I've been researching ways to retrieve orientation information from a JPEG file in pure JavaScript.
An excellent way to get this information is outlined in this SO answer. Essentially one reads the entire file using readAsArrayBuffer and then processes it for the required information.
However, is it really necessary to read the whole file to retrieve EXIF information? Is there an optimization whereby one can read a subset of bytes when doing this?
For instance, this SO answer seems to suggest the first 20 bytes are good enough for the job. However, the former answer's writer himself asserts that he removed the slice statement because sometimes the tag came in after the limit (he had originally set it to 64KB, i.e. reader.readAsArrayBuffer(file.slice(0, 64 * 1024));)
So what's a rule of thumb one can use when programming this sort of a thing? Or does one not exist at all? I want to write code where performance doesn't get heavily affected by the size (in bytes) of file uploaded by a user. That is my goal.
Note: I've tried Googling this information as well, however haven't found anything meaningful.
