Chroma Subsampling Test
Check whether your display is receiving full 4:4:4 color or a subsampled 4:2:2 or 4:2:0 signal. Subsampling halves color resolution, which makes colored text look smeared even when the resolution is correct.
Red and blue text on white is where subsampling hurts most
How to read this
- Full 4:4:4: red and blue text stays as crisp as the black reference line, and the 1px stripes remain distinctly red and blue.
- Subsampled 4:2:2 or 4:2:0: colored text looks soft or fringed while black text stays sharp, and the stripes blur toward a flat purple.
- Black text staying sharp while colored text smears is the signature of subsampling, not of a resolution or scaling problem.
Testing guide
How to test for chroma subsampling
Chroma subsampling saves bandwidth by throwing away color resolution while keeping brightness resolution intact. That trade is invisible in video but obvious in text, which is why a monitor can look perfect for films and produce mushy red or blue text at the same time.
Best for
- Diagnosing blurry colored text on a TV being used as a computer monitor.
- Confirming a cable and port combination actually carries full 4:4:4 at your resolution and refresh rate.
- Checking whether an HDMI input needs to be switched to its PC or enhanced mode.
How to run the test
- 1Set the display to its native resolution before testing, since scaling causes its own blur.
- 2Open the colored text pattern and compare the red and blue lines against the black reference line.
- 3Switch to the 1px color stripes and check whether red and blue stay distinct or merge into purple.
- 4If subsampling is present, try a different cable or port and enable the PC or enhanced input mode on the display.
How to read the result
Black text sharp but colored text soft is the signature of subsampling rather than a resolution problem.
Red and blue 1px stripes collapsing into flat purple confirms color resolution is being halved.
If everything including black text is blurry, the cause is scaling or non-native resolution, not subsampling.
Related tools and guides
Frequently asked questions
What is chroma subsampling?
It is a compression technique that stores full brightness detail but only half or a quarter of the color detail, because human vision is far more sensitive to brightness than to color. 4:4:4 keeps all color information, 4:2:2 halves it horizontally, and 4:2:0 halves it both horizontally and vertically.
Why does chroma subsampling make text blurry?
Text is high-contrast detail at the single-pixel level. When color resolution is halved, the color information for adjacent pixels gets averaged together, so colored text edges smear and fringe. Black text on white survives because that is pure brightness detail, which is preserved.
How do I fix chroma subsampling?
Use a cable with enough bandwidth for your resolution and refresh rate, plug into a port that supports the full spec, and on a TV switch the input to PC mode, enhanced mode, or whatever the manufacturer calls its full-bandwidth setting. Lowering refresh rate can also free enough bandwidth for 4:4:4.
Do I need 4:4:4 for gaming?
For gameplay itself the difference is subtle, since games are mostly smooth gradients and textures. It matters a lot for menus, HUD text, and any desktop use, so if you use the same display for both, 4:4:4 is worth the bandwidth.
Does chroma subsampling affect video?
Barely, because almost all video is mastered in 4:2:0 to begin with. Blu-ray, streaming and broadcast are all subsampled at the source, which is exactly why the technique exists and why a TV defaults to it.