Photomerge panorama problems
in [Digital Cameras]
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From: DanP on 19 Mar 2010 19:03 On 19 Mar, 17:12, bugbear <bugbear(a)trim_papermule.co.uk_trim> wrote: > People with reading skills will note that the statement was "Horizontals (other than a central > one, e.g. the horizon)" > > And your supposed disproof involves presenting a straight horizon. You could have skipped the above > > Idiot. because the above word suffices. > BugBear DanP
From: Neil Harrington on 20 Mar 2010 01:46
"Chris Malcolm" <cam(a)holyrood.ed.ac.uk> wrote in message news:80h0ceFntfU1(a)mid.individual.net... > Neil Harrington <never(a)home.com> wrote: > >> "D.J." <nocontact(a)noaddress.com> wrote in message >> news:86kup5hsq5kvdjbb632iepigk20rgmp6t5(a)4ax.com... >>> On Sat, 13 Mar 2010 12:57:35 -0500, "Neil Harrington" <never(a)home.com> >>> wrote: >>>>"Lobster" <davidlobsterpot601(a)hotmail.com> wrote in message >>>>news:0Pxmn.377994$UQ6.315102(a)newsfe04.ams2... >>>>> Draco wrote: >>>>>> On Mar 12, 2:47 pm, Lobster <davidlobsterpot...(a)hotmail.com> wrote: >>>>>>> I've been playing around with the 'photomerge' function in Photoshop >>>>>>> Elements, attempting to take a wide-angle-type view of a room. > >>>>However, this is not your main problem. You cannot take a panoramic shot >>>>in >>>>this way and have it fully rectilinear, which is apparently what you are >>>>trying to do. That is, you cannot ROTATE the camera and keep the same >>>>perspective as if you had not rotated it. >>>> >>>>You can keep the verticals straight (and parallel if the camera is kept >>>>level), but the horizontals must curve in order to get the whole >>>>stitched >>>>scene in without obvious angular breaks; that is, the perspective >>>>changes >>>>continuously from one side of the picture to the other. >>> >>> PTGUI and other good panorama stitcher utilities allow for straightening >>> these types of problems. > >> You can't "straighten these types of problems" no matter what you do or >> what >> you use. Horizontals (other than a central one, e.g. the horizon) from a >> single camera position must curve since the perspective changes >> continuously >> across the picture. > > Provided the angle of view does not exceed the maximum angle of view > possible in a linear wide angle lens all horizontals (and verticals) > can be straightened and made parallel. In this case what is possible > is limited by what is tolerable. A pinhole camera is in effect using a > linear perspective projection lens. The theoretical maximum possible > from a pinhole is close to 180 degrees, but the amount of edge > stretching involved in preserving linearity increases exponentially as > 180 degrees is approached. So in practice the maximum angle of view is > limited by what is visually tolerable. > > The maximum tolerable angle is probably around 112 degrees horizontal > or 120 diagonal, which is around what the widest ultra wide linear > lenses deliver Sure. But I don't think most people would consider that really a panorama, any more than they'd consider an ultrawide angle shot from a lens such as you describe to be a panorama. I wouldn't consider any pinhole camera to be panoramic, no matter how wide -- and of course you couldn't really get very close to 180 degrees, not only because of edge stretching but also light fall-off. > > If you restrict your panorama pan to what is a tolerable linear > projection wide angle view a panorama program will be able to stitch > together a linear result. Many real estate photographers without a > linear wide angle lens already do that for the odd occasion when they > want one. No doubt -- I have taken quite a few shots with my 10.5mm fisheye that I "de-fished" in Capture NX, producing a result essentially equivalent to that from a 10.5mm rectilinear lens. I haven't calculated the angles but it's pretty darn wide. Still not really a panorama, though. As far as I'm concerned a real panoramic picture must change its perspective continuously from one end to the other, i.e. the camera must swing, which implies that all parallel horizontals except the central one (in the plane of camera swing) must curve. Or if the camera remains fixed the lens itself must swing, producing the same result in one shot on a long negative. I don't know if such cameras are still made, and perhaps the term "panoramic" is more loosely defined now. I understand what you're saying about straightening the curves, but obviously that has severe limits on total angle as you've indicated. I have taken panoramic shots covering (rough estimate) between 220 and 240 degrees, and could have done the full 360 if the subject had been suitable for it. |