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Adjusting an Image

The Image tab in the control rail holds three groups - Frame, Adjust and Dither - that cover the three pipeline stages between opening a picture and dithering it. They share one tab to keep the rail short, not because they are the same kind of setting: Frame decides the picture's shape, Adjust changes its tone, and Dither decides how it gets reduced to a Layer 2 palette. Every control here updates the preview as you move it.

Each group has a Reset button - Reset Frame, Reset Adjust, Reset Dither

  • next to its heading. It puts that group back to the values in the currently loaded preset, never to a fixed default, and it is disabled whenever the group already matches the preset, so a greyed-out Reset button is itself a sign that nothing in that group has been touched. Hovering a disabled Reset button says so directly.

Frame

Frame sets the picture's target size and how the source image is fitted into it.

  • 256x192 and 320x256 are offered as one-click buttons because they are the two Layer 2 shapes NextDAAD's loader accepts - a 256-wide .NXI file up to 192 rows, or a 320-wide .NX2 file up to 256 rows.
  • Width and Height can also be set directly to any other size. This is deliberate free-form entry, not an oversight: any size still converts and previews normally. What actually makes a size a legal Layer 2 shape is the width - 256 wide up to 192 rows, or 320 wide up to 256 rows; a size such as 320x192 is a legal .NX2 even though it is neither of the two one-click sizes above. If either Bitmap or Bitmap-ZX0 is ticked in the Out tab and the current size is not one of those shapes, an amber warning appears naming the size and stating that Bitmap/BitmapZx0 export will fail at it - the preview keeps working and the fields stay editable, because this is a warning about export, not a restriction on what you can set here.
  • Fit chooses how the source image is scaled into the target size: Stretch (ignores the source's aspect ratio), Letterbox (scales to fit inside the target and pads the rest), or Crop to fill (scales to cover the target and crops the overflow).
  • Anchor is a nine-way grid (the corners, edge centres and centre) that decides where the image sits within letterbox padding, or which part of it survives a crop. It has no effect under Stretch, so it is disabled when Stretch is selected.
  • Filter is the resampling filter used to resize the image: Nearest, Triangle, Catmull-Rom or Lanczos3.

The stock preset uses 320x256, Letterbox, anchored Top centre, with the Lanczos3 filter.

Adjust

Adjust covers tone and an optional spatial filter, applied after framing and before the palette is built.

  • Brightness, Contrast, Gamma and Saturation sliders.
  • Perceptual (linear light) - when ticked, brightness, contrast, gamma and saturation operate in linear light rather than directly on the image's stored (sRGB) values.
  • Spatial filter switches between None, Sharpen and Blur. Its parameter rows appear only for the filter you have selected - Sharpen shows Radius, Amount and Threshold; Blur shows Radius alone; None shows nothing. Radius is capped at 4.0 rather than the wider range it once had: at the output sizes NextDither targets, a radius past about 4 looks the same as the next value up, so the slider's usable range was narrowed to give finer control over the part of it that actually changes the picture.

Dither

Dither controls how the adjusted image is reduced onto the palette.

  • Algorithm switches between None (nearest colour, no dithering), Diffusion and Ordered.
    • Diffusion offers a choice of error-diffusion kernels: Floyd-Steinberg, Jarvis-Judice-Ninke, Stucki, Burkes, Sierra-3, Two-row Sierra, Sierra Lite, Atkinson and Stevenson-Arce.
    • Ordered offers Bayer 2x2, 4x4, 8x8, 16x16, or a blue-noise tile.
  • Strength and Serpentine apply while a dithering algorithm is selected (they are disabled under None). Strength scales how strongly the algorithm is applied; Serpentine alternates scan direction row by row, which tends to reduce directional streaking.
  • A metric choice at the bottom of the group selects how colour distance is measured when matching pixels to the palette: Oklab (perceptual) or Weighted RGB (fast).

The stock preset dithers with Floyd-Steinberg, serpentine on, at full strength, using the Oklab metric.

See palette for the Palette tab's colour-count and freeze-palette controls, which sit alongside Dither in the pipeline but are covered separately.