将图像从GIF转换为JPEG

Question

我必须将GIF转换为JPEG。我必须将字节保存到图像，然后重新打开并将其转换为JPEG。我尝试使用两个流来更改类型，但出现错误“ GDI +中发生一般错误”。有什么解释吗？

    public static byte[] GetJpegBytes(byte[] bytes)
    {
        using (var stream = new MemoryStream(bytes))
        {
            var temporaryImage = $"{Path.Combine(System.Web.HttpRuntime.AppDomainAppPath, Guid.NewGuid().ToString())}.jpeg";
            var image = Image.FromStream(stream);

            image.Save(temporaryImage, ImageFormat.Jpeg);
            using (var memoryStream = new FileStream(temporaryImage, FileMode.Open))
            {
                byte[] byteRsult = new byte[memoryStream.Length];
                memoryStream.Read(byteRsult, 0, (int)memoryStream.Length);
                memoryStream.Close();
                File.Delete(temporaryImage);
                return byteRsult;
            }
        }

    } 

Answer 1

如果您不想使用流，可以尝试以下方法：

Bitmap bitmap = new Bitmap("C:\MyFile.jpg");

bitmap.Save("C:\MyNewFile.gif", ImageFormat.Gif);

Answer 2

您可以将此扩展名用于转换格式图像我使用这个简单的扩展名来转换流。

public static Stream ConvertImage(this Stream originalStream, ImageFormat format)
{
                var image = Image.FromStream(originalStream);

               using(var stream = new MemoryStream())
          {
                image.Save(stream, format);
                stream.Position = 0;
                return stream;
          }
    }

用法：

var outputStream = stream.ConvertImage(ImageFormat.Png);

Answer 3

我只是以另一种格式重新保存图像时，也观察到相同的问题。创建新图像并将旧图像绘制到该图像上似乎可以解决问题。

public static byte[] GetJpegBytes(byte[] bytes)
{
    using (var stream = new MemoryStream(bytes))
    using (var image = Image.FromStream(stream))
    using (var targetImage = GetImage(image, image.Width, image.Height))
    using (var targetStream = new MemoryStream())
    {
        targetImage.Save(targetStream, ImageFormat.Jpeg);
        return targetStream.ToArray();
    }
}

private static Bitmap GetImage(Image source, int width, int height)
{
    using (var image = new Bitmap(width, height))
    using (var g = Graphics.FromImage(image))
    {
        g.Clear(Color.White); //if the gif is transparent we want the jpg to have white background.
        g.DrawImage(source, 0, 0, width, height);

        return image;
    }
}