Gamut checks, wide-gamut CSS, and print caveats

Representative automated fixture coverage

Hue Codex imports versioned JSON fixtures and tests the corresponding pure production functions directly. The groups below are the representative regression evidence most relevant to this methodology.

• Parsing fixtures: Accepted CSS color syntax, alpha behavior, clamping, invalid input, and out-of-gamut fallback cases. View the JSON fixtures.
• Conversion fixtures: sRGB, XYZ, Lab/LCH, OKLab/OKLCH conversion values, round trips, and precision boundaries. View the JSON fixtures.

What a pass means. A passing group confirms the named vectors and tested properties still match the documented implementation. It does not prove every possible input, final browser rendering, full accessibility conformance, profile-aware print output, or every downstream export consumer.

Hue Codex resolves HEX, fixed named colors, RGB, HSL, and HWB as sRGB sources. For those inputs, the gamut checker reports sRGB as in gamut, wider RGB display spaces as containing the color, and the browser fallback as the same resolved color.

For supported color(display-p3), Lab/LCH, OKLab/OKLCH, and XYZ input, the checker derives D65 XYZ from the authored coordinates, tests the corresponding linear channels against each gamut boundary, and preserves the original syntax separately from the sRGB fallback.

This is intentionally conservative: the site can know the numeric color you entered, but it cannot know the display profile, printer profile, substrate, ink set, viewing booth, or brand production tolerances.

For resolved sRGB syntax, Hue Codex checks the resulting sRGB coordinates and reports Display P3 and Rec. 2020 containment. For supported perceptual, XYZ, or Display P3 syntax, it converts the authored coordinates to D65 XYZ and tests un-clipped linear channel bounds for sRGB, Display P3, and Rec. 2020.

An authored color outside sRGB receives a separate channel-clipped sRGB fallback. This is not perceptual gamut mapping, and the containment result does not predict a particular uncalibrated display, browser color-management path, printer, paper, or ink.

If a wider source has already been reduced to HEX before it reaches the checker, only that sRGB fallback remains available; the original wider coordinates cannot be reconstructed.

Fallback comparison caveat. If two authored perceptual or wide-gamut colors are clipped to sRGB before they reach this tool, their HEX fallbacks may look identical or closer than the original authored colors. Use the Color Conversion methodology when you need the authored-value versus resolved-fallback boundary.

Containment answers whether a color can be represented inside a color space. Authorship answers which color space the original value belongs to. A CSS HEX value such as #4169E1 is an sRGB-authored color because HEX channels are interpreted as sRGB coordinates.

Display P3 and Rec. 2020 have larger RGB gamuts than sRGB, so an sRGB color can be converted into coordinates inside those spaces and still describe the same intended color. That does not mean the HEX value used extra P3 or Rec. 2020 colors; it only means the wider spaces include the sRGB color.

Hue Codex calls a color wide-gamut only when the authored or computed source uses a wider color space and the represented color is outside sRGB, for example a display-p3 color whose converted sRGB fallback must be clipped or otherwise reduced.

These short definitions cover the terms used throughout the gamut and print notes on this page.

CSS Color 4 defines modern color syntax for device-independent values and predefined color spaces. Hue Codex surfaces these formats when they are useful for CSS handoff and explains when fallbacks should be kept.

CSS Color 5 is cited on this page for draft context around custom color spaces, @color-profile, device-cmyk(), and print-oriented CSS workflows. Hue Codex treats that material as a Working Draft reference, not as stable implementation guidance.

When a color is converted back to sRGB for display or copying, channel values are clamped to the displayable range. A clipped fallback can be usable, but it is not a perceptual gamut-mapping strategy.

The latest published CSS Color 5 document available during this review is a W3C Working Draft. W3C says Working Draft publication is not endorsement and that the document can change, be replaced, or be obsoleted.

Hue Codex cites CSS Color 5 because it describes device-cmyk(), custom ICC-profile color spaces, @color-profile, and print-oriented CSS examples. The same draft currently marks Custom Color Spaces, @color-profile, device-cmyk(), and Relative Alpha Colors as at-risk.

For Hue Codex methodology, that means device-cmyk() and custom color-space examples are explanatory draft references only. They do not make Hue Codex CMYK values press-ready, and they should not replace ICC-based production conversion, proofing, or vendor print specifications.

Hue Codex calculates simple CMYK-like values from sRGB channels by deriving black from the maximum RGB component, then deriving cyan, magenta, and yellow from the remaining distance. This formula is a Hue Codex implementation choice and approximation, useful for rough language only.

The input domain is resolved opaque sRGB with integer channels R, G, and B in [0, 255]. Hue Codex normalizes those channels before calculation, computes raw normalized CMYK components, converts them to percentages, and rounds only for display or export.

CSS Color 5 device-cmyk() remains separate draft/at-risk context for CSS syntax. It does not standardize this simple RGB-derived CMYK equation and does not make Hue Codex CMYK values press-ready.

Real print conversion depends on ICC profiles, total ink limits, black generation, paper, ink, press condition, and vendor setup. Always use proofing and production guidance for final print values.

Profile-aware conversion not performed. Every CMYK value on this page is a simple sRGB-derived approximation, not a color-managed conversion for a printer, paper, ink set, ICC profile, or press condition.

r = clamp(R, 0, 255) / 255
g = clamp(G, 0, 255) / 255
b = clamp(B, 0, 255) / 255

k = 1 - max(r, g, b)

if k == 1:
  c = 0
  m = 0
  y = 0
else:
  c = (1 - r - k) / (1 - k)
  m = (1 - g - k) / (1 - k)
  y = (1 - b - k) / (1 - k)

Displayed percentages:
  C = c * 100
  M = m * 100
  Y = y * 100
  K = k * 100

Profile-aware conversion not performed. CMYK validation rows check the approximation formula only; they do not validate press-ready output.

Hue Codex CMYK output is a deterministic sRGB approximation for communication. It is not a profile-aware conversion.

rgb_to_cmyk_approx(r8, g8, b8):
  r = clamp(r8, 0, 255) / 255
  g = clamp(g8, 0, 255) / 255
  b = clamp(b8, 0, 255) / 255
  k = 1 - max(r, g, b)

  if k == 1:
    c = 0
    m = 0
    y = 0
  else:
    c = (1 - r - k) / (1 - k)
    m = (1 - g - k) / (1 - k)
    y = (1 - b - k) / (1 - k)

  C = c * 100
  M = m * 100
  Y = y * 100
  K = k * 100
  return C, M, Y, K

These vectors validate the simple sRGB-derived CMYK approximation. They are not ICC profile conversions or press targets.

Profile-aware conversion not performed. CMYK values shown here are approximate sRGB-derived communication values, not ICC-profile conversions or press proofs.

Tools using this methodology

These Hue Codex tools link to this methodology because they depend on the formulas, assumptions, limits, or data policy described here.

Report a calculation issue

If a result does not match the documented formula or fixture, send the exact input, tool settings, displayed result, expected result, precision mode, and browser details. Please do not include private images, personal information, or secrets.