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https://github.com/JakubMelka/PDF4QT.git
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CCITT fax decoder - second part
This commit is contained in:
Jakub Melka
@ -17,6 +17,7 @@
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#include "pdfccittfaxdecoder.h"
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#include "pdfexception.h"
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namespace pdf
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{
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@ -27,6 +28,42 @@ constexpr uint8_t operator "" _bitlength()
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return sizeof...(Digits);
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}
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enum CCITT_2D_Code_Mode
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{
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Pass,
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Horizontal,
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Vertical_3L,
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Vertical_2L,
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Vertical_1L,
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Vertical_0,
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Vertical_1R,
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Vertical_2R,
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Vertical_3R,
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Invalid
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};
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struct PDFCCITT2DModeInfo
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{
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CCITT_2D_Code_Mode mode;
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uint16_t code;
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uint8_t bits;
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};
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static constexpr uint8_t MAX_2D_MODE_BIT_LENGTH = 7;
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static constexpr PDFCCITT2DModeInfo CCITT_2D_CODE_MODES[] =
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{
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{ Pass, 0b0001, 0001_bitlength },
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{ Horizontal, 0b001, 001_bitlength },
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{ Vertical_3L, 0b0000010, 0000010_bitlength },
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{ Vertical_2L, 0b000010, 000010_bitlength },
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{ Vertical_1L, 0b010, 010_bitlength },
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{ Vertical_0, 0b1, 1_bitlength },
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{ Vertical_1R, 0b011, 011_bitlength },
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{ Vertical_2R, 0b000011, 000011_bitlength },
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{ Vertical_3R, 0b0000011, 0000011_bitlength }
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};
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struct PDFCCITTCode
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{
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uint16_t length;
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@ -260,12 +297,224 @@ static constexpr PDFCCITTCode CCITT_BLACK_CODES[] = {
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{ 2560, 0b000000011111, 000000011111_bitlength }
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};
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PDFCCITTFaxDecoder::PDFCCITTFaxDecoder(const QByteArray* stream) :
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m_reader(stream, 1)
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PDFCCITTFaxDecoder::PDFCCITTFaxDecoder(const QByteArray* stream, const PDFCCITTFaxDecoderParameters& parameters) :
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m_reader(stream, 1),
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m_parameters(parameters)
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{
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}
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PDFImageData PDFCCITTFaxDecoder::decode()
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{
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PDFBitWriter writer(1);
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std::vector<int> codingLine;
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std::vector<int> referenceLine;
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int row = 0;
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const size_t lineSize = m_parameters.columns + 2;
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codingLine.resize(lineSize, m_parameters.columns);
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referenceLine.resize(lineSize, m_parameters.columns);
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bool isUsing2DEncoding = m_parameters.K < 0;
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bool isEndOfLineOccured = m_parameters.hasEndOfLine;
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auto updateIsUsing2DEncoding = [this, &isUsing2DEncoding]()
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{
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if (m_parameters.K > 0)
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{
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// Mixed encoding
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isUsing2DEncoding = !m_reader.read(1);
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}
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};
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isEndOfLineOccured = skipFillAndEOL() || isEndOfLineOccured;
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updateIsUsing2DEncoding();
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while (!m_reader.isAtEnd())
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{
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int a0_index = 0;
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bool isCurrentPixelBlack = false;
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if (isUsing2DEncoding)
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{
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int b1_index = 0;
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// 2D encoding
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while (codingLine[a0_index] < m_parameters.columns)
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{
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CCITT_2D_Code_Mode mode = get2DMode();
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switch (mode)
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{
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case Pass:
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{
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// In this mode, we set a0 to the b2 (from reference line). In pass mode,
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// we do not change pixel color. Why we are adding 2 to the b1_index?
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// We want to skip both b1, b2, because they will be left of new a0.
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const size_t b2_index = b1_index + 1;
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if (b2_index < referenceLine.size())
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{
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addPixels(codingLine, a0_index, referenceLine[b2_index], isCurrentPixelBlack, false);
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b1_index += 2;
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}
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else
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{
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throw PDFException(PDFTranslationContext::tr("CCITT b2 index out of range."));
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}
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break;
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}
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case Horizontal:
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{
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// We scan two sequence length.
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int a0a1 = getRunLength(!isCurrentPixelBlack);
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int a1a2 = getRunLength(isCurrentPixelBlack);
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addPixels(codingLine, a0_index, codingLine[a0_index] + a0a1, isCurrentPixelBlack, false);
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addPixels(codingLine, a0_index, codingLine[a0_index] + a1a2, !isCurrentPixelBlack, false);
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while (referenceLine[b1_index] <= codingLine[a0_index] && b1_index < m_parameters.columns)
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{
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// We do not want to change the color (b1 should have opposite color of a0,
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// should be first changing element of reference line right of a0).
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b1_index += 2;
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}
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break;
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}
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case Vertical_3L:
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case Vertical_2L:
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case Vertical_1L:
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case Vertical_0:
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case Vertical_1R:
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case Vertical_2R:
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case Vertical_3R:
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{
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const int32_t a1 = static_cast<int32_t>(referenceLine[b1_index]) + mode - static_cast<int32_t>(Vertical_0);
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if (a1 < 0 || a1 > m_parameters.columns)
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{
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throw PDFException(PDFTranslationContext::tr("Invalid vertical encoding data in CCITT stream."));
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}
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addPixels(codingLine, a0_index, static_cast<uint32_t>(a1), isCurrentPixelBlack, mode < Vertical_0);
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isCurrentPixelBlack = !isCurrentPixelBlack;
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if (codingLine[a0_index] < m_parameters.columns)
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{
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++b1_index;
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while (referenceLine[b1_index] <= codingLine[a0_index] && b1_index < m_parameters.columns)
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{
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// We do not want to change the color (b1 should have opposite color of a0,
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// should be first changing element of reference line right of a0).
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b1_index += 2;
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}
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}
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break;
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}
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default:
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Q_ASSERT(false);
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break;
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}
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}
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}
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else
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{
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// Simple 1D encoding
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while (codingLine[a0_index] < m_parameters.columns)
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{
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const uint32_t sequenceLength = getRunLength(!isCurrentPixelBlack);
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addPixels(codingLine, a0_index, codingLine[a0_index] + sequenceLength, isCurrentPixelBlack, false);
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isCurrentPixelBlack = !isCurrentPixelBlack;
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}
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}
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// Write the line to the output buffer
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isCurrentPixelBlack = false;
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int index = 0;
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for (int i = 0; i < m_parameters.columns; ++i)
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{
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if (i == codingLine[index])
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{
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isCurrentPixelBlack = !isCurrentPixelBlack;
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++index;
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}
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writer.write((isCurrentPixelBlack != m_parameters.hasBlackIsOne) ? 0 : 1);
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}
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writer.finishLine();
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++row;
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if (!m_parameters.hasEndOfBlock && row == m_parameters.rows)
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{
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// We have reached number of rows, stop reading the data
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break;
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}
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pokracovat zde
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std::swap(codingLine, referenceLine);
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}
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}
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void PDFCCITTFaxDecoder::skipFill()
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{
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// This functions skips zero bits (because codewords have at most 12 bits,
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// we use 12 bit lookahead to ensure, that we do not broke data sequence).
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while (m_reader.look(12) == 0)
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{
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m_reader.read(1);
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}
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}
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bool PDFCCITTFaxDecoder::skipEOL()
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{
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if (m_reader.look(12) == 1)
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{
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m_reader.read(12);
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return true;
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}
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return false;
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}
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void PDFCCITTFaxDecoder::addPixels(std::vector<int>& line, int& a0_index, int a1, bool isCurrentPixelBlack, bool isA1LeftOfA0Allowed)
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{
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if (a1 > line[a0_index])
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{
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if (a1 > m_parameters.columns)
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{
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throw PDFException(PDFTranslationContext::tr("Invalid index of CCITT changing element a1: a1 = %1, columns = %2.").arg(a1).arg(m_parameters.columns));
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}
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// If we are changing the color, increment a0_index. a0_index == 0 is white, a0_index == 1 is black, etc.,
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// sequence of white and black runs alternates.
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if ((a0_index & 1) != isCurrentPixelBlack)
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{
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++a0_index;
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}
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line[a0_index] = a1;
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}
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else if (isA1LeftOfA0Allowed && a1 < line[a0_index])
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{
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// We want to find first index, for which it holds:
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// a1 > line[a0_index - 1], so if we set line[a0_index] = a1,
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// then we get a valid increasing sequence.
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while (a0_index > 0 && a1 <= line[a0_index - 1])
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{
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--a0_index;
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}
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line[a0_index] = a1;
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}
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}
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uint32_t PDFCCITTFaxDecoder::getRunLength(bool white)
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{
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uint32_t value = 0;
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@ -322,7 +571,31 @@ uint32_t PDFCCITTFaxDecoder::getCode(const PDFCCITTCode* codes, size_t codeCount
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}
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}
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throw PDFException(PDFTranslationContext::tr("Invalid CCITT run length code word."));
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return 0;
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}
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CCITT_2D_Code_Mode PDFCCITTFaxDecoder::get2DMode()
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{
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uint32_t code = 0;
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uint8_t bits = 0;
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while (bits <= MAX_2D_MODE_BIT_LENGTH)
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{
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code = (code << 1) + m_reader.read(1);
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++bits;
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for (const PDFCCITT2DModeInfo& info : CCITT_2D_CODE_MODES)
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{
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if (info.bits == bits && info.code == code)
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{
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return info.mode;
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}
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}
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}
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throw PDFException(PDFTranslationContext::tr("Invalid CCITT 2D mode."));
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return Invalid;
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}
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} // namespace pdf
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