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162 lines
4.4 KiB
Markdown
162 lines
4.4 KiB
Markdown
---
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title: images.Dither
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description: Returns an image filter that dithers an image.
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categories: []
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keywords: []
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action:
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aliases: []
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related:
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- functions/images/Filter
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- functions/images/Process
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- methods/resource/Colors
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- methods/resource/Filter
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returnType: images.filter
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signatures: ['images.Dither [OPTIONS]']
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toc: true
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---
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{{< new-in 0.123.0 >}}
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## Options
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colors
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: (`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`).
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[hexadecimal]: https://developer.mozilla.org/en-US/docs/Web/CSS/hex-color
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method
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: (`string`) The dithering method. See the [dithering methods](#dithering-methods) section below for a list of the available methods. Default is `FloydSteinberg`.
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serpentine
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: (`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`.
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strength
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: (`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`.
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## Usage
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Create the options map:
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```go-html-template
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{{ $opts := dict
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"colors" (slice "222222" "808080" "dddddd")
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"method" "ClusteredDot4x4"
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"strength" 0.85
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}}
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```
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Create the filter:
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```go-html-template
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{{ $filter := images.Dither $opts }}
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```
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Or create the filter using the default settings:
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```go-html-template
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{{ $filter := images.Dither }}
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```
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{{% include "functions/images/_common/apply-image-filter.md" %}}
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## Dithering methods
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See the [Go documentation] for descriptions of each of the dithering methods below.
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[Go documentation]: https://pkg.go.dev/github.com/makeworld-the-better-one/dither/v2#pkg-variables
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Error diffusion dithering methods:
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- Atkinson
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- Burkes
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- FalseFloydSteinberg
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- FloydSteinberg
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- JarvisJudiceNinke
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- Sierra
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- Sierra2
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- Sierra2_4A
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- Sierra3
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- SierraLite
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- Simple2D
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- StevenPigeon
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- Stucki
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- TwoRowSierra
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Ordered dithering methods:
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- ClusteredDot4x4
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- ClusteredDot6x6
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- ClusteredDot6x6_2
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- ClusteredDot6x6_3
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- ClusteredDot8x8
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- ClusteredDotDiagonal16x16
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- ClusteredDotDiagonal6x6
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- ClusteredDotDiagonal8x8
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- ClusteredDotDiagonal8x8_2
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- ClusteredDotDiagonal8x8_3
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- ClusteredDotHorizontalLine
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- ClusteredDotSpiral5x5
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- ClusteredDotVerticalLine
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- Horizontal3x5
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- Vertical5x3
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## Example
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This example uses the default dithering options.
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{{< img
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src="images/examples/zion-national-park.jpg"
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alt="Zion National Park"
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filter="Dither"
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filterArgs=""
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example=true
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>}}
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## Recommendations
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Regardless of dithering method, do both of the following to obtain the best results:
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1. Scale the image _before_ dithering
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2. Output the image to a lossless format such as GIF or PNG
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The example below does both of these, and it sets the dithering palette to the three most dominant colors in the image.
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```go-html-template
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{{ with resources.Get "original.jpg" }}
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{{ $opts := dict
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"method" "ClusteredDotSpiral5x5"
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"colors" (first 3 .Colors)
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}}
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{{ $filters := slice
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(images.Process "resize 800x")
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(images.Dither $opts)
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(images.Process "png")
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}}
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{{ with . | images.Filter $filters }}
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<img src="{{ .RelPermalink }}" width="{{ .Width }}" height="{{ .Height }}" alt="">
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{{ end }}
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{{ end }}
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```
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For best results, if the dithering palette is grayscale, convert the image to grayscale before dithering.
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```go-html-template
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{{ $opts := dict "colors" (slice "222" "808080" "ddd") }}
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{{ $filters := slice
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(images.Process "resize 800x")
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(images.Grayscale)
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(images.Dither $opts)
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(images.Process "png")
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}}
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{{ with images.Filter $filters . }}
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<img src="{{ .RelPermalink }}" width="{{ .Width }}" height="{{ .Height }}" alt="">
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{{ end }}
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```
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The example above:
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1. Resizes the image to be 800 px wide
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2. Converts the image to grayscale
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3. Dithers the image using the default (`FloydSteinberg`) dithering method with a grayscale palette
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4. Converts the image to the PNG format
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