Enlarge Image Sarah Tew/CNET

If you turn up the sharpness control on your TV, you'll get a sharper picture, right? Nope. In fact, it's the opposite.

Sharpness is found among the basic picture settings on every TV, and its very name seems to encourage you to turn it all the way up. After all, who doesn't want to see the sharpest, clearest most detailed picture possible?

The problem is that the sharpness control itself doesn't really do anything to increase detail, and can often obscure that detail behind a mask of artificial-looking enhancement.

You should almost always turn it all the way down, especially with high-quality sources like Blu-ray discs, HDTV broadcasts, video games, some HD streaming services, and so on. Here's why.

Enlarge Image Geoffrey Morrison

Enlarge Image Geoffrey Morrison

Sharpness is edge enhancement.

On nearly all TVs, the sharpness control adds something called "edge enhancement." That's exactly what it sounds like. The edges in the image are enhanced, essentially by adding a thin outline or halo to them. This makes them more visible.

Take a look at the two images above. The first image is the au naturale version. The second has significant amounts of edge enhancement added. Note the outline around the buildings.

The picture below is a closeup of the "sharpened" edge-enhanced image:

Enlarge Image Geoffrey Morrison

As you can see, a sort of white halo appears around distinct edges. This is exactly what the sharpness controls on most TVs do.

The problem is, that halo shouldn't be there and it's replacing what should be. In this image it may not seem like a big deal, but with most content that halo is covering the actual detail in the image. In addition it often brings out grainy noise in other parts of the image. See how much cleaner the top image looks, compared to the enhanced image.

Edge enhancement definitely gives the image a certain look. It can even provide the appearance of more detail. Most TVs have their sharpness controls turned up by default, so we're used to this enhanced faux-detail look.

In fact, un-enhanced images can look soft by comparison. In reality however, the softer-looking image is actually more detailed, because it shows fine textures in walls, pores on faces, even tiny hairs -- all of which can be hidden by too much edge enhancement.

Other controls

Depending on the brand and model of your TV or projector, there could be detail enhancements that go beyond just the sharpness control. These could just be variations of edge enhancement or it could be something more.

There are ways to improve apparent detail, without resorting to ham-fisted edge enhancement. For example, Darbee does an impressive job making the image seem sharper without any noticeable artifacts and Epson's Super-Resolution does this as well; Sony's labyrinthine Reality Creation does, but you'll need some time to work out what's adding apparent sharpness and what's just edge enhancement.

Generally, we advise turning any of these features off. Professional TV calibrators usually try to eliminate any such enhancements in an effort to present the image as close as possible to the source. We do the same thing when we calibrate TVs for CNET reviews.

If you're curious about the effects of these enhancements, feel free to try out each in turn to see what it does, and if you like the look of the image better. Purists will keep these enhancements off, but if you like the look of it better, hey, it's your TV.

Consider the source

Occasionally, the edge enhancement is in the source. This was common on early DVDs. If it's in the source, there's nothing you can do about it. It's just something to keep in mind if you're trying out different settings, don't use just one source or program.

TV manufacturers love edge enhancement, largely because it makes their TVs seem super detailed when viewed in a store.

There are also some sources, generally low-quality video like standard-def TV channels or even VHS tapes, that can benefit from a TV's detail enhancement circuits. These sources are so soft and low-resolution to begin with, that when blown up to the size of today's large televisions they may look better enhanced.

What if you can't turn it off?

Some TVs, especially older ones, have edge enhancement that's permanently enabled. Even turning the sharpness control to zero and going through every setting (and picture preset) in your TV, you still may see edge enhancement or other processing. Last year's Vizio P series showed undefeatable edge-enhancement, for example, until Vizio issued a software update to address the issue.

Conversely, some TVs, such as some recent models from Sony, actively soften the image when you turn the sharpness control to zero (below 50 on some LG models). I have no idea why this is the case, or in what universe it makes sense. On these TVs, the proper setting could be one or two ticks up from zero, or even as high as the halfway point on the sharpness control.

The best way to be sure your sharpness control is set properly is to use a calibration Blu-ray, such as Disney WOW: World of Wonder. Specialized test patterns can quickly reveal extra processing and allow you to minimize it.

Bottom line

If you go to your TV right now and turn the sharpness control all the way down the picture is absolutely going to look soft. Much like high color temperatures, anyone who isn't used to making fine adjustments to their TV controls has gotten used to a certain "look" to their TV's picture.

If you experiment with this and find you don't like the look of the un-enhanced image, that's fine. It's your TV. Just know that as TVs and content move to higher 4K resolutions, edge enhancement is going to block more and more of the actual detail possible in these TVs.

My advice? Give it a few days at or near "0," then try watching a show with the sharpness control back where it was. I bet you hate it; I did.

Got a question for Geoff? First, check out all the other articles he's written on topics such as why all HDMI cables are the same, LED LCD vs. OLED vs. Plasma, why 4K TVs aren't worth it and more. Still have a question? Send him an email! He won't tell you what TV to buy, but he might use your letter in a future article. You can also send him a message on Twitter @TechWriterGeoff or Google+.