Pixel Vignetting
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photography Photography is the visual arts, art, application, and practice of creating 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 empl ...
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 optical instruments, instruments that use or Photodetector, detect it. Optics usually describes t ...
, vignetting ( ) is a reduction of an image's
brightness Brightness is an attribute of visual perception in which a source appears to be radiating/reflecting light. In other words, brightness is the perception dictated by the luminance of a visual target. The perception is not linear to luminance, and ...
or
saturation Saturation, saturated, unsaturation or unsaturated may refer to: Chemistry *Saturated and unsaturated compounds, a classification of compounds related to their ability to resist addition reactions ** Degree of unsaturation **Saturated fat or satu ...
toward the
periphery Periphery or peripheral may refer to: Music *Periphery (band), American progressive metal band * ''Periphery'' (album), released in 2010 by Periphery *"Periphery", a song from Fiona Apple's album '' The Idler Wheel...'' Gaming and entertainme ...
compared to the image center. The word ''
vignette Vignette may refer to: * Vignette (entertainment), a sketch in a sketch comedy * Vignette (graphic design), decorative designs in books (originally in the form of leaves and vines) to separate sections or chapters * Vignette (literature), short, i ...
'', from the same root as ''
vine A vine 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 themselves, for instance, when used in wicker work.Jackson; Benjamin; Da ...
'', originally referred to a decorative border in a book. Later, the word came to be used for a
photographic portrait Photography is the art, application, and practice of creating 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 employed in many ...
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 An image or picture is a visual representation. An image can be two-dimensional, such as a drawing, painting, or photograph, or three-dimensional, such as a carving or sculpture. Images may be displayed through other media, including a project ...
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 on a wall, as in a movie theater, mounte ...
, resulting in a so-called "hotspot" effect. Vignetting is often an unintended and undesired effect caused by
camera A camera is an instrument used to capture and store images and videos, either digitally via an electronic image sensor, or chemically via a light-sensitive material such as photographic film. As a pivotal technology in the fields of photograp ...
settings or
lens A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements'') ...
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 Filtration is a physical process that separates solid matter and fluid from a mixture. Filter, filtering, filters or filtration may also refer to: Science and technology Computing * Filter (higher-order function), in functional programming * Fil ...
or post-processing procedures. When using
zoom lens A zoom lens is a system of camera lens elements for which the focal length (and thus angle of view) can be varied, as opposed to a fixed-focal-length (FFL) lens (''prime lens''). A true zoom lens or optical zoom lens is a type of '' parfocal ...
es, vignetting may occur all along the zoom range, depending on the
aperture In optics, the aperture of an optical system (including a system consisting of a single lens) is the hole or opening that primarily limits light propagated through the system. More specifically, the entrance pupil as the front side image o ...
and the
focal length The focal length of an Optics, optical system is a measure of how strongly the system converges or diverges light; it is the Multiplicative inverse, inverse of the system's optical power. A positive focal length indicates that a system Converge ...
. 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 In photography, exposure value (EV) is a number that represents a combination of a camera's shutter speed and f-number, such that all combinations that yield the same exposure (photography), exposure have the same EV (for any fixed scene luminanc ...
(EV) difference of up to 3EV.


Causes

There are several causes of vignetting. Sidney F. RaySidney 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 photographic emulsion, emulsion containing microscopically small light-sensitive silver halide crystals. The sizes and other characteristics of the ...
vignetting


Mechanical vignetting

Mechanical vignetting occurs when light beams emanating from object points located off-axis (laterally or vertically off from the optical axis of an optical system under consideration) are partially blocked by external objects of the optical system 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 optical elements in front of the stop. The corresponding image of the aperture stop as seen through the optical elements behin ...
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 The field of view (FOV) is the angle, angular extent of the observable world that is visual perception, seen at any given moment. In the case of optical instruments or sensors, it is a solid angle through which a detector is sensitive to elec ...
(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 of the lens 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, the aperture of an optical system (including a system consisting of a single lens) is the hole or opening that primarily limits light propagated through the system. More specifically, the entrance pupil as the front side image o ...
and can often be cured by a reduction in aperture of 2–3 stops. (An ''increase'' in the
F-number An f-number is a measure of the light-gathering ability of an optical system such as a camera lens. It is calculated by dividing the system's focal length by the diameter of the entrance pupil ("clear aperture").Smith, Warren ''Modern Optical ...
.)


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 cos4 or "cosine fourth" law of illumination fall off. Here, the light fall off is proportional to the fourth power of the
cosine In mathematics, sine and cosine are trigonometric functions of an angle. The sine and cosine of an acute angle are defined in the context of a right triangle: for the specified angle, its sine is the ratio of the length of the side opposite that ...
of the angle at which the light impinges on the film or
sensor array A sensor array is a group of sensors, usually deployed in a certain geometry pattern, used for collecting and processing electromagnetic or acoustic signals. The advantage of using a sensor array over using a single sensor lies in the fact that an ...
. Wide angle rangefinder designs and the lens designs used in compact cameras are particularly prone to natural vignetting. Telephoto lenses, retrofocus wide angle lenses used on SLR cameras, and
telecentric A telecentric lens is a special optical lens (often an objective lens or a camera lens) that has its entrance or exit pupil, or both, at infinity. The size of images produced by a telecentric lens is insensitive to either the distance between an ...
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 ( , short for Joint Photographic Experts Group and sometimes retroactively referred to as JPEG 1) is a commonly used method of lossy compression for digital images, particularly for those images produced by digital photography. The degr ...
or
TIFF Tag Image File Format or Tagged Image File Format, commonly known by the abbreviations TIFF or TIF, is an image file format for storing raster graphics images, popular among graphic artists, the publishing industry, and photographers. TIFF is w ...
. The use of offset
microlens A microlens is a small lens, generally with a diameter less than a millimetre (mm) and often as small as 10 micrometres (μm). The small sizes of the lenses means that a simple design can give good optical quality but sometimes unwanted effects ...
es over the image sensor can also reduce the effect of pixel vignetting. 220px, Vignetting can be applied in the post-shoot phase with 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. Combust ...
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 Adobe Photoshop is a raster graphics editor developed and published by Adobe for Windows and macOS. It was created in 1987 by Thomas and John Knoll. It is the most used tool for professional digital art, especially in raster graphics editin ...
can also achieve the same effect. In digital imaging, this technique is used to create a low fidelity appearance in the picture. To give a photo a 'retro' look - that it was made with an old camera or lens - one could add an obvious 'vignette' using 'lens correction' or burning in margins by any of several techniques. There is a much more general use. Viewers' eyes are attracted to brightness so if the areas to the corners or edges are brighter than the desired center of interest, eyes may wander towards that brightness. To direct the viewers' attention, the bright corners or margins are barely perceptibly darkened. This darkening 'fences off' the bright area and keeps the viewer's eyes where the photographer wants. The object is to keep the view inside the image but, at the same time, not be obvious.


See also

*
Dodging and burning Dodging and burning are techniques used during the printing process to manipulate the exposure of select areas on a photographic print, deviating from the rest of the image's exposure. In a darkroom print from a film negative, ''dodging'' decrea ...
*
Feathering Feathering is a technique used in computer graphics software to smooth or blur the edges of a feature. The term is inherited from a technique of fine retouching using fine feathers. Paintbrush feathering Feathering is most commonly used on a ...
* Flat-field correction *
Metering mode In photography, the metering mode refers to the way in which a camera determines exposure (photography), exposure. Cameras generally allow the user to select between ''spot'', ''center-weighted average'', or ''multi-zone'' metering modes. The diffe ...
*
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 postage stamp, stamp. The central vignette is often surrounded by a fr ...


Footnotes


References

* 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 Sing Bing Kang is a computer scientist known for his work in image-based modeling and rendering. He is a distinguished scientist at Zillow. Kang has a Ph.D. from Carnegie Mellon University, completed in 1994. His dissertation, ''Robot Instruction ...

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 Image defects Photographic techniques Optics