A de-emphasized element can drop to unimportant, but it must never drop all the way to invisible

What it is

De-emphasis has a floor: background elements may drop to "unimportant," never to "invisible." Once contrast falls below the discrimination threshold, what readers perceive is no longer "present but unimportant" but "absent" — the series looks broken, the data looks missing. De-emphasis reallocates attention; it does not destroy information, and the floor is the line between the two.

Why it happens

Below the threshold, a classification jump occurs: the visual system stops treating the element as chart content and files it as blank canvas or noise — it simply does not exist in the scene model. That is a categorically different outcome from the semantic goal of de-emphasis (present in the scene, low priority). The floor's height depends on two variables: the job the dimmed elements must still support — "findable" has a low floor, "value-readable" a high one — and the final display conditions: projection and low-grade screens eat contrast, and a grey barely visible on the design file vanishes in the meeting room. Accessibility contrast requirements supply a general lower-bound reference for text and critical graphics.

Where it stops holding

The floor is a task function, not a fixed number: in interactive charts dimmed elements need only enough presence to be hoverable — reading is outsourced to interaction, so the floor sits lower; static print has no interactive fallback, so dimmed elements that still carry comparison duty must keep value-reading contrast. With multi-level de-emphasis (two hierarchy layers dimmed at once), each level passes the floor check separately. Under colour deficiency and greyscale, de-emphasis often works by desaturation, and desaturation affects deficient readers differently from typical viewers — re-check with this family's simulation methods.

Applying it

• Standardise two de-emphasis tiers: findable (one can tell a line or point is there) and value-readable (values can be estimated); choose per the dimmed element's duty.
• After dimming, re-check non-target elements under the worst display conditions — projection, low brightness, greyscale.
• Verification: ask readers how many series the chart contains; a count below the actual number means an element fell through the floor — ease off the dimming.

Related

• Same group: U5.05.1 Highlighting works through contrast with the rest, not through its own intensity · U5.05.2 Dimming the rest disturbs the whole less than amplifying the target · U5.05.4 Highlighting too many items at once is highlighting none · U5.05.5 State the basis for a highlight, or it reads as a data property
• Nearby: U11.04.1 Data marks must meet the discrimination threshold against the background · U4.05.2 Lightness, shape, pattern, and direct labels are colour's main substitutes
• Search terms: minimum contrast · de-emphasis floor · readability threshold