iTextSharp.text.pdf.codec.PngImage.DecodePass C# (CSharp) Method

        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.ReadByte();
                    ReadFully(dataStream,curr, 0, bytesPerRow);
                } catch {
                    // 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 Exception(MessageLocalization.GetComposedMessage("png.filter.unknown"));
                }

                ProcessPixels(curr, xOffset, xStep, dstY, passWidth);

                // Swap curr and prior
                byte[] tmp = prior;
                prior = curr;
                curr = tmp;
            }
        }