Reading an image with fread and displaying this image again issues?

hi all

came into a problem with some code. this is being used for a bigger project so ive simplified my issue into a smaller example problem

im basically reading peppers.png, converting this data to JPEG format so i can compress it by quality factor.

reading this compressed image file data.

and trying to reshow this compressed image as a new file with a different name.

but right now i lose the image completely. Below is a copy of my code and images so far

compressedImage.jpg

hmm.jpg

ImageData = imread('peppers.png'); 
imwrite(ImageData,'compressedImage.jpg','jpg','quality',100); %compress the image by different quality factor 
G = size('compressedImage.jpg');
fileID =fopen('compressedImage.jpg'); 
A = fread(fileID,[384,512]); 
fclose(fileID);
imwrite(A,'hmm.jpg','jpg');

Answer 1

[Image Analyst]

You can't open a JPG image like that - just a raw stream of pixels. It's not like that. There is compression going on so you need to decompress. imread() decompresses but fread() does not. So of course it looks like garbage. Plus A might be floating point which would make it display weird like that.

[Sam Austin]

but for the example i gave above isnt the quality at 100 so no decompression should be happening

[Image Analyst]

Regardless, even for a file format with no compression, like BMP, there is metadata in the image, like the first thousand or so is just header data. Using fread() assumes that everything is a pixel value. You'd have to extract the pixel data after that header data.

[jacob cunnison]

@Image Analyst so in order to get anything that resemebels that image you'd need to extract the header data first and then the pixel data and somehow combine the two sets of information? If so which functions would you use?

Thanks

[Image Analyst]

I don't see any need to combine them. If you can figure out where the uncompressed pixels live, just read them into an array and start using it in your MATLAB code. If any header is needed when writing it out again, imwrite() will add it.