This feature requires the Analyze-License
After selecting a f-stop in the tree view a vignetting analysis view appears on the right side:
In addition the following buttons are available:
The two check boxes Fixed Range and Smooth Curve serve the same purpose as they do the distortion analysis context (see section Distortion analysis).
The curve represents the standard illumination fall-off (IFOStandard) in [%], dependent on the distance to the vignetting center (on the original, distorted image).
IFOStandard considers the circumstance, that the strength of the vignetting effect also depends on the subject brightness B (beneath the captured parameters focal length and aperture). The relationship between brightness and illumination fall-off is determined by many factors, among others to what extent contrast and brightness were preadjusted by the camera.
Therefore this dependence is approximated by the following curve:
According to this approximation the affected image area ought to be brightened up by the amount of IFOStandard for a brightness greater than 50%, in order to compensate the vignetting effect. For e.g. black (brightness = 0%) the area would not have to be brightened up.
Note that the illumination fall-off always refers to the white level, and not to the examined grey value. If the color depth is 8 bit for example, the correction factor, by which the grey value finally must be multiplied, can be determined as follows:
All precise standard illumination fall-off values for all focal lengths and all f-stops can be found in the ssv-table "Vignetting profile ...".
Note: Please read in the section "Save distortion profile in ssv-table", how to import ssv-tables into OpenOffice or Excel!
Use the button "Vignetting profile ..." to save the complete vignetting data from the current Calibration-Set in a ssv-table (semicolon separated value).
The contained standard illumination fall-off values are grouped by focal length and f-stop and are indicated for 24 distances from the vignetting center.