This TestUFO screen tests your display for chroma subsampling behavior. Colors can become pixelated or blurry on some displays when chroma subsampling is enabled. Color resolution is degraded during 4:2:0 or 4:2:2 instead of 4:4:4 full resolution.

Blurry Computer Text: Colorful computer text and line graphics can become blurry during reduced color resolution during 4:2:2 or 4:2:0 chroma resolution. This can occur depending on display, cables, and settings, including refresh rate, bit depth, HDR, GPU, operating system, bandwidth, and poor quality cables. Also, motion can change how chroma subsampling appears in certain graphics. This test allows you to verify system adjustments that affects chroma subsampling.

TestUFO provides multiple chroma subsampling test patterns including RTINGS (credit) and Madshi of MadVR (credit). Your color resolution will be highest with sharper computer text, if you use 4:4:4 mode. Make you view these test patterns in 1:1 display native resolution.

• View RTINGS Chroma Test and instructions on RTINGS.com. In short: You have chroma subsampling if the red/blue/purple text is the most blurry/shimmering.
• View Madshi Chroma Test and instructions on reddit. In short: You have chroma subsampling if '4:2:2' text is more visible than '4:4:4'.