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Updated README.md documentation for multiple back-end support. #21

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35 changes: 33 additions & 2 deletions README.md
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Expand Up @@ -9,6 +9,24 @@

<a href='https://ko-fi.com/F1F8CLXG' target='_blank'><img height='36' style='border:0px;height:36px;' src='https://az743702.vo.msecnd.net/cdn/kofi2.png?v=0' border='0' alt='Buy Me a Coffee at ko-fi.com' /></a>

# Back Ends

**AnimatedGif** supports multiple back-ends to perform the actual image compression. Each back end is provided in a separate NuGet package. The back end is selected by passing a corresponding `ImageLibrary` implementation into the `GifEngine` constructor.

## Back End: System.Drawing

The integrated System.Drawing library in .NET can be used for compression. This library, provided by Microsoft, is based on [GDI+](https://learn.microsoft.com/en-us/windows/win32/gdiplus/-gdiplus-gdi-start), and is supported only on Windows.

To use System.Drawing, install the `AnimatedGif.SystemDrawing` NuGet package, and then pass an instance of `SystemDrawingImageLibrary` into the `GifEngine` constructor.

## Back End: SixLabors.ImageSharp

An image library called [SixLabors.ImageSharp](https://github.com/SixLabors/ImageSharp) can be used for compression. This third-party library is cross-platform and can be used on any platform where AnimatedGif can run.

To use ImageSharp, install the `AnimatedGif.ImageSharp` NuGet package, and then pass an instance of `ImageSharpImageLibrary` into the `GifEngine` constructor.

ImageSharp does not directly support palettized images. It quantizes the image to an 8-bit palette at the moment of GIF compression. It is not presently possible to select 1bpp or 4bpp with ImageSharp. As such, only `GifQuality.Bit8` can be used with ImageSharp. If other `GifQuality` values are supplied, `ImageSharpImageLibrary` will throw `NotSupportedException`.

# How to use

## Add to your Project
Expand All @@ -19,20 +37,33 @@ Install-Package AnimatedGif

> or download manually [on NuGet](http://www.nuget.org/packages/AnimatedGif/)

### Image Library

```nuget
Install-Package AnimatedGif.SystemDrawing
```

or

```nuget
Install-Package AnimatedGif.ImageSharp
```

## Creating a GIF

Create a GIF with the filename `"mygif.gif"` and a `33`ms delay between frames (~30fps). Use `16`ms for 60fps and so on.

```cs
using (var gif = AnimatedGif.Create("mygif.gif", 33))
var gifEngine = new GifEngine(new SystemDrawingImageLibrary()); // or ImageSharpImageLibrary,
// or any supported implementation
using (var gif = gifEngine.Create("mygif.gif", 33))
{
var img = Image.FromFile("myimage.png");
gif.AddFrame(img, delay: -1, quality: GifQuality.Bit8);
}
```

> If you don't want to write to a File, create a new `AnimatedGifCreator` instance directly. The constructor takes a `Stream`.
> If you don't want to write to a file directly, the `GifEngine.CreateGif` method also has an overload that accepts a `Stream`.

## Reading a GIF

Expand Down