Class Contrast

java.lang.Object
org.glavo.monetfx.internal.contrast.Contrast
public final class Contrast extends Object
Color science for contrast utilities.

Utility methods for calculating contrast given two colors, or calculating a color given one color and a contrast ratio.

Contrast ratio is calculated using XYZ's Y. When linearized to match human perception, Y becomes HCT's tone and L*a*b*'s' L*.

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    static final double
    RATIO_30
     
    static final double
    RATIO_45
     
    static final double
    RATIO_70
     
    static final double
    RATIO_MAX
     
    static final double
    RATIO_MIN
     

  • Method Summary

    Modifier and Type
    Method
    Description
    static double
    darker(double tone, double ratio)
    Returns T in HCT, L* in L*a*b* invalid input: '<'= tone parameter that ensures ratio with input T/L*.
    static double
    darkerUnsafe(double tone, double ratio)
    Tone invalid input: '<'= tone parameter that ensures ratio.
    static double
    lighter(double tone, double ratio)
    Returns T in HCT, L* in L*a*b* >= tone parameter that ensures ratio with input T/L*.
    static double
    lighterUnsafe(double tone, double ratio)
    Tone >= tone parameter that ensures ratio.
    static double
    ratioOfTones(double t1, double t2)
    Contrast ratio of two tones.
    static double
    ratioOfYs(double y1, double y2)
    Contrast ratio is a measure of legibility, its used to compare the lightness of two colors.

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

  • Field Details

  • Method Details

    • ratioOfYs

      public static double ratioOfYs(double y1, double y2)
      Contrast ratio is a measure of legibility, its used to compare the lightness of two colors. This method is used commonly in industry due to its use by WCAG.

      To compare lightness, the colors are expressed in the XYZ color space, where Y is lightness, also known as relative luminance.

      The equation is ratio = lighter Y + 5 / darker Y + 5.

    • ratioOfTones

      public static double ratioOfTones(double t1, double t2)
      Contrast ratio of two tones. T in HCT, L* in L*a*b*. Also known as luminance or perpectual luminance.

      Contrast ratio is defined using Y in XYZ, relative luminance. However, relative luminance is linear to number of photons, not to perception of lightness. Perceptual luminance, L* in L*a*b*, T in HCT, is. Designers prefer color spaces with perceptual luminance since they're accurate to the eye.

      Y and L* are pure functions of each other, so it possible to use perceptually accurate color spaces, and measure contrast, and measure contrast in a much more understandable way: instead of a ratio, a linear difference. This allows a designer to determine what they need to adjust a color's lightness to in order to reach their desired contrast, instead of guessing invalid input: '&' checking with hex codes.

    • lighter

      public static double lighter(double tone, double ratio)
      Returns T in HCT, L* in L*a*b* >= tone parameter that ensures ratio with input T/L*. Returns -1 if ratio cannot be achieved.
      Parameters:
      tone - Tone return value must contrast with.
      ratio - Desired contrast ratio of return value and tone parameter.

    • lighterUnsafe

      public static double lighterUnsafe(double tone, double ratio)
      Tone >= tone parameter that ensures ratio. 100 if ratio cannot be achieved.

      This method is unsafe because the returned value is guaranteed to be in bounds, but, the in bounds return value may not reach the desired ratio.

      Parameters:
      tone - Tone return value must contrast with.
      ratio - Desired contrast ratio of return value and tone parameter.

    • darker

      public static double darker(double tone, double ratio)
      Returns T in HCT, L* in L*a*b* invalid input: '<'= tone parameter that ensures ratio with input T/L*. Returns -1 if ratio cannot be achieved.
      Parameters:
      tone - Tone return value must contrast with.
      ratio - Desired contrast ratio of return value and tone parameter.

    • darkerUnsafe

      public static double darkerUnsafe(double tone, double ratio)
      Tone invalid input: '<'= tone parameter that ensures ratio. 0 if ratio cannot be achieved.

      This method is unsafe because the returned value is guaranteed to be in bounds, but, the in bounds return value may not reach the desired ratio.

      Parameters:
      tone - Tone return value must contrast with.
      ratio - Desired contrast ratio of return value and tone parameter.