Windows DIB(設備獨立的位圖)文件格式比較簡單。與純位圖格式不同,DIB 格式保留着用於在內存中存儲圖像的明確信息。問題是圖像格式的變體如此之多(1 位、4 位、8 位和 16 位,以及其他格式)。本篇 Java 技巧中提供的解決方案只處理 8 位和 24 位兩種格式。這兩種格式代表了最常見的變體。
loadbitmap() 方法由 Windows C 代碼轉換而來。
只能讀取未壓縮的 24 位和 8 位圖像。已在
Windows 95 上用 Microsoft Paint 保存的圖像
對它進行了測試。如果圖像不是 24 位或 8 位圖像,
該程序拒絕進行任何嘗試。我猜測如果先用 1100,
然後用 0011 對字節執行掩碼操作,則也可將 4 位
圖像包括在內。我實際上對這些圖像不感興趣。
如果嘗試讀取壓縮圖像,該例程可能失敗,併產生
一個 IOException 異常。如果變量 ncompression
不爲 0,則表示已經過壓縮。
sdir 和 sfile 是 FileDialog 的
getDirectory() 和 getFile() 方法的結果。
Image 對象,切記要檢查 (Image)null !!!!
public Image loadbitmap (String sdir, String sfile)
{
Image image;
System.out.println("loading:"+sdir+sfile);
try
{
FileInputStream fs=new FileInputStream(sdir+sfile);
int bflen=14; // 14 字節 BITMAPFILEHEADER
byte bf[]=new byte[bflen];
fs.read(bf,0,bflen);
int bilen=40; // 40 字節 BITMAPINFOHEADER
byte bi[]=new byte[bilen];
fs.read(bi,0,bilen);
int nsize = (((int)bf[5]&0xff)<<24)
| (((int)bf[4]&0xff)<<16)
| (((int)bf[3]&0xff)<<8)
| (int)bf[2]&0xff;
System.out.println("File type is :"+(char)bf[0]+(char)bf[1]);
System.out.println("Size of file is :"+nsize);
| (((int)bi[2]&0xff)<<16)
| (((int)bi[1]&0xff)<<8)
| (int)bi[0]&0xff;
System.out.println("Size of bitmapinfoheader is :"+nbisize);
| (((int)bi[6]&0xff)<<16)
| (((int)bi[5]&0xff)<<8)
| (int)bi[4]&0xff;
System.out.println("Width is :"+nwidth);
| (((int)bi[10]&0xff)<<16)
| (((int)bi[9]&0xff)<<8)
| (int)bi[8]&0xff;
System.out.println("Height is :"+nheight);
System.out.println("Planes is :"+nplanes);
System.out.println("BitCount is :"+nbitcount);
int ncompression = (((int)bi[19])<<24)
| (((int)bi[18])<<16)
| (((int)bi[17])<<8)
| (int)bi[16];
System.out.println("Compression is :"+ncompression);
| (((int)bi[22]&0xff)<<16)
| (((int)bi[21]&0xff)<<8)
| (int)bi[20]&0xff;
System.out.println("SizeImage is :"+nsizeimage);
| (((int)bi[26]&0xff)<<16)
| (((int)bi[25]&0xff)<<8)
| (int)bi[24]&0xff;
System.out.println("X-Pixels per meter is :"+nxpm);
| (((int)bi[30]&0xff)<<16)
| (((int)bi[29]&0xff)<<8)
| (int)bi[28]&0xff;
System.out.println("Y-Pixels per meter is :"+nypm);
| (((int)bi[34]&0xff)<<16)
| (((int)bi[33]&0xff)<<8)
| (int)bi[32]&0xff;
System.out.println("Colors used are :"+nclrused);
| (((int)bi[38]&0xff)<<16)
| (((int)bi[37]&0xff)<<8)
| (int)bi[36]&0xff;
System.out.println("Colors important are :"+nclrimp);
{
// 24 位格式不包含調色板數據,但掃描行被補足到
// 4 個字節。
int npad = (nsizeimage / nheight) - nwidth * 3;
int ndata[] = new int [nheight * nwidth];
byte brgb[] = new byte [( nwidth + npad) * 3 * nheight];
fs.read (brgb, 0, (nwidth + npad) * 3 * nheight);
int nindex = 0;
for (int j = 0; j < nheight; j++)
{
for (int i = 0; i < nwidth; i++)
{
ndata [nwidth * (nheight - j - 1) + i] =
(255&0xff)<<24
| (((int)brgb[nindex+2]&0xff)<<16)
| (((int)brgb[nindex+1]&0xff)<<8)
| (int)brgb[nindex]&0xff;
// System.out.println("Encoded Color at ("
+i+","+j+")is:"+nrgb+" (R,G,B)= ("
+((int)(brgb[2]) & 0xff)+","
+((int)brgb[1]&0xff)+","
+((int)brgb[0]&0xff)+")");
nindex += 3;
}
nindex += npad;
}
( new MemoryImageSource (nwidth, nheight,
ndata, 0, nwidth));
}
else if (nbitcount == 8)
{
// 必須確定顏色數。如果 clrsused 參數大於 0,
// 則顏色數由它決定。如果它等於 0,則根據
// bitsperpixel 計算顏色數。
int nNumColors = 0;
if (nclrused > 0)
{
nNumColors = nclrused;
}
else
{
nNumColors = (1&0xff)<<nbitcount;
}
System.out.println("The number of Colors is"+nNumColors);
// 這些情況並對它們進行修正。
if (nsizeimage == 0)
{
nsizeimage = ((((nwidth*nbitcount)+31) & ~31 ) >> 3);
nsizeimage *= nheight;
System.out.println("nsizeimage (backup) is"+nsizeimage);
}
int npalette[] = new int [nNumColors];
byte bpalette[] = new byte [nNumColors*4];
fs.read (bpalette, 0, nNumColors*4);
int nindex8 = 0;
for (int n = 0; n < nNumColors; n++)
{
npalette[n] = (255&0xff)<<24
| (((int)bpalette[nindex8+2]&0xff)<<16)
| (((int)bpalette[nindex8+1]&0xff)<<8)
| (int)bpalette[nindex8]&0xff;
// System.out.println ("Palette Color "+n
+" is:"+npalette[n]+" (res,R,G,B)= ("
+((int)(bpalette[nindex8+3]) & 0xff)+","
+((int)(bpalette[nindex8+2]) & 0xff)+","
+((int)bpalette[nindex8+1]&0xff)+","
+((int)bpalette[nindex8]&0xff)+")");
nindex8 += 4;
}
// 掃描行仍被補足到 4 個字節。
int npad8 = (nsizeimage / nheight) - nwidth;
System.out.println("nPad is:"+npad8);
byte bdata[] = new byte [(nwidth+npad8)*nheight];
fs.read (bdata, 0, (nwidth+npad8)*nheight);
nindex8 = 0;
for (int j8 = 0; j8 < nheight; j8++)
{
for (int i8 = 0; i8 < nwidth; i8++)
{
ndata8 [nwidth*(nheight-j8-1)+i8] =
npalette [((int)bdata[nindex8]&0xff)];
nindex8++;
}
nindex8 += npad8;
}
( new MemoryImageSource (nwidth, nheight,
ndata8, 0, nwidth));
}
else
{
System.out.println ("Not a 24-bit or 8-bit Windows Bitmap, aborting...");
image = (Image)null;
}
return image;
}
catch (Exception e)
{
System.out.println("Caught exception in loadbitmap!");
}
return (Image) null;
}
您已掌握了讀取位圖文件的技巧。很容易對此方法進行擴展,使它能夠讀取單色和 16 色(4 位)格式。