Using JavaScript to Adjust Saturation and Brightness of RGB Colors

Recently, I've been exploring color design principles, drawing inspiration from Adam Wathan and Steve Schroger's work. Their advice highlights the need for a comprehensive color palette beyond a few aesthetically pleasing hex codes. Building robust applications requires a broader range, encompassing numerous grays and several primary colors, each with varying levels of brightness and saturation.

My development workflow often involves hex codes or RGB colors, but manually adjusting lightness and saturation proves cumbersome. To streamline this process and prevent repetitive strain injuries from constant color picker adjustments, let's explore some code to efficiently manipulate colors.

Leveraging HSL Values

HSL (Hue, Saturation, Lightness) offers a superior method for defining web colors, particularly when manual color adjustments are anticipated. HSL represents hue as a number (0-360), saturation and lightness as percentages. For example:

div {
  background-color: hsl(155, 30%, 80%);
}

This generates a light, muted mint green. To add dark text, maintaining consistency, we can adjust the lightness:

div {
  background-color: hsl(155, 30%, 80%);
  color: hsl(155, 30%, 5%);
}

This creates a dark text that harmonizes with the background. For a call-to-action button, we might increase saturation and slightly lower lightness:

.call-to-action {
  background-color: hsl(155, 80%, 60%);
  color: hsl(155, 30%, 5%);
}

Less important text could be further de-emphasized by reducing saturation and increasing brightness:

div {
  background-color: hsl(155, 30%, 80%);
  color: hsl(155, 30%, 5%);
}

.lessimportant {
  color: hsl(155, 15%, 40%);
}

HSL's browser compatibility and declarative nature make it preferable to RGB. However, existing RGB projects or legacy browser support concerns might necessitate alternative approaches.

Utilizing Color Libraries

Numerous color manipulation libraries simplify HSL-to-RGB/hex conversions and offer advanced color scheme generation. Some notable examples include:

• Colvertize (Philipp Mildenberger): Lightweight library with conversion and manipulation functions.
• Color (Josh Junon): Fluent interface for color declaration, processing, and extraction.
• TinyColor (Brian Grinstead): Handles various input types and provides scheme generation utilities.

CSS-Tricks also offers a valuable resource on color format conversions.

The Colour Grid Tool

For a more interactive approach, consider the Colour Grid tool. As Refactoring UI emphasizes, mathematical precision alone doesn't guarantee optimal color palettes. Colour Grid, a React application I developed, generates a palette based on a selected hue, offering 100 variations in saturation and lightness. Users can copy hex codes or CSS custom properties directly from the interface.

RGB Color Manipulation Techniques

The following techniques focus on RGB color processing.

Determining RGB Lightness

Note: This method doesn't account for the inherent brightness of a hue (e.g., yellow's higher perceived brightness than purple). It measures the amount of black or white mixed in. Visual assessment remains crucial for accurate lightness judgment.

Lightness is calculated by averaging the highest and lowest RGB values, then dividing by 255:

function getLightnessOfRGB(rgbString) {
  const rgbIntArray = (rgbString.replace(/ /g, '').slice(4, -1).split(',').map(e => parseInt(e)));
  const highest = Math.max(...rgbIntArray);
  const lowest = Math.min(...rgbIntArray);
  return (highest   lowest) / 2 / 255;
}

Saturating RGB without Affecting Lightness or Hue

Saturating RGB presents challenges: grays lack hue information, and achieving pure hues requires 50% lightness. This example maintains lightness:

To saturate, increase the difference between the lowest and highest RGB values. Maintaining lightness requires equal increases/decreases of the highest and lowest values, constrained by 0-255 limits. The available saturation range is determined by:

• The difference between a gray (same lightness) and 255.
• The difference between a gray (same lightness) and 0.

// ... (getLightnessOfRGB function from above) ...

const grayVal = getLightnessOfRGB('rgb(205, 228, 219)') * 255; // 217
const saturationRange = Math.round(Math.min(255 - grayVal, grayVal)); // 38

// ... (rest of saturation calculation) ...

The middle value's adjustment is proportional to the changes in the highest and lowest values. The complete saturation function is quite involved and omitted for brevity, but the core concepts are presented.

Desaturating RGB Colors

Desaturation reverses the saturation process, moving towards a gray value. A complete desaturation results in a gray with equal RGB values. Partial desaturation involves proportionally reducing the difference between the highest and lowest RGB values. The complete desaturation function is also omitted for brevity.

Lightening and Darkening RGB while Preserving Hue

Lightening involves proportionally increasing RGB values towards 255, while darkening proportionally decreases them towards 0. Both processes gradually reduce saturation. The complete functions for lightening and darkening are omitted for brevity.

These functions provide a foundation for RGB color manipulation. However, HSL, color libraries, and the Colour Grid tool offer alternative, potentially more efficient solutions depending on your needs and project constraints.

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