Canon EOS 90D Advanced User's Manual page 207

Peripheral Illumination Correction
Vignetting (dark image corners) can be corrected.
Depending on shooting conditions, noise may appear on the image periphery.
o
The higher the ISO speed, the lower the correction amount will be.
o
The correction amount applied will be lower than the maximum correction
o
amount that applied with Digital Photo Professional (EOS software).
Peripheral illumination is corrected automatically in Basic Zone modes when
o
correction data is registered on the camera.
Distortion Correction
Distortion (image warping) can be corrected.
To correct distortion, the camera captures a narrower image area than the
o
area seen when shooting, which crops the image a little and slightly lowers the
apparent resolution.
Setting distortion correction may change the angle of view slightly.
o
When you magnify images, distortion correction is not applied to the images
o
displayed.
Distortion correction is not applied in movie recording.
o
Images with distortion correction applied will not have the Dust Delete Data
o
( = 241) appended. Also, the AF point may be displayed out of position,
relative to the time of shooting.
Distortion is corrected automatically when < 8 > mode is set to < q > mode
o
and correction data is registered on the camera.
Correction of Lens Aberrations due to Optical Characteristics
207