question: public WritableRaster decode ( RenderedImage img , Rectangle newRect , byte [ ] bpixels ) { if ( image == null ) { setupSourceImage ( img ) ; } setupBufferForDecoding ( ) ; unitsInThisTile = newRect . width * newRect . height * numBands ; decodeTilePixels ( bpixels , newRect ) ; decodeColor ( newRect ) ; return setTilePixels ( newRect ) ; }
target:  Decode a rectangle of data stored in bpixels into a raster tile. Usually you will not need to override this, but instead implement the decodeTilePixels methods.