CMYK Contrast Checker

Purpose & User Intent: The CMYK Contrast Checker solves the problem of ensuring legible text in print workflows by evaluating foreground vs background combinations in CMYK space. It targets graphic designers, prepress operators, packaging teams, and marketing professionals who must meet legibility and accessibility requirements on printed materials. The tool is intended for use during color approvals, proofs, or press-ready setups to quickly assess whether a given CMYK pairing yields sufficient contrast before committing to a run. Example: foreground CMYK (C=0, M=0, Y=0, K=100) on background CMYK (C=0, M=0, Y=0, K=0) yields a high contrast ratio and a clear result for proofing.
Core Logic & Features: Required features include foreground and background CMYK inputs (C, M, Y, K values in 0–100) and an immediate contrast result. Optional/advanced features include printer-ICC profile rendering simulation and dot gain adjustments to reflect real-world press behavior. The tool converts CMYK to RGB using standard 0–1 channel math, then computes relative luminance per sRGB with gamma correction, and finally reports a contrast ratio via a WCAG-inspired formula. Outputs include the numeric ratio and a pass/fail verdict against common targets (e.g., 4.5:1 for body text, 7:1 for emphasis).
Inputs & Outputs: Inputs are foreground CMYK and background CMYK (C, M, Y, K in 0–100). Outputs provide foreground RGB, background RGB, the calculated contrast ratio, and a recommended accessibility verdict. Advanced options may expose ICC-adjusted RGB values. Validation ensures all four channels are numeric and within 0–100; missing inputs generate explicit errors.
Algorithms & Calculations: 1) CMYK to RGB conversion: R = 255*(1-C)*(1-K), G = 255*(1-M)*(1-K), B = 255*(1-Y)*(1-K) with C,M,Y,K in 0…1. 2) sRGB to linear gamma correction for each channel. 3) Luminance L = 0.2126*Rlin + 0.7152*Glin + 0.0722*Blin. 4) Contrast ratio = (L1+0.05)/(L2+0.05), where L1 is the lighter color. 5) Thresholds reflect WCAG-inspired targets for print with optional printer-adjusted presets.
Error & Edge Cases: Invalid ranges (not 0–100 for any channel) trigger explicit errors; missing inputs produce validation errors; ICC simulation failures fall back to basic CMYK→RGB. Edge cases include nearly identical foreground/background colors and extremely saturated ink combinations where rounding affects the ratio.
Industry/Region & Localization: Units are percentages; calculations assume standard print viewing conditions and light sources consistent with typical press proofs. Excludes non-CMYK workflows, spot colors, varnishes, or specialty inks. Assumptions assume ICC-rendered approximations and standard lighting; local print guidelines may adjust acceptable ratios.
Assumptions & Exclusions: Assumes CMYK inputs represent typical press inks with no spot or metallic colors; excludes color-managed display constraints and on-screen rendering factors; not a full color-management validator for all media types.