how to create an animated gif in .net

问题:

Does anyone know how to create an animated gif using c#? Ideally I would have some control over the color reduction used.

Is using imagemagick (as an external started process) the best choice?

回答1:

There is a built in .NET class which will encode GIF files. GifBitmapEncode MSDN

System.Windows.Media.Imaging.GifBitmapEncoder gEnc = new GifBitmapEncoder();

foreach (System.Drawing.Bitmap bmpImage in images)
{
    var bmp = bmpImage.GetHbitmap();
    var src = System.Windows.Interop.Imaging.CreateBitmapSourceFromHBitmap(
        bmp,
        IntPtr.Zero,
        Int32Rect.Empty,
        BitmapSizeOptions.FromEmptyOptions());
    gEnc.Frames.Add(BitmapFrame.Create(src));
    DeleteObject(bmp); // recommended, handle memory leak
}
using(FileStream fs = new FileStream(path, FileMode.Create))
{
    gEnc.Save(fs);
}

回答2:

This Gif Animation Creater code from https://github.com/DataDink/Bumpkit can set Delay foreach Frame:

Uses .Net standard Gif Encoding and adds Animation headers.

EDIT: Made the code similar to a typical file writer.

using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;
using System.Threading.Tasks;

/// <summary>
/// Creates a GIF using .Net GIF encoding and additional animation headers.
/// </summary>
public class GifWriter : IDisposable
{
    #region Fields
    const long SourceGlobalColorInfoPosition = 10,
        SourceImageBlockPosition = 789;

    readonly BinaryWriter _writer;
    bool _firstFrame = true;
    readonly object _syncLock = new object();
    #endregion

    /// <summary>
    /// Creates a new instance of GifWriter.
    /// </summary>
    /// <param name="OutStream">The <see cref="Stream"/> to output the Gif to.</param>
    /// <param name="DefaultFrameDelay">Default Delay between consecutive frames... FrameRate = 1000 / DefaultFrameDelay.</param>
    /// <param name="Repeat">No of times the Gif should repeat... -1 not to repeat, 0 to repeat indefinitely.</param>
    public GifWriter(Stream OutStream, int DefaultFrameDelay = 500, int Repeat = -1)
    {
        if (OutStream == null)
            throw new ArgumentNullException(nameof(OutStream));

        if (DefaultFrameDelay <= 0)
            throw new ArgumentOutOfRangeException(nameof(DefaultFrameDelay));

        if (Repeat < -1)
            throw new ArgumentOutOfRangeException(nameof(Repeat));

        _writer = new BinaryWriter(OutStream);
        this.DefaultFrameDelay = DefaultFrameDelay;
        this.Repeat = Repeat;
    }

    /// <summary>
    /// Creates a new instance of GifWriter.
    /// </summary>
    /// <param name="FileName">The path to the file to output the Gif to.</param>
    /// <param name="DefaultFrameDelay">Default Delay between consecutive frames... FrameRate = 1000 / DefaultFrameDelay.</param>
    /// <param name="Repeat">No of times the Gif should repeat... -1 not to repeat, 0 to repeat indefinitely.</param>
    public GifWriter(string FileName, int DefaultFrameDelay = 500, int Repeat = -1)
        : this(new FileStream(FileName, FileMode.OpenOrCreate, FileAccess.Write, FileShare.Read), DefaultFrameDelay, Repeat) { }

    #region Properties
    /// <summary>
    /// Gets or Sets the Default Width of a Frame. Used when unspecified.
    /// </summary>
    public int DefaultWidth { get; set; }

    /// <summary>
    /// Gets or Sets the Default Height of a Frame. Used when unspecified.
    /// </summary>
    public int DefaultHeight { get; set; }

    /// <summary>
    /// Gets or Sets the Default Delay in Milliseconds.
    /// </summary>
    public int DefaultFrameDelay { get; set; }

    /// <summary>
    /// The Number of Times the Animation must repeat.
    /// -1 indicates no repeat. 0 indicates repeat indefinitely
    /// </summary>
    public int Repeat { get; }
    #endregion

    /// <summary>
    /// Adds a frame to this animation.
    /// </summary>
    /// <param name="Image">The image to add</param>
    /// <param name="Delay">Delay in Milliseconds between this and last frame... 0 = <see cref="DefaultFrameDelay"/></param>
    public void WriteFrame(Image Image, int Delay = 0)
    {
        lock (_syncLock)
            using (var gifStream = new MemoryStream())
            {
                Image.Save(gifStream, ImageFormat.Gif);

                // Steal the global color table info
                if (_firstFrame)
                    InitHeader(gifStream, _writer, Image.Width, Image.Height);

                WriteGraphicControlBlock(gifStream, _writer, Delay == 0 ? DefaultFrameDelay : Delay);
                WriteImageBlock(gifStream, _writer, !_firstFrame, 0, 0, Image.Width, Image.Height);
            }

        if (_firstFrame)
            _firstFrame = false;
    }

    #region Write
    void InitHeader(Stream SourceGif, BinaryWriter Writer, int Width, int Height)
    {
        // File Header
        Writer.Write("GIF".ToCharArray()); // File type
        Writer.Write("89a".ToCharArray()); // File Version

        Writer.Write((short)(DefaultWidth == 0 ? Width : DefaultWidth)); // Initial Logical Width
        Writer.Write((short)(DefaultHeight == 0 ? Height : DefaultHeight)); // Initial Logical Height

        SourceGif.Position = SourceGlobalColorInfoPosition;
        Writer.Write((byte)SourceGif.ReadByte()); // Global Color Table Info
        Writer.Write((byte)0); // Background Color Index
        Writer.Write((byte)0); // Pixel aspect ratio
        WriteColorTable(SourceGif, Writer);

        // App Extension Header for Repeating
        if (Repeat == -1)
            return;

        Writer.Write(unchecked((short)0xff21)); // Application Extension Block Identifier
        Writer.Write((byte)0x0b); // Application Block Size
        Writer.Write("NETSCAPE2.0".ToCharArray()); // Application Identifier
        Writer.Write((byte)3); // Application block length
        Writer.Write((byte)1);
        Writer.Write((short)Repeat); // Repeat count for images.
        Writer.Write((byte)0); // terminator
    }

    static void WriteColorTable(Stream SourceGif, BinaryWriter Writer)
    {
        SourceGif.Position = 13; // Locating the image color table
        var colorTable = new byte[768];
        SourceGif.Read(colorTable, 0, colorTable.Length);
        Writer.Write(colorTable, 0, colorTable.Length);
    }

    static void WriteGraphicControlBlock(Stream SourceGif, BinaryWriter Writer, int FrameDelay)
    {
        SourceGif.Position = 781; // Locating the source GCE
        var blockhead = new byte[8];
        SourceGif.Read(blockhead, 0, blockhead.Length); // Reading source GCE

        Writer.Write(unchecked((short)0xf921)); // Identifier
        Writer.Write((byte)0x04); // Block Size
        Writer.Write((byte)(blockhead[3] & 0xf7 | 0x08)); // Setting disposal flag
        Writer.Write((short)(FrameDelay / 10)); // Setting frame delay
        Writer.Write(blockhead[6]); // Transparent color index
        Writer.Write((byte)0); // Terminator
    }

    static void WriteImageBlock(Stream SourceGif, BinaryWriter Writer, bool IncludeColorTable, int X, int Y, int Width, int Height)
    {
        SourceGif.Position = SourceImageBlockPosition; // Locating the image block
        var header = new byte[11];
        SourceGif.Read(header, 0, header.Length);
        Writer.Write(header[0]); // Separator
        Writer.Write((short)X); // Position X
        Writer.Write((short)Y); // Position Y
        Writer.Write((short)Width); // Width
        Writer.Write((short)Height); // Height

        if (IncludeColorTable) // If first frame, use global color table - else use local
        {
            SourceGif.Position = SourceGlobalColorInfoPosition;
            Writer.Write((byte)(SourceGif.ReadByte() & 0x3f | 0x80)); // Enabling local color table
            WriteColorTable(SourceGif, Writer);
        }
        else Writer.Write((byte)(header[9] & 0x07 | 0x07)); // Disabling local color table

        Writer.Write(header[10]); // LZW Min Code Size

        // Read/Write image data
        SourceGif.Position = SourceImageBlockPosition + header.Length;

        var dataLength = SourceGif.ReadByte();
        while (dataLength > 0)
        {
            var imgData = new byte[dataLength];
            SourceGif.Read(imgData, 0, dataLength);

            Writer.Write((byte)dataLength);
            Writer.Write(imgData, 0, dataLength);
            dataLength = SourceGif.ReadByte();
        }

        Writer.Write((byte)0); // Terminator
    }
    #endregion

    /// <summary>
    /// Frees all resources used by this object.
    /// </summary>
    public void Dispose()
    {
        // Complete File
        _writer.Write((byte)0x3b); // File Trailer

        _writer.BaseStream.Dispose();
        _writer.Dispose();
    }
}

回答3:

You might also consider using the ImageMagick library.

There are two .net wrappers for the library listed at http://www.imagemagick.org/script/api.php

Here is an example on how to do it using the Magick.net wrapper:

using (MagickImageCollection collection = new MagickImageCollection())
{
  // Add first image and set the animation delay to 100ms
  collection.Add("Snakeware.png");
  collection[0].AnimationDelay = 100;

  // Add second image, set the animation delay to 100ms and flip the image
  collection.Add("Snakeware.png");
  collection[1].AnimationDelay = 100;
  collection[1].Flip();

  // Optionally reduce colors
  QuantizeSettings settings = new QuantizeSettings();
  settings.Colors = 256;
  collection.Quantize(settings);

  // Optionally optimize the images (images should have the same size).
  collection.Optimize();

  // Save gif
  collection.Write("Snakeware.Animated.gif");
}

回答4:

Whether or not calling imagemagick is the best choice is kind of hard to awnser without knowing the quality parameters that are important. Some other options would be:

• Rick van den Bosch's code archive.org mirror
• NGif article on codeplex

these have the advantage that you don't have a dependency on a third partly library which might or might not be available on all systems executing your code.

This article at MS Support explains how to save a gif with a custom color table (this does require full trust). A animated gif is just a set of gifs for each image with some additional information in the header. So combining these two articles should get you what you need.

回答5:

To use the sample from a Windows Forms app, add references to these assemblies:

C:\Program Files\Reference Assemblies\Microsoft\Framework.NETFramework\v4.0\PresentationCore.dll C:\Program Files\Reference Assemblies\Microsoft\Framework.NETFramework\v4.0\System.Xaml.dll C:\Program Files\Reference Assemblies\Microsoft\Framework.NETFramework\v4.0\WindowsBase.dll

Then

• Int32Rect is in the System.Windows namespace

• BitmapSizeOptions is in the System.Windows.Media.Imaging namespace

• BitmapFrame is in the System.Windows.Media.Imaging namespace

Also, don't forget to close the file stream (something like this):

using(FileStream targetFile = new FileStream(path, FileMode.Create))
{
   gEnc.Save(targetFile);
}

回答6:

I noticed that one more great alternative to ImageMagic and NGif is not listed in answers yet.

FFMpeg can be used for creating animated GIFs from:

• sequence of images (files)
• existing video clip (say, mp4 or avi)
• from C# bitmap objects by providing input data as "ravvideo" through stdin (without using any temp files)

You can start ffmpeg.exe directly from C# code (with System.Diagnostics.Process) or use one of the existing .NET ffmpeg wrappers:

var ffmpeg = new NReco.VideoConverter.FFMpegConverter();
ffmpeg.ConvertMedia("your_clip.mp4", null, "result.gif", null, new ConvertSettings() );

(this code example uses free NReco VideoConverter - I'm an author of this component, feel free to ask any questions about its usage).

GIF size can be easily reduced by decreasing frame rate and/or frame size. Also it is possible to get fine-looking animated GIFs with 2-pass approach that generates optimal GIF palette.