Lens vignetting in photography: correcting and maintaining the image’s balance
What Is Lens Vignetting?
Lens vignetting is a reduction in brightness or saturation on the periphery of an image. It is produced by a certain number of factors, including defects in the design of the lens, the focal length, or the aperture. The loss of brightness grows as the distance from the center of the photo increases.
What Causes Lens Vignetting in photos?
Lens vignetting is especially visible in images taken with a short focal length, zoom lenses, and telephoto lenses. Vignetting is even more apparent when the photo is taken with a wide aperture because it is caused when the front part of the lens blocks the camera from receiving light.
Vignetting results in a progressive loss of brightness as the distance from the center of the image increases.
The use of an evenly lit dot plot makes it possible to precisely map out the vignetting effect produced by the lens.
Measuring Vignetting: a cartographic and customized defect analysis
For each combination of aperture and focal length, DxO’s specialists create a customized map of the vignetting effect. To create each correction map, they photograph an evenly lit dot diagram, then create a model for the darkening effect for the position of each pixel in the image.
The engineers then attribute a value from 0 to 1 to each pixel. This value is used to correct JPEG images pixel by pixel.
Using the same light diagram, the vignetting values are also collected for each color channel in the original RAW file and the final RVB image. These values are measured under various brightness conditions. Based on the lens/camera pair being analyzed, it takes between 100 to 500 sample images to generate the data needed to make a vignetting map.
The calibration data obtained through this analysis are compiled in a correction file for each corresponding lens and camera pairing called the optical module.
Comprehensive vignetting correction
DxO’s vignetting correction feature does much more than simply restore brightness levels to the edges of the frame. Instead, it takes into account several factors:
- It compensates for exposure levels when the correction might result in over-exposing the edges of the image
- It limits the risk of color alteration
- It does not increase noise levels when brightening darkened areas
Nikon D4S (AF-S 200-400mm f4), 400mm f/4, 1/8000, ISO360
DxO’s vignetting correction feature compensates for exposure, limits color alteration, and does not generate additional noise.
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