Image

Suppose you have an image file (a PNG or JPG) and wish to get its width and height in a Go program. This can be done with the "image" package.

Some details

With images, we can get the Width and Height from the image file just by parsing the file. We simply call DecodeConfig on a JPG or PNG.

Example

To begin, we must import the "image" module. If we import the "image/jpeg" and "image/png" modules as well, we get full support for those types.

package main

import (
    "fmt"
    "os"
    "bufio"
    "image"
    _ "image/jpeg"
    _ "image/png"
)

func main() {
    path := `C:\programs\zip-chart.png`

    // Open file.
    inputFile, _ := os.Open(path)
    reader := bufio.NewReader(inputFile)

    // Decode image.
    config, _, _ := image.DecodeConfig(reader)

    // Print config.
    fmt.Printf("IMAGE: width=%v height=%v\n", config.Width, config.Height)
}
IMAGE: width=300 height=151

Note, imports

If you try to open a JPEG or PNG file without the special import statement for that type, it will not work correctly.

_ "image/jpeg"
_ "image/png"

Summary

Image parsing can be done with built-in libraries like the "image" module in Go. It is rarely worth implementing yourself, unless you are trying to learn about image formats.