ComfyUI NKD Preview Tools

A small set of preview and masking tools for ComfyUI:

• NKD Popup Preview — preview generated images in a persistent floating popup window, ideal for multi-monitor setups.
• NKD Mask Painter — paint a mask on top of any procedural image and pipe both the image and the mask downstream. Drop-in replacement for Impact Pack's Preview Bridge with a few extras.

https://github.com/user-attachments/assets/e52f40df-36a2-4027-8f7b-1e987ed2615f

Updates!

I’ve added a "set primary" state that lets you use multiple popup previews in the same workflow. Once you’ve set one as the primary node, you can trigger its output with a shortcut or call up the preview from anywhere in the UI. This means you can queue only what you're actually previewing on a second monitor or floating window, without having to scroll back and forth from the middle of nowhere.

https://github.com/user-attachments/assets/75a9a3de-9ded-4d41-95f2-3de4421d63ac

The new node: Mask Painter

https://github.com/user-attachments/assets/fea39b77-1e47-4006-ba7f-51197db0f106

🌟 Features

NKD Popup Preview

• Floating Image Preview: Automatically opens a popup window showing the current output image during execution.
• Multi-Monitor Support: Drag the preview popup to any monitor you prefer.
• Fullscreen Mode: Maximize the popup to preview images without any UI distractions.
• Unobtrusive: Cleanly integrates into your workflow without taking up space on your main ComfyUI canvas.

NKD Mask Painter

• Bridge node: accepts any IMAGE upstream — no need to duplicate Load Image to paint a mask.
• Native mask editor integration: opens the same painting UI as Preview Bridge / Load Image.
• Three outputs: IMAGE (passthrough), MASK and MASK (inverted).
• Optional mask input: feed any mask from upstream as a starting point — it is fused into the editor canvas so you can refine it by adding or erasing parts. All blend modes only act when the upstream mask content actually changes, so a noisy queue never disturbs your edits. The mask_input_mode combo uses VFX/compositing vocabulary:
  • Use as start (default): import only if the node has no painted mask yet. After that, your manual edits stick even if the upstream mask changes.
  • Replace: overwrite your painted mask with upstream every time it changes.
  • Add: union — adds the upstream mask to whatever you painted.
  • Subtract: removes the upstream mask from yours. Useful for excluding regions marked by upstream.
  • Intersect: keeps only the area where painted and upstream masks overlap.
  • Disconnected: input connected but ignored.
• Persistent across restarts: painted masks are mirrored to input/nkd_masks/ so they survive temp cleanup and ComfyUI restarts.
• Edit / Clear / Reseed button row:
  • Edit opens the native mask editor.
  • Clear wipes the painted mask, refreshes the node preview, and re-runs the node so downstream consumers immediately see the cleared mask.
  • Reseed arms the node to re-apply the current mask_input_mode operation against the upstream mask on the next Run (useful when you want to re-blend without changing upstream). See the example below.
• Visual feedback: the node turns green when it carries a non-empty mask.
• on_image_change combo: choose clear_mask (default) to wipe the mask when the upstream image changes, or keep_mask to preserve it.
• One mask per node: instantiate multiple Mask Painter nodes from the same image to paint independent masks.

🛠️ Installation

Method 1: Git Clone (Recommended)

1. Go to your ComfyUI custom_nodes folder.
2. Open a terminal or command prompt in that folder and run:

   git clone https://github.com/Nekodificador/ComfyUI-NKD-Preview-Tools.git
   

3. Restart ComfyUI.

Method 2: Download ZIP

1. Click the Code button on this repository in GitHub, then select Download ZIP.
2. Extract the downloaded folder and place it directly inside your ComfyUI/custom_nodes/ directory.
3. Restart ComfyUI.

💡 Usage

NKD Popup Preview

1. Open your ComfyUI workspace.
2. Double-click on the canvas to open the node search box, or right-click to find the node menu.
3. Add the node under NKD Nodes/Preview -> NKD Popup Preview.
4. Connect any valid IMAGE output (for example, from a VAE Decode node) to the image input socket.
5. Click Queue Prompt. The pop-up window will open automatically and display the generated image.

NKD Mask Painter

1. Add the node under NKD Nodes/Masking -> NKD Mask Painter.
2. Connect any IMAGE source (procedural or Load Image) to the images input.
3. Click Queue Prompt once so the node loads the image.
4. Click Edit to open the native mask editor. Paint, then Save & Close.
5. Click Queue Prompt again — MASK and MASK (inverted) are now populated.
6. The node preview shows the image with the painted area as transparency (the same way Preview Bridge does it).
7. Click Clear at any time to wipe the mask. The node re-runs automatically so any downstream nodes also see the cleared mask.
8. With a mask connected upstream, click Reseed then Run to re-apply the current mask_input_mode operation against the upstream mask without changing upstream.

For multiple independent masks of the same image, instantiate the Mask Painter node several times.

Clear vs Reseed — what's the difference?

Both buttons interact with mask state, but they do different things:

| | Painted mask | Upstream mask input | Use when… | |---|---|---|---| | Clear | Wiped | Forgotten (re-imported on next Run) | You want to start over from scratch. | | Reseed | Kept | Forgotten (re-applied on next Run) | You want to re-blend the upstream mask into your current painted mask. |

Example with mask_input_mode = Add:

1. Connect a face-detector node to mask. Run.
2. The painter shows the detected face mask. You paint over an extra region by hand.
3. You manually erase the original face area in the editor (Edit → erase → Save).
4. The next Run will not re-add the face, because the upstream mask hasn't changed (its fingerprint matches the cached one). Your edits are preserved across executions — that is the intended behaviour.
5. To pull the face back in, click Reseed then Run: the upstream mask is treated as freshly arrived and re-applied via Add, without losing the rest of your painted mask. Clear would wipe everything you painted, so it's the wrong tool here.

📝 Troubleshooting

• Pop-up Blocker (Popup Preview): Your web browser might block the window from opening the first time you use this node. If this happens, please check your browser's address bar and make sure to allow pop-ups for the URL or localhost where ComfyUI is running.
• Mask not appearing in preview (Mask Painter): the node thumbnail uses transparency (checkerboard) to represent the mask. If you only see the RGB image, the mask is empty.
• Mask seems to disappear after a restart (Mask Painter): masks are restored from input/nkd_masks/<node_id>_mask.png on the first queue after restart. Hit Queue Prompt to refresh.