protected void computeRect(Raster[] sources,
                               WritableRaster dest,
                               Rectangle destRect) {

        int formatTag = MediaLibAccessor.findCompatibleTag(sources,dest);

        MediaLibAccessor srcAccessor = new MediaLibAccessor(sources[0],
							    destRect,formatTag);
        MediaLibAccessor dstAccessor = new MediaLibAccessor(dest,
							    destRect, formatTag);

        mediaLibImage[] srcML = srcAccessor.getMediaLibImages();
        mediaLibImage[] dstML = dstAccessor.getMediaLibImages();

        switch (dstAccessor.getDataType()) {
        case DataBuffer.TYPE_BYTE:
        case DataBuffer.TYPE_USHORT:
        case DataBuffer.TYPE_SHORT:
        case DataBuffer.TYPE_INT:
            for (int i = 0 ; i < dstML.length; i++) {
                Image.Abs(dstML[i], srcML[i]);
            }
            break;

        case DataBuffer.TYPE_FLOAT:
        case DataBuffer.TYPE_DOUBLE:
            for (int i = 0 ; i < dstML.length; i++) {
                Image.Abs_Fp(dstML[i], srcML[i]);
            }
            break;

        default:
            String className = this.getClass().getName();
            throw new RuntimeException(className + JaiI18N.getString("Generic2"));
        }

        if (dstAccessor.isDataCopy()) {
            dstAccessor.clampDataArrays();
            dstAccessor.copyDataToRaster();
        }
    }