Writing BMP image in pure c c without other libraries

Question

In my algorithm  I need to create an information output  I need to write a boolean matrix into a bmp file  It must be a monocromic image  where pixels are white if the matrix on such element is true  Main problem is the bmp header and how to write this

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See if this works for you    In this code  I had 3 2-dimensional arrays  called red green and blue   Each one was of size  width  height   and each element corresponded to a pixel - I hope this makes sense   FILE  f  unsigned char  img   NULL  int filesize   54   3 w h     w is your image width  h is image height  both int  img    unsigned char   malloc 3 w h   memset img 0 3 w h    for int i 0  i lt w  i          for int j 0  j lt h  j                  x i  y  h-1 -j          r   red i  j  255          g   green i  j  255          b   blue i  j  255          if  r  gt  255  r 255          if  g  gt  255  g 255          if  b  gt  255  b 255          img  x y w  3 2     unsigned char  r           img  x y w  3 1     unsigned char  g           img  x y w  3 0     unsigned char  b            unsigned char bmpfileheader 14      B   M   0 0 0 0  0 0  0 0  54 0 0 0   unsigned char bmpinfoheader 40     40 0 0 0  0 0 0 0  0 0 0 0  1 0  24 0   unsigned char bmppad 3     0 0 0    bmpfileheader  2     unsigned char  filesize       bmpfileheader  3     unsigned char  filesize gt  gt  8   bmpfileheader  4     unsigned char  filesize gt  gt 16   bmpfileheader  5     unsigned char  filesize gt  gt 24    bmpinfoheader  4     unsigned char         w       bmpinfoheader  5     unsigned char         w gt  gt  8   bmpinfoheader  6     unsigned char         w gt  gt 16   bmpinfoheader  7     unsigned char         w gt  gt 24   bmpinfoheader  8     unsigned char         h       bmpinfoheader  9     unsigned char         h gt  gt  8   bmpinfoheader 10     unsigned char         h gt  gt 16   bmpinfoheader 11     unsigned char         h gt  gt 24    f   fopen  img bmp   wb    fwrite bmpfileheader 1 14 f   fwrite bmpinfoheader 1 40 f   for int i 0  i lt h  i          fwrite img  w  h-i-1  3  3 w f       fwrite bmppad 1  4- w 3  4  4 f      free img   fclose f

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C   answer  flexible API  assumes little-endian system to code-golf it a bit  Note this uses the bmp native y-axis  0 at the bottom    include  lt vector gt   include  lt fstream gt   struct image          image int width  int height          w width   h height   rgb w   h   3             uint8 t  amp  r int x  int y    return rgb  x   y w  3   2         uint8 t  amp  g int x  int y    return rgb  x   y w  3   1         uint8 t  amp  b int x  int y    return rgb  x   y w  3   0          int w  h      std  vector lt uint8 t gt  rgb      template lt class Stream gt  Stream  amp  operator lt  lt  Stream  amp  out  image const amp  img           uint32 t w   img w  h   img h      uint32 t pad   w   -3  amp  3      uint32 t total   54   3 w h   pad h      uint32 t head 13     total  0  54  40  w  h   24 lt  lt 16  1       char const  rgb    char const  img rgb data         out write  quot BM quot   2       out write  char  head  52       for uint32 t i 0   i lt h   i            out write rgb    3   w   i   3   w           out write  char   amp pad  pad             return out     int main         image img 100  100       for int x 0   x lt 100   x            for int y 0   y lt 100   y                img r x y    x              img g x y    y              img b x y    100-x                      std  ofstream  quot  tmp out bmp quot    lt  lt  img

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If you get strange colors switches in the middle of your image using the above C   function  Be sure to open the outstream in binary mode   imgFile open filename  std  ios base  out   std  ios base  binary   Otherwise windows inserts unwanted characters in the middle of your file   been banging my head on this issue for hours   See related question here  Why does ofstream insert a 0x0D byte before 0x0A

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Note that the lines are saved from down to up and not the other way around   Additionally  the scanlines must have a byte-length of multiples of four  you should insert fill bytes at the end of the lines to ensure this

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Without the use of any other library you can look at the BMP file format   I ve implemented it in the past and it can be done without too much work      Bitmap-File Structures      Each bitmap file contains a   bitmap-file header  a   bitmap-information header  a color   table  and an array of bytes that   defines the bitmap bits  The file has   the following form       BITMAPFILEHEADER bmfh    BITMAPINFOHEADER bmih    RGBQUAD aColors      BYTE aBitmapBits              see the file format for more details

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I edited ralf s htp code so that it would compile  on gcc  running ubuntu 16 04 lts   It was just a matter of initializing the variables       int w   100     Put here what ever width you want        int h   100     Put here what ever height you want        int red w  h        int green w  h       int blue w  h         FILE  f      unsigned char  img   NULL      int filesize   54   3 w h     w is your image width  h is image height  both int     if  img               free  img        img    unsigned char   malloc 3 w h       memset img 0 sizeof img        int x      int y      int r      int g      int b       for int i 0  i lt w  i                      for int j 0  j lt h  j                                      x i  y  h-1 -j                      r   red i  j  255                      g   green i  j  255                      b   blue i  j  255                      if  r  gt  255  r 255                      if  g  gt  255  g 255                      if  b  gt  255  b 255                      img  x y w  3 2     unsigned char  r                       img  x y w  3 1     unsigned char  g                       img  x y w  3 0     unsigned char  b                            unsigned char bmpfileheader 14      B   M   0 0 0 0  0 0  0 0  54 0 0 0       unsigned char bmpinfoheader 40     40 0 0 0  0 0 0 0  0 0 0 0  1 0  24 0       unsigned char bmppad 3     0 0 0        bmpfileheader  2     unsigned char  filesize           bmpfileheader  3     unsigned char  filesize gt  gt  8       bmpfileheader  4     unsigned char  filesize gt  gt 16       bmpfileheader  5     unsigned char  filesize gt  gt 24        bmpinfoheader  4     unsigned char         w           bmpinfoheader  5     unsigned char         w gt  gt  8       bmpinfoheader  6     unsigned char         w gt  gt 16       bmpinfoheader  7     unsigned char         w gt  gt 24       bmpinfoheader  8     unsigned char         h           bmpinfoheader  9     unsigned char         h gt  gt  8       bmpinfoheader 10     unsigned char         h gt  gt 16       bmpinfoheader 11     unsigned char         h gt  gt 24        f   fopen  img bmp   wb        fwrite bmpfileheader 1 14 f       fwrite bmpinfoheader 1 40 f       for int i 0  i lt h  i                      fwrite img  w  h-i-1  3  3 w f               fwrite bmppad 1  4- w 3  4  4 f             fclose f

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Clean C Code for Bitmap  BMP  Image Generation Generated Image     The code does not use any library other than stdio h  So  the code can be easily incorporated in other languages of C-Family  like- C    C   Java      include  lt stdio h gt   const int BYTES PER PIXEL   3      red  green   amp  blue const int FILE HEADER SIZE   14  const int INFO HEADER SIZE   40   void generateBitmapImage unsigned char  image  int height  int width  char  imageFileName   unsigned char  createBitmapFileHeader int height  int stride   unsigned char  createBitmapInfoHeader int height  int width     int main          int height   361      int width   867      unsigned char image height  width  BYTES PER PIXEL       char  imageFileName    char    quot bitmapImage bmp quot        int i  j      for  i   0  i  lt  height  i              for  j   0  j  lt  width  j                  image i  j  2     unsigned char    i   255   height                   red             image i  j  1     unsigned char    j   255   width                    green             image i  j  0     unsigned char     i j    255    height width        blue                      generateBitmapImage  unsigned char   image  height  width  imageFileName       printf  quot Image generated   quot        void generateBitmapImage  unsigned char  image  int height  int width  char  imageFileName        int widthInBytes   width   BYTES PER PIXEL       unsigned char padding 3     0  0  0       int paddingSize    4 -  widthInBytes    4    4       int stride    widthInBytes    paddingSize       FILE  imageFile   fopen imageFileName   quot wb quot         unsigned char  fileHeader   createBitmapFileHeader height  stride       fwrite fileHeader  1  FILE HEADER SIZE  imageFile        unsigned char  infoHeader   createBitmapInfoHeader height  width       fwrite infoHeader  1  INFO HEADER SIZE  imageFile        int i      for  i   0  i  lt  height  i              fwrite image    i widthInBytes   BYTES PER PIXEL  width  imageFile           fwrite padding  1  paddingSize  imageFile              fclose imageFile      unsigned char  createBitmapFileHeader  int height  int stride        int fileSize   FILE HEADER SIZE   INFO HEADER SIZE    stride   height        static unsigned char fileHeader               0 0          signature         0 0 0 0      image file size in bytes         0 0 0 0      reserved         0 0 0 0      start of pixel array             fileHeader  0     unsigned char   B        fileHeader  1     unsigned char   M        fileHeader  2     unsigned char  fileSize             fileHeader  3     unsigned char  fileSize  gt  gt   8       fileHeader  4     unsigned char  fileSize  gt  gt  16       fileHeader  5     unsigned char  fileSize  gt  gt  24       fileHeader 10     unsigned char  FILE HEADER SIZE   INFO HEADER SIZE        return fileHeader     unsigned char  createBitmapInfoHeader  int height  int width        static unsigned char infoHeader               0 0 0 0      header size         0 0 0 0      image width         0 0 0 0      image height         0 0          number of color planes         0 0          bits per pixel         0 0 0 0      compression         0 0 0 0      image size         0 0 0 0      horizontal resolution         0 0 0 0      vertical resolution         0 0 0 0      colors in color table         0 0 0 0      important color count             infoHeader  0     unsigned char  INFO HEADER SIZE       infoHeader  4     unsigned char  width             infoHeader  5     unsigned char  width  gt  gt   8       infoHeader  6     unsigned char  width  gt  gt  16       infoHeader  7     unsigned char  width  gt  gt  24       infoHeader  8     unsigned char  height             infoHeader  9     unsigned char  height  gt  gt   8       infoHeader 10     unsigned char  height  gt  gt  16       infoHeader 11     unsigned char  height  gt  gt  24       infoHeader 12     unsigned char  1       infoHeader 14     unsigned char  BYTES PER PIXEL 8        return infoHeader

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The best bitmap encoder is the one you do not write yourself  The file format is a lot more involved  than one might expect  This is evidenced by the fact  that all proposed answers do not create a monochrome  1bpp  bitmap  but rather write out 24bpp files  that happen to only use 2 colors   The following is a Windows-only solution  using the Windows Imaging Component  It doesn t rely on any external 3rd party libraries  other than what ships with Windows   Like every C   program  we need to include several header files  And link to Windowscodecs lib while we re at it    include  lt Windows h gt   include  lt comdef h gt   include  lt comip h gt   include  lt comutil h gt   include  lt wincodec h gt    include  lt vector gt    pragma comment lib   Windowscodecs lib     Next up  we declare our container  a vector  of vectors  Of bool    and a few smart pointers for convenience   using  com util  CheckError  using container   std  vector lt std  vector lt bool gt  gt     COM SMARTPTR TYPEDEF IWICImagingFactory    uuidof IWICImagingFactory     COM SMARTPTR TYPEDEF IWICBitmapEncoder    uuidof IWICBitmapEncoder     COM SMARTPTR TYPEDEF IWICBitmapFrameEncode    uuidof IWICBitmapFrameEncode     COM SMARTPTR TYPEDEF IWICStream    uuidof IWICStream     COM SMARTPTR TYPEDEF IWICPalette    uuidof IWICPalette      With that all settled  we can jump right into the implementation  There s a bit of setup required to get a factory  an encoder  a frame  and get everything prepared   void write bitmap wchar t const  pathname  container const amp  data           Create factory     IWICImagingFactoryPtr sp factory   nullptr        CheckError sp factory CreateInstance CLSID WICImagingFactory  nullptr                                           CLSCTX INPROC SERVER            Create encoder     IWICBitmapEncoderPtr sp encoder   nullptr        CheckError sp factory- gt CreateEncoder GUID ContainerFormatBmp  nullptr   amp sp encoder            Create stream     IWICStreamPtr sp stream   nullptr        CheckError sp factory- gt CreateStream  amp sp stream        CheckError sp stream- gt InitializeFromFilename pathname  GENERIC WRITE            Initialize encoder with stream     CheckError sp encoder- gt Initialize sp stream  WICBitmapEncoderNoCache            Create new frame     IWICBitmapFrameEncodePtr sp frame   nullptr        IPropertyBag2Ptr sp properties   nullptr        CheckError sp encoder- gt CreateNewFrame  amp sp frame   amp sp properties            Initialize frame with default properties     CheckError sp frame- gt Initialize sp properties            Set pixel format        SetPixelFormat   requires a pointer to non-const     auto pf   GUID WICPixelFormat1bppIndexed        CheckError sp frame- gt SetPixelFormat  amp pf        if     IsEqualGUID pf  GUID WICPixelFormat1bppIndexed                    Report unsupported pixel format         CheckError WINCODEC ERR UNSUPPORTEDPIXELFORMAT                 Set size derived from data argument     auto const width   static cast lt UINT gt  data size           auto const height   static cast lt UINT gt  data 0  size           CheckError sp frame- gt SetSize width  height            Set palette on frame  This is required since we use an indexed pixel format         Only GIF files support global palettes  so make sure to set it on the frame        rather than the encoder      IWICPalettePtr sp palette   nullptr        CheckError sp factory- gt CreatePalette  amp sp palette        CheckError sp palette- gt InitializePredefined WICBitmapPaletteTypeFixedBW  FALSE        CheckError sp frame- gt SetPalette sp palette      At that point everything is set up  and we have a frame to dump our data into  For 1bpp files  every byte stores the information of 8 pixels  The left-most pixel is stored in the MSB  with pixels following all the way down to the right-most pixel stored in the LSB   The code isn t entirely important  you ll be replacing that with whatever suits your needs  when you replace the data layout of your input anyway          Write data to frame     auto const stride    width   1   7    8        auto const size   height   stride        std  vector lt unsigned char gt  buffer size  127u          Convert data to match required layout  Each byte stores 8 pixels  with the        MSB being the leftmost  the LSB the right-most      for  size t x   0    x  lt  data size      x                for  size t y   0    y  lt  data x  size      y                        auto shift   x   8                auto mask   0x80  gt  gt  shift                auto bit   mask   data x  y                 auto amp  value   buffer y   stride   x   8                 value  amp    mask              value    bit                      CheckError sp frame- gt WritePixels height  stride                                       static cast lt UINT gt  buffer size     buffer data        What s left is to commit the changes to the frame and the encoder  which will ultimately write the image file to disk          Commit frame     CheckError sp frame- gt Commit             Commit image     CheckError sp encoder- gt Commit         This is a test program  writing out an image to a file passed as the first command-line argument    include  lt iostream gt   int wmain int argc  wchar t  argv    try       if  argc    2                return -1             CheckError   CoInitializeEx nullptr  COINIT APARTMENTTHREADED             Create 64x64 matrix     container data 64  std  vector lt bool gt  64  false           Fill with arrow pointing towards the upper left     for  size t i   0    i  lt  data size      i                data 0  i    true          data i  0    true          data i  i    true              write bitmap argv 1   data           CoUninitialize      catch   com error const amp  e        std  wcout  lt  lt  L Error  n   lt  lt  L   Message     lt  lt  e ErrorMessage    lt  lt  std  endl      It produces the following image  true 1bpp  574 bytes in size

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Here is a C   variant of the code that works for me  Note I had to change the size computation  to account for the line padding      mimeType    image bmp    unsigned char file 14           B   M      magic     0 0 0 0     size in bytes     0 0     app data     0 0     app data     40 14 0 0 0    start of data offset    unsigned char info 40          40 0 0 0     info hd size     0 0 0 0     width     0 0 0 0     heigth     1 0     number color planes     24 0     bits per pixel     0 0 0 0     compression is none     0 0 0 0     image bits size     0x13 0x0B 0 0     horz resoluition in pixel   m     0x13 0x0B 0 0     vert resolutions  0x03C3   96 dpi  0x0B13   72 dpi      0 0 0 0      colors in pallete     0 0 0 0      important colors         int w waterfallWidth  int h waterfallHeight   int padSize     4- w 3  4  4  int sizeData   w h 3   h padSize  int sizeAll    sizeData   sizeof file    sizeof info    file  2     unsigned char   sizeAll       file  3     unsigned char   sizeAll gt  gt  8   file  4     unsigned char   sizeAll gt  gt 16   file  5     unsigned char   sizeAll gt  gt 24    info  4     unsigned char   w      info  5     unsigned char   w gt  gt  8   info  6     unsigned char   w gt  gt 16   info  7     unsigned char   w gt  gt 24    info  8     unsigned char   h       info  9     unsigned char   h gt  gt  8   info 10     unsigned char   h gt  gt 16   info 11     unsigned char   h gt  gt 24    info 20     unsigned char   sizeData       info 21     unsigned char   sizeData gt  gt  8   info 22     unsigned char   sizeData gt  gt 16   info 23     unsigned char   sizeData gt  gt 24    stream write   char  file  sizeof file     stream write   char  info  sizeof info      unsigned char pad 3     0 0 0    for   int y 0  y lt h  y           for   int x 0  x lt w  x                   long red   lround  255 0   waterfall x  y             if   red  lt  0   red 0          if   red  gt  255   red 255          long green   red          long blue   red           unsigned char pixel 3           pixel 0    blue          pixel 1    green          pixel 2    red           stream write   char  pixel  3              stream write   char  pad  padSize

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this is a example code copied from https   en wikipedia org wiki User Evercat Buddhabrot c void drawbmp  char   filename     unsigned int headers 13   FILE   outfile  int extrabytes  int paddedsize  int x  int y  int n  int red  green  blue   extrabytes   4 -   WIDTH   3    4                      How many bytes of padding to add to each                                                        horizontal line - the size of which must                                                        be a multiple of 4 bytes  if  extrabytes    4     extrabytes   0   paddedsize     WIDTH   3    extrabytes    HEIGHT      Headers       Note that the  quot BM quot  identifier in bytes 0 and 1 is NOT included in these  quot headers quot                         headers 0     paddedsize   54          bfSize  whole file size  headers 1     0                        bfReserved  both  headers 2     54                       bfOffbits headers 3     40                       biSize headers 4     WIDTH      biWidth headers 5     HEIGHT     biHeight     Would have biPlanes and biBitCount in position 6  but they re shorts     It s easier to write them out separately  see below  than pretend    they re a single int  especially with endian issues     headers 7     0                        biCompression headers 8     paddedsize               biSizeImage headers 9     0                        biXPelsPerMeter headers 10    0                        biYPelsPerMeter headers 11    0                        biClrUsed headers 12    0                        biClrImportant  outfile   fopen filename   quot wb quot           Headers begin       When printing ints and shorts  we write out 1 character at a time to avoid endian issues      fprintf outfile   quot BM quot     for  n   0  n  lt   5  n         fprintf outfile   quot  c quot   headers n   amp  0x000000FF      fprintf outfile   quot  c quot    headers n   amp  0x0000FF00   gt  gt  8      fprintf outfile   quot  c quot    headers n   amp  0x00FF0000   gt  gt  16      fprintf outfile   quot  c quot    headers n   amp   unsigned int  0xFF000000   gt  gt  24         These next 4 characters are for the biPlanes and biBitCount fields   fprintf outfile   quot  c quot   1   fprintf outfile   quot  c quot   0   fprintf outfile   quot  c quot   24   fprintf outfile   quot  c quot   0    for  n   7  n  lt   12  n         fprintf outfile   quot  c quot   headers n   amp  0x000000FF      fprintf outfile   quot  c quot    headers n   amp  0x0000FF00   gt  gt  8      fprintf outfile   quot  c quot    headers n   amp  0x00FF0000   gt  gt  16      fprintf outfile   quot  c quot    headers n   amp   unsigned int  0xFF000000   gt  gt  24            Headers done  now write the data        for  y   HEIGHT - 1  y  gt   0  y--         BMP image format is written from bottom to top         for  x   0  x  lt   WIDTH - 1  x                red   reduce redcount x  y    COLOUR OFFSET    red multiplier        green   reduce greencount x  y    COLOUR OFFSET    green multiplier        blue   reduce bluecount x  y    COLOUR OFFSET    blue multiplier               if  red  gt  255  red   255  if  red  lt  0  red   0        if  green  gt  255  green   255  if  green  lt  0  green   0        if  blue  gt  255  blue   255  if  blue  lt  0  blue   0                  Also  it s written in  b g r  format           fprintf outfile   quot  c quot   blue         fprintf outfile   quot  c quot   green         fprintf outfile   quot  c quot   red           if  extrabytes          See above - BMP lines must be of lengths divisible by 4             for  n   1  n  lt   extrabytes  n                     fprintf outfile   quot  c quot   0                   fclose outfile   return      drawbmp filename

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I just wanted to share an improved version of Minhas Kamal s code because although it worked well enough for most applications  I had a few issues with it still   Two highly important things to remember    The code  at the time of writing  calls free   on two static arrays   This will cause your program to crash   So I commented out those lines  NEVER assume that your pixel data s pitch is always  Width BytesPerPixel    It s best to let the user specify the pitch value   Example  when manipulating resources in Direct3D  the RowPitch is never guaranteed to be an even multiple of the byte depth being used   This can cause errors in your generated bitmaps  especially at odd resolutions such as 1366x768     Below  you can see my revisions to his code   const int bytesPerPixel   4      red  green  blue const int fileHeaderSize   14  const int infoHeaderSize   40   void generateBitmapImage unsigned char  image  int height  int width  int pitch  const char  imageFileName   unsigned char  createBitmapFileHeader int height  int width  int pitch  int paddingSize   unsigned char  createBitmapInfoHeader int height  int width      void generateBitmapImage unsigned char  image  int height  int width  int pitch  const char  imageFileName         unsigned char padding 3      0  0  0        int paddingSize    4 -    width bytesPerPixel   pitch    4    4       unsigned char  fileHeader   createBitmapFileHeader height  width  pitch  paddingSize       unsigned char  infoHeader   createBitmapInfoHeader height  width        FILE  imageFile   fopen imageFileName   wb         fwrite fileHeader  1  fileHeaderSize  imageFile       fwrite infoHeader  1  infoHeaderSize  imageFile        int i      for  i   0  i  lt  height  i              fwrite image    i pitch   width bytesPerPixel     bytesPerPixel  width  imageFile           fwrite padding  1  paddingSize  imageFile              fclose imageFile         free fileHeader         free infoHeader      unsigned char  createBitmapFileHeader int height  int width  int pitch  int paddingSize        int fileSize   fileHeaderSize   infoHeaderSize      bytesPerPixel width  pitch   paddingSize    height       static unsigned char fileHeader               0 0      signature         0 0 0 0      image file size in bytes         0 0 0 0      reserved         0 0 0 0      start of pixel array             fileHeader 0     unsigned char   B        fileHeader 1     unsigned char   M        fileHeader 2     unsigned char  fileSize       fileHeader 3     unsigned char  fileSize  gt  gt  8       fileHeader 4     unsigned char  fileSize  gt  gt  16       fileHeader 5     unsigned char  fileSize  gt  gt  24       fileHeader 10     unsigned char  fileHeaderSize   infoHeaderSize        return fileHeader     unsigned char  createBitmapInfoHeader int height  int width        static unsigned char infoHeader               0 0 0 0      header size         0 0 0 0      image width         0 0 0 0      image height         0 0      number of color planes         0 0      bits per pixel         0 0 0 0      compression         0 0 0 0      image size         0 0 0 0      horizontal resolution         0 0 0 0      vertical resolution         0 0 0 0      colors in color table         0 0 0 0      important color count             infoHeader 0     unsigned char  infoHeaderSize       infoHeader 4     unsigned char  width       infoHeader 5     unsigned char  width  gt  gt  8       infoHeader 6     unsigned char  width  gt  gt  16       infoHeader 7     unsigned char  width  gt  gt  24       infoHeader 8     unsigned char  height       infoHeader 9     unsigned char  height  gt  gt  8       infoHeader 10     unsigned char  height  gt  gt  16       infoHeader 11     unsigned char  height  gt  gt  24       infoHeader 12     unsigned char  1       infoHeader 14     unsigned char  bytesPerPixel   8        return infoHeader

[c++] Writing BMP image in pure c/c++ without other libraries

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