亮/暗/透明部分的图像

我正在将图像加载到BitmapImage中并将其转换为PixelColor的数组。我想要的是能够操纵这些像素中的一些，使它们更亮/更暗/透明，但我似乎不能让它工作。它可以将其设置为特定的颜色，但alpha通道被忽略。

这是一个使用c# 4的WPF应用程序

谢谢!
代码…

namespace BitmapTest {
using System;
using System.Drawing;
using System.Runtime.InteropServices;
using System.Windows;
using System.Windows.Interop;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using Image = System.Windows.Controls.Image;
public partial class MainWindow {
    public MainWindow() {
        InitializeComponent();
        LoadImage();
    }
    [DllImport("gdi32")]
    private static extern int DeleteObject(IntPtr o);
    public static BitmapSource LoadBitmap(Bitmap source) {
        var ip = source.GetHbitmap();
        try {
            return Imaging.CreateBitmapSourceFromHBitmap(ip,
                                                         IntPtr.Zero, Int32Rect.Empty,
                                                         BitmapSizeOptions.FromEmptyOptions());
        } finally {
            DeleteObject(ip);
        }
    }
    private void LoadImage() {
        var i = new Image();
        var src = new BitmapImage();
        src.BeginInit();
        src.UriSource = new Uri("road.jpg", UriKind.Relative);
        src.CacheOption = BitmapCacheOption.OnLoad;
        src.EndInit();
        var pixels = GetPixels(src);
        for (var x = 0; x < Math.Min(50, pixels.GetLength(0)); x++) {
            for (var y = 0; y < Math.Min(50, pixels.GetLength(1)); y++) {
                pixels[x, y] = new PixelColor {Alpha = 100, Red = pixels[x, y].Red, Green = pixels[x, y].Green, Blue = pixels[x, y].Blue};
            }
        }
        var bitmap = new WriteableBitmap(src.PixelWidth, src.PixelHeight, src.DpiX, src.DpiY, src.Format, src.Palette);
        PutPixels(bitmap, pixels, 0, 0);
        i.Source = bitmap;
        i.Stretch = Stretch.Fill;
        RootGrid.Children.Add(i);
    }
    public PixelColor[,] GetPixels(BitmapSource source) {
        if (source.Format != PixelFormats.Bgra32)
            source = new FormatConvertedBitmap(source, PixelFormats.Bgra32, null, 0);
        var pixels = source.CopyPixels();
        return pixels;
    }
    public void PutPixels(WriteableBitmap bitmap, PixelColor[,] pixels, int x, int y) {
        var width = pixels.GetLength(0);
        var height = pixels.GetLength(1);
        var sourceRect = new Int32Rect(0, 0, width, height);
        bitmap.WritePixels(sourceRect, pixels, width*4, x, y);
    }
    [StructLayout(LayoutKind.Sequential)]
    public struct PixelColor {
        public byte Blue;
        public byte Green;
        public byte Red;
        public byte Alpha;
    }
}

public static class BitmapSourceHelper {
    public static MainWindow.PixelColor[,] CopyPixels(this BitmapSource source) {
        if (source.Format != PixelFormats.Bgra32)
            source = new FormatConvertedBitmap(source, PixelFormats.Bgra32, null, 0);
        var pixels = new MainWindow.PixelColor[source.PixelWidth, source.PixelHeight];
        var stride = source.PixelWidth * ((source.Format.BitsPerPixel + 7) / 8);
        var pinnedPixels = GCHandle.Alloc(pixels, GCHandleType.Pinned);
        source.CopyPixels(
            new Int32Rect(0, 0, source.PixelWidth, source.PixelHeight),
            pinnedPixels.AddrOfPinnedObject(),
            pixels.GetLength(0) * pixels.GetLength(1) * 4,
            stride);
        pinnedPixels.Free();
        return pixels;
    }
}
}

    public Bitmap Lighten(Bitmap bitmap, int amount)
{
  if (amount < -255 || amount > 255)
    return bitmap;
  // GDI+ still lies to us - the return format is BGR, NOT RGB.
  BitmapData bmData = bitmap.LockBits(new Rectangle(0, 0, bitmap.Width, bitmap.Height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);
  int stride = bmData.Stride;
  System.IntPtr Scan0 = bmData.Scan0;
  int nVal = 0;
  unsafe
  {
    byte* p = (byte*)(void*)Scan0;
    int nOffset = stride - bitmap.Width * 3;
    int nWidth = bitmap.Width * 3;
    for (int y = 0; y < bitmap.Height; ++y)
    {
      for (int x = 0; x < nWidth; ++x)
      {
        nVal = (int)(p[0] + amount);
        if (nVal < 0) nVal = 0;
        if (nVal > 255) nVal = 255;
        p[0] = (byte)nVal;
        ++p;
      }
      p += nOffset;
    }
  }
  bitmap.UnlockBits(bmData);
  return bitmap;
}
private void btnLighten_Click(object sender, EventArgs e)
{
  Bitmap image = pictureBox1.Image as Bitmap;
  pictureBox1.Image = Lighten(image, 10);
}
private void btnDarken_Click(object sender, EventArgs e)
{
  Bitmap image = pictureBox1.Image as Bitmap;
  pictureBox1.Image = Lighten(image, -10);
}

Bitmap clonedImage = originalImage.Clone(rect, originalImage.PixelFormat);
float gamma = 1.0f; // no change in gamma
float adjustedBrightness = brightness - 1.0f;
// create matrix that will brighten and contrast the image
float[][] ptsArray ={
        new float[] {contrast, 0, 0, 0, 0}, // scale red
        new float[] {0, contrast, 0, 0, 0}, // scale green
        new float[] {0, 0, contrast, 0, 0}, // scale blue
        new float[] {0, 0, 0, alpha, 0},
        new float[] {adjustedBrightness, adjustedBrightness, adjustedBrightness, 0, 1}};
var imageAttributes = new ImageAttributes();
imageAttributes.ClearColorMatrix();
imageAttributes.SetColorMatrix(new ColorMatrix(ptsArray), ColorMatrixFlag.Default, ColorAdjustType.Bitmap);
imageAttributes.SetGamma(gamma, ColorAdjustType.Bitmap);
// Copy back to the original image from the cloned image
Graphics g = Graphics.FromImage(originalImage);
g.DrawImage(clonedImage, new Rectangle(0, 0, clonedImage.Width, clonedImage.Height)
    , rect.left, rect.top, rect.Width, rect.Height,
    GraphicsUnit.Pixel, imageAttributes);
g.Flush();