C# 将 24 位 bmp 转换为 16 位？
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Convert 24-bit bmp to 16-bit?
提问by drowneath
I know that the .NET Framework comes with an image conversion class (the System.Drawing.Image.Save method).
我知道 .NET Framework 带有一个图像转换类（System.Drawing.Image.Save 方法）。
But I need to convert a 24-bit (R8G8B8) bitmap image to a 16-bit (X1R5G5B5) and I really got no idea on this kind of conversion, and a 24-to-16-bit change in the bmp header wouldn't work (since we need to convert the entire image data).
但是我需要将 24 位 (R8G8B8) 位图图像转换为 16 位 (X1R5G5B5) 并且我真的不知道这种转换，并且 bmp 标头中的 24 到 16 位更改不会t 工作（因为我们需要转换整个图像数据）。
Also I would like to know if I can control over the image Dither, etc.
另外我想知道我是否可以控制图像抖动等。
Ideas? Any kind of help would be appreciated.
想法？任何形式的帮助将不胜感激。
采纳答案by Hans Passant
The Format16bppRgb1555 pixel format is declared but GDI+ doesn't actually support it. There is no main-stream video driver or image codec that ever used that pixel format. Something that the GDI+ designers guessed couldhave happened, their time machine wasn't accurate enough. Otherwise a pretty sloppy copy/paste from the programmer that worked on System.Drawing.
Format16bppRgb1555 像素格式已声明，但 GDI+ 实际上并不支持它。没有使用过这种像素格式的主流视频驱动程序或图像编解码器。GDI+ 设计师猜测可能会发生一些事情，他们的时间机器不够准确。否则来自从事 System.Drawing 的程序员的相当草率的复制/粘贴。
Rgb555 is the closest match for available hardware and codecs:
Rgb555 是可用硬件和编解码器最接近的匹配：
public static Bitmap ConvertTo16bpp(Image img) {
var bmp = new Bitmap(img.Width, img.Height,
System.Drawing.Imaging.PixelFormat.Format16bppRgb555);
using (var gr = Graphics.FromImage(bmp))
gr.DrawImage(img, new Rectangle(0, 0, img.Width, img.Height));
return bmp;
}
回答by Dead account
You need to save the bitmap with an Encoderparameter specifying color depth.
您需要使用指定颜色深度的编码器参数保存位图。
myEncoder = Encoder.ColorDepth;
myEncoderParameters = new EncoderParameters(1);
// Save the image with a color depth of 24 bits per pixel.
myEncoderParameter = new EncoderParameter(myEncoder, 24L);
myEncoderParameters.Param[0] = myEncoderParameter;
myBitmap.Save("MyBitmap.bmp", myImageCodecInfo, myEncoderParameters);
回答by Blindy
A really straightforward way to do this is to loop over the old bitmap data and covert every pair of r8-g8-b8 values to x1-r5-g5-b5, something akin to this function:
一个非常直接的方法是循环旧位图数据并将每对 r8-g8-b8 值转换为 x1-r5-g5-b5，类似于此函数：
char condense(char i)
{
return (char)(i*255.0f/31.0f);
}
short transform(long input)// note that the last 8 bytes are ignored
{
return condense(input&0xff) || (condense((input&0xff00)>>8)<<5)
|| (condense((intput&0xff0000)>>16)<<10);
}
// and somewhere in your program
{
int len; // the length of your data in pixels
char *data; // your data
char *newdata; // this is where you store the new data; make sure it's allocated
for(char *p=data; p<data+len*3; p+=3)
*(short *)newdata=transform(*(long *)data);
}
