I don't understand the question in the context of the title?
A 4.7k byte if that is what you mean is a small file not a large file
What kind of image file is it (PSD, TIFF, JPEG, PNG......)?
How was it saved?
Was it tagged with a grayscale profile?
Can you post a link to one example file and we can take a look at it. That way we can tell you if it is the file itself or something in your set up or that you are doing.