創建8位圖像

Question

我試圖用純色背景色創建一個8位圖像。它看起來應該是非常直接的，但文件中的細節列出它爲32位顏色深度。我錯過了什麼？

public void CreateImage() 
    { 
     var bmpOut = new Bitmap(300, 300); 
     var g = Graphics.FromImage(bmpOut); 
     g.FillRectangle(new SolidBrush(Color.Gray), 0, 0, 300, 300); 

     var stream = new MemoryStream(); 
     bmpOut.Save(stream, GetPngCodecInfo(), GetEncoderParameters()); 

     bmpOut.Save(@"C:\image.png", GetPngCodecInfo(), GetEncoderParameters()); 
    } 

    public EncoderParameters GetEncoderParameters() 
    { 
     var parameters = new EncoderParameters(); 
     parameters.Param[0] = new EncoderParameter(Encoder.ColorDepth, 8); 

     return parameters; 
    } 

    public ImageCodecInfo GetPngCodecInfo() 
    { 
     var encoders = ImageCodecInfo.GetImageEncoders(); 

     ImageCodecInfo codecInfo = null; 

     foreach (var imageCodecInfo in encoders) 
     { 
      if (imageCodecInfo.FormatID != ImageFormat.Png.Guid) 
       continue; 

      codecInfo = imageCodecInfo; 
      break; 
     } 

     return codecInfo; 
    } 

Answer 1

使用此構造指定的像素格式：http://msdn.microsoft.com/en-us/library/3z132tat.aspx

因爲你不能在創建索引像素格式的圖形，你可以只寫原始像素的8位圖像。

Bitmap bitmap = new Bitmap(32, 32, PixelFormat.Format8bppIndexed); 
var bitmapData = bitmap.LockBits(new Rectangle(Point.Empty, bitmap.Size), ImageLockMode.ReadWrite, bitmap.PixelFormat); 
Random random=new Random(); 
byte[] buffer=new byte[bitmap.Width*bitmap.Height]; 
random.NextBytes(buffer); 
Marshal.Copy(buffer,0,bitmapData.Scan0,buffer.Length); 
bitmap.UnlockBits(bitmapData); 
bitmap.Save("test.bmp",ImageFormat.Bmp); 

您可以使用上的WinForms這樣的代碼：http://www.codeproject.com/Articles/17162/Fast-Color-Depth-Change-for-Bitmaps

或者，如果你可以從WPF引用此類就會容易得多： http://msdn.microsoft.com/en-us/library/system.windows.media.imaging.formatconvertedbitmap(v=vs.85).aspx

Answer 2

• ImageExtensions.cs

  using System.Runtime.InteropServices; 
  using System.Linq; 
  
  using System.Drawing.Imaging; 
  using System.Drawing; 
  using System; 
  
  public static partial class ImageExtensions { 
      public static ColorPalette ToGrayScale(this ColorPalette palette) { 
       var entries=palette.Entries; 
  
       for(var i=entries.Length; i-->0; entries[i]=entries[i].ToGrayScale()) 
        ; 
  
       return palette; 
      } 
  
      public static Color ToGrayScale(this Color color, double[] luminance=null) { 
       var list=(luminance??new[] { 0.2989, 0.5870, 0.1140 }).ToList(); 
       var channel=new[] { color.R, color.G, color.B }; 
       var c=(byte)Math.Round(list.Sum(x => x*channel[list.IndexOf(x)])); 
       return Color.FromArgb(c, c, c); 
      } 
  
      public static Bitmap To8bppIndexed(this Bitmap original) { 
       var rect=new Rectangle(Point.Empty, original.Size); 
       var pixelFormat=PixelFormat.Format8bppIndexed; 
       var destination=new Bitmap(rect.Width, rect.Height, pixelFormat); 
  
       using(var source=original.Clone(rect, PixelFormat.Format32bppArgb)) { 
        var destinationData=destination.LockBits(rect, ImageLockMode.WriteOnly, pixelFormat); 
        var sourceData=source.LockBits(rect, ImageLockMode.ReadOnly, source.PixelFormat); 
  
        var destinationSize=destinationData.Stride*destinationData.Height; 
        var destinationBuffer=new byte[destinationSize]; 
  
        var sourceSize=sourceData.Stride*sourceData.Height; 
        var sourceBuffer=new byte[sourceSize]; 
  
        Marshal.Copy(sourceData.Scan0, sourceBuffer, 0, sourceSize); 
        source.UnlockBits(sourceData); 
  
        destination.Palette=destination.Palette.ToGrayScale(); 
        var list=destination.Palette.Entries.ToList(); 
  
        for(var y=destination.Height; y-->0;) { 
         for(var x=destination.Width; x-->0;) { 
          var pixelIndex=y*destination.Width+x; 
          var sourceIndex=4*pixelIndex; 
  
          var color= 
           Color.FromArgb(
            sourceBuffer[0+sourceIndex], 
            sourceBuffer[1+sourceIndex], 
            sourceBuffer[2+sourceIndex], 
            sourceBuffer[3+sourceIndex] 
            ).ToGrayScale(); 
  
          destinationBuffer[pixelIndex]=(byte)list.IndexOf(color); 
         } 
        } 
  
        Marshal.Copy(destinationBuffer, 0, destinationData.Scan0, destinationSize); 
        destination.UnlockBits(destinationData); 
       } 
  
       return destination; 
      } 
  } 
  

呼叫bmpOut=bmpOut.To8bppIndexed();你之前將其保存到文件中。

Answer 3

您還可以在創建映像更高的比特率，然後在保存之前將其轉換爲8位。這將允許您在創建圖像時使用Graphics上下文。看到這個問題的建議如何轉換爲8位：C# - How to convert an Image into an 8-bit color Image?