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README.md

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 # resigif
+
+[![CI Pipeline](https://github.com/logica0419/resigif/actions/workflows/ci.yml/badge.svg)](https://github.com/logica0419/resigif/actions/workflows/ci.yml) [![Go Reference](https://pkg.go.dev/badge/github.com/logica0419/resigif.svg)](https://pkg.go.dev/github.com/logica0419/resigif) [![license](https://img.shields.io/badge/license-MIT-blue.svg)](https://github.com/logica0419/resigif/blob/main/LICENSE)
+
 Animated GIF resizing library w/o cgo nor any third-party Libraries
+
+## Installation
+
+You can install resigif with the `go get` command
+
+```sh
+go get -u github.com/logica0419/resigif
+```
+
+## Quick Start
+
+The only API of this library is `Resize()` function.  
+You can easily resize an animated GIF image by passing `*gif.GIF` struct and the target size.
+
+Here's a simple example:
+
+```go
+package main
+
+import (
+  "context"
+  "image/gif"
+  "os"
+
+  "github.com/logica0419/resigif"
+)
+
+func main() {
+  ctx := context.Background()
+
+  src, err := os.Open("image.gif")
+  if err != nil {
+    panic(err)
+  }
+  defer src.Close()
+
+  srcImg, err := gif.DecodeAll(src)
+  if err != nil {
+    panic(err)
+  }
+
+  width := 480
+  height := 360
+
+  dstImg, err := resigif.Resize(ctx, srcImg, width, height)
+  if err != nil {
+    panic(err)
+  }
+
+  dst, err := os.OpenFile("resized.gif", os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0o644)
+  if err != nil {
+    panic(err)
+  }
+  defer dst.Close()
+
+  err = gif.EncodeAll(dst, dstImg)
+  if err != nil {
+    panic(err)
+  }
+}
+
+```
+
+## Customization
+
+- Aspect Ratio Preservation
+  - You can choose from `Ignore` or `Maintain`
+
+  ```go
+  dstImg, err := resigif.Resize(
+    ctx,
+    srcImg,
+    width,
+    height,
+    resigif.WithAspectRatio(resigif.Maintain),
+  )
+
+  dstImg, err := resigif.Resize(
+    ctx,
+    srcImg,
+    width,
+    height,
+    resigif.WithAspectRatio(resigif.Ignore),
+  )
+  ```
+
+- Changing resizing algorithm
+  - You can use you own resizing algorithm by implementing `ImageResizeFunc` interface and passing it to `WithImageResizeFunc()`
+  - If you want to use `golang.org/x/image/draw.Scaler`, you can use `FromDrawScaler()` to convert it to `ImageResizeFunc`
+
+  ```go
+  dstImg, err := resigif.Resize(
+    ctx,
+    srcImg,
+    width,
+    height,
+    resigif.WithImageResizeFunc(resigif.FromDrawScaler(draw.BiLinear)),
+  )
+  ```
+
+- Parallelism
+  - You can control the number of goroutines used for resizing by passing `WithParallel()`
+
+  ```go
+  dstImg, err := resigif.Resize(
+    ctx,
+    srcImg,
+    width,
+    height,
+    resigif.WithParallel(3),
+  )
+  ```