Code to store PGM file as a workable array

This is a discussion on Code to store PGM file as a workable array within the C++ Programming forums, part of the General Programming Boards category; I've been hacking my brais trying to figure this out and all the resources I keep using get me errors. ...

  1. #1
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    Code to store PGM file as a workable array

    I've been hacking my brais trying to figure this out and all the resources I keep using get me errors. I'm using Dev-C++ and I can't figure out the code to simply take a pgm file (let's call it test.pgm) and open it or read it and then store it as a 2D array. Is there a function like in MATLAB or something. In MATLAB it's rather simple. All you do is:
    Code:
    A = imread('test.pgm');
    This will put the image in matrix A, and then you can play arround with it from there. How does this work in Dev-C++?

  2. #2
    Registered User major_small's Avatar
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    it looks to me like you can skip (or take in) the first four lines, and then take in one line at a time into a two-dimensional char array... for example:

    Code:
    char matrix[90][90];
    int index=0;
    
    ifstream infile("something.pgm");
    
    infile.ignore(1000'\n');  //ignore the first line
    infile.ignore(1000'\n');  //these can also be changed to
    infile.ignore(1000'\n');  //infile.getline(...) so that you
    infile.ignore(1000'\n');  //can use the data if need be.
    
    while(!infile.eof())
    {
       infile.getline(matrix[index],90,'\n');
       index++;
    }
    
    infile.close();
    for ifstream, you'll need to #include <fstream>

    I don't know much (really anything) about .pgm files, but I used google to find this page... you may then want/need to go through this matrix and convert each char to an integer and put it in an integer matrix...
    Last edited by major_small; 11-09-2004 at 07:58 AM.
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  3. #3
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    major, your code doens't work. You ignore the image resolution, and use a fixed size array, when the image can be any size.
    I have code to read the image in C, if you want I'll post it.
    Meanwhile
    Code:
    unsigned char* readPGMImage(const  char *filename, int* height, int* width, int* grayscale){
    	//open the file to read
    	//read 1st 2 chars: have to match P5
    	//then skip all lines (ended with '\n') started with #
    	//read 3 ints: width, height, grayscale
    	//start reading info which is width*height bytes big to a buffer
    	//close file and return buffer
    }

  4. #4
    Registered User major_small's Avatar
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    it works, but you have to modify it to make it do what you want... I'm not going to hand-code everything for everybody... and I already said I didn't know what the file was really for... the OP called for putting it into a matrix, so I put it into a matrix for them... and I provided for the first few lines of input... the size of the matrix need not be hardcoded, just don't allocate the space until after you read the first four lines...
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  5. #5
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    Thanks everyone, yeah I found that resource too online, but the PGM files weren't in the format given in the text file you linked, I got some help with this and I'm banging throught the program now, thanks all.

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