Does moving video and picture files back and forth from one external hard drive to another deplete the image quality?
An interesting question was left on the Ask A Question page by Ronnie regarding the possibility of losing image quality when moving files from one place to another. I guess the source of this question comes from the experience you get when you copy an audio tape from one cassette to another, say if you’re making a copy of a ColdPlay tape. The target cassette has the same music, but the copying process introduces “noise” which reduces the quality of the music. If you copy it again and again, you’ll notice a progressive deterioration in the overall sound. Another example of this deterioration can be seen when you photocopy a leaflet about diet pills for example, then photocopy the photocopy etc. After a number of generations you can see the gradual deterioration in the quality of your image.
Luckily, when we move a file from one disk to another, we don’t experience this same symptom. Coping a file from one place to another, for example, from a hard disk to a floppy disk, from a removable hard disk to a CD, the resulting file remains 100% intact. This is definitely a good thing. Media files would lose quality otherwise, but even worse, data files and executables can be completely destroyed if even one bit of the data has been inadvertently changed.
So, what’s the difference between the two processes? Well, in the latter case, moving a file from one place to another is a purely digital process. Files on a disk are stored as a digital sequence of 1s and 0s and this sequence can be replicated perfectly. The former case however, involves converting or translating information from an “analogue” format to a “digital” format and back to “analogue”. The problem here is that the conversion process is approximate and can never be 100%. Even if the process is “practically” perfect, the target can never be exactly the same as the source, and the more generations we make of the copy, the more the differences become obvious.
Okay, that wasn’t a very technical explanation, but my aim here is to convey what is happening in layman terms and to assure Ronnie that it doesn’t matter if you copy a file once, a hundred times or a million times; as long as there’s no fault in the media you are copying to, your file will never lose quality. (If you want something a bit more technical, there’s a great write up on analogue to digital conversion on Wikipedia)