Bitmap Mask Node

The Bitmap Mask solves the problem: "I have an image that contains a mask, how do I use it as an Effect Mask?". It reads the chosen channel of the source image and outputs a mask you can connect elsewhere.

Advantages over connecting an image straight to an Effect Mask: threshold clipping to binarize it, built-in soft edge feathering, a paint mode to combine it with other masks, and support for special channels (Object/Material ID from 3D renders).

• Effects Library: Tools > Mask > Bitmap
• Quick add: right-click in the Node Editor → Add Tool > Mask > Bitmap

• Input (orange) - the 2D source image that holds the mask you want (alpha, luma, ID channel, etc.).
• Effect Mask (blue) - optional. A mask to combine through the Paint Mode.

External alpha as a mask:
MediaIn_mask (image with a clean alpha) → Bitmap Mask (Channel = Alpha)
                                        → Effect Mask of a Color Corrector

Luma-based mask:
MediaIn → Bitmap Mask (Channel = Luminance, Threshold Low 0.5)
       → Effect Mask for an effect on the highlights only

3D AOV Object ID mask:
EXR render → Loader → Bitmap Mask (Channel = Object ID, range on one ID)
          → Effect Mask for grading specific to one 3D object

Channel

Source channel used to generate the mask. See the dedicated section for the list.

Low / High Threshold

Clips the bitmap. A high Low forces dark pixels to 0. A low High forces bright pixels to 1. Lets you binarize the mask or isolate a specific range of values.

Soft Edge

Feathers the mask edges. Box/Bartlett/Multi-box/ Gaussian filter.

Level

Mask opacity (0-1).

Invert

Inverts the mask (masked ↔ unmasked areas).

Paint Mode

How it combines with an incoming mask: Merge, Add, Subtract, Minimum, Maximum, Average, Multiply, Replace, Invert, Copy, Ignore.

RGB (Red/Green/Blue)

Separate color channels. Useful to isolate an area dominated by a specific color.

Alpha

The source alpha channel. The standard choice when the source already has a mask in its alpha.

Luminance

Computed luminance (weighted RGB average). The equivalent of a basic luma key.

Hue

Hue channel. For masks based on the dominant color with no sensitivity to brightness.

Saturation

Saturation channel. For masks that isolate colorful areas from neutral ones.

Aux Coverage

Auxiliary coverage channel (for some 3D renders).

Object ID

For 3D renders: each object has a unique ID. Lets you mask only one specific object (e.g. the character, the set, a prop).

Material ID

For 3D renders: each material/shader has an ID. Masks only the surfaces with a specific material.

• Using an external alpha as a mask - a PNG image with a clean alpha → Bitmap Mask (Channel = Alpha) → Effect Mask for precise compositing.
• Basic luma key - a quick alternative to a real keyer: Channel = Luminance + Threshold to isolate bright/dark areas.
• Mask from a 3D AOV render - use the Object ID / Material ID channels of a multichannel EXR to mask only one object/material.
• Combining several source masks - several Bitmap Masks chained through the Paint Mode (Add/Subtract) to build a complex mask.
• Mask from a Fusion procedural - Fast Noise + Threshold → Bitmap Mask to use the pattern as an effect mask.
• Threshold cleanup - a noisy mask (in luma or alpha) can be cleaned with Low/High Threshold to binarize it neatly.
• Hue-based mask for sky/skin - Channel = Hue + an adjusted Threshold to isolate only the areas of a specific hue.

• Alpha channel by default if the source has a dedicated alpha. Luminance if there is no alpha but the areas of interest are bright/dark.
• Threshold to binarize - Low = 0.5 and High = 0.5 = a binary mask (all or nothing). Soft Edge for feathering after binarization.
• Object/Material ID = gold for VFX - if you work on 3D renders, always ask the 3D artist to export Object/Material ID AOVs. They allow perfect localized grades without manual roto.
• Alternative to a direct Effect Mask - connecting an image directly to an Effect Mask works, but the Bitmap Mask adds threshold, soft edge and paint mode - more flexible.
• Hue for skin tones - Channel = Hue + a threshold around skin orange = a rough skin mask. Not as good as a pro HSL qualifier, but fast.
• Invert often - depending on the source, the channel sometimes gives the opposite of what you want. One click on Invert fixes it.
• For precise keying (green/blue screen), use a real keyer (Delta Keyer, Chroma Keyer) - Bitmap Mask + Luminance is too basic.