Bud Black wrote:
What is the difference between deleting all files or formatting an SD card?
Formatting storage media usually only replaces the file directory with an empty one, allowing all space on the media to be overwritten with new data.
Deleting a file or files simply erases the directory *entries* for those files.
In both cases, the files are still there, and can be recovered with file recovery software, unless you use the media to store NEW files.
SOME cameras and operating systems allow "low level formatting" or "secure formatting", which simply writes zeros to all storage locations on the media. It is generally unnecessary to do secure formatting unless you work with sensitive information or subject matter. It takes so long to do on some systems that it may be impractical... Drilling a big hole in a card, then flushing it, may be less expensive and quicker for small capacity cards than waiting for low level/secure formatting.
From a workflow standpoint, it is probably smart to use a freshly-formatted card for each new session. I never delete images in the camera, for a long list of reasons that usually have to do with a desire for file redundancy, the inability to truly see the image on the small LCD of the camera, time, and so forth. I edit on a minimum 21" monitor, so I can see what is really there.
My workflow is:
Format the card in the exact camera I'm going to use it. (If the camera needs special directory structures beyond the standard DCIF folder, it creates them and stores them then.)
Expose until I'm done with the session.
Remove the card, place it in a USB 3 reader, and download the contents to my computer.
BACK UP the images in an off-line, remote location, using a removable hard drive, a cloud account, DVDs, flash drives... (I use all of these).
VERIFY the backup.
Put the card back in the camera and re-format it there.
Edit the images... Back up the edits.
I tend to keep everything from a job backed up off-line. I keep things in chronological order, everywhere. I never delete from an SD/CF card in the camera. I always format.
There is nothing technically wrong with file deletion. I just don't believe it suits my workflow, because I WANT a backup of every image I record. I have gone back to my backups several times and chosen different files to work on, sometimes at customer requests. The moment or pose I chose originally wasn't what they wanted, and they asked for options, or a reshoot. Sometimes the "culls" are usable.