source: OniSplit/Motoko/TextureExporter.cs

using System;
using System.Collections.Generic;
using Oni.Imaging;

namespace Oni.Motoko
{
    internal class TextureExporter : Exporter
    {
        protected string fileType;

        public TextureExporter(InstanceFileManager fileManager, string outputDirPath, string fileType)
            : base(fileManager, outputDirPath)
        {
            this.fileType = fileType;
        }

        protected override List<InstanceDescriptor> GetSupportedDescriptors(InstanceFile file)
        {
            return file.GetNamedDescriptors(TemplateTag.TXMP);
        }

        protected override void ExportInstance(InstanceDescriptor descriptor)
        {
            var texture = TextureDatReader.Read(descriptor);
            var filePath = CreateFileName(descriptor, "." + fileType);

            switch (fileType)
            {
                case "tga":
                    TgaWriter.Write(texture.Surfaces[0], filePath);
                    break;

                case "dds":
                    DdsWriter.Write(texture.Surfaces, filePath);
                    break;

                case "png":
                case "jpg":
                case "bmp":
                case "tif":
#if !NETCORE
                    SysWriter.Write(texture.Surfaces[0], filePath);
#endif
                    break;

                default:
                    throw new NotSupportedException(string.Format("Extracting textures as '{0}' is not supported", fileType));
            }
        }
    }
}