When comparing GrafX2 vs Piskel, the Slant community recommends GrafX2 for most people. In the question“What are the best pixel art / sprite editors?” GrafX2 is ranked 3rd while Piskel is ranked 10th.
Ranked in these QuestionsQuestion Ranking
Pro Supports tileset addition and extraction
Pro Scriptable using Lua
GrafX2 is scriptable using the Lua language, which can be used to automate tasks and add new functionality to it. The script library features advanced color reduction and enhancement tools, palette analysis, and much more.
Pro Free, open source, and cross-platform
GrafX2 is totally free to use, copy, and modify. It's available on Windows, Linux, Mac OS X, Haiku, AROS, MorphOS, SkyOS, Syllable, Mint, and a few more systems. Basically anything is supported by the SDL library.
Pro Very large number of tools and effects
Pro Supports animations
The program has a basic support for animation using frames in newer versions. Graphics can be cloned and copied between frames and changed slightly.
See here how to animate with GrapfX2 https://www.youtube.com/watch?v=Gnq6zBZOqoM
Pro Supports many file formats
GrafX2 supports many file formats, including the popular gif and png, but also importing and exporting from deluxe paint, degas elite, and various other editors using custom formats.
Pro Has a great palette tool
You can create gradients from one color to another, work in either RGB or HSL color space, save and load palettes, sort and organize palettes, and even work on "color cycling" images.
Pro Has a customizable UI with themes support
Theme UI style can easily be changed from settings including buttons and colors.
Pro Palette Color Cycling
GraphX2 being based on older 256 bitmap software has inherited some tricks that modern pixel editors do not have . One of them being the ability to cycle color palette and produce animations and effects with it.
Pro Works in any browser
WPiskel is HTML5-based so it works in any modern browser.
Pro Animation support
Piskel includes onion skinning, exporting to sprite sheets or gifs, defining frame rate, and present live playback.
Pro Offline versions available
The downloadable version of Piskel (built with node-webkit) is available for Windows, Linux, and Mac OS X.
Pro Very simple for beginners
Once you get the hang of it its a very powerful tool
Pro Enough tools to be powerful
It has enough tools to be powerful, but not too many to put off beginners.
Pro Sleek interface
It is also easy on the eyes.
Pro Easy to use lighten and darken tool
With the click of a button you can create amazing shading.
Pro Open source
Piskel is licensed under Apache License, meaning that the user can use the software for any purpose.
Pro Has a straight foreward tile view mode
... so you can instantly see the result while drawing tiles
Con Doesn't work well with drawpads
In the online tool you can't draw lines at all, yet using a graphic tablet, being in the offline version controls are pretty chunky and everytime you start drawing a line, the screen flickers black for a short period of time.
Con Rotation is limited
Rotation is only made in predefined angles. Does not support variable rotations or mouse based rotation. Does not support rotating selected areas, only frames-layers.
Con Shading by hand
Shading can be difficult.
Con Lacks a true resizing tool
There doesn't seem to be any decent tool in Piskel for an easy stretch or shrink. The only ways possible is resizing the whole image or importing and image and shrinking it from the export tool.