at the source

at first you should create ColorMdel:

byte[] r = new byte[256];
for (int i = 0; i < r.length; i++) {
   r[i] = (byte) i;
}
ColorModel icm = new IndexColorModel(8, 256, r, r, r);

there many ways to create (Buffered)Image:

first way:
^^^^^^
Before you can use DataBuffer you should copy all data to one array.

then create DataBufferByte:
DataBuffer buffer = new DataBufferByte(dataArray, dataArray.length, 0);

create Raster:

WritableRaster wr = Raster.createBandedRaster(buffer, width, height, width,
new int[] {0}, new int [] {0}, new Point(0,0));

create BufferedImage:

BufferedImage bi = new BufferedImage(icm, wr, false, new Hashtable());

second way (better):
^^^^^^^^^

create BufferedImage:
BufferedImage bi = new BufferedImage(width, height, TYPE_BYTE_INDEXED, icm);

I assume that your data is in 2D byte array:
byte [][] data = new byte[height][width];

then create int array to hold temporary data:
int [] buf = new int[width];

transfer your data into BufferedImage:

for(int i = 0; i < height; i++) {
   //create ABGR pixel array
   for(int j = 0; j < width; j++) {
       int a = data[i][j] & 0xFF;
       buf[j] = (0xFF << 24) | (a << 16) | (a << 8) || a;
   }
   //set pixels
   bi.setRGB(0, j, width, 1, buf, 0, width);
}

you are welcome