Subtitle Blooming Test
One of the most noticeable local dimming artifacts in real-world use is subtitle blooming on black letterbox bars. Generates clean synthetic subtitle text with position and size controls.
Technical Scope & Limitations
Visual inspection. Uses clean synthetic text with zero copyrighted movie screenshots.
Browser rendering output can be influenced by OS display scaling, GPU driver color settings, and active HDR profiles.
- Observe the simulated white subtitle text against the pure black background.
- Look at the black space above, below, and between words for glowing halos.
- Adjust subtitle size (Small, Large) and line count (Single, Double line).
- Adjust vertical positioning (Bottom letterbox bar, Lower third, Center).
ScreenCheck Local Dimming Subtitle Inspection
What This Test Checks
- Visible halo glow leaking into dark letterbox bars when subtitles are displayed.
- Backlight zone pumping when dialogue text appears and disappears.
- Impact of subtitle sizing and vertical positioning on blooming radius.
How to Perform the Test
- Enter fullscreen mode in a dark viewing environment.
- Look at the black space directly above and below the simulated white subtitle text.
- Toggle between Single Line, Wide, and Two-Line dialogue presets.
- Adjust vertical positioning to simulate bottom letterbox vs lower-third text.
What to Look For
- Clouding or elevated gray fog around text letters indicates local dimming blooming. Sharp contrast with pitch black surrounding space indicates tight zone control.
Common Display Problems & Diagnostic Guidance
Distracting Letterbox Pumping in Movies
When watching widescreen 2.39:1 films with subtitles, bright white text can cause the bottom black bar to repeatedly flash between black and gray as subtitles appear.
Frequently Asked Questions
How can I reduce subtitle blooming on my Mini-LED display?
In streaming apps (Netflix, YouTube, Prime), change subtitle styling to semi-transparent yellow or gray text with a subtle drop shadow instead of 100% pure white.