> ## Documentation Index
> Fetch the complete documentation index at: https://rdsciv/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Fine-Tuning ASCII Output with Adjustments

> Control contrast, gamma, dithering algorithm, edge detection threshold, and character aspect ratio to shape exactly how your ASCII art renders from any source.

The Adjustments section gives you direct control over how pixel luminance values are translated into characters. You can push contrast to create stark graphic results, pull gamma to open up shadows, compensate for monospace character proportions, and choose a dithering algorithm to add texture or simulate smooth gradients within the character set's limited tonal range.

## Adjustment controls reference

| Name              | Range                                                         | Default | Effect                                                                                                                 |
| ----------------- | ------------------------------------------------------------- | ------- | ---------------------------------------------------------------------------------------------------------------------- |
| Contrast          | 0.1–5 (slider); 0–10 (numeric)                                | 1.2     | Higher values increase separation between light and dark cells, making the output more graphic                         |
| Gamma             | 0.1–5 (slider); 0–10 (numeric)                                | 1.0     | Values below 1 brighten midtones; values above 1 darken them                                                           |
| Char aspect ratio | 0.3–1.0 (slider); 0.1–2.0 (numeric)                           | 0.55    | Corrects for the height-to-width ratio of monospace characters; lower values make rows taller                          |
| Edge threshold    | 0–200 (slider); 0–500 (numeric)                               | 30      | Only visible when Edge-aware chars is on; higher values require a stronger edge before a directional character is used |
| Dither            | None / Floyd-Steinberg / Atkinson / Ordered 4×4 / Ordered 8×8 | None    | Distributes quantization error or Bayer noise to simulate intermediate tones                                           |

## Contrast

Contrast is applied as a linear stretch around the midpoint (0.5). At 1.0 the luminance is unchanged. Raising it to 2–3 creates a high-contrast woodcut look; lowering it toward 0.1 compresses everything toward gray.

## Gamma

Gamma applies a power-curve correction to each cell's luminance before contrast and character mapping. A gamma of 0.5 squares the luminance, brightening midtones and pulling detail out of shadows. A gamma of 2.0 darkens midtones, useful for source images that are overexposed.

## Char aspect ratio

Monospace characters are approximately 0.55 times as wide as they are tall. If you leave this at the default, the output will appear correctly proportioned. If the result looks vertically squished, increase the value toward 1.0. If it looks stretched, lower it toward 0.3.

## Edge threshold

This control is only visible when **Edge-aware chars** is checked. It sets the minimum Sobel magnitude required before a directional line character (`─ ╲ │ ╱`) is substituted. At low values, even subtle texture edges trigger directional characters. At high values, only strong hard edges do.

## Invert

The **Invert** checkbox flips luminance values after gamma and contrast are applied (`l = 1 − l`). This swaps which characters appear on bright vs. dark areas. It is distinct from the `inverse` color mode, which inverts the final color output rather than the luminance used for character selection.

## Edge-aware characters

The **Edge-aware chars** checkbox enables Sobel edge detection. When active, cells where an edge is detected above the edge threshold are drawn with a directional character instead of the brightness-mapped character. See the [character sets](/using/character-sets) page for the full list of directional characters.

## Dithering

Dithering spreads quantization error across neighboring cells so that the overall impression of a region matches its average luminance even when only a limited set of characters is available.

| Algorithm           | Behavior                                                                                                                   |
| ------------------- | -------------------------------------------------------------------------------------------------------------------------- |
| **None**            | Direct brightness-to-character mapping; no error diffusion                                                                 |
| **Floyd-Steinberg** | Error diffusion with 8 quantization steps; produces smooth gradients and natural-looking tonal transitions                 |
| **Atkinson**        | Error diffusion with 16 steps; retains more contrast and creates a halftone-like look, originally from the early Macintosh |
| **Ordered 4×4**     | 4×4 Bayer matrix; adds a regular crosshatch pattern texture across the image                                               |
| **Ordered 8×8**     | 8×8 Bayer matrix; finer regular texture, less visible patterning than 4×4                                                  |

<Tip>
  Try **Atkinson** dithering with the **Newspaper** preset (`dense` character set, `inverse` color mode, cream background). The combination produces a convincing halftone print look reminiscent of newspaper photography.
</Tip>