Credit: Chris Jackson/Getty Images News/Getty Images Creation CTG files are officially known as catalog index files. These files are generated automatically when you capture an image on certain Canon brand digital cameras.
CTG files do not contain an actual image, but rather information that is correlated to a folder containing photographs you took on the Canon digital camera. Storage Canon digital cameras save image data on SD cards, which are inserted into the side of the camera and can be removed when photos need to be transferred. CTG files are stored on the SD card, in a separate folder than where image files are saved. The CTG files correlate to an image folder. For example, file 123.CTG would correspond to the camera images held in folder 123CANON. Opening CTG Files Canon CTG files are not designed to be opened on a computer, either Mac or PC. The files facilitate the indexing of your camera images by your computer, and allow your computer to populate the image files during a transfer.
Once on your computer, an image file can be opened by a variety of photo editing programs. The correlating CTG files, however cannot be opened or edited. When you delete an image file from your camera, the corresponding CTG file is also erased. Conversion A CTG file cannot be converted into an image file, such as a JPEG.
Because the files contain no image data, they will not successfully be converted to an image of any sort. Attempting to alter a CTG file may interfere negatively with your computer's ability to index the images transferred from your Canon digital camera to the computer.
#1 What could have happened is that the computer software has now left its mark on the image file and made it incompatible with the Canon software and Canon camera, though why would you need to still view the photos on your camera? Best thing I can suggest is to put the card back in the 'sim' slot, as you call it and whilst you can see the image on the computer through the sim card, TRANSFER the image file to the computer (along with the others,as well if you want to keep them safe) and get them into a secure place - either CD DVD or another hard drive before you start messing with the images.
What is a ctg file and how do I open a ctg file? CTG is a catalog index file created on Canon digital cameras, stored in the CANONMSC folder which corresponds to other folders saved on the memory card. Having trouble opening CTG files? Learn the most common reasons why you can't open CTG files and how to open them quickly and easily.
A ctg file is a Multiple Use Files developed by Canon. Learn what Mac OS programs can open.ctg files.
The general rule of thumb is to COPY (rather than just move) your images off the card onto the computer then edit them on the computer AWAY from the card AFTER making a copy that will remain untouched for the time being elsewhere. That way you always have a backup somewhere untouched until you finally store them safely, in case something goes wrong - like it has done here. As I said, get the images copied from the card to somewhere safe for now, and try and work on a COPY on the hard drive. Hope this helps. It is a really awful feeling when you think you have lost a picture that is important. As a pro photographer I have had that feeling a lot, but when there is a backup at least all is not lost - just a bit of a faff instead:-).