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Mask Preview

See what a mask really does. It turns a mask into a picture you can look at, like Photoshop's quick-mask overlay or the "show mask" view.

Mask Preview — before / after
In ComfyUI Add Node → ComfyUI-JH-PixelPro → mask → Mask: Preview Overlay
Good for Checking a mask's coverage, spotting holes and halos, judging soft edges, previewing a cutout on a checkerboard

When to use it

A raw mask is a grey image that is hard to judge. Four views make it clear:

Mode What you see Best for
overlay Photo tinted with a colour where the mask is on Checking coverage
heatmap Mask values as a colour map (0 = cold, 1 = hot) Finding soft or partial values
mask_only The mask as grey-scale The plain view
cutout Photo shown only where the mask is on, over a checkerboard Judging the cutout, like a transparent layer

The preview is for looking only. Do not feed its output back as a mask. Connect it to a Preview Image node.

Quick start

  1. Connect the mask to mask and your photo to the optional image.
  2. Choose overlay with opacity 0.5 and show_edges on.
  3. Connect preview to a Preview Image node.
  4. Switch to cutout to see how it would look on a transparent background.

Settings

Setting Default What it does Tip
mode overlay Which of the four views to draw. See the table above.
color red Tint colour for overlay, and the colour of the edge line. Pick a colour that contrasts with the photo. Eight colours are available, from red to white and black.
opacity 0.5 Strength of the tint (overlay) or the heatmap blend. 0 to 1.
colormap turbo The colour scale used by heatmap. Names come from Kornia's colormap list, such as turbo, viridis, jet.
show_edges off Draws the 0.5 contour of the mask as a thin line in color. Handy for judging how tight the edge is.
image (optional) none The background photo. Without it you get a neutral grey background (a bare colour map in heatmap mode). A 4-channel image is accepted; the alpha channel is ignored.

Output: preview (IMAGE).

Tips from retouching

  • Use heatmap on a feathered mask to see exactly how wide the soft band is.
  • Use cutout with a contrasting checkerboard to find halos that a flat background would hide.
  • Use show_edges in overlay mode to compare two masks. Run the node twice with different colours.
  • The image and the mask must have the same width and height.
Under the hood

overlay mixes the photo toward the colour by opacity * mask. heatmap uses kornia.color.apply_colormap with the chosen colormap and blends it with the photo by opacity. cutout mixes the photo and an 8 px checkerboard by the mask. The edge line is a one-pixel band, built from dilation minus erosion of the mask thresholded at 0.5. Source: core/mask_preview.py.

Example workflow

Mask Preview example workflow. Copy workflows/sample_portrait.jpg into ComfyUI/input/ first.