Do I Need to Crop (BR to DVD)?

[ron spencer]

As I had posted in another thread, I have been getting great results going from BR to DVD. I have just been resizing to 720x480 and encoding as 16:9..no cropping.

Is it better to crop from 1920x1080 (1088 actually) and then resize, and then add black bars?

Avisynth would be:

crop(0,140,0,-148) to remove black bars from original
spline64resize(720,300) 300 to keep aspect ratio
addborders(0,90,0,90) add 180 to get the 480 for 720x480

Is cropping the way to go when going back to MPEG2? If so, why would it be preferable to just resizing immediately to 720x480 and encode as 16:9 (which does work perfectly).

thanks!!!!

[cacepi]

Is cropping the way to go when going back to MPEG2? If so, why would it be preferable to just resizing immediately to 720x480 and encode as 16:9 (which does work perfectly).I don't think it makes any difference one way or another; the compression penalties should be pretty negligible. You might notice on some ringing on an analog TV in the transition from black to picture if you remove the bars beforehand, but that's about it.

Although I personally like the look of bilinear resizing if you're downscaling.

[Sharc]

If you want to make sure that no bits are wasted for encoding the transitions from picture to borders within a macroblock, you should crop and add borders such that the active picture and the added borders become mod16. I some cases this means that you might have to crop a few pixels into the active picture.
- resize to DVD resolution
- crop such that the active picture is mod16 (a multiple of 16)
- add borders (which also need to comply with mod16 rule)
- encode

[ron spencer]

well...I tried a mod16 crop....and just a crop.

Ony my 50" Samsung plasma 1080p...I see no difference between that and just resizing from the start. So I am going to keep doing that.

@cacepi

why do you use bilinear? I had thought spline was the choice for downsizing...just curious as to your choice.


Thanks for responses.

[Sharc]

Ony my 50" Samsung plasma 1080p...I see no difference between that and just resizing from the start.
That's likely the case, because the saving is in the order of few percent (2... 4%) which is hardly visible.

[ron spencer]

Yah I thought that

Man the encodes look good though!!

[cacepi]

why do you use bilinear? I had thought spline was the choice for downsizing...just curious as to your choice.Two reasons:

1) The amount of downsizing from 1920x1080 to 720x480 is so great that even a high-tap spline resize like spline64 won't compensate for the reduction of resolution. The information is simply lost; splineresize (heck, any resize) won't preserve it.

2) If an upscale happens anytime during playback - which it will if you're watching on an HDTV - then any benefit of splining is pretty much negated. Again, the information is lost due to the initial downscaling.

The final benefit is that bilinear is a good deal faster than splineresize, especially with HD sources. And with encode times being what they are, every little bit helps.

[jfcarbel]

Let us know what your final avs looks like if you decide to experiment with a bilinear resize and let us know if you saw any improvements in PQ.

Also, I believe the cropping differs based on the type of letterbox i.e. 1:85 vs 2:35). Is there a good guide/thread on how to crop the letterbox when encoding? I know that most GUI frontends help you with this, but I always like to know how it works in the background.

[ron spencer]

I am very happy as is. May try bilinear later. Fun to do I must say

[rica]

Ron,
if you don't make a DVD (say you are making an mkv), cropping black bars saves some bits by avoiding unnecessary encoding of them. Anyways, you will see the black bars (even they are cropped) while watching your encoded media on your display if the AR is different from your display's resolution so as to keep the right AR of the clip. (i mean -again- black bars but with less MB.)

But if you are going to make a DVD, you have to keep the black bars as is since there is no 720*300 NTSC(for instance) and your DVD authoring software will not accept this resolution.

Hope it helps.

_ _ _ __

[ron spencer]

I was not doing 720x300....I was adding borders...see script above

[rica]

I was not doing 720x300....I was adding borders...see script above

I saw that; this is why i wrote :)
Anyway; crop borders and re-add borders: it's up to you.
I guess my previous post clarifies some grey points.