I haven't re-sized the new bitmap file but still i get an output which is same as large.bmp. I dont know how this work even if I haven't changed the size of image or the file
It looks like you scaled it up by a factor of 4, which generates the large.bmp file.
./resize 4 small.bmp copy.bmp
The 4 in this command says to scale up by 4, which is what you have (unless your small file is something different). If you want to copy a file, then you should have used 1 and not 4.
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