Edge Enhancement

 

Ultimate Guide To 'Edge Enhancement' on DVD
by Bjoern Roy , May 2001

Did you ever wonder why videophiles keep complaining about lots of so called 'Edge Enhancement' that is supposed to plague DVD transfers? On your TV the film looks fabulous with spectacular colors, great contrast, good shadow delineation, no compression artefacts and is sharp as a tack. Yet, those snobs call the transfer 'nearly unwatchable' on their front projection setups. Huh?

To shed a little light on this phenomenon, i prepared this little guide to demonstrate what 'Edge Enhancement' is, why the videophiles hate it so much and why you might not be bothered by it... yet!

 

So what is this 'Edge Enhancement' all about?

Edge Enhancement (EE from now) is a digital image processing filter that is used to make pictures look arteficially sharper than they really are. The key word here is look sharper, because the picture isn't really any more detailed than before. The human eye is simply tricked into thinking the picture is sharper.

So it does virtually the same thing as the sharpness control on your TV? Almost, more on that later.

Lets clear up one confusion in the nomenclature first, because it can lead to misunderstandings. Basically, the term sharp is commonly used for 2 slightly different things.

First, it is used to describe a subjectively sharp picture ("Wow, the picture of this TV is very sharp!"). But it is also used to describe a highly detailed picture ("The transfer on this DVD is very sharp")

I prefer using the terms sharp vs. smooth for the first psychological phenomenon and detailed vs. soft for the second, which is actually technically measurable (more detail = higher frequencies).

A picture can actually appear to be quite sharp because the sharpness on the TV is too high or the a considerate EE, but it can still be not very detailed. Lets take a look at an example.

Picture A Picture B

At first glance, picture (B) seems to be somehow sharper than picture (A), right? Well, but picture (A) is actually more detailed! (A) is the original image, as detailed as the used resolution allows, without any processing. It is perfectly smooth. Picture (B) on the other hand is first slightly low-pass filtered (thus some high frequency detail is lost), and then artificially sharpened with EE to somehow compensate for the slightly lower amount of detail. If you don't look too close, this actually seems to work!

If you also believe that (B) looks better/sharper, or at least not worse than (A), then you will probably understand why a lot of people who are sitting not too close to the screen don't complain about a considerate amount of EE used in DVD transfers.

But EE starts to get bothersome when either the amount of EE used is not appropriate but exzessive or you get a bigger screen or move closer to your screen. Let us take a closup look at the two pictures. Does (B) still look sharper? And what side effects are there to the sharper appearance?

Picture A Picture B

Now you should clearly see where EE raises its ugly head. Picture (A) looks very smooth and detailed. (B) looks very artificial and is considerably less detailed. Look at the windows or that block on the side of the left window to see the lack of detail. But while that area only looks softer but not really artificial, the contour of the tower against the sky looks very strange, no? Look at the brown roof of the left tower against the sky. The brown roof has a darker contour that separates it from the sky and the sky has a bright halo seperating it from the roof. If you look closer, you will find that almost all contrasty edges show this ugly ringing artefact.

These contours and halos can completly destroy the picture experience on a high end setup. While an image like the one on the left would look spectacularly close to film on the big screen, the image on the right would look like video, closer to a TV broadcast or a VHS cassette than film.

If you have ever increased the sharpness control on your TV to the max, you will also get the same ringing, so you are well advised to keep it as low as possible. The advantage of controlling the subjective sharpness as a control on the TV, instead of having the DVD transfer sharpened through the use of EE, is that you can adjust the sharpness control on your TV to your liking. But you can't get the video-like look out of a DVD transfer that has EE applied to it! You have to live with it, its an inreversible process.

Note: the ringing that is caused by setting the sharpness control too high on your TV is only a 1-dimensional horizontal effect. It show ringing only at left and right of vertical edges. EE on the other hand is applied in two dimesions, so both horizonal and vertical edges can show ringing. But EE is not necessary a symmetrical filter as we will see. The amount of horizontal and vertical EE used on DVDs can vary considerably.

 

Does 'Edge Enhancement' always look the same?

No, there are several parameters that affect the outcome of an EE processed image. First of all, the amount of EE applied can vary and will result in differnt amplitudes of the modulation. Little EE will result in only faintly visible halos, lots of EE will result in stronly visible, high contrast contours. Secondly, the frequency of the filter can vary. A high frequency filter will render only thin halos, while a low frequency one will render thick halos. Thirdly, the symmetry of the filter can vary. Stronger horizontally than vertically, for example.

Lets look at these 2 further images:

Picture C Picture D

Picture (A) from above had no EE applied at all and (B) had a reasonably amount of EE filter applied, with middle wide halos.

Picture (C) here has very strong EE applied with a very low frequency, thus very wide halos. EE as hefty as this can be found on the original Die Hard 3 DVD. Ugh!

Picture (D) also has a good amount of EE applied, but with a very high frequency, thus the halos are very thin. It is obvious that (D) looks a lot more pleasing than (C), it boosts only the very highest frequencies, which makes it look pretty sharp. Basically all Columbia/Tristar 2.35:1 transfers use the kind of EE as seen in (D). On most setups this will result in a nice, apparently sharp picture. But on high end setups, the thin halos will make the picture look edgy and artifical, simply not pefectly film-like.

 

How about some real world DVD examples?

Sure. Lets have a look at some transfers without any or only few EE, which are in fact very, very few. I chose Braveheart, The Insider and Titanic as prime examples of how an unfiltered, high detailed transfer (even non-anamorphic in the case of Titanic) should look like.

Braveheart 1 Braveheart 2 Braveheart 3

Look closely at these closeup crops from Braveheart. They look completely smooth, yet extremely detailed. This is one of the few transfers that i suppose is as good as it gets in terms of resolution and film-likeness.

Here are two crops from Titanic and one from The Insider:

Titanic 1 Titanic 2 Insider 1

Titanic is probably the only DVD that doesn't have any EE applied to it. I don't mean little, i mean NONE. Nor is the image low-pass filtered in any form, resulting in hefty interlace flicker (rails...) on non-scaled displays, but incredible detail (even for a non-anamorphic transfer) on high end systems. If the transfer were anamorphic, this would probably be the defacto standard as to what can be done with DVD.

The Insider is another sensational film-like transfer. It has no EE to speak of and is extremely detailed (and anamorphic) .Its one of the best if not the best transfers currently out. Cartoony colors you won't find here, though!

 

Now lets blend over to some terrible transfers in regard to EE. I have already sold Die Hard 3, which has probably the worst EE i have ever seen. But here is General's Daugther, which is absolutely horrible as well:

General 1 General 2

Look at all the terrible dark contours and bright halos. If you can't see them here, i could have saved the time on this Guide. No comment.

Here is a comparisson between the old and the new version of Fargo:

Fargo old Fargo new

Look at the shoulders and the red bank, to see just how much EE the old copy had and how much better the new one is. It shouldn't interest us here that the framing and color balance of both is totally different, too.

A similar comparssion between the NTSC and PAL version of Enemy of the State:

Enemy NTSC Enemy PAL

Several interesting notes here. The NTSC version is just terrible. It has very strong and wide halos in both horizontal and vertical direction. The PAL version shows some differences. First, while the halos seem to be just about as strong, they are considerably thinner, especially in the vertical direction! Look at the horizontal lower edge of the mirror or the horizontal edge right how his thumb.

Another striking example of how a transfer should not look like, sadly, is Terminator 2: Ultimate Edition:

T2:UE 1 T2:UE 2 T2:UE 3

In picture 1, look at his right cheek against the bright frame. In picture 3, look at the contours of the legs against the floor. In picture 2, look at the hefty ringing of the police letters. When you look closer at the letters again, you will see that the horizontal ringing is a lot worse than the vertical one. So it resembles the characteristics of a TV sharpness control.

Here are two more common examples from Fifth Element and Titan AE:

The Fifth Element 1 Titan AE 1

Fifth Element, like all Columbia/Tristar 2.35:1 transfers, also has too much EE, although in comparisson to some of the examples above, its a lot more acceptable. Their ringing looks almost always the same: relatively high freq. (thin halos), middle strong, but often with more than one ripple, see LOA below.

The Titan AE transfer from Fox is another step up. It is very highly detailed and has only a slight, quite thin halo in very difficult scenes like the one above. Probably only the trained eye can see that there is some at all. But the transfer is perfect otherwise, it wouldn't have had any EE necessary at all!

If you have a hard time seeing EE on TFE transfer above at all, thats because although its there, its in a different league from some of the earlier examples. Here are 2 larger crops from TFE and T2:UE.

The Fifth Element T2:UE

Look at the lift side of her red hairs to see a bright halo, or at the left side of the blue cloth. To the right of her legs, you can slightly see the multi-ripple ringing, there is a darker halo then a brighter one, then darker again... Its rather faint, but plain obvious on a high-end setup. But you can also see, that the EE in T2:UE, same scale factor, is in a different league!

Lawrence of Arabia, which is sadly also a Col/Tristar 2.2:1 tansfer makes no exception in term of EE:

Lawrence of Arabia 1 Avia 1

You can clearly see the dark contour and the bright halo all around the silhouette. And the C/T multi-ripple effect mentioned above can clearly be seen here, too. Look at the top right of the silhouette, after the usual bright halo, there is another darker one, then a brighter one again and even faintly another dark one... This sometimes looks as if things have a slight ghost image right to them. Ugly.

The Avia pic is only included to proove that the EE ringing is really in the DVD transfers and is NOT due to the way i take screenshots. The pic was taken excatly like others and show no sign of EE , just like Braveheart etc. above.

 

Why is 'Edge Enhancement' used at all?

If only we knew!

Basically all transfers are low-pass filtered to prevent hetfy flickering and aliasing on interlaced display. To compensate the resulting softer picture, the telecine operators seem to apply excessive amount of EE. Few if any operators watch the transfer on a big screen reference system, but rather on the typical video control monitors, which simply aren't up to the task. If they would simply stop using it at all, they wouldn't need to bother checking whether they applied the right amount. Simply give us unfiltered, unenhanced transfers ala The Insider, Titanic, Braveheart, Rules of Engagment, Play it to the Bone.... Please?

The other possibility, which is just as likely, is that some operators don't add the EE 'on purpose', but one (or more) pieces of equipment in the transfer chain adds EE 'by default', so that the operators don't really have control over it. The problem remains, that the control equipment isn't nearly enough to fully analyze the resulting picture, so they might never know that the transfer actually had too much EE.

For us videophiles, it shouldn't really matter 'what' it is, that is causing it. The result is, that most transfers have halos all over the place, some even to a terrible extent. The fact that some transfers are plagued by it, and others aren't, simply shows that its not an 'inherent flaw' of the DVD mastering (MPEG2 compression) scheme. The cause has to be found and eliminated. As easy as that.

 

Resume and final thoughts!

I hope this guide helps people understand what EE is, that it is indeed used on most of todays DVD and that we have to get the studios to investigate the issue and try to stop it, whatever the cause!

Resume as of May 2001:

Columbia / Tristar is very consistent. They always use it on 2.35:1 transfers (recently 6th Day) and don't on 1.85:1 transfer (Starship Troopers is still one of the best non-EE transfers out there).

Paramount is in the hit and miss business. Their transfers are either sensational (Braveheart, Titanic, South Park BLU, Rules of Engagement) or outright terrible (General's Daughter).

The same with Fox. Either sensational (X-Men, White Men Can't Jump) or terrible (Die Hard 3), but they are heading towards always perfect.

Most of Buena Vista's latest offerings are also nothing short of spectacular (Play it to the Bone, Insider, Dinosaur, TS). Kudos to them.

Universal has had some terrible EE ringing (American Psycho) in almost all transfers up to U571 and Pitch Black. Those two are like nothing before from Universal.

Warner is also starting to use it less and less (Red Planet), but they never really used to as excessive as some of the others.

New Line has a few sensational transfers, notably Blade and Seven SE (has a bit, but is almost perfect). But a lot of their DVDs still have too much EE, although of the very high freq variety, like in Detroit Rock City.

Dreamworks transfers are usually very good, but not perfect. SPR has some EE visible in a few scenes, but 95% of the time its among the best currently out.

There seems to be a tendency that the newer transfers of almost all studios, except Col/Tri, seem to get better and better in regard to EE, so there is hope that this will be a non-issue at some point in the future.

Best regards
Bjoern Roy

 

 

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