icostring

Generate a file in the ICO format from a short string of either 16 or 64 characters ('a'..'p', 'q' and 't') + an optional hex encoded color value, for example tttttqqttqqttttt.

The idea is that this can be used for quickly specifying a favicon.ico file, either with a command line utility, or when writing web applications in Go.

Both a Go module and the icostring utility are provided.

Quick installation

For Go 1.21, the latest version of the icostring utility can be installed with:

go install github.com/xyproto/icostring/cmd/icostring@latest

Example use

package main

import (
    "log"
    "os"

    "github.com/xyproto/icostring"
)

func WriteFile(filename, imageString string) error {
    f, err := os.Create(filename)
    if err != nil {
        return err
    }
    if err := icostring.WriteImage(f, imageString); err != nil {
        return err
    }
    return f.Close()
}

func main() {
    if err := WriteFile("favicon.ico", "aaaafqqfaqqapppp"); err != nil {
        log.Fatalln(err)
    }
}

Here aaaafqqfaqqapppp is used, but aaaaaaaa aaaqqaaa ffqqqqff ffqqqqff aaqqqqaa aaqqqqaa pppqqppp pppppppp #08f is also a valid icostring.

String format

• The string represents a 4x4 or 8x8 image that will be scaled up to 16x16 when it is converted to an ICO.
• The string is a maximum of 73 characters long (letters + hex color). Spaces are ignored.
• The first 4 or 8 characters is the top row, the next series of letters is the second row etc.
• a is the darkest grayscale color, b is a bit lighter etc. up to p which is the lightest grayscale color.
• q is a custom color that is either red, or defined at the end of the string with a hex color, either with or without alpha, like #ffffffff or #fff.
• t is transparent.

Example short form image strings and images

• A dark image: aaaaaaaaaaaaaaaa (a is the darkest grayscale color)
• A blue image: qqqqqqqqqqqqqqqq#00f. (q is the custom color that is optionally defined at the end of the string).
• A red image: qqqqqqqqqqqqqqqq (the default custom color is red, #f00)
• A dark gray square surrounded by transparent pixels: tttt taat taat tttt.
• A yellow square surrounded by transparent pixels: tttttqqttqqttttt#ff0.
• A tiny icostring logo: aaaafqqfaqqapppp#5080ff.

aaaaaaaaaaaaaaaa	qqqqqqqqqqqqqqqq	tttttaattaattttt	aaaafqqfaqqapppp#5080ff

General info

• Version: 1.2.1
• License: BSD-3
• Author: Alexander F. Rødseth <[email protected]>