Version 0.54 was released in February 1996, and had a major impact as the first truly professional free image manipulation program. This was the first free program that could compete with the big commercial image manipulation programs.

Version 0.54 was a beta release, but it was so stable that you could use it for daily work. However, one of the major drawbacks of 0.54 was that the toolkit (the slidebars, menus, dialog boxes, etc.) was built on Motif, a commercial toolkit. This was a big drawback for systems like „Linux“, because you had to buy Motif if you wanted to use the faster, dynamically linked GIMP. Many developers were also students running Linux, who could not afford to buy Motif.

When 0.60 was released in July 1996, it had been under S and P (Spencer and Peter) development for four months. Main programming advantages were the new toolkits, GTK (GIMP Toolkit) and gdk (GIMP Drawing Kit), which eliminated the reliance on Motif. For the graphic artist, 0.60 was full of new features like: basic layers; improved painting tools (sub-pixel sampling, brush spacing); a better airbrush; paint modes; etc.

Version 0.60 was only a developer's release, and was not intended for widespread use. It served as a workbench for 0.99 and the final 1.0 version, so functions and enhancement could be tested and dropped or changed. You can look at 0.60 as the alpha version of 0.99.

In February 1997, 0.99 came on the scene. Together with other developers, S and P had made several changes to GIMP and added even more features. The main difference was the new API (Application Programming Interface) and the „PDB“, which made it possible to write scripts; Script-Fus (or macros) could now automate things that you would normally do by hand. GTK/gdk had also changed and was now called GTK+. In addition, 0.99 used a new form of tile-based memory handling that made it possible to load huge images into GIMP (loading a 100 MB image into GIMP is no problem). Version 0.99 also introduced a new native GIMP file format called XCF.

The new API made it really easy to write extensions and plug-ins for GIMP. Several new plug-ins and extensions emerged to make GIMP even more useful (such as SANE, which enables scanning directly into GIMP).

In the summer of 1997, GIMP had reached version 0.99.10, and S and P had to drop most of their support since they had graduated and begun jobs. However, the other developers of GIMP continued under the orchestration of Federico Mena to make GIMP ready for prime time.

GTK+ was separated from GIMP in September 1997. GTK+ had been recognized as an excellent toolkit, and other developers began using it to build their own applications.

GIMP went into feature freeze in October 1997. This meant that no new features would be added to the GIMP core libraries and program. GUM (GIMP Users Manual) version 0.5 was also released early in October 1997. The developing work continued to make GIMP stable and ready for version 1.0.