Green Screen Test: Check Dead Pixels and Green Subpixels
Green Screen Test. Click Start Green Screen Test to fill your display with pure green and check for dead green sub-pixels and uneven brightness. Use the free stuck pixel fixer online to confirm everything looks correct before you rely on it elsewhere.
Interactive Tool
Because green carries most of the perceived brightness in an image, Green Screen Test isolates that sub-pixel on its own so uniformity problems and defects show up more clearly than on any other single-color field. Click Start Green Screen Test, look across the whole screen for blotches or dead spots, and use the arrow keys to move on to blue.
A single dark speck can hide on a busy desktop for weeks, yet it jumps out the moment the whole display turns one color. This green screen test tool fills your display with a pure green screen in fullscreen mode so you can catch display defects such as dead or stuck subpixels and uneven patches on OLED, LCD and LED panels across smartphones, tablets, laptops and TVs. You get a quick, visual verdict on your green subpixel health in under a minute.
What a Green Screen Test Shows on Your Display
Every pixel on a modern display is built from three subpixels: red, green, and blue. A green screen test drives only the green color channel at full strength, #00FF00 in hex or RGB values of 0, 255, 0, while the red and blue elements stay dark. Because only one primary channel is lit, anything that fails to follow it stands out against the solid color. The free blue screen test runs fullscreen so you can inspect your panel edge-to-edge under real viewing conditions.
It runs in your browser with no download, is mobile friendly, and pairs with red and blue screen tests, a white or black screen, a near-black field and a gradient. Solid fields each answer a different question:
| Field | Best at finding | Pair it with |
|---|---|---|
| Green | Dark or wrong-color specks in the green channel | Red and blue fields |
| White | Broad tint and dim zones | Mid-gray |
| Black and near-black | Bright stuck dots, glow at the edge of LCD panels | A dark room |
| Mid-gray | A fixed patch or a retained shape | Gradient |
| Grayscale steps | Abrupt banding between tones | A second app |
When to Run a Green Screen Test
Run it the day a new display arrives, while the return window and warranty are open, and after a 4K screen has been moved. A green screen test is also worth repeating on an OLED that has shown a static taskbar for months.
Chroma Key Green Screen Versus a Test Screen
The same color doubles as a green background for chroma key work in OBS, video editing and VFX, where software removes it from the shot. A green screen display for testing must be one flat field with no tracking markers, and you inspect it rather than film it. 8K wallpaper downloads suit keying, not diagnosis.
How to Run Green Screen Testing Step by Step
- Open the tool and click to start; the field fills the whole display.
- Scan the whole field slowly, row by row.
- Use the arrow keys on a keyboard, or swipe on a phone, to switch to red, blue and white, then compare the same spot.
- Press ESC or tap once to leave.
Enter Fullscreen Mode and Prepare the Room
- Work in a dimly lit room so faint shade changes show up.
- Clean your screen first; a speck of dust or smudges can pass for a failed subpixel.
- Set brightness to maximum for one pass, then repeat at your everyday brightness.
- Angle the display away from lamps and windows to cut reflections.
Fullscreen matters because browser toolbars leave a strip of the display untested, and a green screen test only covers the area it actually lights.
Inspect the Edges, Corners and Center
Start at one edge, sweep the corners, then the center, close enough to see a single dot. View the field from different angles too: a speck that shifts with your viewing angle is a reflection on the glass; one that stays fixed in the same physical area on every color is in the panel. Compare against a known-good screen if unsure, and note the physical location of every patch.
Defects a Green Display Reveals
Each fault has its own signature against green, and it tells you whether the subpixels themselves failed or a setting is to blame. Four kinds of subpixel defects are most common. Run the red screen test online for a few seconds under normal room lighting for the most reliable result.
Dead Pixels
A dead green subpixel produces no green light, so it shows as a black or very dark speck. Our dead pixel checker then shows the same spot on red and blue, which tells you whether one element failed or the whole pixel is dark.
Stuck Subpixels and Red or Blue Dots
Red or blue dots on the green field mean a red or blue element is stuck on while the rest behave. A white dot means all three are stuck. On LCD panels a stuck pixel can sometimes be freed by rapid color flashing that exercises the liquid crystals; on OLED it is usually a hardware defect, which is where the manufacturer's policy comes in.
Color Uniformity and Tint
A healthy panel shows one even shade. Darker bands, a yellowish tint near one side or clouding are uniformity issues. On LCDs, a lighter glow along the frame is backlight bleed, which a black field shows better. A color cast covering the whole field usually comes from a setting rather than the hardware.
OLED Burn-In and Image Retention
On QD-OLED and other OLED screens, green subpixels wear with use, so OLED burn-in from a taskbar, logo or game HUD often appears as ghost images or faded areas on the green field. If the shape fades after a few minutes of moving content, it was temporary image retention. If it stays, it is retained imagery, and a dedicated burn-in test across several colors confirms it.
Why a Green Subpixel Checker Matters Most
The human eye is most sensitive to green light, so a fault in this channel is the one you notice in everyday use.
How Much Brightness Green Carries
The Rec. 709 luminance formula used for HD video weights each channel by how bright it looks:
$$Y = 0.2126R + 0.7152G + 0.0722B$$
Green supplies about 71.5% of the perceived brightness of a white pixel, roughly 3.4 times red and 9.9 times blue. That is why brightness perception, and even how warm or cool a display's white point looks, leans so heavily on green subpixels. A dead green element is therefore the hardest fault to ignore, and the green field is the one that isolates it.
Pixel Policy Limits Behind the Dead Pixel Test
Each manufacturer publishes its own pixel policy, and many still borrow the classes from ISO 13406-2. Class II, the usual consumer level, allows two always-bright and two always-dark defects per million pixels, plus five defects in a single color element.
Allowed Display Defects by Resolution
Take a 27-inch 2560 × 1440 panel: 3,686,400 pixels carrying 11,059,200 subpixels, a third of them green. Scale the per-million rates by the pixel count:
$$\text{Allowed} = \text{rate per million} \times \frac{\text{pixel count}}{1{,}000{,}000}$$
That panel may ship with up to 7 always-bright, 7 always-dark and 18 single-element faults (rounded down from 7.37 and 18.43) and still meet Class II.
| Resolution | Pixel count | Always-bright | Always-dark | Subpixel defects |
|---|---|---|---|---|
| 1920 × 1080 | 2,073,600 | 4 | 4 | 10 |
| 2560 × 1440 | 3,686,400 | 7 | 7 | 18 |
| 3840 × 2160 | 8,294,400 | 16 | 16 | 41 |
Compare the specks you logged on the green field with this table: three dark ones on that 1440p screen sit well inside Class II, so read the policy before you file.
Documenting a Defect for a Claim
Photograph the whole display with an external camera first, then take a close-up of the spot, keeping exposure steady. A screenshot is useless here: it records the image your system sends, not the light the panel emits, so a failed element never appears in it.
Checking a Refurbished Laptop Against a Pure Green Screen
Day three of a 14-day return window on a refurbished 14-inch laptop with a 2240 × 1400 screen, and the question is simple: keep it, or send it back while that is still free? The answer, after ten minutes with the green field, is keep it, but recheck on day 12.
In a dim room at 100% brightness, the green screen field shows two dark specks: one 41 mm in from the left side and 18 mm down from the top, the other near the lower right. Switching to red and blue settles what each one is. The first goes dark on all three colors, so it is a whole always-dark pixel. The second stays dark only on green and lit on red and blue, so it is a single failed green element. On a white field that one shows as a faint magenta point rather than black, which is easy to dismiss as a smudge.
Next comes the policy check. The screen holds 2240 × 1400 = 3,136,000 picture elements, or 3.136 million. Applying the ISO 13406-2 Class II rates gives:
| Screen | Always-dark allowed | Single-element faults allowed | Found |
|---|---|---|---|
| 2240 × 1400 (this laptop) | 6 (6.27) | 15 (15.68) | 1 and 1 |
| 2880 × 1800 (rerun) | 10 (10.37) | 25 (25.92) | 1 and 1 |
I recompute the 6.27 by hand (2 × 3.136) before trusting it. Two faults sit far under Class II, so a defect claim would almost certainly be refused; only a Class I or "zero defect" promise, which allows none, would cover them. The rerun row shows the less obvious point: on a denser screen the same two specks fall even further inside the limit, so a denser model buys you no stronger case.
The number I would watch is not today's count but the trend. One stable dark pixel is a cosmetic flaw; a second always-dark pixel appearing within days suggests a failing row driver or a damaged backplane, which no policy table describes well. So the location of each speck goes in a note, and the same field gets rerun on day 12. If the count is still two, the laptop stays. If it has grown, it goes back under the no-questions return, not a defect claim.
Settings to Retest Before Blaming the Green Background
A color cast across the entire field rarely means faulty hardware. Change one setting at a time and retest the same field.
Night Shift, True Tone and HDR
- Turn off Night Shift on Apple devices or Night Light in Windows, plus any eye comfort or blue-light mode.
- Note whether True Tone or adaptive color is on; both shift the green as room light changes.
- Compare HDR on and off, since HDR tone mapping and HDR-to-SDR conversion can make a full green field look duller.
- Check the picture mode and color temperature preset; a vivid mode can push green toward cyan.
- Look for an accessibility filter or a custom color profile in system settings.
- Keep brightness fixed while you compare.
Source, Cable and Browser Checks
Try another browser, then, for an external display, another input and cable. Check that scaling sits at 100% and the refresh rate is native. A patch that stays put across apps and sources is in the hardware; one that disappears was in the signal path.
Running a Screen Color Test on Phones, Laptops and TVs
The field is the same on every device; the settings around it differ.
Monitors and Laptop Panels
On an external monitor, record the preset and the port before changing anything, and confirm the field covers the entire panel at native scaling. On a laptop, plugging in a second display shows whether a cast follows the built-in panel or the system output.
iPhone, iPad, Android and Televisions
On an iPhone or iPad, switch off True Tone and Night Shift for the run. On Android, note the screen mode, such as Vivid or Natural on many models. Televisions often store a separate HDR picture mode per input, so test from your usual source with overscan off. On a projector, a speck usually sits in the optics.
What an RGB Screen Test Cannot Measure
A browser draws a known value, #00FF00, but it cannot measure the light that leaves the display. Color accuracy, Delta E, gamut coverage and contrast ratio all need an instrument.
Calibration Needs a Colorimeter
For measured results, a colorimeter and calibration software build a profile against a target. That is monitor calibration, a separate job from spotting defects. Likewise, a line, crack or bruise-shaped mark that appears on every color is pressure damage or physical screen damage, not a settings issue, and no retesting will clear it.
Frequently Asked Questions
- Why test with a green screen in particular?
- Your eyes are more sensitive to green light than to red or blue, so a fault in the green channel is the one you notice most in daily use. A pure green field lights only the green subpixels, which makes a dark or wrong-colored one easy to find.
- What do red or blue dots on the green screen mean?
- A red or blue dot means that subpixel is stuck on while the green one beside it isn't lighting. It's a hardware fault, and whether it's covered depends on the maker's pixel policy and your warranty.
- Can a green screen test show OLED burn-in?
- It can. Burn-in that affects the green subpixels shows up as faded areas or ghost shapes, such as a taskbar or logo, on the flat green field. Check the same spot on gray and white to confirm it.
- Do I still need red, blue, white and black screens?
- Yes. Green checks one channel only. Red and blue cover the other two, white shows broad tint and dim zones, and black shows bright stuck dots and backlight bleed, so the full set gives you a complete picture.
- Can this test measure color accuracy?
- No. The browser sets the color value, #00FF00, but it can't measure the light your display gives off. Delta E, gamut and white point need a colorimeter and calibration software.
- Should I turn off HDR, Night Shift or True Tone first?
- Note your normal settings, then turn off one feature at a time and run the same color again. If a tint changes or disappears, the setting caused it rather than the panel.
- Will a screenshot capture a dead pixel?
- No. A screenshot saves the image your device sends, not the light the panel shows, so a dead or stuck subpixel never appears in it. Use a camera to photograph the screen instead.