A simple, stand-alone mask painting tool for making clean RGB/CMY region masks (for SDXL / ComfyUI regional prompting, etc.). Load an image, paint directly on top of it, then export a pure-color mask PNG.<h3 id="core-tools">Core tools</h3><ul><li>Brush: Paints with a configurable brush size. Supports Square or Circle brush shapes.</li><li>Line: Click once to set a start point, release to place the end point and draw a straight line using the current brush size/shape (for nice straight borders).</li><li>Polygon: Click to drop points, then close the shape to fill it.<ul><li>Close by clicking near the first point (it highlights) or double-click to close.</li><li>In polygon mode, right-click removes the last point (useful for fixing a misclick).</li></ul></li><li>Fill: Flood-fills a contiguous area of the current mask layer based on the region’s existing mask color (designed to work with the tool’s pure RGB/CMY colors).</li><li>Erase: Removes mask paint (transparent). When Erase is selected, color buttons are disabled because erase doesn’t use color.</li></ul><h3 id="colors-(pure-mask-output)">Colors (pure mask output)</h3>You can paint with 6 pure channels:<ul><li>RGB: Red, Green, Blue</li><li>CMY: Cyan, Magenta, Yellow Export normalization ensures the saved mask is strictly pure channel colors (plus black background), even if your strokes had edge/preview artifacts.</li></ul><h3 id="ui-+-workflow-features">UI + workflow features</h3><ul><li>Load Image: Imports your guide image and enables the masking UI.</li><li>Opacity slider: Controls how strong the mask overlay preview appears on top of the guide image (view-only; export stays pure).</li><li>Brush size slider + numeric input (px): Fast adjustment with an exact value box.</li><li>Undo / Redo: Buttons plus shortcuts (Ctrl+Z, Ctrl+Y / Ctrl+Shift+Z), with a history stack.</li><li>Clear: Wipes the current mask layer.</li><li>Export Mask: Saves a PNG named <code>&lt;original_filename&gt;_mask.png</code>, with black background and normalized pure RGB/CMY paint.</li><li>Pan &amp; Zoom: Right-click drag to pan, mouse wheel to zoom toward cursor for precise edits on large images.</li></ul>

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