README_dev.md

QR Code(Quick Response Code) Implement by Go

According to ISO/IEC 18004-2015 Standard
(2021-05-17 ~ )

QRCode Types

• QRCode

  With fall range of capabilities and maximum data capacity.

  • QRCode Model1
    
  • QRCode Model2
    

  QRCode Struct:

  

  • Function patterns
    Finder pattern

    (Page 24,6.3.3 Finder pattern)
    There are 3 identical Finder pattern locate at the upper left,upper right and low left corner of the symbol.
    Each finder pattern may be viewed as 3 superimposed concentric squares:
    dark 7 x 7 modules
    light 5 x 5 modules
    dark 3 x 3 modules.
    The ratio of module widths in each finder pattern is 1:1:3:1:1.
    

    Separator

    A one-module wide separator, constructed of all light modules,is placed between each finder pattern and the Encoding Region.

    Timing pattern

    The horizontal and vertical timing patterns respectively consist of a one module wide row or column of alternating dark and light modules,
    commencing and ending with a dark module.
    They enable the symbol density and version to be determined and provide datum positions for determining module coordinates.

    In QR Code symbols,the horizontal timing pattern runs across row 6 of the symbol between the separators for the upper finder patterns;
    the vertical timing pattern similarly runs down column 6 of the symbol between the separators for the left-hand finder patterns.
    See Figure 3;

    In Micro QR Code symbols, the horizontal timing pattern runs across row 0 of the symbol on the right side of the separator to the right-hand edge of the symbol;
    the vertical timing pattern similarly runs downcolumn 0of the symbol below the separator to the bottom edge of the symbol.
    See Figure 4;

    Alignment pattern

    Alignment patterns are present only in QR Code symbol of version 2 or larger.
    Each alignment pattern my be viewd as three superimposed concentric squares and is constructed of:
    dark 5 x 5 modules
    light 3 x 3 modules single central dark module
    The number of alignment patterns depend on the symbol version.

  • Encoding region

    Format information

    Version information Data and error correction codewords

  • Quiet Zone(minimum:4x)

• Micro QRCode

  With reduce overhead,some restrictions on capabilities and reduce data capacity(compared with QR Code symbol)

  

  Micro QRCode Struct:
  

  Finder pattern

  A single finder pattern, as defined [QRCode]

  Separator
  Timing pattern
  Format information
  Encoding region
  Quiet zone(minimum:2x)

Encode procedure overview steps:

(Page 26. Encode procedure overview)

1. Data analysis
   Determine the smallest version or specified version for ues.
   Mode select strategy by Page 107(PDF) optimisation of bit stream length.
   

2. Data encoding
   Convert the data characters into a bit stream in accordance with the rules for the mode in force, as defined in 7.4.2 to 7.4.6, inserting mode indicators as necessary to change modes at the beginning of each new mode segment, and a Terminator at the end of the data sequence.
   Split the resulting bit stream into 8-bit codewords(data codeword).
   Add Pad Characters as necessary to fill the number of data codewords required for the version.

   Mode Indicator Bits + Data Bits + Terminal Bits + Padding Bits(to full version bits count)
   The ECI header(if present) shall comprise:
   --- ECI Mode Indicator(4 bits)
   --- ECI Designator(8,16 or 24 bits)
   The ECI header shall begin with the first(most significant)bit of the ECI mode indicator and end with the final(least significant) bit of the ECI Designator.
   The remainder of the bit stream is then made up of segments each comprising:
   --- Mode indicator
   --- Character count indicator
   --- Data bit stream
   Each mode segment shall begin with the first(most significant) bit of the mode indicator and end with the final(least significant) bit of the data bit stream.
   There shall be no explicit separator between segments as their length is defined unambiguously by the rules for the mode in force and the number of input data characters.
   
   The end of the data in the complete symbol is indicated by a Terminator consisting of between 3 and 9 zero bits(see Table2), which is omitted or abbreviated if the remaining symbol capacity after the data bit stream is less than the required bit length of Terminator.
   The Terminator is not a mode indicator as such.

3. Error correction encoding
   Divide the codeword(2. Data encoding resulting codewords) sequence into the required number of blocks(as defined in Table9) to enable the error correction algorithms to be processed.
   Generate the error correction codewords for each block,appending the error correction codewords to the end of the data codeword sequence.

4. Structure final message
   Interleave the data and error correction codewords from each block as described in 7.6(step3) and add remainder bits as necessary.

5. Module placement in matrix
   Place the codeword modules in the matrix together with the finder pattern,separators,timing pattern,and (if required) alignment patterns.
   Page 54,7.7 Codeword placement in matrix
   7.7.1 Symbol Character representation

   There are two types of symbol character,regular an irregular,in the QR Code symbol.
   Their use depends on their position in the symbol,relative to other symbol characters and function patterns.

   Most codewords shall be represented in regular 2 x 4 module block in the symbol.
   There are two ways of positioning these blocks,
   in a vertical arrangement (2 modules wide 4 modules high) and,if necessary when placement changes direction,
   in a horizontal arrangement(4 modules wide and 2 modules high).

   Irregular symbol characters are used when changing direction or in the vicinity of alignment or other function Patterns. Examples are shown in Figures 16,17 and 18.

6. Data masking
   Apply the data masking patterns in turn to the encoding region of the symbol.
   Evaluate the results and select the pattern which optimizes the dark/light module balance and minimizes the occurrence of undesirable patterns.

7. Format and Version Information
   Generate the format information and (where applicable) the version information and complete the symbol.

Decode procedure overview steps:

(Page 62. Decode procedure overview)

Process flow:

Implement Functions:

To implement specified size (width/height) QR Code.

• Encoder(Page 12-)
  to JPG, PNG, SVG
  (with outer mark image in center(expect SVG))
• Decoder
  From JPG, PNG, SVG
  (Parser multi symbols in one image)

Implementation order

1. Generate: QRCode Model2
   Generate and Simple Test QRCode Model2.
2. Generate: QRCode Model1
   Generate and Simple Test QRCode Model1.
3. Generate: Micro QRCode
   Generate and Simple Test Micro QRCode.
4. Completion Test
   Test for Correctness and Performance

Test:

Test for Correctness and Performance

Compare with ZXING in Correctness and Performance(CPU,Memory and Cost time)

Reference

1. ISO IEC 18004-2015.pdf
2. QR Code Specification-ISO_IEC_18004-2006.pdf
3. https://www.thonky.com/qr-code-tutorial/error-correction-coding
4. https://www.jianshu.com/p/36b1ed153524
5. https://blog.csdn.net/hhygcy/article/details/4280165
6. https://www.cnblogs.com/Imageshop/archive/2013/04/22/3036127.html

Dependency Package

1. imaging

go get -u github.com/disintegration/imaging

2. image

mkdir $GOPATH/golang.org/x/
cd $GOPATH/golang.org/x/
git clone https://github.com/golang/image.git

3. text

cd $GOPATH/golang.org/x/
git clone https://github.com/golang/text.git