如何使用C＃使用运行长度编码压缩图像？有没有可用的库来支持这个？
运行长度编码是否仅适用于位图图像？如果是这样，我将如何使用C＃将图像类型转换为位图？
我还想问一下，在这之后他们得到的文件类型是什么，他们会保留他们的文件类型还是会有新文件类型？
答案 0 :(得分：1)
我知道这是一个老问题，但它是Google搜索中C＃中RLE压缩的少数几个问题之一。对于像我这样根本没有图像处理经验的人来说，这是一次非常令人沮丧的经历，所以希望这个答案可以为将来的其他人带来痛苦。
我知道RLE是一种过时的压缩形式，但我们中的一些人仍然遇到需要我们使用它的约束（例如将bmp导出到自定义设备）。以下需要8bpp索引位图才能工作。如果您需要帮助将图像转换为该格式，可以在线提供大量资源来帮助您。
我将它放在一个名为BmpCompressor的类中。
private enum Compression
{
// others not necessary for the 8bpp compression, but left for reference
//BI_RGB = 0x0000,
BI_RLE8 = 0x0001,
//BI_RLE4 = 0x0002,
//BI_BITFIELDS = 0x0003,
//BI_JPEG = 0x0004,
//BI_PNG = 0x0005,
//BI_CMYK = 0x000B,
//BI_CMYKRLE8 = 0x000C,
//BI_CMYKRLE4 = 0x000D
}
private enum BitCount
{
// others not necessary for the 8bpp compression, but left for reference
//Undefined = (ushort)0x0000,
//TwoColors = (ushort)0x0001,
//Max16Colors = (ushort)0x0004,
Max256Colors = (ushort)0x0008,
//Max32KBColors = (ushort)0x0010,
//Max16MBColors = (ushort)0x0018,
//Max16MBColors_Compressed = (ushort)0x0020
}
private struct RleCompressedBmpHeader
{
// Everything before the HeaderSize is technically not part of the header (it's not included in the HeaderSize calculation)
/// <summary>
/// Size of the .bmp file.
/// Always header size (40), plus palette size, plus image size, plus pre-header size (14);
/// </summary>
public uint Size;
/// <summary>
/// Offset to start of image data in bytes from the start of the file
/// </summary>
public uint Offset;
/// <summary>
/// Size of this header in bytes. (Always 40)
/// </summary>
public uint HeaderSize; // 4 + 4 + 4 + 2 + 2 + 4 + 4 + 4 + 4 + 4 + 4
/// <summary>
/// Width of bitmap in pixels
/// </summary>
public int Width;
/// <summary>
/// Height of bitmap in pixels
/// </summary>
public int Height;
/// <summary>
/// Number of Planes (layers). Always 1.
/// </summary>
public ushort Planes;
/// <summary>
/// Number of bits that define each pixel and maximum number of colors
/// </summary>
public BitCount BitCount;
/// <summary>
/// Defines the compression mode of the bitmap.
/// </summary>
public Compression Compression;
/// <summary>
/// Size, in bytes, of image.
/// </summary>
public uint ImageSize;
// These shouldn't really be all that important
public uint XPixelsPerMeter;
public uint YPixelsPerMeter;
/// <summary>
/// The number of indexes in the color table used by this bitmap.
/// <para>0 - Use max available</para>
/// <para>If BitCount is less than 16, this is the number of colors used by the bitmap</para>
/// <para>If BitCount is 16 or greater, this specifies the size of the color table used to optimize performance of the system palette.</para>
/// </summary>
public uint ColorUsed;
/// <summary>
/// Number of color indexes that are required for displaying the bitmap. 0 means all color indexes are required.
/// </summary>
public uint ColorImportant;
public byte[] ToBytes()
{
var swap = BitConverter.IsLittleEndian;
var result = new List<byte>();
result.AddRange(new byte[] { 0x42, 0x4d }); // signature (BM)
result.AddRange(BitConverter.GetBytes(Size));
result.AddRange(new byte[4]); // reserved
result.AddRange(BitConverter.GetBytes(Offset));
result.AddRange(BitConverter.GetBytes(HeaderSize));
result.AddRange(BitConverter.GetBytes(Width));
result.AddRange(BitConverter.GetBytes(Height));
result.AddRange(BitConverter.GetBytes(Planes));
result.AddRange(BitConverter.GetBytes((ushort)BitCount));
result.AddRange(BitConverter.GetBytes((uint)Compression));
result.AddRange(BitConverter.GetBytes(ImageSize));
result.AddRange(BitConverter.GetBytes(XPixelsPerMeter));
result.AddRange(BitConverter.GetBytes(YPixelsPerMeter));
result.AddRange(BitConverter.GetBytes(ColorUsed));
result.AddRange(BitConverter.GetBytes(ColorImportant));
return result.ToArray();
}
}
public unsafe byte[] RunLengthEncodeBitmap(Bitmap bmp)
{
if (bmp.PixelFormat != PixelFormat.Format8bppIndexed) { throw new ArgumentException("The image must be in 8bppIndexed PixelFormat", "bmp"); }
var data = bmp.LockBits(new Rectangle(0, 0, bmp.Width, bmp.Height), ImageLockMode.ReadOnly, PixelFormat.Format8bppIndexed);
List<byte> result = new List<byte>();
// Actual RLE algorithm. Bottom of image is first stored row, so start from bottom.
for (var rowIndex = bmp.Height - 1; rowIndex >= 0; rowIndex--)
{
byte? storedPixel = null;
var curPixelRepititions = 0;
var imageRow = (byte*)data.Scan0.ToPointer() + (rowIndex * data.Stride);
for (var pixelIndex = 0; pixelIndex < bmp.Width; pixelIndex++)
{
var curPixel = imageRow[pixelIndex];
if (!storedPixel.HasValue)
{
curPixelRepititions = 1;
storedPixel = curPixel;
}
else if (storedPixel.Value != curPixel || curPixelRepititions == 255)
{
result.Add(Convert.ToByte(curPixelRepititions));
result.Add(storedPixel.Value);
curPixelRepititions = 1;
storedPixel = curPixel;
}
else
{
curPixelRepititions++;
}
}
if (curPixelRepititions > 0)
{
result.Add(Convert.ToByte(curPixelRepititions));
result.Add(storedPixel.Value);
}
if (rowIndex == 0)
{
// EOF flag
result.Add(0x00);
result.Add(0x01);
}
else
{
// End of Line Flag
result.Add(0x00);
result.Add(0x00);
}
}
bmp.UnlockBits(data);
var paletteSize = (uint)bmp.Palette.Entries.Length * 4;
var header = new RleCompressedBmpHeader();
header.HeaderSize = 40;
header.Size = header.HeaderSize + paletteSize + (uint)result.Count + 14;
header.Offset = header.HeaderSize + 14 + paletteSize; // total header size + palette size
header.Width = bmp.Width;
header.Height = bmp.Height;
header.Planes = 1;
header.BitCount = BitCount.Max256Colors;
// as far as I can tell, PixelsPerMeter are not terribly important
header.XPixelsPerMeter = 0x10000000;
header.YPixelsPerMeter = 0x10000000;
header.Compression = Compression.BI_RLE8;
header.ColorUsed = 256;
header.ColorImportant = 0; // use all available colors
header.ImageSize = header.HeaderSize + (uint)result.Count;
var headerBytes = header.ToBytes();
var paletteBytes = ConvertPaletteToBytes(bmp.Palette);
return headerBytes.Concat(paletteBytes).Concat(result).ToArray();
}
private byte[] ConvertPaletteToBytes(ColorPalette colorPalette)
{
return colorPalette.Entries.SelectMany(c => new byte[]
{
c.B,
c.G,
c.R,
0
}).ToArray();
}
希望这有帮助！
答案 1 :(得分：0)
如果环顾四周，你会发现很多资源......
Run length encoding可以处理字符串形式的任何类型的数据。
但这是Rosetta Code的一个例子：
public static void Main(string[] args)
{
string input = "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW";
Console.WriteLine(Encode(input));//Outputs: 12W1B12W3B24W1B14W
Console.WriteLine(Decode(Encode(input)));//Outputs: WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
Console.ReadLine();
}
public static string Encode(string s)
{
StringBuilder sb = new StringBuilder();
int count = 1;
char current =s[0];
for(int i = 1; i < s.Length;i++)
{
if (current == s[i])
{
count++;
}
else
{
sb.AppendFormat("{0}{1}", count, current);
count = 1;
current = s[i];
}
}
sb.AppendFormat("{0}{1}", count, current);
return sb.ToString();
}
public static string Decode(string s)
{
string a = "";
int count = 0;
StringBuilder sb = new StringBuilder();
char current = char.MinValue;
for(int i = 0; i < s.Length; i++)
{
current = s[i];
if (char.IsDigit(current))
a += current;
else
{
count = int.Parse(a);
a = "";
for (int j = 0; j < count; j++)
sb.Append(current);
}
}
return sb.ToString();
}
你必须满足你的需要，但它应该让你开始。
答案 2 :(得分：-2)
为了压缩图像，我写了一些函数： 这将调整宽度并根据纵横比确定高度。请注意，如果图像的原始宽度小于新宽度，则图像的大小不会（您可以在代码中更改它）。
public Bitmap ResizedImage(Stream imageStream, int newWidth)
{
Image image = Image.FromStream(imageStream);
int newwidthimg = image.Size.Width;
int newheightimg = image.Size.Height;
if (newWidth <= image.Size.Width)
{
newwidthimg = newWidth;
float AspectRatio = (float)image.Size.Width / (float)image.Size.Height;
newheightimg = Convert.ToInt32(newwidthimg / AspectRatio);
}
Bitmap thumbnailBitmap = new Bitmap(newwidthimg, newheightimg);
using (Graphics thumbnailGraph = Graphics.FromImage(thumbnailBitmap))
{
thumbnailGraph.CompositingQuality = CompositingQuality.HighQuality;
thumbnailGraph.SmoothingMode = SmoothingMode.HighQuality;
thumbnailGraph.InterpolationMode = InterpolationMode.HighQualityBicubic;
var imageRectangle = new Rectangle(0, 0, newwidthimg, newheightimg);
thumbnailGraph.DrawImage(image, imageRectangle);
}
return thumbnailBitmap;