Colors
Syntax
Returns
The Resources.Colors method returns a slice of the most dominant colors in an image, ordered from most dominant to least dominant. This method is fast, but if you also downsize your image you can improve performance by extracting the colors from the scaled image.
Use this method with global resources, page resources, or remote resources.
Methods
Each color is an object with the following methods:
- ColorHex
- New in v0.125.0
- (
string) Returns the hexadecimal color value, prefixed with a hash sign. - Luminance
- New in v0.125.0
- (
float64) Returns the relative luminance of the color in the sRGB colorspace in the range [0, 1]. A value of0represents the darkest black, while a value of1represents the lightest white.
Image filters such as
images.Dither,
images.Padding, and
images.Text accept either hexadecimal color values or images.Color objects as arguments.
Hugo renders an images.Color object as a hexadecimal color value.
Sorting
As a contrived example, create a table of an image’s dominant colors with the most dominant color first, and display the relative luminance of each dominant color:
{{ with resources.Get "images/a.jpg" }}
<table>
<thead>
<tr>
<th>Color</th>
<th>Relative luminance</th>
</tr>
</thead>
<tbody>
{{ range .Colors }}
<tr>
<td>{{ .ColorHex }}</td>
<td>{{ .Luminance | lang.FormatNumber 4 }}</td>
</tr>
{{ end }}
</tbody>
</table>
{{ end }}
Hugo renders this to:
| ColorHex | Relative luminance |
|---|---|
#bebebd | 0.5145 |
#514947 | 0.0697 |
#768a9a | 0.2436 |
#647789 | 0.1771 |
#90725e | 0.1877 |
#a48974 | 0.2704 |
To sort by dominance with the least dominant color first:
{{ range .Colors | collections.Reverse }}
To sort by relative luminance with the darkest color first:
{{ range sort .Colors "Luminance" }}
To sort by relative luminance with the lightest color first, use either of these constructs:
{{ range sort .Colors "Luminance" | collections.Reverse }}
{{ range sort .Colors "Luminance" "desc" }}
Examples
Image borders
To add a 5 pixel border to an image using the most dominant color:
{{ with resources.Get "images/a.jpg" }}
{{ $mostDominant := index .Colors 0 }}
{{ $filter := images.Padding 5 $mostDominant }}
{{ with .Filter $filter }}
<img src="{{ .RelPermalink }}" width="{{ .Width }}" height="{{ .Height }}" alt="">
{{ end }}
{{ end }}
To add a 5 pixel border to an image using the darkest dominant color:
{{ with resources.Get "images/a.jpg" }}
{{ $darkest := index (sort .Colors "Luminance") 0 }}
{{ $filter := images.Padding 5 $darkest }}
{{ with .Filter $filter }}
<img src="{{ .RelPermalink }}" width="{{ .Width }}" height="{{ .Height }}" alt="">
{{ end }}
{{ end }}
Light text on dark background
To create a text box where the foreground and background colors are derived from an image’s lightest and darkest dominant colors:
{{ with resources.Get "images/a.jpg" }}
{{ $darkest := index (sort .Colors "Luminance") 0 }}
{{ $lightest := index (sort .Colors "Luminance" "desc") 0 }}
<div style="background: {{ $darkest }};">
<div style="color: {{ $lightest }};">
<p>This is light text on a dark background.</p>
</div>
</div>
{{ end }}
WCAG contrast ratio
In the previous example we placed light text on a dark background, but does this color combination conform to WCAG guidelines for either the minimum or the enhanced contrast ratio?
The WCAG defines the contrast ratio as:
where $L_1$ is the relative luminance of the lightest color and $L_2$ is the relative luminance of the darkest color.
Calculate the contrast ratio to determine WCAG conformance:
{{ with resources.Get "images/a.jpg" }}
{{ $lightest := index (sort .Colors "Luminance" "desc") 0 }}
{{ $darkest := index (sort .Colors "Luminance") 0 }}
{{ $cr := div
(add $lightest.Luminance 0.05)
(add $darkest.Luminance 0.05)
}}
{{ if ge $cr 7.5 }}
{{ printf "The %.2f contrast ratio conforms to WCAG Level AAA." $cr }}
{{ else if ge $cr 4.5 }}
{{ printf "The %.2f contrast ratio conforms to WCAG Level AA." $cr }}
{{ else }}
{{ printf "The %.2f contrast ratio does not conform to WCAG guidelines." $cr }}
{{ end }}
{{ end }}