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Paint Suite (MEC)

Interactive paint canvas with Nuke-style procedural mask math + smart inpaint composite. Two nodes that work together to draw a region and blend an inpaint back cleanly.

Class Display name Purpose
MECAdvancedPaintCanvas MEC Advanced Paint Canvas Interactive brush widget that produces an image + a multi-stage processed mask
MECContextInpainter MEC Context Inpainter Smart-blend an inpainted region back over the original with color match / lightness rescue / differential diffusion

Both live under MEC/Paint.

MEC Advanced Paint Canvas

The JS widget posts a base64 PNG (RGBA) into the hidden canvas_data string on every serialise. Python decodes it, optionally composites over reference_image, and derives processed_mask from the alpha channel through four ordered stages:

  1. Raw mask — alpha of painted pixels normalised to [0, 1].
  2. mask_hardness — pixels brighter than (1 − hardness) clamp to 1.0 → produces a solid inner core whose width is the user-selected hardness fraction of the brush profile.
  3. mask_expansion — morphological dilate (>0) / erode (<0) in pixels (cv2 ellipse kernel when available).
  4. mask_blur — Gaussian blur of mask_blur_radius px, blended against the hard mask by mask_blur_strength (0 = hard, 1 = full blur).

Parameters

Parameter Default Range Description
canvas_width / canvas_height 512 64–4096 (step 8) Canvas resolution
brush_type paint paint / mask_only paint = composite color strokes; mask_only = build mask without coloring
brush_color #000000 hex Stroke color (ignored in mask_only)
brush_opacity 1.0 0–1 Stroke opacity
brush_hardness 0.8 0–1 Brush profile hardness (0 = soft, 1 = hard edge)
brush_size 20 1–500 px Brush diameter
mask_hardness 0.5 0–1 Threshold for solid inner core
mask_expansion 0 -100…100 px Dilate (+) / erode (-) in pixels
mask_blur_radius 0.0 0–100 px Gaussian blur on edge
mask_blur_strength 1.0 0–1 Blend factor between hard mask (0) and fully blurred mask (1)
canvas_data (hidden) string Internal base64 PNG payload — do not edit

Optional input

Slot Description
reference_image Optional background image; painted strokes are composited over it when supplied

Outputs

Output Type Description
painted_image IMAGE Painted RGB image (composited over reference_image when supplied)
processed_mask MASK Mask after hardness → expansion → blur stages

JS canvas controls

  • Left drag — paint strokes
  • Right drag — erase strokes
  • Scroll wheel — adjust brush size
  • Shift + Scroll — adjust brush hardness
  • Z — undo · Y — redo
  • C — clear all
  • R — reset view

MEC Context Inpainter

Smart-blend an inpainted region back over the original. The math runs in this order:

  1. crop_padding — extend the masked bbox by a multiplier so the inpaint sees context.
  2. mask_expansion_blend — dilate / erode of the blend mask (not the inpaint mask).
  3. blend_softness — Gaussian feather on the expanded mask.
  4. enable_color_correction — Reinhard mean+std color match (per-channel, masked region).
  5. enable_lightness_rescue — CIE LAB L-channel comparison; if the inpaint is more than ~5 % darker, lerp L upward by the deficit.
  6. enable_differential_diffusion — abs(orig − inpaint) per pixel used as a soft preservation weight, so unchanged pixels stay sharp.
  7. sampling_mask_blur_* — extra blur applied to the output debug_mask (used when feeding back into another sampler).

Parameters

Parameter Default Range Description
original_image — IMAGE Base for the blend
mask — MASK Inpainted region
inpainted_image — IMAGE Inpaint output
crop_padding 1.2 1.0–2.0 Multiplier extending masked bbox
blend_softness 8.0 0–200 px Gaussian feather on blend mask
mask_expansion_blend 0 -100–100 px Dilate/erode the blend mask
enable_color_correction true bool Reinhard color match
enable_lightness_rescue true bool Lift CIE LAB L when inpaint is darker
enable_differential_diffusion false bool Soft preservation weight
sampling_mask_blur_size 21 0–201 (odd) Kernel size for output debug_mask blur
sampling_mask_blur_strength 1.0 0–1 Blend factor for that blur

Optional (informational)

Slot Description
face_positive_prompt Region-attached positive prompt; parsed for {a|b|c} wildcards per region and logged. Does not sample here — pair with a downstream sampler
face_negative_prompt Same for negatives

Outputs

Output Type Description
blended_image IMAGE Final composited image
debug_mask MASK Mask used for the blend (after expansion + blur)

Use cases

Quick rotoscope mask

MEC Advanced Paint Canvas (mask_only) ──▶ ViTMatte Refiner ──▶ MASK out

Paint a rough region, refine to compositing-grade alpha. No segmenter needed.

Image generation — paint where to inpaint

Load Image ─▶ MEC Advanced Paint Canvas (paint mode, reference_image=Load Image)
              ├─ painted_image ──▶ Save (debug)
              └─ processed_mask ──▶ Inpaint Crop Pro

Smart compositing of any inpaint result

Inpaint pipeline ─▶ inpainted_image ─┐
Original image ──────────────────────┼─▶ MEC Context Inpainter ─▶ blended_image
Mask ────────────────────────────────┘

Replaces ad-hoc lerp with feather + color match + LAB lightness rescue. Use when an inpaint comes back slightly off in color or brightness.

Recipes

Goal Settings
Soft mask for photoreal blend mask_hardness=0.3, mask_blur_radius=8, mask_blur_strength=1.0
Hard graphic mask mask_hardness=1.0, mask_blur_radius=0
Grow then feather mask_expansion=8, mask_blur_radius=4
Blend with strong color shift correction enable_color_correction=true, enable_lightness_rescue=true, blend_softness=12
Preserve unchanged pixels (small edits) enable_differential_diffusion=true, blend_softness=4

Troubleshooting

Symptom Cause Fix
Empty processed_mask Brush hardness too high + small strokes Lower mask_hardness, raise brush_size
Visible halo around inpaint Color shift not corrected Enable enable_color_correction and enable_lightness_rescue
Inpaint looks flat enable_differential_diffusion too aggressive Disable it for global edits
Canvas resets between runs canvas_data widget cleared Don't refresh the page mid-edit; use Save Workflow