In
photography
Photography is the art, application, and practice of creating durable images by recording light, either electronically by means of an image sensor, or chemically by means of a light-sensitive material such as photographic film. It is emplo ...
and
optics
Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultrav ...
, vignetting is a reduction of an image's
brightness
Brightness is an attribute of visual perception in which a source appears to be radiating or reflecting light. In other words, brightness is the perception elicited by the luminance of a visual target. The perception is not linear to luminance, ...
or
saturation toward the
periphery compared to the image center. The word ''
vignette'', from the same root as ''
vine
A vine (Latin ''vīnea'' "grapevine", "vineyard", from ''vīnum'' "wine") is any plant with a growth habit of trailing or scandent (that is, climbing) stems, lianas or runners. The word ''vine'' can also refer to such stems or runners themsel ...
'', originally referred to a decorative border in a book. Later, the word came to be used for a
photographic portrait that is clear at the center and fades off toward the edges. A similar effect is visible in photographs of
projected
Projected is an American rock supergroup consisting of Sevendust members John Connolly and Vinnie Hornsby, Alter Bridge and Creed drummer Scott Phillips, and former Submersed and current Tremonti guitarist Eric Friedman. The band released the ...
images or
videos
Video is an electronic medium for the recording, copying, playback, broadcasting, and display of moving visual media. Video was first developed for mechanical television systems, which were quickly replaced by cathode-ray tube (CRT) system ...
off a
projection screen
A projection screen is an installation consisting of a surface and a support structure used for displaying a projected image for the view of an audience. Projection screens may be permanently installed, as in a movie theater; painted on the ...
, resulting in a so-called "hotspot" effect.
Vignetting is often an unintended and undesired effect caused by
camera
A camera is an optical instrument that can capture an image. Most cameras can capture 2D images, with some more advanced models being able to capture 3D images. At a basic level, most cameras consist of sealed boxes (the camera body), with ...
settings or
lens limitations. However, it is sometimes deliberately introduced for creative effect, such as to draw attention to the center of the frame. A photographer may deliberately choose a lens that is known to produce vignetting to obtain the effect, or it may be introduced with the use of special
filters
Filter, filtering or filters may refer to:
Science and technology
Computing
* Filter (higher-order function), in functional programming
* Filter (software), a computer program to process a data stream
* Filter (video), a software component that ...
or
post-processing procedures.
When using
superzoom lenses, vignetting may occur all along the zoom range, depending on the
aperture
In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture and focal length of an optical system determine the cone angle of a bundle of rays that come to a focus in the image plane.
An ...
and the
focal length
The focal length of an optical system is a measure of how strongly the system converges or diverges light; it is the inverse of the system's optical power. A positive focal length indicates that a system converges light, while a negative foc ...
. However, it may not always be visible, except at the widest end (the shortest focal length). In these cases, vignetting may cause an
exposure value (EV) difference of up to 0.75EV.
Causes
There are several causes of vignetting. Sidney F. Ray
[Sidney F. Ray, Applied photographic optics, 3rd ed., Focal Press (2002) .] distinguishes the following types:
* Mechanical vignetting
* Optical vignetting
* Natural vignetting
A fourth cause is unique to digital imaging:
* Pixel vignetting
A fifth cause is unique to analog imaging:
*
Photographic film
Photographic film is a strip or sheet of transparent film base coated on one side with a gelatin emulsion containing microscopically small light-sensitive silver halide crystals. The sizes and other characteristics of the crystals determine ...
vignetting
Mechanical vignetting
Mechanical vignetting occurs when light beams emanating from object points located off-axis are partially blocked by external objects such as thick or stacked filters, secondary lenses, and improper lens hoods. This has the effect of changing the
entrance pupil
In an optical system, the entrance pupil is the optical image of the physical aperture stop, as 'seen' through the front (the object side) of the lens system. The corresponding image of the aperture as seen through the back of the lens system ...
shape as a function of angle (resulting in the path of light being partially blocked). Darkening can be gradual or abrupt – the smaller the aperture, the more abrupt the vignetting as a function of angle.
When some points on an image receives no light at all due to mechanical vignetting (the paths of light to these image points is completely blocked), then this results in a restriction of the
field of view (FOV) – parts of the image are then completely black.
Optical vignetting
This type of vignetting is caused by the physical dimensions of a multiple element lens. Rear elements are shaded by elements in front of them, which reduces the effective lens opening for off-axis incident light. The result is a gradual decrease in light intensity towards the image periphery. Optical vignetting is sensitive to the lens
aperture
In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture and focal length of an optical system determine the cone angle of a bundle of rays that come to a focus in the image plane.
An ...
and can often be cured by a reduction in aperture of 2–3 stops. (An ''increase'' in the
F-number.)
Natural vignetting
Unlike the previous types, natural vignetting (also known as natural illumination falloff) is not due to the blocking of light rays. The falloff is approximated by the cos
4 or "cosine fourth" law of illumination falloff. Here, the light falloff is proportional to the fourth power of the
cosine of the angle at which the light impinges on the film or sensor array. Wideangle rangefinder designs and the lens designs used in compact cameras are particularly prone to natural vignetting. Telephoto lenses,
retrofocus wideangle lenses used on
SLR cameras, and
telecentric designs in general are less troubled by natural vignetting. A gradual grey filter or postprocessing techniques may be used to compensate for natural vignetting, as it cannot be cured by stopping down the lens. Some modern lenses are specifically designed so that the light strikes the image perpendicular or nearly so, eliminating or greatly reducing vignetting.
Pixel vignetting
Pixel vignetting only affects digital cameras and is caused by angle-dependence of the digital sensors. Light incident on the sensor at normal incident produces a stronger signal than light hitting it at an oblique angle. Most digital cameras use built-in image processing to compensate for optical vignetting and pixel vignetting when converting raw sensor data to standard image formats such as
JPEG
JPEG ( ) is a commonly used method of lossy compression for digital images, particularly for those images produced by digital photography. The degree of compression can be adjusted, allowing a selectable tradeoff between storage size and imag ...
or
TIFF. The use of offset
microlenses over the image sensor can also reduce the effect of pixel vignetting.
220px, Vignetting can be applied in the post-shoot phase with software.">digital imaging software.
Post-shoot
For artistic effect, vignetting is sometimes applied to an otherwise un-vignetted photograph and can be achieved by
burning
Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combustion ...
the outer edges of the photograph (with film stock) or using digital imaging techniques, such as masking darkened edges. The Lens Correction filter in
Photoshop can also achieve the same effect.
In digital imaging, this technique is used to create a
low fidelity (photography) appearance in the picture.
See also
*
Dodging and burning
*
Feathering
*
Flat-field correction
*
Metering mode
In photography, the metering mode refers to the way in which a camera determines exposure. Cameras generally allow the user to select between ''spot'', ''center-weighted average'', or ''multi-zone'' metering modes. The different metering modes al ...
*
Vignette (philately)
In philately, the vignette is the central part of a postage stamp design, such as, a monarch's head or a pictorial design, which often shades off gradually to the edges of the stamp.
The central vignette is often surrounded by a frame which may ...
Footnotes
References
Van Walree's webpage on vignettinguses some unorthodox terminology, but illustrates very well the physics and optics of mechanical and optical vignetting.
* Peter B. Catrysse, Xinqiao Liu, and Abbas El Gamal
QE Reduction due to Pixel Vignetting in CMOS Image Sensors in Morley M. Blouke, Nitin Sampat, George M. Williams, Jr., Thomas Yeh (ed.): ''Sensors and Camera Systems for Scientific, Industrial, and Digital Photography Applications,'' Proceedings of SPIE, vol. 3965 (2000).
* Yuanjie Zheng, Stephen Lin, and Sing Bing Kang
Single-Image Vignetting Correction IEEE Conference on Computer Vision and Pattern Recognition 2006
* Olsen, Doug; Dou, Changyong; Zhang, Xiaodong; Hu, Lianbo; Kim, Hojin; Hildum, Edward. 2010.
Radiometric Calibration for AgCam Remote Sens. 2, no. 2: 464-477.
{{photography subject
Science of photography
Photographic techniques
Optics