AutoCropBorders

Overview

AutoCropBorders trims uniform borders from an image by sampling edge pixels, estimating their colour statistics, and region-growing inward until the content changes. It optionally returns the detected border mask and reports the crop rectangle, making it useful for automated subject isolation or pre-processing scanned artwork.

Inputs

image (IMAGE): Tensor [B, H, W, C]. Values are clamped to [0, 1] and converted to float32.
fuzz_mode (STRING, default "adaptive"): "percent" uses a fixed threshold derived from fuzz_percent; "adaptive" widens the tolerance based on border variance (adaptive_k multiplier).
fuzz_percent (FLOAT, default 5.0): Maximum per-channel deviation (in 0–100%) allowed when classifying border pixels in "percent" mode.
adaptive_k (FLOAT, default 2.0): Multiplier applied to the median absolute deviation to set per-channel thresholds in "adaptive" mode.
edge_margin_px (INT, default 4): Width of the seed strip sampled along each edge to build the border colour model.
pad_px (INT, default 0): Expands the resulting crop box outward by this many pixels (after detection).
use_luma_only (BOOLEAN, default False): If True, detection runs on luma; otherwise it operates in RGB space.
max_growth_iter (INT, default 4096): Upper bound on the number of dilation iterations when growing the border region.
return_border_mask (BOOLEAN, default False): When enabled, outputs the binary border mask aligned with the cropped image.
use_gpu (BOOLEAN, default True): Moves temporary tensors to CUDA when available for faster region-growing.

Outputs

image (IMAGE): Cropped RGB tensor with even dimensions enforced.
left (INT), top (INT), width (INT), height (INT): Crop rectangle relative to the original image (width/height coerced to even when possible).
border_mask (MASK): Binary mask of removed borders, resized to the cropped output. Zero tensor when return_border_mask is False.

Processing Notes

The algorithm samples all four edges, computes medians and median absolute deviations, then grows a binary mask starting from the border strips.
Detected borders are dilated and optionally padded, after which the surviving region is cropped and padded to even dimensions for latent-friendly downstream nodes.
When return_border_mask is False, the mask socket is still supplied but contains zeros to simplify downstream wiring.

Tips

Raise edge_margin_px for thicker frames to capture more representative samples.
Switch to "percent" mode with a low fuzz_percent when dealing with synthetic borders that have exact RGB values.
Disable use_gpu on systems with limited VRAM; the logic gracefully continues on CPU.*** End Patch

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