Gordian Knot Aspect Ratio Question

[Staz]

Hey!
I have a PAL DVD with an AR of (4:3)
When backing it up in Gordian Knot, I am having a bit of trouble.

So originally the aspect ratio is 1.333. But then I get to cropping.
There is a large black bar on the right side only as can be seen by this image.

http://img246.imageshack.us/img246/6801/test3pl.jpg

After cropping the entire black area the AR is now 1.286. I then chose a resolution of 576 x 448. (Aspect Error % of 0.9%).

I am used to encoding my 4:3 movies to XviD with a resolution of 576 x 432.
But in this case I get a resoultion of 576 x 448.

Aspect Error % = Output AR - Original AR)/Original AR x 100 ???

In the calculation of the Aspect Error % is the "Original AR" part the original AR BEFORE cropping or the original AR AFTER cropping?

Is this resolution of 576 x 448 acceptable since the AR made a significant change after cropping? Is a resolution of 576 x 448 the best handling of this situation?

Basically what I'm asking is whether my output resolution should be based on the original AR before cropping OR the original AR after cropping??

Thanks a million. Hopefully my explanation wasn't too terrible to understand :D

[unskinnyboy]

Your output resolution (and hence the output AR) should/would be after cropping _and_ resizing.

You shouldn't crop haphazardly and even end up with non-MoD16 values just so that you will get a 1.33:1 AR. First step is to crop away all the black and then resize accordingly so that you will get a 1.33 or near 1.33 AR. 577x432 is 1.33 alright, but in the process you failed to notice that your width is non-MoD16 which isn't an advisable value for encoding purposes.

Crop all black first and then resize to 576x432.

[Staz]

One problem though, after cropping the entire black area. I am unable to choose 432 as a resize height. If I want a width of 576 then I must have a height of 448.

[unskinnyboy]

Change H-Modul to 16. Currently you have it at 32.

[Staz]

Nope it's at 16 already :)
I have a feeling that since the AR changes quite significantly after cropping that this changes the height I can choose?

[unskinnyboy]

Not sure what you are doing wrong (could be the Crop part). Could you either post a screenshot of your Resolution tab of GK and/or cut me a small sample (~10 MB) and upload to rapidshare.de (use ChopperXP to cut)?

As I said before, your final AR will depend upon the final resolution you choose for your .avi.

[CWR03]

The same problem has arisen for me before when I had to do some excessive cropping on one side. The only way I was able to fix it was to enter a custom height under Input Resolution. I've had to use anywhere from 388 to 576 on a 480 source in some cases.

[Staz]

Here ya go :)

http://img529.imageshack.us/img529/3954/test28wq.jpg

I appreciate all your help!!!!

[Staz]

CWR03 : Could you explain to me your method in more detail regarding that situation you faced? I'm not sure if I fully understand how changing custom height in the input resolution would help? Thanks :)

[unskinnyboy]

Check ITU-R BT.601 standard under Options and you will get 576x432. But could you also give the sample I asked for so that I can be sure? All I saw of the source is that 577x432 cropped image and that isn't much to work with.

[Staz]

Yep sure! My upload speed is slow so it will be up in about 20 mins.
I always have had the ITU-R BT.601 standard unchecked but maybe in this case I will try it.

Thanks again. :)

[unskinnyboy]

To check or uncheck ITU-R BT.601 is a big 50-50 around here. A bit of search will give you lots of 'for' and 'against' arguments about it. I am neutral. Usually in pure 1.33:1 material, one shouldn't be checking ITU-R. But here in this case it looks like it needs to be checked to get 1.33:1 which makes me think "ok, so we get 1.33:1, but does the picture looks distorted or something"? If 576x448 is what looks better, then that's what you should go with. Don't force it to 576x432 just to get 1.33:1.

OK, will shut up now and wait for the sample.

[Staz]

I'm just comparing the two resolutions now. (576 x 432 with 576 x 448)

To be honest a height of 432 makes some faces seem a little squashed. But then again, a height of 448 makes some faces look a little long. Aaggh I'm going crazy :D

[CWR03]

Checking/unchecking ITU-R BT.601 made some difference in my situations, but it wouldn't always correct the aspect if it was off significantly.

What's not to understand about changing height? If the cropped video is too tall, decrease the input height setting. I'm usually too lazy to do the math, so I reduced it by 32 at a time until it was correct.

You may have a source that isn't meant to be 1.333:1 after cropping. What is it exactly? They may have left a lot of extra video to allow for overscan which is throwing off your resize - perhaps you'd want to crop top and bottom more to correct the aspect.

Edit: I downloaded the test sample, cropped away all the black edges and set the height to 544 - the resulting 1.333:1 output didn't look distorted at all, but then I didn't have anything round to check more carefully.

[unskinnyboy]

@Staz, Yup. Compare resolutions across the whole of the DVD and go with whatever looks more proper to your eyes. Based on what I saw in the sample, for me 432 was more like it. But you have the whole DVD to compare, so you should be able to come to a better conclusion.

[Staz]

In the end I decided best action was to tick the ITU-R box and output with a 576 x 432 resolution. Looks great. Thanks everybody :D