Image processing with Go
All New
To compile the helper library in Listing 1, which is later needed by the main program in Listing 2, move it to the directory src/darkenthreshold under your Go path (usually ~/go) and run go install there.
To compile the main program, call go build thresmain.go, and the resulting binary thresmain will be writing any modified image file (e.g., portrait.jpg) to a new file with a name sporting an -s suffix, as in portrait-s.jpg. To rewrite the filename, Line 60 in Listing 2 extracts the .jpg extension from the name of the old file and then chops it off with TrimSuffix, before the Sprintf function then inserts a -s from the fmt package and puts the suffix back. The target file won't exist yet at this point, so the OpenFile() function in line 66 needs the read/write/create flags (os.O_RDWR and os.O_CREATE) to create a new file.
With jpeg.Encode() and a quality value of 80, Listing 2 encodes the modified data into JPG format and writes the result to the specified file (Figure 6). If you like, you can try other algorithms, such as the Flood Fill [3] method, which colorizes pixels that are similar in value. After all, the raw pixel data is at your fingertips, and there are no limits as to what you can accomplish with them!
Figure 6: With a suitable threshold value, the algorithm performs the task as expected.
Infos
- Listings for this article: ftp://ftp.linux-magazine.com/pub/listings/linux-magazine.com/221/
- The Go image/draw package: https://blog.golang.org/go-imagedraw-package
- Flood Fill: https://en.wikipedia.org/wiki/Flood_fill
The Author
Mike Schilli works as a software engineer in the San Francisco Bay area, California. Each month in his column, which has been running since 1997, he researches practical applications of various programming languages. If you email him at mailto:mschilli@perlmeister.com he will gladly answer any questions.
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