Tcl/Tk with C for Image Processing

See how to use a mix of Tcl, Tk, and C to make image manipulation both easy and efficient.
About the Program

The complete C code for this program is in Listing 1, and the Tcl code is in Listing 2.

Figure 2 is a snapshot of the program in action.

Figure 2. An Example of all possible output clusters, when the vertical size is five. The criterion of choice is the nearest average.

Listing 2

The program can be downloaded from:

An Important Remark about C and Tcl/Tk Interaction

When Tcl/Tk calls a function in C, it can still receive interface events, such as button presses or slider movements; however, it cannot run the associated scripts (or C functions) bound to these events, since for the moment the C function controls the flow.

A good example is a mass-spring simulator, where the C function has a loop doing the simulation and canvas drawing. It would be wonderful to be able to change the constants during the simulation, or even abort it before the pre-determined time. This option is also needed in long Tcl scripts. The solution in both cases is to use the update command from time to time in order to process user input.

From the update man page:

The update command with no options is useful in scripts where you are performing a long-running computation but you still want the application to respond to user interactions; if you occasionally call update, user input will be processed during the next call to update.


A powerful combination is achieved by letting Tcl/Tk deal with the interface and C with the critical tasks of a program.

A lot of useful extra widgets can be found on the Internet for using sound (see tkSound), moving objects and so on. The principle for integration of these widgets is the same—you can create a new wish-like shell, or use the new available functions together with come extra C code of your own.

Another good package is Tix, which is included with many Linux distributions. It adds many wonderful widgets to Tk, and has an object-oriented approach to building new “mega-widgets”.

I hope you find this article useful, and have a nice hack.


Siome Goldenstein is an Electronics Engineer who is currently finishing a Masters degree in Computer Graphics. He loves Aikido and non-technical reading. Siome lives in Rio de Janeiro, Brazil. Comments can be sent to him via e-mail at