Image Processing

CIS 193 – Go Programming

Course Logistics

• Final Project Proposal (guidelines available on course website) is due on April 11th on Canvas at 11:59 PM
• Feel free to talk to us after class, on Piazza, or OH by appointment about your proposals
• Piazza Link: piazza.com/class/ixxxkc67kac4vp
• Canvas Link: canvas.upenn.edu/courses/1350686

Image packages

Go Standard Library

Blank imports - remember these?

import _ "image/png"

Creating a Simple Image

package main

import "image"
import "image/color"
import "image/png"
import "os"

func main() {
    img := image.NewRGBA(image.Rect(0, 0, 100, 100))

    // Color the pixel at 5, 5 green
    img.Set(2, 3, color.RGBA{0, 250, 0, 255})

    // Save to image.png
    f, _ := os.Create("image.png")
    defer f.Close()
    png.Encode(f, img)
}

Creating Images Demo

Creating a GIF

package main

import "image"
import "image/gif"
import "image/png"
import "os"

func main() {
    files := []string{"img1.png", "img2.png","img3.png", "img2.png"}

    outGif := &gif.GIF{}
    for _, name := range files {
        f, _ := os.Open(name)
        img, _ := png.Decode(f)
        f.Close()

        outGif.Image = append(outGif.Image, img.(*image.Paletted))
        outGif.Delay = append(outGif.Delay, 0)
    }

    f, _ := os.Create("output.gif")
    defer f.Close()
    gif.EncodeAll(f, outGif)
}

Creating GIF Demo

Go Image Processing Packages

The Go standard library is amazing, but it's often easier to use external packages

Go Image Libraries

Making Memes

Debugging

Inspecting your program for bugs, usually line by line. Other languages such as Java or Python have sophisticated debugging tools. What about Go?

So far, how have you been debugging?

• Running code in main()
• fmt.Println()
• Tests?

Native Debugging with GDB

GDB is the GNU Debugger, which is intended for debugging C, C++, and Fortran programs. You can also use GDB with Go, but with many caveats. It also requires a UNIX-like environment, so Linux or MacOS. In other words, no Windows support.

See the documentation: golang.org/doc/gdb

Basic GDB Operations

gdb ./mygoexecutable

• l [list] to list lines of source code
• l line to list lines around provided line number
• b [break] line to set a breakpoint at provided line number
• b _function name_ to set a breakpoint at function name, wrapped in quotes
• r [run] to actually run the program
• n [next] to go to the next line
• s [step] to step inside any calls
• c [continue] to continue until next breakpoint
• p [print] to print a variable or Go expression

Warning: some operations and expressions will be substantially more verbose in GDB

Debugging with godebug

A few other debugging tools have sprung up, currently the 2 favorites are delve and godebug.

• Cross-platform
• Beta software
• Cannot step into standard library packages

$ go get github.com/mailgun/godebug

Basic godebug Usage

1. Insert a breakpoint anywhere in your code

_ = "breakpoint"

2. Start program with debugger

godebug run mygofile.go

Commands very similar to GDB:

• l [list] to show lines around current context
• n [next] to go to the next line
• s [step] to step inside any calls
• c [continue] until next breakpoint
• p [print] to print a variable or Go expression

Caveats

• Debugging is currently a major weak point in Go
• Solution has been promised, but not announced
• Your IDE/editor may offer specialized Go debugging tools

Homework

No new homework, start working on final projects!

Thank you