# `FrenchCurve.Backend.Sixel`
[🔗](https://github.com/jaman/french_curve/blob/v0.1.4/lib/french_curve/backend/sixel.ex#L1)

Renders a raster as a sixel image, a palette-indexed DCS sequence.

Sixel encodes six vertical pixels per character, so the image is written as horizontal
bands six pixels tall, one pass per colour used in the band, run-length compressed.

The format is indexed, not truecolour: the image is limited to 256 colours. Rasters with
more are quantized by dropping low bits from each channel, as many as it takes to fit.

Sixel has no alpha. Pixels below the alpha threshold are left unwritten and show
whatever the terminal already had there, unless `:background` names a colour to paint
them instead.

    IO.write(FrenchCurve.Backend.Sixel.render(raster, background: {0, 0, 0}))

# `render`

```elixir
@spec render(
  FrenchCurve.Raster.t(),
  keyword()
) :: binary()
```

Returns the DCS sequence that draws `raster` at the cursor.

## Options

  * `:alpha_threshold` — the smallest alpha treated as an opaque pixel, default `1`.
    Pixels below it are transparent.
  * `:background` — an `{r, g, b}` tuple painted behind transparent pixels. Omitted by
    default, which leaves those pixels unwritten.

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*Consult [api-reference.md](api-reference.md) for complete listing*