Canon EOS Rebel T3 18-55mm IS II Kit Instruction Manual page 76

3 Setting the Image-recording Quality
About 1
1 is the raw image data before it is made into 73 or other images.
Although 1 images require software like Digital Photo Professional
(provided, p.270) so they can be displayed on the computer, they also
offer flexibility for image adjustments possible only with 1. 1 is
effective when you want to precisely adjust the image yourself or shoot
an important subject.
About 1+73
1+73 records both a 1 and 73 image with a single shot. The
two images are saved to the card simultaneously. The two images will
be saved in the same folder with the same file numbers (file extension
.JPG for JPEG and .CR2 for RAW). 73 images can be viewed or
printed even with a computer which does not have the software
provided with the camera installed.
Commercially-available software might not be able to display RAW images.
Using the provided software is recommended.
76
1 image
73 image
File number
0001 . CR2
0001 . JPG
File extension