Blend By Mask

Overview

PixPipeline correction nodes such as Brightness and Gaussian Blur do not have their own mask inputs (the local-correction principle in §2.8). Instead, use this node to combine a globally corrected version with the original through a mask.

Original ─────────────────┐
                         ├─ [Blend By Mask] ─→ Result
Original → [Brightness] ──┘        ↑
Mask ──────────────────────────────┘

Technical details

• A mask value from 0 to 1 linearly interpolates original → processed, so a grayscale mask can control partial strength.
• Use the default Premultiplied mode for ordinary image compositing. It ignores RGB hidden in fully transparent pixels, avoids dark or colored fringes, and canonicalizes a zero-alpha result to transparent black.
• Choose StraightRGBA only when the raw RGBA values, including transparent RGB, must be interpolated independently. Existing v2 projects migrate to this mode to preserve their previous output.
• If the processed image is smaller than the canvas, areas outside it are treated as transparent during blending.

Usage tips

• When you want to brighten or blur only one area, do not look for a mask input on the correction node. Always build this pattern: original + globally corrected version
  • mask. This is the standard PixPipeline approach.
• Branch the original image in two, correct only one branch, then merge both in this node. This Y-shaped merge is the visual signature to look for in the graph.
• A grayscale mask also supports partial application, such as 50% strength, through linear interpolation.
• Keep Premultiplied for visual compositing; reserve StraightRGBA for compatibility or workflows that intentionally edit hidden transparent RGB.
• Common combinations are also available as official custom nodes such as MaskedBrightness.

Common pitfalls

• original and processed are reversed: processed appears in white mask areas. If the effect is reversed, swap the connections or turn invert ON.
• A small mask behaves strangely at the edge: use outside to explicitly choose how areas outside the mask are handled (original, processed, or transparent).
• Preparing three inputs feels cumbersome: branch from the same image; you do not need to draw the original twice.

Examples

1. Local brightness adjustment: combine the original and its Brightness version only in an area drawn with Path Mask.
2. Partial blur: blend a Gaussian Blur version with a soft mask from Histogram Scan for a depth-of-field look.
3. Official custom nodes: MaskedBrightness / MaskedBlur / MaskedHSVAdjust are wrappers around this node.

Related nodes

• mask / erase_by_mask — cut out or erase instead of blending
• threshold / path_mask — mask sources
• blend — full-image blending without a mask
• mask_boolean — combines multiple masks