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Topic: Perspective distortion

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Perspective projection distortion

Perspective distortion caused by lens focal length

Perspective distortion (caused by camera to subject distance)

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	Perspective projection distortion - Wikipedia, the free encyclopedia
		Perspective projection distortion is an error introduced in drawing when images are created by the use of "projectors".
		Both types of projection involve a distortion; parallel lines never intersect in nature, but they always intersect in perspective projections, with the rare exception wherein both the surface of projection is planar and an object plane is spatially parallel to the plane of projection.
		Figure 8 shows that the perspective projection of the horizontal top line of the wall intersects at the retina (actually, in true life, at the focal point slightly in front of the retina and from where it is inverted).
	en.wikipedia.org /wiki/Perspective_projection_distortion (1898 words)

	Perspective distortion (caused by camera to subject distance) - Wikipedia, the free encyclopedia
		In photography and cinematography, perspective distortion describes the appearance of a part of the subject appearing abnormally large, relative to the rest of the scene.
		It is affected solely by the distance between the camera and subject, and the smaller this distance the greater the perspective distortion.
		Perspective distortion is particularly noticeable in en face portraits.
	en.wikipedia.org /wiki/Perspective_distortion_caused_by_lens_focal_length (404 words)

	Perspective (graphical) - Wikipedia, the free encyclopedia
		Perspective in the graphic arts, such as drawing, attempts to approximate an image as it is perceived by the eye on a flat surface, such as paper.
		In the former case it is generally referred to as artistic, spatial foreshortening; in the latter case it is referred to as perspective projection or if calculated using matrix multiplication (usually by a computer) as a perspective transform.
		Natural perspective projection is the name given by Leonardo to the projection that produces the image beheld by the human eye.
	en.wikipedia.org /wiki/Perspective_(graphical) (1378 words)

	Distortion
		Distortion is difficult to correct for in zoom lenses, which usually go from barrel at the wide end to pincushion at the tele end.
		Distortion is measured as the relative change of h compared to its value predicted by the paraxial theory.
		The designation 'perspective distortion' is frequently encountered to describe converging verticals and other manifestations of the perspective, but this is questionable as it unjustly suggests a misrepresentation of the reality.
	www.vanwalree.com /optics/distortion.html (1625 words)

	Quality Magazine: Handling Distortion and Perspective Errors in Imaging Systems (Site not responding. Last check: 2007-11-07)
		Distortion is an optical error or aberration, caused by the lens, which results in differences in magnification at different points in the image.
		If the distortion at the edge of the sensor is less than the size of a pixel, then the distortion will have no effect on the recorded image.
		Perspective errors are most troublesome in measurement applications involving objects with depth or objects moving relative to the lens.
	www.qualitymag.com /CDA/ArticleInformation/features/BNP__Features__Item/0,6425,98071,00.html (542 words)

	[No title] (Site not responding. Last check: 2007-11-07)
		Forward perspective correction means that the picture will be distorted in whatever directions we stretch the perspective tool grid.
		When the GIMP distorts the image, it will adjust the photograph so that the grid lines -- and the positions on the image they correspond with -- are exactly vertical.
		Click on the image with the perspective tool, then click the bottom left handle and drag it horizontally to the left until the grid is aligned with the image.
	www.bethelks.edu /bstucky/gimp/perspective_correct (1014 words)

	Perspective distortion - Encyclopedia.WorldSearch (Site not responding. Last check: 2007-11-07)
		Distortion or development?: Contending perspectives on the multinational corporation
		Punjab politics in national perspective: A study in democracy, development, and distortion
		Frieze and wallpaper symmetry groups classification under affine and perspective distortion (Technical report.
	encyclopedia.worldsearch.com /perspective_distortion.htm (120 words)

	Perspective Correction Tutorial - Lonestardigital.com
		The distortion is caused by the camera's digital sensor (the focal plane) not being parallel to an object's surface and/or not level with the center of the object.
		Sometimes perspective distortion is unavoidable because of shooting situations or locations, sometimes it's actually desirable for the dramatic visual effect.
		The Perspective* tool ties two opposite sides of the picture together and should only be used in situations where the perspective distortion is absolutely equal from side to side or from top to bottom (which is rare).
	www.lonestardigital.com /perspective_correction.htm (532 words)

	Encyclopedia: Perspective distortion caused by lens focal length (Site not responding. Last check: 2007-11-07)
		Encyclopedia: Perspective distortion caused by lens focal length
		People who viewed "Perspective distortion caused by lens focal length" also viewed:
		Other descriptions of Perspective distortion caused by lens focal length
	www.nationmaster.com /encyclopedia/Perspective-distortion-caused-by-lens-focal-length (459 words)

	Digital Imaging Software Review: Andromeda's LensDoc Plug-in
		In a word (or three), the problem is distortion, perspective and rotation.
		Perspective: Tilt your camera up to shoot some skyscraper and (unless you're lucky enough to have a view camera) the vertical lines in your images are condemned to converge.
		The first thing to do is select whether you want to fix a distortion, perspective or rotation, by clicking the corresponding red radio button in the top right corner.
	www.imaging-resource.com /SOFT/LDOC/LDOC.HTM (2104 words)

	camera calibration (Spurl.net stream) (Site not responding. Last check: 2007-11-07)
		Snip: Geometric lens distortion is long-known phenomena and it is one of the most stubborn type of image distortion caused by lens [1].
		Projective and perspective camera model are analyzed and between the reported examples, self-acquired images and old monocular videos of sports events are considered.
		Snip: In photography and cinematography, perspective distortion caused by lens focal length is an effect that is more pronounced the more the focal length differs from a normal lens.
	stream.spurl.net /camera_calibration (1023 words)

	Digital Artform: Telephoto and Wide-angle Lenses
		Barrel distortions and pincushions are lens defects that TEND TO be associated with certain kinds of lenses.
		The perspective projection of a camera (both an idealised pin-hole camera and a real one) acts just like the classic renaissance illustration of linear perspective, where one places a plate of glass between the artist and the subject and lets him trace it.
		This is what I mean by saying that the distortions of the perspective in a picture doesn't come from the distance to the objects when the photo was taken, but rather from the size of the print when it was shown to the viewer.
	www.digitalartform.com /archives/2004/12/telephoto_and_w.html (3747 words)

	David Ruether - Lens Distortion and Perspective-Correction (Site not responding. Last check: 2007-11-07)
		Some people complain about the barrel distortion common with WA lens converters, but I find the curvature useful for making pans and tilts smoother-looking (without the curvature, straight lines "swing" more in angle with camera movement).
		It turns out that we see in spherical (curved) perspective, with the same advantages for keeping tilting and swinging points of view from being unsettling, for maintaining more consistent-looking near-to-far distance proportion relationships, and for showing kinder representations of rounded objects (like people) near the image edges than a very wide angle "rectangular-perspective" view would.
		The top frame shows the original, with obvious linear distortion showing; the other two are frames with different amounts of correction applied in Adobe Premiere.
	www.ferrario.com /ruether/perspective-correction.htm (517 words)

	Daynotes
		To better illustrate the differences, I setup a short series of AB comparative demonstration pages showing the corrective effects of lens distortion, lens distortion and perspective, and finally lens distortion, perspective and rotation.
		Of the three problems, only lens distortion was the problem with no solution readily at hand historically.
		Amazingly enough at the time of this writing no graphics or image editing program easily accounts for this distortion if at all but I did find a free Photoshop plugin made by Richard Rosenman called the lens distortion corrector.
	webpages.charter.net /daynotes/2003/0929.html (774 words)

	Perspective Distortion (caused By Camera To Subject Distance) Encyclopedia Article, Definition, History, Biography (Site not responding. Last check: 2007-11-07)
		Perspective Distortion (caused By Camera To Subject Distance) Encyclopedia Article, Definition, History, Biography
		Home: Encyclopedia: Perspective distortion (caused by camera to subject distance)
		Other Perspective Distortion (caused By Camera To Subject Distance) Categories:
	www.karr.net /encyclopedia/Perspective_distortion_%28caused_by_camera_to_subject_distance%29 (617 words)

	[No title] (Site not responding. Last check: 2007-11-07)
		Depending on the distance of the camera to the graphical scene (set by the attribute Position), the scene is subject to some natural perspective distortion.
		The distortion is large when the camera is near the scene.
		For technical reasons, however, you should not suppress perspective distortion by placing the camera yourself somewhere far away via the attribute Position and turning the camera’s lense into a tele lense by setting a small value for its opening angle (cf.
	www.sciface.com /STATIC/DOC30/eng/plot_OrthogonalProjection.html (447 words)

	panoguide - Correcting image distortion, perspective and converging verticals
		Quite a few image stitching tools are capable of correcting linear distortion in images (whether concave or convex distortion, such as the barrel distortion in poor quality rectilinear lenses or in fisheye lenses).
		These are listed in the products section and the thing to look out for is the capability to correct linear distortion.
		Using the crop tool, drag a bounding area into the image, and now, because of the perspective option, you can drag each corner of the bounding area around.
	www.panoguide.com /howto/panoramas/distortion_correction.jsp (397 words)

	Controlling perspective-distortion in M7 43/4.5
		zero distortion, look for pictures that more or less fit in with this aesthetic, if you have to start tilting upwards, do it very sparingly, or discart the shot, work within these limitations.
		John, with a lens as wide as your 43mm in 6 x 7 cm format, some distortion is normal.
		the second technique is to correct the perspective while using an enlarger...you prop up the narrow end closer to the lens and stop way down to increase DOF of the enlarging lens.
	www.photo.net /bboard/q-and-a-fetch-msg?msg_id=0046UB (1022 words)

	PCPhoto Magazine \| Correcting The Vertical Convergence \| March/April 2000 (Site not responding. Last check: 2007-11-07)
		But the distortion of size and shape that happens—tall buildings or trees that lean where we know they shouldn't or get thinner and thinner as they ascend toward the sky—can be distracting or just plain irritating.
		What's happening is that due to the wide perspective of the lens, objects close to the lens appear bigger than those further away, making straight and parallel vertical lines in the scene appear to bend and converge toward each other as they get further away from the lens.
		It's worth it, though—the wide-angle perspective minus the vertical distortion gives you the benefit of an open, inclusive view while keeping the objects in the image true in proportion and space.
	www.pcphotomag.com /content/pastissues/2000/mar/vertical.html (1151 words)

	CGTalk - Q: Field of Vision for Modeling?
		This might finally fix the distortion problem I've been having with my Hayden Christensen model-- the back of his skull would keep getting really huge when I tried to line it up to the photos, and his ear was sticking way out to one side.
		One lil thing I've noticed about distortion, is that when I need a quick-fix for how the head looks front-on, I can just apply a 2x2 lattice to it, and then scale the front of the lattice.
		When such model is seen from a perspective, you get bad results sometimes...because, your model has now a default distortion already applied in it [as you exactly matched a photo], and the perspective view adds its own distortion over it....So a dual distortion sort of.
	forums.cgsociety.org /printthread.php?t=40871&pp=50 (4745 words)

	Super Wide-angle and distortion
		These results were acquired by taking a picture of a target at the selected focal lengths and guessing the distortion levels until the target lines became straight (free of barrel distortion).
		For barrel distortion compensation 'b' must be negative.
		When tilting your lens upwards or downwards, you may have to correct the perspective as well.
	www.fredmiranda.com /distortion (523 words)

	CGTalk - Q: Field of Vision for Modeling?
		Of course, when I put in perspective photos for reference, and try to match the FOV on those, that's a whole new barrel of monkeys...
		The object won't change much in distortion whether you are close to, or far away from it...
		There is still some distortion if you zoom in too much; but there's enough perspective in the camera for it to not look wrong when u see if with a natura eyel 40 degree AOV or higher (unlike if you were to model in orthgraphic).
	forums.cgsociety.org /printthread.php?t=40871&pp=50 (2585 words)

	PCWorld.com - Digital Focus: Fix Perspective in Architectural Photos (Site not responding. Last check: 2007-11-07)
		You'll avoid perspective distortion by shooting shorter buildings, since you can keep the camera level with the ground when you take the shot.
		Eliminating Distortion on the PC That said, perspective distortion is sometimes unavoidable.
		The Perspective Correction tool is in the second cubby from the top in the toolbar on the left side of the screen.
	www.pcworld.com /reviews/article/0,aid,115658,00.asp (957 words)

	Robotics Institute: Frieze and Wallpaper Symmetry Groups Classification under Affine and Perspective Distortion
		Frieze and Wallpaper Symmetry Groups Classification under Affine and Perspective Distortion
		Several symmetry invariants of these groups under affine transformations are analyzed in detail and used to extend the Euclidean group classification algorithm for patterns that are distorted under affine transformations.
		Collins, Frieze and Wallpaper Symmetry Groups Classification under Affine and Perspective Distortion, tech.
	www.ri.cmu.edu /pubs/pub_2605.html (297 words)

	PS 6 Tip: Correcting perspective distortion with Crop. - PhotoshopTechniques Forums
		Now click-drag the corners to align the bounding box lines with the perspective lines to be corrected.
		You may want to increase the canvas size before you apply this technique as the distortion may increase the image size beyond the document boundaries.
		Once you have aligned the bounding box but before you apply the crop, you may want to increase the size of the bounding box so that it doesn't crop into the image.
	www.photoshoptechniques.com /forum/showthread.php?t=70 (254 words)

	Television Production: Lenses: Distance, Speed and Perspective Changes
		Again, this type of "distortion" could be virtually eliminated by moving the camera back and using a longer focal length lens.
		Since we are used to seeing the world in this perspective, this 25-degree angle represents a normal perspective for film and TV cameras.
		However, in the latter case, "normal" depends on the focal length of the camera lens, and that depends on the area (size) of the film or target.
	www.cybercollege.com /tvp011.htm (1236 words)

	DigiCad 3D Support
		The Dynamic Attachment feature is also used to transform pictures and to eliminate perspective distortion.
		Is it possible to eliminate perspective distortion from a photo without any measured point?
		Yes, it is. This is when you do not have the precise measurements necessary for an exact operation – you have perhaps a few horizontal/vertical indications, which can help reconstruct an approximate situation.
	www.interstudio.net /DigiCad3DSupport.html (988 words)

	Correcting Optical Distortion by Thom Hogan
		At the wide angle focal length, most Coolpix models exhibit barrel distortion, while pin cushion distortion is sometimes found at the telephoto end.
		For barrel distortion, choose the Spherize filter from the Distort submenu on the Filter menu and enter a negative value (usually no more than –25; typically in the -5 to -10 range for Coolpix lenses).
		Third party programs exist that provide more automated and sophisticated distortion correction abilities: the two most often mentioned are a free tool written by Helmut Dersch, and while Andromeda Software has a Photoshop filter called LensDoc that is also quite helpful.
	www.bythom.com /distortion.htm (618 words)

	ImageAlign - Lens Distortion Correction Tool (Site not responding. Last check: 2007-11-07)
		The intractable problem of perspective distortion has never been completely solved, even with expensive hardware, so Grasshopper consider this a breakthrough that could well revolutionise two-dimensional imaging.
		But when even the untrained eye is shown the distorted and corrected images together, there are gasps of delight at the dramatic improvement.
		When photographing a subject with vertical or horizontal lines, the film plane must be perpendicular to the centre of the subject to avoid converging lines, which make objects seem to lean away from or towards the camera, or make their height change unnaturally.
	www.imagealign.com /news.htm (2421 words)

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