All photographic images have some degree of vignetting, a gradual darkening of the image toward its periphery. We have developed a technique to calibrate and remove vignetting, using only a sequence of images such as those used to create a panoramic mosaic. We can also recover exposure variations between the frames in the sequence. Although the radiometric response of the camera or film is needed to recover relative radiance values, it need not be known in advance if all you need to do is remove vignetting from your images. Above you can see an aligned input image, and below it the same sequence after vignettes and exposures have been corrected and the frames blended together. Blending alone cannot remove the exposure differences and vignetting distortions.
This technology has been implemented as the "Vignette Removal" checkbox in Photoshop CS4's Auto-Align and Photomerge workflows. Although the checkbox only mentions vignetting, this feature does also remove small exposure differences between images as well, making it possible to compose panoramic image sequences using aperture-priority mode on an SLR.
This technology is also used in the "Adobe Lens Profile Creator" that can be used with Photoshop CS5 to create custom lens profiles and corrections for geometric distortion, vignetting, and chromatic aberration.