RGB Channel Test.
Light up one subpixel channel at a time — pure red, green and blue, plus the additive mixes — to spot a dead or weak subpixel and see how the three channels build every colour.
How the RGB channel test works
Each pixel on your display is really three tiny lights — a red, a green and a blue subpixel. Every colour you see is those three added together at different brightnesses. By flooding the screen with one channel at a time, this test lets you inspect each subpixel in isolation instead of guessing from a mixed image.
- 1. Isolate a channel. Go full screen on pure red — only the red subpixels light. The field should be perfectly even; any black speck is a dead red subpixel.
- 2. Repeat green and blue. Step through with the arrow keys. A fault usually shows on one channel only, which tells you exactly which subpixel is affected.
- 3. Check the mixes. Yellow, magenta and cyan each use two channels. If a mix looks wrong, compare it to the additive reference below to see which channel is weak.
- 4. Run the ramps. The black→red / green / blue ramps fade one channel from off to full — a smooth fade is healthy; visible steps mean banding in that channel.
What your results mean
Each pure channel and mix is a known-good reference — match what you see against the outcomes below to pin the fault on a specific subpixel or channel.
| What you see | What it means | What to do |
|---|---|---|
| An even, solid field on every pure channel — red, green and blue — with no dots | All three subpixels drive fully and evenly — healthy | Nothing to do. |
| A black speck on one pure-channel field only (say, red) and not the others | A dead subpixel on that channel | Try the stuck-pixel cycling tool on the dead-pixel test; if it's permanent on a new display, return it while in warranty. |
| A dot that stays lit no matter which pure channel is showing | A stuck (always-on) subpixel | Run the stuck-pixel cycling tool on the dead-pixel test — it sometimes clears a stuck subpixel. |
| Yellow looks orange, or magenta looks more pink than purple | The green (or blue) channel is weaker than the one it's mixed with | Check white balance on the colour accuracy test and adjust RGB gain in the monitor menu. |
| Visible steps on one channel's black→colour ramp, but the other two fade smoothly | That channel bands — lower effective bit depth than the others | Set the display to its highest colour depth output and check the colour depth test. |
Additive colour reference
Which subpixels light up for each field. Use it to attribute a fault to a single channel: if a mix looks off, the missing or weak channel is the one to blame.
| Field | Red | Green | Blue |
|---|---|---|---|
| Red | ● | — | — |
| Green | — | ● | — |
| Blue | — | — | ● |
| Yellow | ● | ● | — |
| Magenta | ● | — | ● |
| Cyan | — | ● | ● |
| White | ● | ● | ● |
A single wrong-looking field points at one channel; a tint that shifts every field the same way is a white-balance issue instead — check the colour accuracy test for that.
Frequently asked questions
What does the RGB channel test do?
Every colour on your screen is made by mixing three subpixels — red, green and blue — at different intensities. This test lights up one channel at a time (pure red, then green, then blue) and then the combinations, so you can check each channel on its own. It is the quickest way to isolate a fault to a single subpixel or colour channel.
How do I find a dead or stuck subpixel with it?
Go full screen on pure red and look closely (a phone camera macro helps): the whole screen should be an even, solid red. A tiny black dot on the red field is a dead red subpixel; a dot that stays bright on every field is a stuck subpixel. Repeat on green and blue. Because each field isolates one channel, you can tell exactly which subpixel is affected.
Why does yellow look orange (or off) on my screen?
Yellow is red + green with no blue. If yellow looks orange, your green channel is weaker than red; if it looks greenish, red is weak. The additive-mix reference on this page shows which two channels make each colour, so a wrong-looking mix points straight at the channel that is off. A uniform tint across every field instead points at white balance — use the colour or accuracy test for that.
What is the difference between this and the colour test?
The colour test cycles full-screen primaries and secondaries to judge overall colour reproduction and spot a tint. The RGB channel test is narrower and more diagnostic: it isolates one subpixel channel at a time and shows the black→channel ramps, so it is aimed at attributing a problem to a specific channel or subpixel rather than judging colour balance overall.
What are the black→red, green and blue ramps for?
Each ramp fades one channel from off to full. On a healthy panel it is a smooth, even fade; visible steps or a colour shift along the ramp reveal banding or non-linearity in that single channel. Running all three separately makes it obvious if one channel bands more than the others.
Can this tell me my subpixel layout?
Not by itself, but it helps you see it: zoom in with a camera on the white field and you will see the subpixel arrangement — a standard RGB vertical stripe, BGR, or a PenTile pattern on many OLED phones. Knowing the layout explains why text can look slightly fringed on some panels even when every channel is working perfectly.