Check Video Caption Contrast Ratios Against Accessibility Guidelines — Free
Low-contrast captions make video content inaccessible. Check text and background relative luminance values against WCAG accessibility contrast targets.
The proof surface
Color pickers identify RGB values. This computes the exact contrast ratio between text and background, flagging segments that fall short of guidelines.
Why the flat version breaks
Assuming bright text is always readable
White text over light or moving video backgrounds loses contrast.
Evaluating static frames only
Video backgrounds shift; check contrast across the worst-case frames.
Ignoring font weight
Thin font weights require higher contrast ratios to remain legible.
How to work the subtitle contrast matrix
Record the relative luminance value of caption text (0.0 to 1.0).
Record the relative luminance value of the video background beneath text.
Enter required target ratio (e.g. 4.5:1 for standard text).
Identify low-contrast caption segments and add background boxes or drop shadows.
What the subtitle contrast matrix replaces
| Question | Before | Visible working |
|---|---|---|
| Assuming bright text is always readable | White text over light or moving video backgrounds loses contrast. | Measure background luminance |
| Evaluating static frames only | Video backgrounds shift; check contrast across the worst-case frames. | Set WCAG contrast target |
| Ignoring font weight | Thin font weights require higher contrast ratios to remain legible. | Review contrast margins |
A local arithmetic aid replaces hand calculation, not expert review. No paid AI service is needed.
Run it on the samples, right here
FIRST-LOAD
Input is processed locally and a draft is saved automatically in this browser profile when storage is available. Reset to sample clears that draft; Pro history has its own clear button. A state link encodes your inputs in its URL: share only non-sensitive rows. Browser history, clipboard and anyone receiving the link may retain it. Optional AI use below leaves this device; it is not required.
Contrast ratio calculation based on relative luminance inputs. Not legal WCAG compliance certification; verify with automated accessibility tools.
Data note: Everything runs in this browser tab on the subtitle contrast matrix: your video segment | text luminance value | background luminance value stays on this device, nothing is uploaded, and the reading is rebuilt only when you press run.
Go deeper: the companion app files the same reading as a scored comparison matrix
The article demo above runs without limits. The companion app keeps a local history, exports the rows as CSV, prints the subtitle contrast matrix reading, and holds your drafts on this device — one free run, then $ 4 one-time for the layer that keeps filing.
The subtitle contrast matrix reading is complete for free. The optional $4 layer adds print, row CSV and the last five local reading summaries; it does not add hidden answers. Checkout is not configured yet; the article demo remains unlimited.
Open the check video caption contrast ratios against accessibility guidelines companionBoundary
Contrast ratio calculation based on relative luminance inputs. Not legal WCAG compliance certification; verify with automated accessibility tools.
What this is built on
- Method: Enter required target ratio (e.g. 4.5:1 for standard text).
- All sample records are invented examples. The app does not fetch measurements, policies, files or personal records.
- Google’s official pricing page, fetched 2026-09-28, lists free-tier access including AI Studio. Optional formatting only; limits and availability can change. Free-tier content may be used to improve products. Never paste private records there.
Before: White text over light or moving video backgrounds loses contrast. After: the subtitle contrast matrix shows the working beside each named row so the reader can change the assumption and inspect the consequence.
Optional AI formatting, not calculation
For this subtitle contrast matrix, use the free AI Studio interface only if available to you, with no paid API key. Manual entry completes the same workflow for free. Supply only fictional or non-sensitive notes. Review its output against the source; never paste unresolved questions into the numeric rows.
Format my non-sensitive notes for a subtitle contrast matrix. Return plain rows only: video segment | text luminance value | background luminance value. Preserve supplied quantities exactly. Do not guess missing values; list questions separately. Do not calculate or add advice. I will check every row before pasting into the local tool.
Accepted schema: video segment | text luminance value | background luminance value. No AI response is executed as code.