有人知道如何使用 c# 创建动画 gif 吗？ 理想情况下，我会对所使用的颜色减少进行一些控制。
使用 imagemagick（作为外部启动进程）是最佳选择吗？
【问题讨论】：
标签： c# .net dynamic animated-gif
https://github.com/DataDink/Bumpkit 的这个 Gif Animation Creater 代码可以为每一帧设置延迟：
使用 .Net 标准 Gif 编码并添加动画标题。
编辑：使代码类似于典型的文件编写器。
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();
}
}
【讨论】：
有一个内置的 .NET 类可以对 GIF 文件进行编码。 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);
}
【讨论】：
bmpImage.GetHbitmap()。如MSDN notes, this has to be cleared manually。 Here 是一个代码示例，说明如何避免 GDI 位图对象占用过多内存。
您也可以考虑使用 ImageMagick 库。
http://www.imagemagick.org/script/api.php 列出的库有两个 .net 包装器
这是一个关于如何使用Magick.net wrapper 的示例：
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");
}
【讨论】：
在不知道重要的质量参数的情况下，是否调用 imagemagick 是最佳选择有点难以理解。其他一些选择是：
这些的优点是您不依赖第三方库，该库可能在执行您的代码的所有系统上都可用，也可能不可用。
MS 支持的 article 解释了如何使用自定义颜色表保存 gif（这需要完全信任）。动画 gif 只是每个图像的一组 gif，标题中包含一些附加信息。因此，将这两篇文章结合起来应该可以满足您的需求。
【讨论】：
要使用 Windows 窗体应用中的示例，请添加对这些程序集的引用：
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
然后
Int32Rect 位于 System.Windows 命名空间中
BitmapSizeOptions 位于 System.Windows.Media.Imaging 命名空间中
BitmapFrame 位于 System.Windows.Media.Imaging 命名空间中
另外，不要忘记关闭文件流（类似这样）：
using(FileStream targetFile = new FileStream(path, FileMode.Create))
{
gEnc.Save(targetFile);
}
【讨论】：
AnimatedGif 包可以制作动画 gif。
using (var gif = AnimatedGif.AnimatedGif.Create(Path.Combine(outputPath, "output.gif"), 20))
{
for (var i = 0; i < 10; i++)
{
Image img = Image.FromFile(Path.Combine(outputPath, $"{i.ToString().PadLeft(3, '0')}.png"));
gif.AddFrame(img, delay: -1, quality: GifQuality.Bit8);
}
}
【讨论】：
我注意到答案中还没有列出 ImageMagic 和 NGif 的另一种很好的选择。
FFMpeg 可用于从以下位置创建动画 GIF：
您可以直接从 C# 代码（使用 System.Diagnostics.Process）启动 ffmpeg.exe 或使用现有的 .NET ffmpeg 包装器之一：
var ffmpeg = new NReco.VideoConverter.FFMpegConverter();
ffmpeg.ConvertMedia("your_clip.mp4", null, "result.gif", null, new ConvertSettings() );
（此代码示例使用免费的NReco VideoConverter - 我是此组件的作者，请随时询问有关其使用的任何问题）。
可以通过降低帧速率和/或帧大小轻松减小 GIF 大小。 此外，还可以通过生成最佳 GIF 调色板的 2-pass 方法获得精美的动画 GIF。
【讨论】：
引用来自 fireydude 的回答： https://stackoverflow.com/a/16598294/8917485
此方法不完整，导致.gif 无法重复。 我在其他问题上发现了一些额外的代码，让 .gif 重复。
.NET - Creating a looping .gif using GifBitmapEncoder http://www.matthewflickinger.com/lab/whatsinagif/bits_and_bytes.asp
完整的代码应该如下所示：
System.Windows.Media.Imaging.GifBitmapEncoder gEnc = new GifBitmapEncoder();
foreach (System.Drawing.Bitmap bmpImage in bitMaps)
{
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
bmpImage.Dispose(); // recommended, handle memory leak
}
// After adding all frames to gifEncoder (the GifBitmapEncoder)...
using (var ms_ = new MemoryStream())
{
gEnc.Save(ms_);
var fileBytes = ms_.ToArray();
// This is the NETSCAPE2.0 Application Extension.
var applicationExtension = new byte[] { 33, 255, 11, 78, 69, 84, 83, 67, 65, 80, 69, 50, 46, 48, 3, 1, 0, 0, 0 };
var newBytes = new List<byte>();
newBytes.AddRange(fileBytes.Take(13));
newBytes.AddRange(applicationExtension);
newBytes.AddRange(fileBytes.Skip(13));
File.WriteAllBytes("abc.gif", newBytes.ToArray());
}
【讨论】：