Gray uniformity describes how well a TV is able to maintain a single, uniform color on the screen. Uniformity issues can look like darker patches around the screen, with corners and edges especially susceptible to looking darker than intended. It’s particularly an issue for sports, where darker patches on the screen can affect the look of playing surfaces.
To evaluate gray uniformity of TVs, we take a photograph of the screen while it is displaying a single, solid color. Using that picture, we calculate both the standard deviation of the color values of the pixels across the entire screen, and the number and severity of darker patches in the center of the screen (where they matter most).
Update 2017/02/03: We updated our methodology and we are now also testing the gray uniformity on a 5% white (dark gray) image. We retested the most popular TVs of the 2016 lineup.
When it matters
You’re most likely to notice gray uniformity issues while watching sports, since playing surfaces are usually large stretches of a single color. Dirty screen effect will also be most obvious when there is a panning shot during sports. Most non-sports media tends to be a bit more varied, so you shouldn’t have gray uniformity issues with anything else unless your TV has particularly poor uniformity.
Because it's only usually really bad gray uniformity that is obvious, it’s not hugely important most of the time. If a particular TV has really bad gray uniformity, or if a person is very sensitive to this kind of problem, then the importance could increase some. If you get a TV with gray uniformity that you can’t live with, try making an exchange for a different unit.
50% Gray Picture
Our 50% gray test pattern
Our picture test captures the gray uniformity imperfections on a TV screen, and to show you the quality of the uniformity as you would actually see it on a TV. Of our tests, we consider this the most useful for most people who are trying to get a sense of what kind of uniformity they can expect from a TV.
To evaluate the gray uniformity on TVs, we take a photograph (F4, 1/4 second exposure and ISO 200) of this 50% white (medium gray) image while it is being displayed on the screen. The image shows any imperfections in the reproduction.
5% Gray Picture
Our 5% gray test pattern
Similar to the 50% gray uniformity picture test, the 5% gray is to show you the quality of the uniformity as you would see it on a TV, but with a darker image. This test is more useful to visualize the uniformity of TVs using emissive technologies like OLED TVs.
To evaluate the 5% gray uniformity on TVs, we take a photograph (F4, 1/4 second exposure and ISO 200) of this 5% white (dark gray) image while it is being displayed on the screen. The image shows any imperfections that would appear in very dark shots.
50% Standard deviation
What it is:
Average squared difference of pixels when displaying a mid 50% gray.
When it matters:
Solid colors. Sports, panning shots.
Our 50% standard deviation test measures the evenness of color reproduction across the screen, and tells us the average squared difference of the color values of pixels when a full-screen, 50% white (medium gray) or 5% white (dark gray) images is displayed. A lower standard deviation means less difference is present, and that the picture is better.
This allows us to score the overall uniformity of the entire screen objectively. It’s useful for comparing TVs in absolute terms but isn’t as useful as the picture test for comparing TVs for what you’ll actually experience.
Photo from 'Picture' test
Photo after processing
For this test, we take the photo of the screen from the picture test and process it with a low pass filter (Gaussian blur) to remove noise and artifacts (like moiré) created by the camera. We then calculate the standard deviation of the color values of the pixels using the following formula:
50% Dirty screen effect (DSE)
What it is:
High-frequency variance of uniformity. Dark spots on the screen.
When it matters:
Solid colors. Sports, panning shots.
Our 50% dirty screen effect test also evaluates the amount of difference the color values of pixels have from the target color but focuses only on the area around the middle of the screen, where variance tends to look like dirty patches.
This is a bit more important for sports than the standard deviation test is, because while the standard deviation test gives us an idea of how far the uniformity is from ideal in absolute terms, it doesn’t fully represent the issues people will notice with poor gray uniformity. Compare these two images. On the left is a TV with a higher standard deviation, but less DSE. On the right is a TV with lower standard deviation, but higher DSE. You can see the second has more dark patches around the middle, where they are likely to be problematic.
To take this into account, we once again use the photo from our 'Picture' test, only this time we pass it through a high pass filter so that low frequencies are removed from the image. The result is something like the image below and to the left (result multiplied by 50 for purposes of illustration). This isolates all the variations that cause the dirty screen effect but does so for the entire screen.
In order to test just the middle of the screen, we multiply the values of that picture with those of the image in the below-middle, resulting in the below image to the right.
TV's 50% white image through high pass filter
Finally, we calculate the root of the average of the squared values of the final image. The equation is similar to that of the standard deviation calculation above but uses ‘0’ instead of the mean.
5% Standard deviation
What it is:
Average squared difference of pixels when displaying a mid 5% gray.
When it matters:
Our 5% standard deviation test use the same procedure as the 50% standard deviation test, but run it on our 5% gray picture instead. For more information on the procedure, refer to the 50% standard deviation test.
Once again here, a lower standard deviation means less difference is present, and that the picture is better.
5% Dirty screen effect (DSE)
What it is:
High-frequency variance of uniformity. Dark spots on the screen.
When it matters:
Our 5% dirty screen effect test uses the same procedure as the 50% dirty screen effect test, but run it on our 5% gray picture instead. For more information on the procedure, refer to the 50% dirty screen effect test.
The 5% dirty screen effect is based on a darker image, so this test is more important for any content that has dark scenes.
Gray uniformity is unique to each individual panel. This means that no two TVs, even of the same model, will have matching uniformity. Generally, though, higher-end TVs will have better gray uniformity, as the manufacturers will have stricter standards for the panels being used.
Causes of gray uniformity issues
With LED TVs, gray uniformity issues are caused by a couple of factors. LCD panels are pretty sensitive to pressure, so extra pressure caused by misalignment of the TV's components, or by mishandling of the panel during manufacturing, could lead to defects appearing. Likewise, improper pressure can interfere with the light diffuser doing its job correctly, which can cause certain portions of the screen to be lit darker or lighter than intended.
With LED TVs, full-array and direct backlighting can also contribute to worse gray uniformity. It's often possible to see a faint grid on the screen, corresponding to the placement of the LEDs.
With OLED TVs, the gray uniformity issues are more related to imperfections in the panel itself, independent of pressure-related problems. Also, LG's 2015 OLED TVs suffered from vignetting that was particularly visible when displaying a dark gray image, but since then most OLED TVs do much better when tested under our new 5% gray image.
Getting the best results
Unfortunately, gray uniformity is entirely down to the panel you get. There are no steps available that will help you improve the gray uniformity.
Related settings & other notes
There are no settings to adjust.
OLED TVs tend to do quite well with our test, which uses a 50% white (medium gray) image, but they have much worse uniformity with darker colors, which can be an issue. This is why we have added a 5% white (dark gray) image in our gray uniformity test.
Gray uniformity refers to how well a TV can display a single, solid color across the screen. It matters for any images containing a wide expanse of a single color, and in particular sports, where bad gray uniformity affects the appearance of playing surfaces. For each TV, we take 2 photos of the grays uniformity (dark and medium gray), calculate the standard deviation of the color values of the pixels, and then calculate the amount of dirty screen effect that is present for each picture.
Unfortunately, there are no steps that can be taken to improve gray uniformity – it’s entirely down to the panel you get. If you find yourself with uniformity that you cannot live with, you should exchange your TV for a different unit, or even a different model.
Two things: imperfections in the LCD layer and in the backlight diffuser.
1) The LCD layer is fragile. It is soft and flexible. Try pressing it with your thumb and see what happens. The surrounding area either gets darker or brighter. If there is any pressure by miss-aligning the frame or miss-handling the LCD layer in the assembling process, a DSE could happen.
2) The light diffuser of the LEDs in the backlight is also very dependent on pressure. Edge-lit and thinner TVs in particular have problems with this. Imagine LEDs only on the left and right edges of the screen (a configuration very common in Samsung TVs). The goal of the diffuser is to equally distribute light from the edges to the center of the screen. This is done with multiple layers of semi-transparent and reflective materials. If the layers are squeezed too much somewhere in the panel, the light will either be reduced in that section or augmented. This causes the vertical banding problems.
Just got the new 4k Sony TV xbr x900b. Great picture, but on lighter backgrounds like grey, you see a shadow blooming effect around the whole edge of the screen. I love the TV. I showed my dad and he said he sees it but not to worry, as it's ok. Wow, what a picture. Please help.
Send us a picture by email and we will be able to tell you if it is normal or not. You can't expect an LED to be perfect for this, but it shouldn't be really bad.
I own a new Samsung UN60H6350 and there is a slightly noticeable darker (almost reddish) section to my panel only when viewing a gray and/or white screen. From reading this page, it must be a bit of DSE. (My wife swears she can't see it though.) I'm wondering if its worth even having a technician look at it? Maybe I need to just accept that panels with this technology are going to have some amount of DSE. I'd hate to replace my TV just to have one with worse gray uniformity. The rest of my screen is perfect, as far as I can tell.
Don't worry about it, because as you said, no TV is perfect anyway and you risk getting a worse one. If your wife can't see it, this means it is within acceptable margins. A tech will likely say the same.
Thanks for the useful info on your site. What picture settings should I use to do a grey backlight uniformity test? Should I turn both backlight and brightness up to max and check in dark room?
Don't touch the brightness setting! In 95% of cases, the default value is the good one (the other 5% are off by only 1 or 2 pts). If you want to change the luminosity of the screen, change the backlight setting. The brightness setting clips the output range, which reduces the contrast ratio - something that you don't want. Now, back to your original question: use the luminosity that you will use normally, in your normal room lighting. The goal is not to over-expose the flaws, because LEDs will always have flaws, so you will just end up disappointed by your new TV. For our tests, our pictures are taken in a pitch black room with a backlight set so that a pure white is 100 cd/m2 (usually this means a backlight setting of around 25% when the ECO mode is off).
What are the low points and high points in the white balance settings? I followed both pictures in the calibration settings for the "points," low and high. Am I doing it right? I pretty much followed everything, except I decided to keep TruMotion set to "Clear." Is that okay?
Think of it as a simple linear function. Y=mx+b. The low points are b, the offset of the color no matter its intensity. The high points are m, the gain that increases with the intensity. In short, high points are for the bright whites, low points are for every intensity.
Is the gray uniformity issue highly variable within models? Your test is amazing, but should I expect the results to apply to all TVs of the same model? I ask because I'm considering getting a Samsung UN55J6200, but the DSE you measured would really bother me, making me lean more toward the Vizio E55-C1. Is it possible you just got a bad J6200 for your test or do these trends hold true within the model line?
It is variable, but since we only test one unit for each model, we can't say to what extent. That said, based on what we've seen of other Samsung TVs this year, we think our J6200 is pretty representative of what you can expect.
Hello. Recently purchased a sharp Roku 4K uhd model: LC50LBU591U. Seeing some slight black vertical lines as in the pics above on only gray screens. Is this normal?
Depending on the severity of it, it may or may not be normal. No LCD TV is perfect, but if you find that these lines are distracting you while watching normal content, it's worth considering replacing your TV.
I recently bought a 55" LG LB6300 and can't stop noticing the DSE while watching soccer (or playing soccer games on PS4). I also notice a lot of clouding when playing PS4 games that have darker scenes, which is fairly often. I can handle some uniformity issues, but this set seems to exceed my tolerance level. I was thinking of returning the LB6300 and picking up a Sony W800B, which I can get for less than the LG through my work discount. My question is, is there any reason why I shouldn't return the LG for the Sony, especially if I can get it for cheaper? Again, my main uses are watching soccer and playing PS4 games (many of which have very dark scenes). I don't really care about smart TV features, number of inputs, 3D, etc. Thanks for your help, your site is awesome!
The only downside to returning it and going for that Sony would be the more limited viewing angle. But that's a small price to pay for better uniformity and contrast. Go for it.
I did my own calibration using LG's picture wizard III built into the TV. Is it technically inaccurate that way?
Here are the basic settings that were in the step by step, and an explanation of how the calibration led me in terms of setting the picture.
It asked me if I wanted original or preferred. I picked original, which is supposed to be closer to being accurate, or how it was filmed on camera, and I guess the preferred option is more enhanced.
In expert mode I just set the gamma to 2.4, because it helps with black levels and detail, as well as playing around with my own preferences for settings like TruMotion, color temp, processing, etc. I did not touch the white balance.
You did good. Using the TV's built in calibration wizard is a easy way to adjust the basic settings. You can't adjust the more advanced options with it (like white balance), but it is still useful for the basic ones.
I understand it's a part of this technology, but I have a few questions on this subject.
1. How do I test it properly? If the higher the backlight, the more you see the clouding, what backlight setting should I use to check it? (50? from 0 to 100)
Should I check the DSE with a white/gray background?
2. What backlight setting and brightness should I set to get reliable results? And what is the most recommended, anyway?
3. Can the cloudiness and the dirty screen effect get worse? If so, what could cause this and how can you avoid from making it worse?
(Is using a bright backlight setting going to make it get worse in the long term?)
4. Are clouding and DSE common on most LED panels? Is there anything that can be done instead of making an exchange (potentially for something even worse)?
Are there any examples of acceptable clouding and acceptable dirty screen effect vs unacceptable examples?
I own a 40" Samsung h6400.
You should set your TV's backlight setting to whichever it is you'll be using when you watch TV. We recommend using our gray background (find it in here. It will make it easier to compare your TV to our test results.
It's unlikely that your uniformity will get worse. That mainly happens when there is a dramatic change in temperature in a short amount of time, or if the TV is moved/jostled without care. Using the backlight on a high setting for the long-term will not make your uniformity worsen.
Clouding and DSE are indeed common on LED TVs, and there isn't anything to be done about it. If you would like guidance, you can send us a photo of your TV with the gray uniformity image on it, and we can tell you how good/bad it is.
As for examples of good and bad gray uniformity, check out our results. It is a personal preference, and the threshold should be if it doesn't bother you too much in normal footage.
What is vignetting and banding and what does it look like on an OLED panel? How do I test my OLED B7 panel to see if it’s experiencing banding and vignetting? Also, is there anything else I should look for on the panel aside from these 2 issues before I get past my 30 day return window?
Vignetting is an effect that causes the corners of the screen to look darker than the center region, and banding is, as the name suggest, the appearance of off-color bands on the screen (usually vertically). The best way to test for these is by opening up a uniform grey image (here is a link to our 50% grey test pattern), but it is important to also test using real content to see if it is actually visible in a realistic scenario. Most TVs will have some of either of these issues, and it is up to you to decide if it is problematic enough to warrant a replacement.
Hello all, great site, just a few questions and comments. I just recently purchased a 65in LG UH6030 (pretty sure it's a big box exclusive t.v. as I don't see it everywhere) and I hate it, dse to the point of unwatchable on certain uses (vg/sports/some movies). After researching online, DSE seems to be a bit of a norm unless you spend a boatload of money, and even then its just less. I'm curious what you guys think about this beyond testing. The 4k picture is garbage if it looks like your watching t.v. through a screen door (torn nylons comes to mind to me.) Wasn't that the point of 4k, to look at images as if it was right there, unfiltered or modified. I know I'm not alone in feeling that it completely pulls me out of whatever I'm watching/playing if my screen looks perpetually dirty. I (regrettably) just sold my 1080p 55in Toshiba TV with almost no DSE, and Toshiba is not exactly known for being high end. How has this become acceptable? I would appreciate some expert opinion as I feel I'm taking crazy pills here. This all seems like a huge step backwards. Again, great site and it will be my go-to site in the future.
In general, LG IPS TVs such as the UH6030 will perform worse when it comes to DSE. The LG UH6100 is a very similar TV to the UH6030 that you own and indeed doesn't perform very well in this aspect. As for the screen door effect, this could be explained by TV's RGBW subpixel arrangement. This is kind of a "fake" 4k and most of LG's budget models use this. It can cause straight vertical lines to seem jagged and uneven. Some IPS TVs do better than others, though, since quality control has a big impact on DSE. Sony TVs such as the X850D and X750D still do quite well even if they use an IPS panel.
Greetings and thank you for providing such an awesome site! I recently purchased a TCL 55" S405 LED Edge-Lit TV. When watching brighter scenes I can see the corners are darker than the rest of the screen and when panning occurs in a bright(er) scene I can see vertical bars throughout the panel. Is this "DSE"? I was looking at getting the 55" P607 to replace my aging Panasonic Plasma but if this is indicative of the TCL brand then I may stay clear.
You're correct, dirty screen effect occurs during slow movement like panning, where the same object looks different as it moves to a different part of the screen. Gray uniformity unfortunately varies between different units, so you may have gotten a bad unit. You can compare to our S405's test photo to get a rough idea if yours is worse than average. Our TCL P607 unit actually had worse grey uniformity than our S405. Our Samsung MU7000 unit had quite good grey uniformity for its price, but its picture quality overall is worse than the P607. Unfortunately most LCDs can't hold a candle to the excellent uniformity of a plasma, OLEDs can but are much more expensive.
I bought a Sony w850b in December. It had pretty bad DSE, very noticeable watching soccer and baseball. I must have gotten a pretty bad unit because my purchase was refunded. I think I just got a fluke bad panel, that being said, it seems that DSE has gotten worse for the 2015 year based on your reviews. Is this the case? Or have you changed your scales?
No, the levels of gray uniformity have not gotten worse. We've just changed our method of scoring. Last year's ratings were subjective, but we've now switched to a calculation, with the scores automatically generated. We're also being stricter with our ratings.
We discuss our new method of scoring in the body of the gray uniformity article.
You mentioned that grey uniformity will not increase on an LED screen unless temperature or force is applied to the screen, but what about an OLED screen?
I've read on various message boards that grey screen uniformity on OLED screens generally increases with time because of the 'Pixel Refresh' feature on the TV, but I'm curious to know if that is actually one of the designed intents of this feature, or if it is just internet speculation. Have you experienced improved grey uniformity over time with OLED screens?
Generally, the job of the screen compensation feature found on OLED TVs is to maintain the grey uniformity relative to the TV's previous state. Because of this, we haven't noticed and don't expect the uniformity to get better over time.
I purchased an LG OLED 65B7A and noticed slightly pink or blue tinted vertical sections on the screen at 100% white. If viewed from a 30 degree angle the tinting gets worse. I have had the panel replaced by LG and the tinting changed but only where the pink and blue were located. The factory direct technician said mine was average and that all of LGs OLED TVs have this condition to some extent. Could Rtings include a 100% white screen test to show any uniformity issues? The 50% gray screen is quite good on my LG OLED TV. The tinting only becomes noticeable on values above 50%, gray to white.
Uniformity issues on white screens are quite frequent on OLED displays, but are generally not noticeable during normal usage as 100% white windows are rare in regular content. Since every OLED panel is different, not all of them will have this issue at the same level and you should probably return your TV to have a better panel if it really bothers you during normal viewing. As for the 100% white screen test, we will take your suggestion into account and might add it to our next test bench update.
I had an issue with dirty screen effect on my new Visio M75-E1. It had a narrow brighter vertical area a few pixels wide in the middle of the screen that was noticeable with blue sky horizons. I made solid color images with MS paint and created .png files to place on a USB stick - I chose a USB stick to prove the problem was within the TV. I then downloaded Open Camera app to my Android phone to get a lossless option to take a picture (100% quality jpeg).
I sent the photo to Visio and they are sending me a re-certified TV.
So for the DSE issues with vendors:
1) use USB file of pure image to prove issue is inside the TV
2) use a lossless format from your camera - the standard 90% JPG is not good enough.
We didn't have any serious issues like what you are seeing with our M65-E0. Hopefully the refurbished one they are sending you will be better. There is always some variation between panels. Thank you for the information.