如何降低圖像亮度？

Question

我需要使用c＃降低圖片的亮度。經過一些分析，我發現了一種解決方案，通過調整其每個像素顏色的RGB值來降低圖像的亮度。請從下面找到代碼：

 Bitmap bmp = new Bitmap(Picture); 
     Reduce the picture color brightness 
     for (int i = 0; i < bmp.Width; i++) 
     { 
      for (int j = 0; j < bmp.Height; j++) 
      { 
       Color color = bmp.GetPixel(i, j); 
       color = ChangeColorBrightness(color, 0.80f); 
       bmp.SetPixel(i, j, color); 
      } 
     } 

方法，以減少特定顏色的RGB值：

private Color ChangeColorBrightness(Color color, float correctionFactor) 
    { 
     float red = (float)color.R; 
     float green = (float)color.G; 
     float blue = (float)color.B; 

     if (correctionFactor < 0) 
     { 
      correctionFactor = 1 + correctionFactor; 
      red *= correctionFactor; 
      green *= correctionFactor; 
      blue *= correctionFactor; 
     } 
     else 
     { 
      red = (255 - red) * correctionFactor + red; 
      green = (255 - green) * correctionFactor + green; 
      blue = (255 - blue) * correctionFactor + blue; 
     } 

     return Color.FromArgb(color.A, (int)red, (int)green, (int)blue); 
    } 

此代碼對我的要求，工作正常，但它會花費這樣的時間量當我執行大量寬度和高度較大的圖像。 有沒有其他的可能性來達到這個要求？

Answer 1

.GetPixel()和.SetPixel()是昂貴的 - 這裏是一個更快appraoch

public static Bitmap ChangeColorBrightness(Bitmap bmp, float correctionFactor) 
{ 
    Rectangle rect = new Rectangle(0, 0, bmp.Width, bmp.Height); 
    System.Drawing.Imaging.BitmapData bmpData = bmp.LockBits(rect, System.Drawing.Imaging.ImageLockMode.ReadWrite, bmp.PixelFormat); 
    IntPtr ptr = bmpData.Scan0; 
    int bytes = Math.Abs(bmpData.Stride) * bmp.Height; 
    byte[] rgbValues = new byte[bytes]; 
    System.Runtime.InteropServices.Marshal.Copy(ptr, rgbValues, 0, bytes); 
    float correctionFactortemp = correctionFactor; 
    if (correctionFactor < 0) 
    { 
     correctionFactortemp = 1 + correctionFactor; 
    } 
    for (int counter = 1; counter < rgbValues.Length; counter ++) 
    { 
     float color = (float)rgbValues[counter]; 
     if (correctionFactor < 0) 
     { 
      color *= (int)correctionFactortemp; 
     } 
     else 
     { 
      color = (255 - color) * correctionFactor + color;     
     } 
     rgbValues[counter] = (byte)color;   
    } 
    System.Runtime.InteropServices.Marshal.Copy(rgbValues, 0, ptr, bytes); 
    bmp.UnlockBits(bmpData); 
    return bmp; 
}