/// <summary>
/// 将源图像灰度化，但是没有转化为8位灰度图像。
/// http://www.bobpowell.net/grayscale.htm
/// </summary>
/// <param name="original"> 源图像。 </param>
/// <returns> 灰度RGB图像。 </returns>
public static Bitmap MakeGrayScale(Bitmap original)
{
//create a blank bitmap the same size as original
Bitmap newBitmap = new Bitmap(original.Width, original.Height, PixelFormat.Format24bppRgb);
//get a graphics object from the new image
Graphics g = Graphics.FromImage(newBitmap);
//create the grayscale ColorMatrix
ColorMatrix colorMatrix = new ColorMatrix(
new float[][]
{
new float[] { .3f, .3f, .3f, 0, 0 },
new float[] { .59f, .59f, .59f, 0, 0 },
new float[] { .11f, .11f, .11f, 0, 0 },
new float[] { 0, 0, 0, 1, 0 },
new float[] { 0, 0, 0, 0, 1 }
});
/* * * * * * * * * * * * * * * * * * * * * * * * * * * * *
┌ ┐
│ 0.3 0.3 0.3 0 0 │
│ 0.59 0.59 0.59 0 0 │
│ 0.11 0.11 0.11 0 0 │
│ 0 0 0 1 0 │
│ 0 0 0 0 1 │
└ ┘
* * * * * * * * * * * * * * * * * * * * * * * * * * * * */
//create some image attributes
ImageAttributes attributes = new ImageAttributes();
//set the color matrix attribute
attributes.SetColorMatrix(colorMatrix);
//draw the original image on the new image
//using the grayscale color matrix
g.DrawImage(original, new Rectangle(0, 0, original.Width, original.Height),
0, 0, original.Width, original.Height, GraphicsUnit.Pixel, attributes);
//dispose the Graphics object
g.Dispose();
return newBitmap;
}
/// <summary>
/// 将源图像灰度化，并转化为8位灰度图像。
/// </summary>
/// <param name="original"> 源图像。 </param>
/// <returns> 8位灰度图像。 </returns>
public static Bitmap RgbToGrayScale(Bitmap original)
{
if (original != null)
{
// 将源图像内存区域锁定
Rectangle rect = new Rectangle(0, 0, original.Width, original.Height);
BitmapData bmpData = original.LockBits(rect, ImageLockMode.ReadOnly,
original.PixelFormat);
// 获取图像参数
int width = bmpData.Width;
int height = bmpData.Height;
int stride = bmpData.Stride; // 扫描线的宽度
int offset = stride - width * 3; // 显示宽度与扫描线宽度的间隙
IntPtr ptr = bmpData.Scan0; // 获取bmpData的内存起始位置
int scanBytes = stride * height; // 用stride宽度，表示这是内存区域的大小
// 分别设置两个位置指针，指向源数组和目标数组
int posScan = 0, posDst = 0;
byte[] rgbValues = new byte[scanBytes]; // 为目标数组分配内存
Marshal.Copy(ptr, rgbValues, 0, scanBytes); // 将图像数据拷贝到rgbValues中
// 分配灰度数组
byte[] grayValues = new byte[width * height]; // 不含未用空间。
// 计算灰度数组
for (int i = 0; i < height; i++)
{
for (int j = 0; j < width; j++)
{
double temp = rgbValues[posScan++] * 0.11 +
rgbValues[posScan++] * 0.59 +
rgbValues[posScan++] * 0.3;
grayValues[posDst++] = (byte)temp;
}
// 跳过图像数据每行未用空间的字节，length = stride - width * bytePerPixel
posScan += offset;
}
// 内存解锁
Marshal.Copy(rgbValues, 0, ptr, scanBytes);
original.UnlockBits(bmpData); // 解锁内存区域
// 构建8位灰度位图
Bitmap retBitmap = BuiltGrayBitmap(grayValues, width, height);
return retBitmap;
}
else
{
return null;
}
}
/// <summary>
/// 用灰度数组新建一个8位灰度图像。
/// http://www.cnblogs.com/spadeq/archive/2009/03/17/1414428.html
/// </summary>
/// <param name="rawValues"> 灰度数组(length = width * height)。 </param>
/// <param name="width"> 图像宽度。 </param>
/// <param name="height"> 图像高度。 </param>
/// <returns> 新建的8位灰度位图。 </returns>
private static Bitmap BuiltGrayBitmap(byte[] rawValues, int width, int height)
{
// 新建一个8位灰度位图，并锁定内存区域操作
Bitmap bitmap = new Bitmap(width, height, PixelFormat.Format8bppIndexed);
BitmapData bmpData = bitmap.LockBits(new Rectangle(0, 0, width, height),
ImageLockMode.WriteOnly, PixelFormat.Format8bppIndexed);
// 计算图像参数
int offset = bmpData.Stride - bmpData.Width; // 计算每行未用空间字节数
IntPtr ptr = bmpData.Scan0; // 获取首地址
int scanBytes = bmpData.Stride * bmpData.Height; // 图像字节数 = 扫描字节数 * 高度
byte[] grayValues = new byte[scanBytes]; // 为图像数据分配内存
// 为图像数据赋值
int posSrc = 0, posScan = 0; // rawValues和grayValues的索引
for (int i = 0; i < height; i++)
{
for (int j = 0; j < width; j++)
{
grayValues[posScan++] = rawValues[posSrc++];
}
// 跳过图像数据每行未用空间的字节，length = stride - width * bytePerPixel
posScan += offset;
}
// 内存解锁
Marshal.Copy(grayValues, 0, ptr, scanBytes);
bitmap.UnlockBits(bmpData); // 解锁内存区域
// 修改生成位图的索引表，从伪彩修改为灰度
ColorPalette palette;
// 获取一个Format8bppIndexed格式图像的Palette对象
using (Bitmap bmp = new Bitmap(1, 1, PixelFormat.Format8bppIndexed))
{
palette = bmp.Palette;
}
for (int i = 0; i < 256; i++)
{
palette.Entries[i] = Color.FromArgb(i, i, i);
}
// 修改生成位图的索引表
bitmap.Palette = palette;
return bitmap;
}
速度最快
public static unsafe void ConvertTo8BitBitmap(Bitmap img, string destFile)
{
var bit = new Bitmap(img.Width, img.Height, PixelFormat.Format8bppIndexed);
BitmapData data = img.LockBits(new Rectangle(0, 0, img.Width, img.Height), ImageLockMode.ReadOnly,
PixelFormat.Format24bppRgb);
var bp = (byte*)data.Scan0.ToPointer();
BitmapData data2 = bit.LockBits(new Rectangle(0, 0, bit.Width, bit.Height), ImageLockMode.ReadWrite,
PixelFormat.Format8bppIndexed);
var bp2 = (byte*)data2.Scan0.ToPointer();
for (int i = 0; i != data.Height; i++)
{
for (int j = 0; j != data.Width; j++)
{
//0.3R+0.59G+0.11B
float value = 0.11F * bp[i * data.Stride + j * 3] + 0.59F * bp[i * data.Stride + j * 3 + 1] +
0.3F * bp[i * data.Stride + j * 3 + 2];
bp2[i * data2.Stride + j] = (byte)value;
}
}
img.UnlockBits(data);
bit.UnlockBits(data2);
ColorPalette palette = bit.Palette;
for (int i = 0; i != palette.Entries.Length; i++)
{
palette.Entries[i] = Color.FromArgb(i, i, i);
}
bit.Palette = palette;
bit.Save(destFile, ImageFormat.Bmp);
img.Dispose();
bit.Dispose();
}
bp[i * data.Stride + j * 3]
