MaskPreview - ComfyUI Built-in Node Documentation - ComfyUI

The MaskPreview node displays a visual preview of the mask data directly in the ComfyUI interface, without saving it to the output directory. This lets you inspect the mask at any point in your workflow, while the mask also passes through the node unchanged so it can continue to be used downstream.

Inputs

Parameter	Description	Data Type	Required	Range
`mask`	The mask data to preview	MASK	Yes	-
`filename_prefix`	Filename prefix used for the preview (default: “ComfyUI”)	STRING	No	-
`prompt`	Prompt information for metadata (automatically provided)	PROMPT	No	-
`extra_pnginfo`	Additional PNG information for metadata (automatically provided)	EXTRA_PNGINFO	No	-

Only mask is a visible input that needs to be connected. The filename_prefix, prompt, and extra_pnginfo parameters are supplied by the system: filename_prefix falls back to its default value, while prompt and extra_pnginfo are hidden and provided automatically by the ComfyUI runtime.

Outputs

Output Name	Description	Data Type
`mask`	The same mask data that was previewed, returned unchanged so it can be used elsewhere in the workflow	MASK

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