Merge PNG Images
Merge two PNG images online with a per-pixel mask. Transparency is preserved end to end, and the result downloads as a lossless PNG. Nothing is uploaded.
Files never leave your browser.
Compose two PNGs by painting a per-pixel mask. The result downloads as a lossless PNG with transparency intact.
About PNG Merge
Builds one PNG from two source images. You paint a mask that says which side each region comes from, and the detected differences seed it. The download is a lossless PNG that keeps the alpha channel.
How to use
- Pick a left and a right PNG of the same size.
- The detected difference groups seed the mask. Refine it with the Brush, the Bucket, or the buttons on each group.
- Set Download format to PNG and download the result. PNG keeps transparency and adds no loss.
What this tool doesn't handle
- Both images must reach one common size. Turn on auto-scale for a mismatch; resampling can soften edges.
- Only the pixels are merged. The metadata chunks and the colour profile of the sources are not carried over.
Frequently asked questions
Do my files ever leave my browser?
No. Every comparison runs locally in your browser. Nothing you paste, drop, or load is uploaded to a server; the tool keeps working even if you go offline after the page loads.
Is this tool free to use?
Yes. All DiffResolver tools are free, with no account, sign-up, or installation. Because processing happens on your device, there are no server-imposed usage limits.
Does the merged PNG keep transparency?
Yes. The mask copies RGBA pixels, so a transparent area stays transparent. PNG stores an alpha channel, which is why this page starts on PNG as the download format.
Does the merge lose quality?
No. PNG compression is lossless, so pixels from either source arrive unchanged. Only an image that auto-scale resizes is resampled.
Can the two PNG files have different sizes?
Turn on Auto-scale and align mismatched sizes. The smaller image is then scaled over the larger one, and you correct scale and offset in the alignment workspace. Same-size exports give the cleanest mask.
Is there a file size limit?
No server limit applies, because nothing is uploaded. The memory of your device sets the practical limit. Above 10 MB for text, 40 MB for images, 100 MB for documents, or 500 MB for archives, the tool warns you that the work can be slow, but it never blocks the file.
Does this tool work offline?
Yes. The browser keeps a copy of the tool after the first visit, so a page you opened before still works without a network. You can also install DiffResolver as an app from the browser menu. Installation stays optional; the site works the same in a normal tab.
Where is my data stored?
Your files are stored nowhere. They stay in the memory of the page and are gone when you close the tab. Only what you save yourself stays in this browser: a snapshot, your tool options, and your theme. To remove it, open Settings and select Clear all local data.