[SOLVED] How are these PGM files encoded?

How are these PGM files encoded?

I exported a grayscale image as PGM using MATLAB (and OpenCV) and got this file as an output.

    im = imread(src);
    im = rgb2gray(im);
    imwrite(im, dst);

According to the PGM Specification the header contains the "magic number", the width, the height, and the max value of the image.

But below the header, there should be a matrix of grayscale intensity values written in plaintext. But as you can see in the pasted file, I just get some kind of junk out (although it's a completely valid, viewable image)

I want to be able to read in the PGM files and access the individual intensity values as integers using a C/C++ program but I don't know how to interpret this output since it doesn't follow the spec. Perhaps the text encoding is different?

Thanks for any assistance.

Solution

You're misreading the spec.

Each gray value is represented in pure binary by either 1 or 2 bytes. If the Maxval is less than 256, it is 1 byte. Otherwise, it is 2 bytes. The most significant byte is first.

So each pixel is either one or two bytes (depending on the Maxval) and in binary, not ASCII.