请问怎样把 byte[ ]转换为 Bitmap对象?

[atlone]

以下是把bitmap b转换为byte[]然后传输出去的,现在我想把byte[] bytes转换回Bitmap对象,请问怎样实现? 谢谢.

MemoryStream ms = new MemoryStream();
b.Save(ms ,System.Drawing.Imaging.ImageFormat.Gif);
byte[] bytes= ms.GetBuffer();

[atlone]

saucer(思归),谢谢你,你的方法是可以转换,但转换后,Bitmap的size 增大了一倍有多,例如以下:没转换前得到的dd3.jpg是60k, 但是dd4.jpg就变成了130k,而且图像质量也比dd3.jpg差,请问为什么?

MemoryStream ms = new MemoryStream();
b.Save(ms ,System.Drawing.Imaging.ImageFormat.Gif);
byte[] bytes= ms.GetBuffer();

b.Save("c:\\dd3.jpg");

byte[] bytelist=bytes;
MemoryStream ms1 = new MemoryStream(bytelist);
Bitmap bm = (Bitmap)Image.FromStream(ms1);

bm.Save("c:\\dd4.jpg");

[saucer]

b.Save(ms ,System.Drawing.Imaging.ImageFormat.Gif);???

[atlone]

我把b.Save(ms ,System.Drawing.Imaging.ImageFormat.Gif)改成是

b.Save(ms ,System.Drawing.Imaging.ImageFormat.Jpeg),或者

把b.Save("c:\\dd3.jpg");bm.Save("c:\\dd4.jpg");里面的jpg改成Gif,结果还是一样:(

[saucer]

I cannot reproduce your problems


string sFile = "test.jpg";
Image img = Image.FromFile(sFile);

MemoryStream ms = new MemoryStream();
img.Save(ms ,System.Drawing.Imaging.ImageFormat.Jpeg);
byte[] bytes= ms.GetBuffer();
//Console.WriteLine(bytes.Length);

byte[] bytelist=bytes;
MemoryStream ms1 = new MemoryStream(bytelist);
Bitmap bm = (Bitmap)Image.FromStream(ms1);

bm.Save("test3.jpg");

test3.jpg and test.jpg are identical

[atlone]

我试过你上面的例子,test3.jpg 也是比test.jpg 增大了一倍有多:)

[saucer]

I am using .NET 1.1 with vs.net 2003, what are you using?

string sFile = "test.jpg";
Image img = Image.FromFile(sFile);

MemoryStream ms = new MemoryStream();
img.Save(ms ,System.Drawing.Imaging.ImageFormat.Jpeg);
ms.Position = 0;
byte[] bytes= ms.GetBuffer();
//Console.WriteLine(bytes.Length);

byte[] bytelist=bytes;
MemoryStream ms1 = new MemoryStream(bytelist);
ms1.Position = 0;
Bitmap bm = (Bitmap)Image.FromStream(ms1);

bm.Save("test5.jpg",System.Drawing.Imaging.ImageFormat.Jpeg);

[xixigongzhu]

斑竹，如果你用了MemoryStream，就不能说效果差不多。因为我用java重新开发了MemoryStream这个类，所以象这样的并且应该注意的问题基本上都很清楚，其中GetBuffer就是，有很多人认为用这个方法就是得到写入MemoryStream的字节，其实不是这样的。因为MemoryStream是用byte[]来存储数据，在写入数据的时候就有个扩充的过程，也就是说这个流的长度并不是它的byte[]字段的长度。而GetBuffer返回的就是byte[]这个字段。
下面是GetBuffer的部分实现方法，也许看了这个会更明白：
public byte[] GetBuffer() {
return this._buffer;
}
下面是ToArray的实现方法：
public byte[] ToArray() {
byte[] bs = new byte[this._length - this._origin];
for (int i = this._origin, j = 0; i < this._length; i++)
bs[j++] = this._buffer[i];
return bs;
}

我写这么多并不是想证明什么，只是觉得如果不说明白，斑竹总有一天会走入这个误区。:)

[atlone]

我的也是vs.net2003 with 1.1 in win2003,你上面那例子是没问题,虽然变换前后的size还有些许不同. 但我的Bitmap b是直接从Graphic处来的,所以经过以下改变后,还是一样,不过好象变换后的size不是多一倍了,只是多1/2,真奇怪啊.

Bitmap b=new Bitmap(800,600);
Graphics graphics = Graphics.FromImage(b);

IntPtr hDCPanel = graphics.GetHdc();
IntPtr hDCDesktop = Win32.GetDC(hWndDesktop);

Win32.StretchBlt(hDCPanel, 0, 0, 800, 600,
hDCDesktop, 0, 0,800 / zoomRate, 600 / zoomRate,Win32.SRCCOPY);

graphics.ReleaseHdc(hDCPanel);
Win32.ReleaseDC(hWndDesktop, hDCDesktop);

MemoryStream ms = new MemoryStream();
ms.Position = 0;
b.Save(ms ,System.Drawing.Imaging.ImageFormat.Jpeg);
byte[] bytes= ms.GetBuffer();

b.Save("c:\\dd3.jpg");

byte[] bytelist=bytes;
MemoryStream ms1 = new MemoryStream(bytelist);
ms1.Position = 0;
Bitmap bm = (Bitmap)Image.FromStream(ms1);

bm.Save("c:\\dd4.jpg",System.Drawing.Imaging.ImageFormat.Jpeg);

是不是因为Bitmap和Image的区别所造成的?

[atlone]

因为我是直接从屏幕截图,而且所截的图随着mouse移动而改变,dd3.jpg和dd4.jpg有时候只是相差几k,但有时候就相差一半,但经过你的修改后,基本没有相差一倍的出现了.

[saucer]

b.Save(ms ,System.Drawing.Imaging.ImageFormat.Jpeg);
byte[] bytes= ms.GetBuffer();
b.Save("c:\\dd3.jpg", System.Drawing.Imaging.ImageFormat.Jpeg);

or try to save it as System.Drawing.Imaging.ImageFormat.Bmp

[atlone]

sorry,还是不行,调换了顺序后就出错,改成Bmp后,dd3.bmp的size相比于原来的jpeg format好象还少了,但dd4.bmp或dd4.jpg就不得了了,竟然是dd3.bmp的30倍.

[saucer]

look at your code, the first time you were doing

b.Save("c:\\dd3.jpg");

the second time, you were doing

bm.Save("c:\\dd4.jpg",System.Drawing.Imaging.ImageFormat.Jpeg);

[atlone]

如果把b.Save("c:\\dd3.jpg");改成

b.Save("c:\\dd3.jpg",System.Drawing.Imaging.ImageFormat.Jpeg);

那样dd3.jpg就和dd4.jpg一样大了,但那是dd3.jpg的size变大,所以我还是选b.Save("c:\\dd3.jpg");

但是在dd4.jpg部分,如果改成是b.Save("c:\\dd4.jpg");dd4.jpg的size还是和没改一样的.

[atlone]

我把Bitmap bm = (Bitmap)Image.FromStream(ms1);改成:

Bitmap bm = (Bitmap)Bitmap.FromStream(ms1);

那样有时候dd4.jpg就比dd3.jpg小了,真是奇怪啊.

[saucer]

you missed the point, with

Bitmap b=new Bitmap(800,600);

the pixelformat is Format32bppARGB, when you call

b.Save("c:\\dd3.jpg");

it is saved as the ImageFormat.Bmp even if you specified ".jpg"

if you want to compare, you need to make them have same format

[atlone]

yes,you are right,temporary i found the code below can give me the smallest size for dd4.

MemoryStream ms = new MemoryStream();
ms.Position = 0;
b.Save(ms ,System.Drawing.Imaging.ImageFormat.Jpeg);
byte[] bytes= ms.GetBuffer();

b.Save("c:\\dd3.bmp");

byte[] bytelist=bytes;
MemoryStream ms1 = new MemoryStream(bytelist);
ms1.Position = 0;
Bitmap bm = (Bitmap)Bitmap.FromStream(ms1);

bm.Save("c:\\dd4.bmp", System.Drawing.Imaging.ImageFormat.Jpeg);

wishing these is another better way,anyway,thank you very much.

[xixigongzhu]

Bitmap b = new Bitmap("test.bmp");
MemoryStream ms = new MemoryStream();
b.Save(ms,System.Drawing.Imaging.ImageFormat.Bmp);
byte[] bytes= ms.ToArray();

b.Save("c:\\dd3.jpg");

byte[] bytelist=bytes;
MemoryStream ms1 = new MemoryStream(bytelist);
Bitmap bm = (Bitmap)Image.FromStream(ms1);

bm.Save("c:\\dd4.jpg");

1、因为如果不用Bmp的方式转换字节的话，在转换到字节的时候将会丢失数据；
2、MemoryStream的GetBuffer并不是得到这个流所存储的内容，而是返回这个流的基础字节数组，可能包括在扩充的时候一些没有使用到的字节。

[saucer]

do the reverse

byte[] bytelist;
MemoryStream ms = new MemoryStream(bytelist);
Bitmap bm = (Bitmap)Image.FromStream(ms);

[atlone]

xixigongzhu(夕夕公主),谢谢你,你的方法也可以,效果差不多:)