The mother of interface design tools. Probably the most used tool out there today. There is an infinite amount or resources, tutorials, articles for it. Photoshop has been around almost since the beginning of interface design.
As its name suggests, the first intention of the program wasn't interface design but photo or bitmap retouching. It evolved over the year and with the birth of interface design, designers appropriated it and re-purposed it. Part of this was because they were used to it and because it was the only program around that was able to do things as good as needed.
Photoshop is, to this day, the master of Bitmap editing and is still the most used program out there for UI design. Its decades long legacy makes it a hard program to approach and learn though. As a gigantic swiss army knife of a software, you'll be able to do anything, but not always in the most efficient way.
As it it bitmap based initially, it is DPI dependent, the opposite of Illustrator and Sketch described below.
Photoshop's vector based sibling. As its name indicates, it is aimed at Illustrators but it is also usable as an interface design tool.
Illustrator is suited for print design as well so its interface, color management, scale, rulers and units may throw you off at first and it requires a few tweaks to be easily usable for interface design only. Like Photoshop, it is an incredibly powerful tool with a steep learning curve.
What differs from Photoshop is that it is DPI independent due to its reliance on vector shapes. Contrary to bitmap or raster images, graphics made using vector shapes, relying on mathematical formulas, will be rescaled programmatically without any quality loss.
Understanding the difference between rasterized and vectorized image is key to build scalable visual design and assets.
If you want to get started with using Illustrator for web/interface design, I recommend reading "My vector workflow" by @janoskoos.
Sketch is new compared to Photoshop and Illustrator. With only 4 years of age, this program generated a lot of hype (in a good way) in the UI designer industry. The reason is that Sketch is aimed, from the start, to be used by interface and UX designers. Without the legacy of Photoshop or Illustrator, Sketch positions itself as the perfectly adapted tool for the niche audience that is interface designers.
Sketch is suited for fast wireframing as well as more complex visual design. It is entirely vector based, like Illustrator, with a minimal and well thought UI. The combination of artboards and the ease of use and flexibility of its asset generation system makes it the fastest tool for multi-DPI and multi-platform design. The recent release of its 3.0 version make it a very solid alternative to Photoshop.
On the downside, Sketch is supported by a smaller team and is still fairly recent. Its team is extremely reactive but doesn't have the scale of the Adobe (Photoshop and Illustrator) one. Sketch offers (by
I'm Sebastien Gabriel aka @Kounterb and I'm a visual designer for @googlechrome. I like towrite things and create freebies.
One thing I wish I had when I started is a clear guide explaining to me what DPI is and what the challenges of multi-platform design were going to be. This is what I'm trying to do here. By designing Chrome for almost every platforms out there, I learned a lot about these subjects and this is my effort to try and deliver it in the simplest way possible. As mentionned in the intro, if you think I got anything wrong, if anything lacks detail or if you would like to learn more about something, send me a message at firstname.lastname@example.org.