如何降低图像亮度？ [复制]

Question

我需要使用 c# 降低图片的亮度。经过一些分析，我找到了一种通过调整其每个像素颜色 RGB 值来降低图像亮度的解决方案。请从下面找到代码：

        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);
            }
        }

降低特定颜色RGB值的方法：

    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);
    }

这些代码可以很好地满足我的要求，但是当我执行大量具有更大宽度和高度的图像时，它会花费大量时间。 是否有其他可能实现这一要求？

Answer 1

.GetPixel() 和 .SetPixel() 很昂贵 - 这里有一个更快的方法

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;
}