void decodePass(int xOffset, int yOffset, int xStep, int yStep, int passWidth, int passHeight) { if ((passWidth == 0) || (passHeight == 0)) { return; } int bytesPerRow = (inputBands * passWidth * bitDepth + 7) / 8; byte[] curr = new byte[bytesPerRow]; byte[] prior = new byte[bytesPerRow]; // Decode the (sub)image row-by-row int srcY, dstY; for (srcY = 0, dstY = yOffset; srcY < passHeight; srcY++, dstY += yStep) { // Read the filter type byte and a row of data int filter = 0; try { filter = dataStream.read(); dataStream.readFully(curr, 0, bytesPerRow); } catch (Exception e) { // empty on purpose } switch (filter) { case PNG_FILTER_NONE: break; case PNG_FILTER_SUB: decodeSubFilter(curr, bytesPerRow, bytesPerPixel); break; case PNG_FILTER_UP: decodeUpFilter(curr, prior, bytesPerRow); break; case PNG_FILTER_AVERAGE: decodeAverageFilter(curr, prior, bytesPerRow, bytesPerPixel); break; case PNG_FILTER_PAETH: decodePaethFilter(curr, prior, bytesPerRow, bytesPerPixel); break; default: // Error -- uknown filter type throw new RuntimeException("PNG filter unknown."); } processPixels(curr, xOffset, xStep, dstY, passWidth); // Swap curr and prior byte[] tmp = prior; prior = curr; curr = tmp; } }