Raw pixel storage 1

[fabien]

Hi!

Image files in raw format can have different pixel storage length (1bit 8bit 16bit, unsigned 8bit etc) WHat is the best way to determine in C++ the type from the file?

Thanks!

 

[TonyGroves]

That depends on the file type. You would have to consult the file format specification to find out where the colour-depth information is stored.

 

[fabien]

After some searches I found out I could use the formula: filesize = ((xdim*ydim*zdim)*(datatype/8))+ offset Now I need a way to determine the filesize: what is the best way?

THanks!

 

[Salem]

man 2 stat
stat returns a structure containing lots of useful information about a file.

Or if you want something really portable, then
fopen(), fseek() to end of file, ftell() to get the offset (or file size) and fclose() also works.

--

 

[fabien]

THanks Salem,

Something like:

// obtaining file size
#include <iostream.h>
#include <fstream.h>

const char * filename = "example.txt";

int main () {
  long l,m;
  ifstream file (filename, ios::in|ios::binary);
  l = file.tellg();
  file.seekg (0, ios::end);
  m = file.tellg();
  file.close();
  cout << "size of " << filename;
  cout << " is " << (m-l) << " bytes.\n";
  return 0;
}

 

[xwb]

There are various encoding schemes used to save on storage. For instance, in 16-colour bmp format, they have the width, height and colour encodings at the start of the file and then only use 4 bits per pixel for the picture. Similar scheme is used for 256 colour.