Reading PNG Images

• A libpng-Based, PNG-Reading Demo Program
• Preliminaries
• readpng_init()
• readpng_get_bgcolor()
• Design Decisions
• Gamma and Color Correction
• readpng_get_image()
• readpng_cleanup()
• Compositing and Displaying the Image
• Getting the Source Code
• Alternative Approaches

As with almost any kind of programming project, there are numerous alternatives one can take when writing a PNG-supporting program. Complete or partial code for reading and/or writing PNGs is available for the C, C++, Java, Pascal, tcl/tk, Python, and Visual Basic languages, at a minimum; some of it is in the form of commercial libraries, some as free source code, and some as a combination of both. Many of these in alternatives are listed in Chapter 16, "Other Libraries and Concluding Remarks". One can even read and write PNG images directly, in effect implementing one's own PNG library, but this is a rather large undertaking and is generally not recommended except under special circumstances.

The granddaddy of all PNG libraries is libpng, the free reference library available as Standard (ANSI) C source code and used by many, if not most, PNG-supporting applications. It uses the similarly free zlib library (portable C source code) for compression and decompression, and in these next few chapters I'll provide detailed demonstrations of how to write programs with both.