Code to store PGM file as a workable array

**InnerCityBlues** · 11-09-2004

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++?

**major_small** · 11-09-2004

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...

**xErath** · 11-09-2004

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
}

**major_small** · 11-10-2004

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...

**InnerCityBlues** · 11-10-2004

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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