How to save image as png or jpg instead of .dat file

Following is the code in Simulink's motion sensor and camera model for raspberry pi. When I am running the model on raspberry pi, the images are stored as .dat file. If I change the extension .dat to .png or .jpg, the files do not open. How could I store RGB image as png or jpg instead of .dat file?

Code:

format = ['%d ', 0];
fname  = coder.nullcopy(uint8(zeros(1, 32)));
coder.ceval('sprintf', coder.wref(fname), ['/var/www/html/photos/img%d.png', 0], counter);
fd = coder.opaque('FILE *');
fd = coder.ceval('fopen', fname, ['w', 0]);
for i = 1:320
    for j = 1:240
        coder.ceval('fprintf', fd, format, R(i, j));
    end
end
coder.ceval('fclose', fd);

[Stephen23]

"If I change the extension .dat to .png or .jpg, the files do not open."

Changing the file extension of any file does not magically convert the file format. A text file of numbers does not magically become a compressed binary image file just because you put .jpg or .png on the end of its filename.

It would be simple to use post-processing to convert the file to an image format: simply use MATLAB to read that text file of numbers and then save as an image.

[Marium Malik]

I am running it on raspberry pi and I cannot do it manually in Matlab. I want it to done automatically in this code. Any suggestion? RGB values are passed as input to this code

[Walter Roberson]

If RGB values are being passed to the code, then why are you only accessing two dimensions, R(i,j) ? Or is R the red component and there are also G and B matrices?

[Marium Malik]

Yes, R is the red component, I have G and B matrices as well. I am getting them as ouput from Raspberry Pi camera.

Answer 1

[Walter Roberson]

That code does not even attempt to write an image file at the moment: it writes out space separated decimal numbers, all in one line, and not color. Only the Portable Graymap (PGM) format is close to that; it might be easiest for you to write that; https://en.wikipedia.org/wiki/Netpbm_format#PGM_example

[Marium Malik]

Any way to write an image instead of dat file? The code is getting RGB values

[Walter Roberson]

PGM format is an image file format, and it is easy to write.

[Marium Malik]

How could it be written in my case? I am getting R,G and B values from Raspberry pi camera

[Walter Roberson]

Use that link I posted about PGM format but look at the very next part where it shows PPM format where it writes out RGB triples. The main thing to watch out for is that the header line has width followed by height instead of the more common height followed by width.