JAI: Tiff b/w to gray

[Akbarr]

I'm using JAI for reading Tiff images: black and white, 1 bit depth. I
want to scale them to reduce their size, but I want to do
antialiasing. If I scale them as they are (using the scale operator)
the images remain b/w and no antialiasing is done (I'm using bilinear
interpolation).

So I'm trying to convert the image to gray before scaling. But an
exception raises when trying to do the ColorConvert operation, because
"the number of bands in the source raster image is different of the
number of components in the source color space" (normal, because it's
an IndexedColorModel).

Anyone can help me?. This is the source code:
MemoryCacheSeekableStream seekStream = new
MemoryCacheSeekableStream (image);
TIFFDecodeParam tiffParam = new TIFFDecodeParam();
img = TIFFDescriptor.create (seekStream, tiffParam, new
Integer(0), null);
byte [] c = new byte[256];
for (int i=0; i<c.length; i++) c[i] = (byte) i;
ColorModel cm = new IndexColorModel (8,256, c,c,c);
img = ColorConvertDescriptor.create (img, cm,
null).getAsBufferedImage();
Thanks in advance,
Andres