When comparing Sumo Paint vs Pyxel Edit, the Slant community recommends Pyxel Edit for most people. In the question“What are the best pixel art / sprite editors?” Pyxel Edit is ranked 6th while Sumo Paint is ranked 40th. The most important reason people chose Pyxel Edit is:
Tiles can be animated within Pyxel Edit, with "onion skin" frame overlays to assist in making smooth frame transitions.
Specs
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Pros
Pro Has most of standard Photoshop filters
Pro Has a Chrome App
Chrome app can be downloaded here.
Pro Has advanced layers support
Pro Can save to cloud, locally, or directly copy to clipboard
Pro Supports animations
Tiles can be animated within Pyxel Edit, with "onion skin" frame overlays to assist in making smooth frame transitions.
Pro Intuitive UI
Pyxel Edit is widely acclaimed for its ease of use.
Pro Tileset extraction
Given an image and specified tile dimensions, Pyxel Edit will extract a tileset with no duplicate tiles. This mostly works for flat images though. If you feed Pyxel "finished maps" you will still get a lot of duplicates.
Pro Tilemap serialization support
Tile-based images (maps) built in Pyxel Edit can be serialized via XML or JSON for easy import elsewhere.
Pro Cheap compared to others
For only $9 (£6), this is one of the cheapest but also one of the best pixel editors out there.
Pro Live tile-update
Instantly see if your tiles are tileable and/or seamless and fix it easily.
Pro Indexed tiles can be used for reusing objects in animations
Cons
Con Requires Flash
Con Slow to open
Sumo Paint is pretty slow to open when compared to other online photo editors.
Con Lacks drag and drop support
Doesn't yet support dragging & droping images in to the browser window.
Con Cannot zoom using mouse wheel
Con development has stopped -- developer has stated 8/20 that a new version will be released soon
Con Lacks some tools
Con No Linux version
There is no Linux version of the editor.
Con Free version lacks features
The free version of Pyxel Edit is an outdated beta. It does not receive updates.
Con Proprietary, closed-source software
This software does not respect your freedom.
Con Mac version is dependent on Adobe Air
The OSX version of the application requires Adobe Air to run.