stuff like that...you will probably have a lot of difference even between different tv at the same standalone player...most tvs are not adjusted very well afaik
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Old 9th February 2003, 20:38   #12  |  Link
Loul
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I finally went for another test.

I have this Pink Floyd - The Wall dvd.
And in the menus you got those pages where you have to select between 4 options. One of those was with 4 arrows symetrically drawn like that :

..................^.........
..................|.........
...............<-...->......
..................|.........
..................\/........

(well my drawing ain't perfect but I think you got the idea).

The arrows were significally large enough (between 100 and 130 pixels).

What I did is that I captured the picture I got with Power DVD and made some edition of it in a Photoshop like software.

I took one of the "horizontal arrow" and made it turn by 90 (then by another 180 to check on the other one).
And it fitted quite perfectly on the vertical arrows.

Then I "compressed" the image quite like the ITU checkbox does (by 2.5%) and did the same test again.
This time the Vertical arrows were significally shorter than the horizontal one.

I attached a jpeg version of this image so you could have a clearer idea of what I did (if a moderator could approve this attachment, thank you).

The learning of this test is, imho, that the Power Dvd resizing method gives a correct display aspect ratio.
Hence according to this, the correct option would be to leave the ITU checkbox unchecked.

If you have better pictures on other dvds to do the same test, please do it to check if you have the same results.

I don't want to bother anyone especially the author(s) of gordian knot whom I'd like to thank on this occasion.
I just wanted to see what was the correct thing to do to do a proper encode with this test.

I hope this will prove useful or at least interesting.

Last edited by Loul; 9th February 2003 at 20:46.
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Old 10th February 2003, 01:54   #13  |  Link
valnar
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The end all comparison

Since I started a lot of these debates on the validity of the "ITU Standard Checkbox" in Gordian Knot, I took what will be the FINAL step.

I made a DivX out part of my AVIA test disc. We've got perfect circles to measure.

I made four 1MB DivX files. 4x3 and 16x9 each with/without the ITU standard checkbox. I did the aspect error either a perfect 0 or 0.1 (as much as I could with that ITU standard check). Part of the AVIA test disc has 16x9 patterns so you can measure circles there too.

My results? I had perfect aspect ratio on the files without it checked, with BSPlayer and PowerDVD. With the ITU standard, the circles were slightly squished vertically. I can send the files to whomever wants them. They are less than 2MB. I welcome more tests.

Edit: I also did the test on a laptop screen with a set ratio of pixels, so there was no monitor setup inaccuracies, and got the same results.

Edit: (Removed FTP link to AVIA test files. Email if interested.)
-Robert

Last edited by valnar; 3rd March 2003 at 14:33.
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Old 10th February 2003, 03:46   #14  |  Link
Loul
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Thank you Valnar for providing such interesting material.
I did check your results and I find too that the itu checkbox version of your divx files are squished.

The only (minor) doubts remaining are :

- are those tests right (it seems to be used for high end equipment testing so I would think they did the things right)
- did Valnar check the correct format when resizing with Gordian knot (ie anamorphic, non anamorphic) (I think so, no reason to think he made any mistake besides that would be then very hard for any test circle to be actually a perfect circle)

So I guess that the final word is that Itu checkbox would be best unchecked.

Quote:
i will remove the ITU checkbox in the next release.
Well consider leaving it if you feel it's necessary to keep that resizing method providing you find the results of the Avia tests convincing.

Just a comment.

I did some tests on my tv and through a capture card on my pc. It's far from being accurate, especially as I used a Playstation 2 as a Dvd player which ain't the best one available for sure.

Anyway the on screen measurements are quite weird as the picture is actually even more squished vertically than what you would obtain with the Itu resizing method.

Confusing hey ?
Of course my Tv ain't high end equipment hence is not correctly tuned.

Well as for me I feel it's better to have the correct aspect ratio on digital format, and provided the tests made by Valnar do not suffer criticism, I would still prefer unchecking that box.

Last thing is that I would deeply appreciate comments about what did Valnar by people having written in that topic as most seem to have a solid knowledge about it.

Have a nice day in a world with a good aspect ratio ! (so honey finally you ain't that fat, it was the video that had an improper DAR )
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Old 10th February 2003, 12:06   #15  |  Link
valnar
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Yes, the four files are (with Gordian Knot parameters)
Input rez: NTSC; Input PAR: NTSC 4:3 (both with and without ITU checkbox)
Input rez: NTSC; Input PAR: NTSC anamorphic 16:9 (both with and without ITU checkbox)

That gave me every combination. I got the aspect error on 3 of the files to be a perfect 0.0%. I think one of the ITU checkbox files had to settle for 0.1%, because I kept the W-Module at 32 and the H-Module at 16, which limited choices.

It has been mentioned by other users that unless you watch a DivX movie in full screen, it won't set the correct DAR like a DVD player. I watch most of my DivX movies in a window anyway, but I remeasured the circles full screen and didn't see much of a difference in AR, if any.

I am not discounting the vast knowledge of TheWEF or Manono, but just need my results explained to this layman!

-Robert

Last edited by valnar; 10th February 2003 at 12:10.
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Old 10th February 2003, 14:43   #16  |  Link
Chibi Jasmin
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Quote:
Originally posted by TheWEF

i will remove the ITU checkbox in the next release.
[/B]
And always calculate the same way, as 'checked' is now, I hope
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Old 10th February 2003, 14:47   #17  |  Link
Chibi Jasmin
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Well, if you have the ITU-Box checked, GKnot provides you with spec-compliant resizing...this works, if the source material (DVD) has been done according to that specs...you learn from experience, that this is not always the case...

If your DVD is made according to specs, ITU-box checked is fine, if not...well, you have to use your own judgement...
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Old 10th February 2003, 14:54   #18  |  Link
valnar
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Quote:
Originally posted by Chibi Jasmin
Well, if you have the ITU-Box checked, GKnot provides you with spec-compliant resizing...this works, if the source material (DVD) has been done according to that specs...you learn from experience, that this is not always the case...

If your DVD is made according to specs, ITU-box checked is fine, if not...well, you have to use your own judgement...
If anyone else has an original AVIA disc to confirm or deny my tests, please do. I'm just saying it looks more correct without that ITU standard on the Avia disc. There is another test disc (Video Essentials?); someone else can try it as a second opinion.

Robert
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Old 10th February 2003, 17:30   #19  |  Link
Loul
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Quote:
Valnar :
It has been mentioned by other users that unless you watch a DivX movie in full screen, it won't set the correct DAR like a DVD player. I watch most of my DivX movies in a window anyway, but I remeasured the circles full screen and didn't see much of a difference in AR, if any.
After saving your divx as image sequence I made an avi of the 14th frame (numbered 13 by virtualdub) of the NTSC-4x3-No-ITU.avi and NTSC-4x3-With-ITU.avi (the circle with the squares).

After calibrating the display aspect ratio of my computer screen (quite easy to do as pixels are square) I did some window and fullscreen measurements playing those two "test frames turned into AVIs" with my usual media player (Bsplayer).

Results are identical in window and full screen mode : circles look like circles with the "no itu" file and look vertically squished with the "with itu" one...

Quote:
movmasty :
Now, are you sure that the software dvd players dont crops those 8+8 pels before sending to the computer?
After some testing I can tell that PowerDVD don't crop any pixel in width.


Quote:
Chibi Jasmin
Well, if you have the ITU-Box checked, GKnot provides you with spec-compliant resizing...this works, if the source material (DVD) has been done according to that specs...you learn from experience, that this is not always the case...
Well I certainly believe that not all Dvds are mastered exactly according to the specs (they're not that crystal clear, when you master a Dvd you can have different choices because of different "philosophies" of the way it should be seen on a TV through a dvd standalone player, besides in the end differences ain't that big so you Mr Everybody would never complain).

I would be curious to know the proportion of commerical released Dvds made according/not according to the specs (nobody knows any database on the subject ?).
In other words : What is the norm ? Dvds following the specs (especially the ITU DAR for Dvds) or Dvds using the more usual DAR (16/9, 4/3) ?

It still remains that that Avia disc (Here's a link to the Avia Faq :
http://www.ovationsw.com/avia_faq.html) test results are interesting.
If one disk must follow the standards, it must be the calibration disc !
But well they might also have done it wrong (how ironic would it be), if only we could have their opinion on the subject...

Quote:
Valnar :
There is another test disc (Video Essentials?); someone else can try it as a second opinion.
That would be great, this is so puzzling...

And finally a couple of question for Valnar regarding the encoding of the Avia test disc :

What was the original resolution (I guess 720 * 480) ?
Did you crop anything before encoding (no extra pixels on the sides that you would have removed) ?

Last edited by Loul; 11th February 2003 at 23:14.
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Old 13th February 2003, 14:43   #20  |  Link
valnar
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I assume the test patterns on AVIA were 720x480 since it's the standard, but I can check. I did crop some pixels in the "ITU checkbox" versions to make the aspect error 0.0 or 0.1. If I didn't do that, this testing would be meaningless.

If anyone can point out a DVD that has some definite, measureable circles in the video, I'd be happy to rent it and test. My whole point is to get the correct AR while viewing videos with software players, like PowerDVD, BSPlayer, WinDVD, etc. I don't care what an actual DVD player does. Since these are now DivX files, its irrelevant.

Robert

Last edited by valnar; 13th February 2003 at 14:46.
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