I have a EOS T3i that I purchased about three months ago. I have the camera set to capture .jpg and .cr2 files with each shot. I like the ability to edit the .cr2 files and then convert to .jpg without the quality loss induced by directly editing the .jpg files and recompressing.
My question is, is there a way to delete only the .cr2 files from the camera itself? I know that using a card reader to directly modify the files on the SD card can be dangerous, but is it any less dangerous to plug the camera in via USB and delete files individually through Windows? I would like to keep only the .jpg files on the camera to save space while maintaining the ability to "show off" my previously taken images via HDMI when I'm not at home to access my PC.
You could just "protect" all the good ones you don't want to delete.
I'd download all the files to a computer, clear the card, pick the ones I liked & wanted to keep on my card & use trial & error to see just what quality of file was needed for a good image on a TV screen. Once I knew that I'd downsize all the files I wanted on the card to that resolution & then transfer them back to the card. This will give you the best result & keep more of the card cleared for the next batch of photos you'll shoot. I'd use a card reader for all of this & I don't see any problems with deleting or modifying during the download or when re installing them later. Card readers simplify things.
I don't know of any way to delete the CR2 files in camera but doing it via the file system by plugging your card into your computer should never cause an issue. I've been doing it for more than 5 years without any issues. The only issue that might occur is if you format your card while it's plugged into the computer. I only ever format the SD card using the camera.
I also find it a lot faster to transfer the images to the computer through the SD card rather than plugging the camera in with the cords and I find the camera battery lasts longer.