Image transparency mask editor
Paint a soft-edged transparency mask over an image to hide or bring back areas, then download the masked PNG and the mask itself as an editable grayscale PNG.
Accepted files: .png,.jpg,.jpeg,.webp. Choose one file. Up to 20 MiB in total.
Images stay in this browser and are never uploaded. Use one still PNG, JPEG or WebP image up to 20 MiB, 16,384 pixels per side and 8 million pixels. Up to 64 strokes, 20,000 points, 400,000 characters of stroke text and 32 million brushed pixel visits per run; brush radius 0.5 to 1,024 pixels. Processing stops after 30 seconds. You get the masked PNG, a grayscale mask PNG and a JSON report. Source metadata and color profiles are not copied. One still image up to 20 MiB and 8 million pixels. Run once, then paint on the preview. Up to 1,000,000 characters. Review the settings before running.
Your result
How to use Image transparency mask editor
- Choose an image and run the tool once to open the painter.
- Pick erase or paint, set the brush radius and feather, and drag over the preview.
- Use Undo or Redo as needed, then choose Apply strokes.
- Check the mask and changed-pixel count, then download the masked PNG and the mask PNG.
Useful next steps
How the mask works
The mask is a layer mask from 0 (hidden) to 255 (visible). The new alpha of each pixel is the original alpha x mask / 255, so existing transparency is kept and only reduced or restored by your strokes. Start fully visible to erase areas away, or fully hidden to paint areas in.
Brush and feather
Each stroke is a round brush dragged along straight segments between the points you paint. Inside the radius minus the feather the brush is solid; across the feather it fades along a Gaussian curve to exactly zero at the radius, so pixels outside every brush radius keep their transparency byte for byte. Strength scales the whole stroke.
Strokes and undo
Strokes are stored as a short JSON list of points, not as copies of the image, so undo never uses much memory. Points are in image pixels, where 0,0 is the center of the top-left pixel. The painter preview is approximate; Apply strokes recomputes the exact mask. You can save the strokes text from the report and paste it back later to repeat an edit.