How to format an SD card in your camera, without losing a photo

Before you format: check everything is copied

Formatting erases everything on the card, protected images included. So you need a copy, and above all a verified copy. That's where drag and drop falls short: Finder and Windows File Explorer write each file elsewhere, but never read the copy back to compare it with the original.

A worn cable or card reader, a card that reads badly, a drive that disconnects for a second: the copied file exists, has the right name and often the right size, but it's damaged. No message warns you. You find out when you open the photo in Lightroom, after the card has been formatted.

Only the last one lets you format with peace of mind. You can do it for free with one command (see below), or let Récolte do it on every copy.

How to format an SD card in your camera

Always format in the camera that will use the card, not on your computer. The camera creates the folder structure and file system it expects. Nikon and Sony both recommend reformatting in the camera any card that was formatted on a computer or in another camera.

Menu names change from one model to the next. Here is the path on recent bodies from each brand; if in doubt, search for “format” in your camera's online manual.

Canon

MENU → Set-up tab (wrench icon) → Format card, then pick the card if your body has two slots, and confirm. Some models also offer a low-level format, which takes longer and rewrites the whole card.

Sony

MENU → Shooting → Media → Format, then pick the slot and select Enter. On several models, holding the MENU button and then the delete button for about two seconds opens the format screen directly. The most recent bodies offer a quick or full format.

Nikon

MENU → Setup menu (wrench icon) → Format memory card, the first item in the menu. Pick the slot, then Yes. Don't turn the camera off or remove the card while the formatting message is on screen.

Fujifilm

MENU → Set-up tab (wrench icon) → User setting → Format, then confirm. On some X bodies, such as the X100VI, holding the delete (trash) button while pressing the center of the rear command dial opens the format screen directly.

Panasonic Lumix

MENU → Setup (wrench icon) → Format, or Card/File → Card Format on recent models, then Yes.

Quick or full format?

A quick format, the default, only erases the table that says where the files are. It's instant, and plenty between two shoots.

A full format (“low-level” at Canon) rewrites the whole card. It takes several minutes, but it helps if the card has become slow, or before you lend or sell it, since it makes the old photos unrecoverable.

What about formatting on a computer?

If you need to prepare a card without your camera at hand, avoid Finder's or File Explorer's format option, which doesn't always follow the SD standard. Use SD Memory Card Formatter instead, the free tool from the SD Association, on Mac and Windows. Then format the card again in your camera before the next shoot.

Verify your copy for free, on Mac and Windows

Your computer can already compare two folders without installing anything. It takes a terminal, but it's a single command to copy and paste.

On a Mac, with Terminal

Open the Terminal app and paste this command, replacing the two paths: first your card's DCIM folder, then its copy on your drive. You can drag a folder into the Terminal window to type its path.

diff -rq -x '._*' -x '.DS_Store' "/Volumes/EOS_DIGITAL/DCIM" "/Volumes/SSD/Wedding/DCIM" && echo "All identical."

The command compares the content of every file, byte for byte. If everything matches, it prints All identical. Otherwise it lists the differences: Files … differ for a damaged file, Only in … for a file missing on one side. The -x options skip the small technical files macOS adds on its own.

On Windows, with PowerShell

Open PowerShell, replace the two paths on the first lines, then paste it all:

$card = "E:\DCIM"
$copy = "D:\Wedding\DCIM"
Get-ChildItem $card -Recurse -File | ForEach-Object {
  $twin = Join-Path $copy $_.FullName.Substring($card.Length)
  if (-not (Test-Path -LiteralPath $twin)) { "Missing: $($_.FullName)" }
  elseif ((Get-FileHash -LiteralPath $_.FullName).Hash -ne (Get-FileHash -LiteralPath $twin).Hash) { "Different: $($_.FullName)" }
}
"Check complete."

The script computes a fingerprint (hash) of every file on the card and of its copy. If nothing shows up before Check complete., everything matches.

With Récolte: verification is part of the copy

I built Récolte, as a wedding photographer, so I'd never have to wonder at format time again. There are two ways to use it.

Copy and verify in one pass

Plug in your cards: Récolte copies every file to your drive, then reads the copy back and compares it with the original, byte for byte. A file is only marked “verified” once that comparison succeeds. Several cards can run at once, and files already secured from the twin card of a dual-slot pair aren't copied again. At the end, a report tells you card by card what's verified, and so what you can format.

Check a card you already copied by hand

For cards copied by drag and drop, the Verify cards tool does the terminal's job without its limits. Pick the folder that should hold your files, insert your cards one by one, and Récolte tells you whether every photo and video on the card is in there. It matches by content, so it doesn't matter if you've renamed, sorted or merged your files since.

You can choose between two methods. Standard reads the start and end of each file: it's fast and catches a truncated or missing file, but not an isolated corruption in the middle of a file. Thorough reads every byte: full certainty, at the cost of reading everything again.

Either way, Récolte never touches your card: it doesn't modify, move or delete any file, and never formats it. Formatting stays your call, in your camera. Everything happens locally, without sending your files anywhere.

Your checklist before you format

1. The copy is verified, by comparing content, not just the number of files.
2. A second copy exists on another drive. A verified copy on a single drive is only as safe as that drive. The full method is in the 3-2-1 backup rule for photographers.
3. You know which card you're holding. When several cards go through the same reader, a label or a colored sticker keeps you from formatting the wrong one.
4. You format in the camera, picking the right slot if it has two.

FAQ

Related guides

• The 3-2-1 backup rule for photographers →
• Offloading dual card slot cameras →
• Finding duplicate photos on an external hard drive →