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If your smart TV’s picture looks wrong, run the TV’s built-in picture test before you change any settings. A clean test points you toward the signal, cable, input, source device or content. A fault that appears inside the TV’s own test is a TV problem, and adjusting picture controls will not fix it.
The steps below follow the order that LG USA and Samsung USA support pages use, reflecting their guidance as of early October 2026. Menu names and paths change with model year, software generation and region. Treat the paths here as examples, and confirm them in your model’s manual. Readers outside the US should also check their local manufacturer support site.
Record the symptom before you open a menu
A precise description makes the rest of the diagnosis faster. Write down the following:
- Whether the problem appears in every app and channel, or only on one input such as HDMI 1 or the antenna tuner.
- Whether it follows one external device, one particular show, or one streaming app.
- Whether it changes with room lighting or with the brightness of the scene.
- The exact TV model number and software version. Manufacturers give different menu paths for different model years, so this information determines which instructions apply to you.
- Whether the problem started after a settings change, a software update, or the connection of a new device.
Run the built-in picture test
The built-in test is the fastest way to separate a TV fault from an outside cause. It generates its own test image, so the result does not depend on your broadcast, streaming app or connected device.
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On newer Samsung models, Samsung’s current support guide places the test at Support → Device Care → Self Diagnosis → Picture Test. Earlier Samsung models use a different Support or Self Diagnosis path. LG’s location for the picture test depends on its webOS generation. If the labels on your screen do not match these examples, use your model’s manual to find the test.
Some models do not include an HDMI diagnostic. Samsung’s HDMI test is designed for cables shorter than 2 meters, and longer cables may not produce reliable results.
Read the test result
The test result tells you which branch of the diagnosis to follow.
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| What you see | What it indicates | What to do next |
|---|---|---|
| The test image is clean, but the live picture shows the problem | The fault is in the signal, input, cable, source device or source settings | Work through the settings and connection checks below |
| The test shows the same lines, dots, flicker or abnormal color | The built-in diagnosis points to a TV fault | Stop changing picture values and contact manufacturer support |
| The problem appears on one app, channel or device only | The problem is outside the TV’s display hardware | Test a different source or cable. For broadcast problems, the signal provider may need to be involved |
Change one setting at a time
Once the test has narrowed the cause to the settings, adjust them in this order. Change one value, compare the picture, and then move on.
- Choose a picture mode that suits your room and content. Section below explains LG’s mode groups.
- Adjust Backlight and Brightness, which control the overall light output of the screen.
- If the screen brightness changes on its own, check automatic brightness and energy-saving features (see the flicker and brightness section below).
- Adjust Sharpness and noise reduction last, and only if the image still looks soft or noisy.
- If you have changed many values and cannot tell which caused the problem, reset the picture settings (see the reset section below).
What the picture controls do
Samsung’s current support guide describes the main controls as follows. Names and behavior can vary across models.
| Control | What it changes |
|---|---|
| Backlight | How much light the screen produces |
| Brightness | Overall screen brightness |
| Contrast | The difference between dark and light elements |
| Sharpness | The apparent sharpness of edges |
| Color | Color saturation |
| Tint | The hue balance between green and red |
| Digital Clean View | Reduces picture noise |
Samsung also documents picture clarity controls, HDMI black level, dynamic contrast, color tone, white balance, gamma, color space and a reset option. Game Mode is available on select models. According to Samsung, it may slightly reduce graphics quality while prioritizing speed. These advanced controls are optional. Change them only when you know your model, your source and what you are trying to achieve.
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LG advises choosing a picture mode based on the viewing environment, your preference or the type of video. Its guidance groups modes as Natural Light or Vivid, Artificial Light or Standard, and Dark Room or Cinema. LG notes that the TV’s capability, room lighting, screen reflectance, your settings and the video content all affect the final picture. Its suggested values apply only to the modes it names, and they are not universal calibration values for other models or brands.
Troubleshooting by symptom
Picture too dim, too bright, or unstable
Start with a picture mode that suits your room, then adjust Backlight and Brightness. If the brightness shifts with room light or scene changes, the cause is often an automatic feature. Samsung names Ambient Light Detection, Power Saving Mode and Motion Lighting on some model generations. According to Samsung, these features can adjust the image based on ambient light or power-saving needs. They can also make brightness appear to flicker when the room or content changes. Turn off or adjust one of these features at a time, then compare the picture before changing anything else.
Lines, dots, or part of the picture missing
If lines or dots stay visible in the built-in test, the problem is inside the TV, and manufacturer support should inspect it. If the test is clean, check the HDMI or antenna connection, the connected device and the aspect ratio. LG recommends a 16:9 or Original aspect ratio for the symptoms it describes. Samsung advises testing with a different source device and cable where possible. Picture settings cannot repair a cracked screen or an internal display fault.
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Flicker or changing brightness
If the flicker follows changes in room light or on-screen scenes, review the automatic brightness and energy-saving features described above. If the flicker appears on an HDMI source, power off the TV, reseat the cable, and run the TV’s HDMI diagnostic if your model has one. Remember that Samsung’s HDMI test is designed for cables under 2 meters. If flicker persists in the built-in test image, it is a service issue, and you should raise it with the manufacturer.
Abnormal or bleeding colors
Use the built-in picture test to see whether the color problem appears without an external source. If the test image looks normal, inspect the source device and its connection. On LG TVs, the HDMI Deep Color setting (labeled HDMI Ultra HD Deep Color on some models) must match what the connected device supports. Older LG guidance says to set it to On for a 4K-capable set-top box and HDMI connector, and to Off for an HD (1920×1080) or lower device. LG’s newer lines-and-dots guidance emphasizes turning the feature off for any device that does not support it. Follow the instructions for your exact model and device rather than applying one blanket rule.
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Confirm that the source is sending the resolution and aspect ratio that your TV expects. Adjust Sharpness and noise reduction carefully, because excessive processing changes the look of the image. The manufacturers’ guidance does not support a single numeric value for these controls, so judge the result by eye. Use Original or 16:9 where it suits the source and model. If the softness appears only on one broadcast or one external device, and the built-in test is normal, the signal or the source provider is the likely cause.
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Check HDMI, antenna and aspect ratio connections
Connection faults often look like picture-quality problems. Work through these checks in order:
- Turn the TV off before you unplug or reseat an HDMI or antenna cable.
- Look for bent connectors, cracked housings or a damaged cable jacket.
- Reseat the cable firmly at both ends. Use the same port on the TV when you retest, so you know the result applies to that input.
- If you have a known-working source device or cable, swap it in to see whether the problem follows the device or the cable.
- Confirm that the aspect ratio on the TV and on the source matches. An incorrect ratio can stretch the image or create edge artifacts.
A replacement cable is worth trying only after the test points outside the TV. Samsung advises trying a new cable for an external device when lines do not appear in its picture test, and replacing the cable if its compatible HDMI test identifies a problem. LG recommends trying a spare cable when lines or dots persist. Check that the connector type and the cable’s condition suit your device, and that the device meets the requirements of the input. A premium-priced cable is not needed to fix a problem. A new cable cannot fix a defect that appears in the TV’s own test.
Reset the picture settings
On Samsung models that document it, you can restore the picture defaults at Picture → Expert Settings → Reset Picture. Use this step when you have changed several values and suspect that your own adjustments are causing the problem. A reset returns the values to their defaults, so you will need to reapply any preferences you want to keep. A reset cannot fix a damaged panel or a faulty source connection.
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Contact support when the built-in test shows a fault, when lines, dots or abnormal color remain in the test image, or when the screen is physically damaged. Before you call or submit a request, gather the following information:
Quick Recap
- The TV’s exact model number and serial number.
- The software version shown in the TV’s information or software update screen.
- The result of the built-in picture test, with a photo or short video of the test image.
- Which input and external device are involved, and whether the problem appears on other inputs.
- The settings you have already changed, including any reset you performed.
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