Exporting to resolution higher than sequence

[atcold]

Say, my sequence size is 1280 × 720, having a scaled down 1920 × 1080 video in it.

I wonder if exporting the sequence in 1920 × 1080 will cause any loss of resolution. Meaning, does Premiere skip the 1920 × 1080 → 1280 × 720 step, and use the original higher resolution for the final encoding?

[atcold]

Anyone?

[Peru Bob · Accepted solution]

You will lose resolution.

[atcold]

Any reference to the documentation confirming this?

[Ann Bens]

Nope. Just common sense.

[atcold]

I see. Common sense would be just the opposite, if you are an engineer.

So, I'll assume there is no loss of resolution, then.

[Ann Bens]

As mentioned before: you will lose image quality.

[atcold]

I don't understand why you do insist when there is lack of evidence.

I've asked a technical question and I'm getting an opinion as an answer.

I'll email directly the engineering team at Adobe to get an actual response.

[Ann Bens]

You are not getting an opinion.

1080p in a 720p sequence will be treated as 720p footage on export.

720p exported to 1080p will blow up the pixels hence image quality loss.

[juliusa72541073]

Opinion or not this is such a snarky, unhelpful answer.

[Andy 1968]

Why are you placing 1920 X 1080 video into a 1280 X 720 sequence if you plan to output at 1920 X 1080?

[atcold]

Good question.

My footage is 1280 × 720.

Therefore, I did initially create a sequence with this resolution.

When my footage is covering the entire screen the effective resolution is 1280 × 720.

I use to switch to a different layout, most of the time, where my camera feed is scaled to 50%.

Now, exporting the sequence at 1280 × 720 would lead to a reduction of resolution (Premiere is applying an aliasing low-pass filter and perform subsampling of the footage).

Now, when encoding videos, we apply the final transformation as a combination of intermediate transformations, and not each of them separately. For sake of explanation, let's think of appying a rotation of 30° 3 times. The overall roation would be of 90°, which is a non-destructice transformation. The same is not true if talking about any rotation which is not a multiple of 90°.

So, here I was asking a confirmation about normal computer vision practices, which would imply not losing resolution when a footage undergoes two subsequent scalings.

[Averdahl]

Say, my sequence size is 1280 × 720, having a scaled down 1920 × 1080 video in it.

I wonder if exporting the sequence in 1920 × 1080 will cause any loss of resolution. Meaning, does Premiere skip the 1920 × 1080 → 1280 × 720 step, and use the original higher resolution for the final encoding?

By @atcold

If you have a 1280x720 sequence and put 1920x1080 video on it and scale it down so it fits the 1280x720 sequence the following will happen upon export to 1920x1080: Premiere Pro will scale down the 1920x1080 footage to 1280x720 and then up-scale from 1280x720 to your selected output, iow 1920x1080. Premiere Pro will not skip the 1920x1080 > 1280x720 step.

So yes, Premiere pro will scale down the footage and then upscale it and you will loose quality, as have already been pointed out in this thread several times. 

That´s how the render pipeline works in Premiere Pro in your example: 1920x1080 > 1280x720 > 1920x1080

All scaling is destructive in every video application available on the market. The good news is that many times one will get away with it since the scaling algorithms have been improved over the years and since non-video people tend to look at the content itself rather than the technical quality.

[atcold]

Premiere Pro will not skip the 1920x1080 > 1280x720 step.

By @Averdahl

Is there a way to verify this?

[Andy 1968]

atcold,

You can always do some testing of your own.

[Averdahl]

Premiere Pro will not skip the 1920x1080 > 1280x720 step.

By @Averdahl

Is there a way to verify this?

By @atcold

Yes, test it yourself and see what you get. Compare a 1920x1280 > 1280x720 > 1920x1080 export with a 1920x1080 > 1920x1080 export. This takes max two minutes.

[atcold]

Using some default still images with some high frequency grating? Any other recommendation / suggestions?

 

[RjL190365]

Yes, you will lose image quality out of the 1920x1080 source. If you are using a 1280 x 720 sequence, and your final export will be 1920 x 1080, then all NLEs, not just Premiere Pro, will convert 1920 x 1080 to 1280 x 720, and then back up to 1920 x 1080. There is simply no way at all whatsoever to circumvent that.

The only way to minimize this image quality loss will be to simply use a 1920 x 1080 timeline, and then upscale the 1280 x 720 footage. That way, you will avoid the image-degrading double-conversion. The key is to use a timeline resolution that is exactly the same as your final export resolution when dealing with mixed-resolution footage.

[atcold]

Okay, thank you.

[Jeff Bugbee]

If you place a 1920x1080 video in a 720 sequence, Premiere assumes you WANT the video scaled down. In this case Premiere does not think "hmm, maybe this user doesn't want the video scaled, I'll just skip that instruction and go ahead and use the higher resolution."

It does what it's told, and in this case, you told it to scale down a 1080 video to 720, then export the 720 video at 1080, resulting in a lossy scale up.