Quick Tip: Adjust Image Geometry So You See Every Pixel

Image Geometry is the combination of Image Cropping -- whether the image fills your screen from top to bottom and left to right, and with no pixels lost off any side -- and Aspect Ratio -- whether circles in the content actually look like circles on your screen, instead of tall ovals or wide ovals.

If your video setup has a problem with Aspect Ratio, you will likely notice it pretty quickly.  Indeed you may even have CHOSEN to use incorrect Aspect Ratio -- typically because you don't want to see Pillar Box Bars or Letter Box Bars padding the image on your screen.

But Image Cropping problems can be subtle.  And getting them wrong can have a surprisingly large effect on image quality!

Disregarding bugs in your source device(s) or TV, Image Cropping arises in two ways:  Overscan and Burn-in Protection.

Overscan dates back to the earliest days of TV.  Early TV cameras had problems capturing a clean picture around the edges.  Then technical details of how a TV program was broadcast added additional cruft around the edges.  And finally the original, CRT TVs could not render the incoming image cleanly around the edges.  The solution to all of these problems was to include a bezel in front of the TV tube -- part of the TV cabinet -- which blocked the edges from view!  The portion of the image thus concealed from view around all 4 sides was the Overscan.  When setting up a TV, the horizontal and vertical size of the image were adjusted LARGER than the visible area of the TV tube so that the desired, Overscan portion of the image was actually concealed behind the bezel.

As TV technology improved, the need for a physical bezel went away.  Newer TVs could render a clean image edge to edge -- so long as the incoming content was clean to begin with.  But there was still plenty of content out there (both recorded and live) with poor quality edges.  So Overscan was still employed.  I.e., the TVs were adjusted so that a portion of the incoming image on all 4 sides was set BEYOND the sides of the TV screen -- and thus not displayed.  That portion of the image was simply discarded from all 4 sides.

With modern digital TVs and digital content -- both recorded and live -- the need for Overscan has greatly diminished.  HOWEVER, most TVs -- even the newest -- are still set by default to apply Overscan.  That is, they are set to discard a portion of the image around all 4 sides.  This is a Marketing choice:  If a new TV buyer plays crufty content and sees garbage on the edges of the screen he might panic and return the TV!  If we make it IMPOSSIBLE for him to see that -- via Overscan -- he probably won't notice we've done that until after the return window has closed!  Ka-ching!

I.e., it is one of the Torch Mode Settings, I've previously discussed.

Burn-in Protection, on the other hand, is a Marketing "check off item" -- something added to TVs to help convince buyers it is safe to buy them.  I'm not going to go into a lot of detail on Burn-in (nor its less dangerous cousin, Image Retention) in this post.  Suffice it for now to say it is not a good idea to keep a static image -- an image with elements that do not move around or change appearance -- displayed for a long time.  Classic examples are the news "ticker" that runs across the bottom of cable TV news channels, and the various logo "bugs" overlaid on the program by some cable channels so you can't ignore which channel you are watching.

The problem is, these static image elements can alter the pixels in the TV in such a way that when you go view something else you see the ghost of those old, static elements still on the screen!  Their ghost has been "burned-in" to the TV!

The REAL protection against this issue is to be careful in your viewing habits.  Don't leave such stuff on the screen for hours on end, day after day.  Alternate with viewing other content that doesn't have such static elements.

But the Burn-in "problem" has become hyped to the degree some buyers are leery of paying the big bucks for a new TV out of fear the TV will quickly become unwatchable!  So the makers have added a Burn-in Protection feature to allay such fears.

What is it?  Well, it's really nothing more than a bit of processing to shift the image around a bit in all 4 directions -- typically called "Screen Shift" or "Image Orbiting".  The idea is that any static elements will be moved around, so they won't sit on the same spot on the screen forever.

If you think about it, you'll realize this is hardly a solution.  All you've really done is widen the area of the screen impacted by those static elements!  But it sounds good, and serves the Marketing purpose.  And it is almost ALWAYS enabled by default in the Factory Settings.

For the purposes of our discussion in THIS post, what's important about Burn-in Protection is it needs to crop a set of pixels around all 4 sides of the image so it has space to move around in while it is shifting the picture.

And now we get to the crux of the problem:  If you have cropped pixels off all 4 sides, either for Overscan or for Burn-in Protection, how do you present the REMAINING part of the picture?

Do you leave a black strip of unused screen all around the picture?  Nope!  You "Scale" up the remaining part of the picture to fit the size of the screen!  Think of this as a small amount of "Zoom".

And without getting too technical, know this:

Scaling (up or down in size) by SMALL amounts is a CLASSIC way to introduce image artifacts!

It's a sort of rounding error in the scaling.  Since the image is not changing size by very much, the rounding error gets distributed across enough space that it becomes easy to see.  Typically this will appear as a loss of horizontal and vertical resolution (i.e., ability to see fine details).

So the goal of getting rid of any Image Cropping is not simply out of some Purist Ideal you should see every pixel the filmmakers intended you to see.  It's that Image Cropping, and the consequent, small-order Scaling, produces a poorer QUALITY image!

To avoid this you need to find the settings in your TV to disable both Overscan and the image shift processing Marketed as Burn-in Protection.  That is, you want to be able to see every pixel of your content -- from edge to edge -- left to right, and top to bottom -- without ANY pixel cropping!

But umm, is that SAFE?  Yes.

First of all, virtually all of the content you will watch these days is of high enough quality that Overscan is simply not needed.  If you ever DO find yourself watching some content with cruft on the edges, my advice would be to just live with it.  Think of it as a reminder of the history of that content -- how it got to be that way.  And of course, also a reminder to be careful in selecting the quality of the content you view.

As for Burn-in Protection, remember my description above.  It's not really doing anything except blurring the area of potential burn-in:   Making it bigger!  The REAL protection, as I said, is to be mindful of your viewing habits.

Now FINDING the correct settings in your TV to accomplish this can be a neat trick.  There's is no industry agreement on what to call this stuff, or where to put it in the TV's menus.  So you may have to hunt around in the settings, or ask other owners of your model of TV for help.

For example, the relevant setting for disabling Overscan appeared in various TVs I'm familiar with under the names:  "Just Scan", "Dot By Dot", and "Mask".

Burn-in Protection, on the other hand, frequently rejoices in the names "Orbiter" and "Image Shift".

In addition, you have to check these Image Geometry settings for EACH FORMAT of video you are sending to your TV.  Partly this is because modern TVs typically have separate Picture settings for each incoming format (and also for each input!), but also because TVs sometimes come with Factory Installed Gotchas on this stuff!

For example my LG E6 OLED TV imposes non-defeatable Overscan whenever you send it video of resolution LESS than 720p!  So if you play SD content and want to send that to the TV at SD  video resolution (so the TV itself handles the up-scaling to its 4K pixel matrix), you are stuck with Overscan!  By a  bunch:  10 SD pixels cropped top and bottom and 14 SD pixels cropped left and right.  To avoid that, you have to let your source device upscale the content!

This is why I like to limit the different formats I send to the TV for different types of content.  E.g., just 4K/24 or 4K/60 for all content.  It minimizes the number of combinations I have to check!

OK, you know what you are trying to accomplish -- NO IMAGE CROPPING! -- and you think you've found the relevant settings.  How do you tell whether they are really working?

The problem is each pixel is small, and you are not going to have much luck spotting whether a small number of them have been cropped off any edge playing real world content.

What you need is a calibration chart specific to this task!

Most calibration discs will include such a chart.  For example, the "Spears & Munsil, 2nd Edition", Blu-ray, which I've linked in my post on Calibration Discs, offers a set of such charts.

You'll find them in Advanced Video > Evaluation > Image Cropping.  There are three such charts differing only in the frame rate:  24p, 30p, and 60i -- again for testing for gotchas in different formats.  These are all 16:9 1080 resolution content.

The Advanced Video > SD Evaluation section includes the same three charts at 480 resolution -- useful for checking what your Blu-ray player does with SD "Extras" content for example.

The retail package for that Spears & Munsil Blu-ray also includes an SD-DVD, and it too includes these three, 16:9 charts at 480 resolution.  So you can check  actual SD-DVD playback as well.

All of these charts are laid out the same way -- with an identical check pattern on each of the 4 sides of the full screen, 16:9 image.

I'll describe the check pattern on the left side as an example:  It consists of a stack of horizontal rectangles that differ, top to bottom, in the location of their left hand edge line.  Each rectangle also has a number next to it.  The rectangle with the "1" next to it at the top of the stack has its left edge line at the first pixel on the left side of the screen.  Rectangle "2" has its left edge line at the 2nd pixel in.  And so on.

If the Image Geometry is CORRECT, you should be able to see the outer edge line of the "1" rectangle on all 4 sides of the chart.

If on a given side, the first rectangle showing its outer edge line is "5", then you have Cropped the 1, 2, 3, and 4 pixels on that side of the screen.

For an added refinement, check that the edge lines of the "1" rectangles on the 4 sides are equal in thickness!  These lines are authored on the Spears & Munsil, Blu-ray as HD (1080p) pixels.  If you are displaying the chart on a UHD (4K) TV, then more than 1 UHD pixel is involved in rendering each HD pixel.

Note that you should be using no "Zoom" when displaying this 16:9 chart.  You want to be able to see the edges of the content on all 4 sides.

But suppose you LIKE to use Zoom when playing content that is not already 16:9 -- such as when playing Cinemascope movies.  How do you know the Zoom itself has not messed up your Image Geometry?

I'm not going to go into much detail on Aspect Ratio in this post, except to say my RECOMMENDATION is that you do not use Zoom to alter the Aspect Ratio of the content.  I.e., watch the show in its Original Aspect Ratio -- as it was intended to be seen -- even if that means you have Letter Box Bars or Pillar Box Bars padding the image on your screen.

But if you would rather not do that, there's another chart on this Spears & Munsil disc you may find helpful.  It is found at Advanced Video > Setup > Framing.  It is a 16:9 chart, with markers inside it for various, common, content Aspect Ratios.  Whether you are using Zoom in your source device or in your TV you can use this chart to check exactly what it is doing.   I.e., whether it positions the markers for, say 2.40:1 content at the edges of the screen as you'd like, or whether there is a flaw in the Zoom result.  The flaw might be that the Zoom is either going too far, or not far enough, or that the Zoom is not acting uniformly, as desired, with respect to all 4 edges.

It is unlikely you will be able to alter the results of the Zoom function in either your source device or the TV itself.  However, this chart will at least give you a handle on what that Zoom choice is actually DOING, should you decide to continue using it.