Chroma subsampling test. Fine colour, sharp or not.
Video sends colour at lower resolution than brightness, because eyes barely notice it in pictures. Text and fine lines notice it at once. This shows one-pixel red lines and red text on blue: sharp means full colour detail is reaching the screen; smeared means it is being subsampled, which is why text looks soft on many TVs used as monitors.
One check
- Chroma subsampling
One check after another, with your progress along the top and a plain verdict on each. Nothing you show the camera or say into the microphone leaves this page.
What it measures
Measured here, not assumed.
- The pattern
- Red on blue, the pair that subsampling smears most: one-pixel lines on the left, small text on the right.
- What sharp means
- The screen receives full colour detail, 4:4:4. Text is as sharp as it can be.
- What smeared means
- Colour is subsampled, 4:2:2 or 4:2:0. Common over HDMI to a TV that is not in its PC mode, and at high resolutions and rates a cable cannot carry in full.
If it fails
The usual failures, and what fixes each.
- On a TV
- Name the HDMI input PC, or turn on its deep colour or enhanced format setting for that input. Both enable full colour.
- On a PC
- Set the output colour format to RGB or YCbCr 4:4:4 in the graphics driver's control panel. If it will not allow it at the current resolution and rate, the cable or port cannot carry it; try DisplayPort or a certified HDMI cable.
- Still smeared
- Lower the refresh rate a step; full colour at 4K and high rates needs bandwidth some ports do not have.
Where a browser stops
What it cannot tell you.
- View at native size with no browser zoom, or the one-pixel pattern lands on more than one pixel and blurs for that reason instead.
- Your eyes judge it; the page cannot see what the cable carries.
- Video content is fine with subsampling; only text and fine lines suffer.
Privacy
Nothing leaves this page.
The camera and microphone are read on this page and stopped as soon as they have been measured. The clip you can play back lives in the browser's memory and is discarded when you leave. The location check discards the position. The internet test sends random bytes to this site and nothing else. The result is stored nowhere unless you ask for it by email, and then only the fact that an email was sent is kept.
Questions
Chroma subsampling test, answered
- Why is text blurry on my TV when used as a monitor?
- Usually chroma subsampling: the TV is receiving colour at lower resolution than brightness, which is fine for video and bad for text. Naming the input PC or enabling its enhanced colour setting fixes it on most TVs.
- What is 4:4:4 versus 4:2:2?
- How many colour samples are sent per four pixels: four, or two. At 4:2:2 and 4:2:0 fine colour detail is averaged across pixels, which smears coloured text and thin lines.
- Does chroma subsampling matter for games and video?
- Rarely. It matters for text, interfaces and fine lines, which is why it is the first thing to fix on a TV used as a desktop monitor and the last thing to worry about for films.
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