images.Dither

Options

colors

(string array) A slice of two or more colors that make up the dithering palette, each expressed as an RGB or RGBA hexadecimal value, with or without a leading hash mark. The default values are opaque black (000000ff) and opaque white (ffffffff).

method

(string) The dithering method. See the dithering methods section below for a list of the available methods. Default is FloydSteinberg.

serpentine

(bool) Applicable to error diffusion dithering methods, serpentine controls whether the error diffusion matrix is applied in a serpentine manner, meaning that it goes right-to-left every other line. This greatly reduces line-type artifacts. Default is true.

strength

(float) The strength at which to apply the dithering matrix, typically a value in the range [0, 1]. A value of 1.0 applies the dithering matrix at 100% strength (no modification of the dither matrix). The strength is inversely proportional to contrast; reducing the strength increases the contrast. Setting strength to a value such as 0.8 can be useful to reduce noise in the dithered image. Default is 1.0.

Usage

Create the options map:

{{ $opts := dict
  "colors" (slice "222222" "808080" "dddddd")
  "method" "ClusteredDot4x4"
  "strength" 0.85
}}

Create the filter:

{{ $filter := images.Dither $opts }}

Or create the filter using the default settings:

{{ $filter := images.Dither }}

Apply the filter using the images.Filter function:

{{ with resources.Get "images/original.jpg" }}
  {{ with . | images.Filter $filter }}
    <img src="{{ .RelPermalink }}" width="{{ .Width }}" height="{{ .Height }}" alt="">
  {{ end }}
{{ end }}

You can also apply the filter using the Filter method on a Resource object:

{{ with resources.Get "images/original.jpg" }}
  {{ with .Filter $filter }}
    <img src="{{ .RelPermalink }}" width="{{ .Width }}" height="{{ .Height }}" alt="">
  {{ end }}
{{ end }}

Dithering methods

See the Go documentation for descriptions of each of the dithering methods below.

Error diffusion dithering methods:

• Atkinson
• Burkes
• FalseFloydSteinberg
• FloydSteinberg
• JarvisJudiceNinke
• Sierra
• Sierra2
• Sierra2_4A
• Sierra3
• SierraLite
• Simple2D
• StevenPigeon
• Stucki
• TwoRowSierra

Ordered dithering methods:

• ClusteredDot4x4
• ClusteredDot6x6
• ClusteredDot6x6_2
• ClusteredDot6x6_3
• ClusteredDot8x8
• ClusteredDotDiagonal16x16
• ClusteredDotDiagonal6x6
• ClusteredDotDiagonal8x8
• ClusteredDotDiagonal8x8_2
• ClusteredDotDiagonal8x8_3
• ClusteredDotHorizontalLine
• ClusteredDotSpiral5x5
• ClusteredDotVerticalLine
• Horizontal3x5
• Vertical5x3

Example

This example uses the default dithering options.

Original

Processed

Recommendations

Regardless of dithering method, do both of the following to obtain the best results:

1. Scale the image before dithering
2. Output the image to a lossless format such as GIF or PNG

The example below does both of these, and it sets the dithering palette to the three most dominant colors in the image.

{{ with resources.Get "original.jpg" }}
  {{ $opts := dict
    "method" "ClusteredDotSpiral5x5"
    "colors" (first 3 .Colors)
  }}
  {{ $filters := slice
    (images.Process "resize 800x")
    (images.Dither $opts)
    (images.Process "png")
  }}
  {{ with . | images.Filter $filters }}
    <img src="{{ .RelPermalink }}" width="{{ .Width }}" height="{{ .Height }}" alt="">
  {{ end }}
{{ end }}

For best results, if the dithering palette is grayscale, convert the image to grayscale before dithering.

{{ $opts := dict "colors" (slice "222" "808080" "ddd") }}
{{ $filters := slice
  (images.Process "resize 800x")
  (images.Grayscale)
  (images.Dither $opts)
  (images.Process "png")
}}
{{ with images.Filter $filters . }}
  <img src="{{ .RelPermalink }}" width="{{ .Width }}" height="{{ .Height }}" alt="">
{{ end }}

The example above:

1. Resizes the image to be 800 px wide
2. Converts the image to grayscale
3. Dithers the image using the default (FloydSteinberg) dithering method with a grayscale palette
4. Converts the image to the PNG format