Canon EOS rebel xs - Manual (Page 66)

3 Setting the Image-recording Quality
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1 is the raw data before it is made into a 73 or other images.
Although 1 images require software like Digital Photo Professional
(provided) 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 create your own art or shoot an important
subject.
For example, with a 1 image, you can use the provided software to
create various versions of the same image having a different Picture
Style. Also, if you took the picture with the wrong white balance (p.90),
you can change the white balance without degrading the image quality.
Note that 1 images will not work with direct printing or print ordering
(DPOF).
1 +73 records both a 1 and 73 image with a single shot. The
two images are saved to the card. Since the 73 image is recorded as a
processed image, you can view it as is on a personal computer without
the bundled software or print it as is. With 1+73, the two images are
saved with the same file number in the same folder. You can distinguish
between them with the image type or extension. The 1 image’s
extension is “CR2,” and the 73 image’s extension is “JPG.”
About 1
About 1+73
File number
File extension
0001 . JPG
0001 . CR2
1 image
73 image
The Auto Lighting Optimizer (p.156) will not work with 1 and 1+73
images.