private byte[] extractOverlay(int gg0000, WritableRaster raster) {
Attributes attrs = metadata.getAttributes();
if (attrs.getInt(Tag.OverlayBitsAllocated | gg0000, 1) == 1) return null;
int ovlyRows = attrs.getInt(Tag.OverlayRows | gg0000, 0);
int ovlyColumns = attrs.getInt(Tag.OverlayColumns | gg0000, 0);
int bitPosition = attrs.getInt(Tag.OverlayBitPosition | gg0000, 0);
int mask = 1 << bitPosition;
int length = ovlyRows * ovlyColumns;
byte[] ovlyData = new byte[(((length + 7) >>> 3) + 1) & (~1)];
Overlays.extractFromPixeldata(raster, mask, ovlyData, 0, length);
return ovlyData;
}
