The names assigned to image files vary slightly with different EOS cameras. Here's a guide to what you may see, and what it means.
JPG shows that image has been saved in JPEG format
. IMG is short for image, and it is followed by the four-digit file number. This means that the highest file number within a folder is 9999. After this, a new folder is created on the card and the numbering starts again. This means you should be careful downloading from multiple folders to the same location on your computer, because files may have the same name. To help prevent images being overwritten accidentally, use the Rename tool in Canon's Digital Photo Professional (DPP) software – see the section about file renaming below.
An underscore at the start of a JPEG file name indicates that the image was shot using the Adobe RGB colour space. When sRGB is set, there is no underscore. This occurs automatically on any camera where the colour space can be selected, so the rest of the file name may vary, and it enables software as well as users to simply identify what colour space was used and open the image with the correct colour profile.
EOS professional digital cameras use a four-character camera code as the prefix to the file name. This code is unique to the individual camera and is preset by Canon during manufacture, but with more recent cameras – the EOS 5D Mark IV, the EOS-1 D series, and the EOS R5 – it can be customised by the photographer, and changed as frequently as you wish. So you might, for example, wish to use a custom code for a particular shoot, such as 21NY for your 2021 shoot in New York. See your camera manual for details. Note that you cannot set an underscore as the first character, because that is reserved for shots taken using Adobe RGB, as noted above.
XXXL0001.JPG, XXXN0001.JPG, XXXM0001.JPG, XXXS0001.JPG, _XXL0001.JPG, _XXN0001.JPG, _XXM0001.JPG, _XXS0001.JPG
An L, M, N or S in the file name indicates that the camera’s file size was set to L = Large, M = Medium1, N = Medium2, S = Small.
CRW_0001.CRW, XXXX0001.CR2, XXXX0001.CR3
These are the Canon RAW files for still images. EOS cameras released since 2018 use the newer CR3 format.
The HIF extension indicates that the image is an HEIF (High Efficiency Image File Format) file. This is a newer file format with more efficient file compression than JPEG. It has 10-bit colour rather than the 8-bit of a JPEG.
These are movie file formats. Most EOS cameras record in the MP4 format. Cameras that record 4K footage might use various container formats including .MXF or .MTS.
This is the Canon RAW video format, which means that the footage has much greater scope for post-capture adjustment and grading. Some cameras also use .RMF.