A short introduction to panoramic images

Transcription

1 A short introduction to panoramic images By Richard Novossiltzeff Bridgwater Photographic Society March 25,

2 What is a panorama Some will say that the word Panorama is over-used; the better word might be panoramic image ; others will just call it a pano... One dictionary defines it as: an unbroken view of the whole region surrounding an observer. A panorama is an unusually wide picture that shows at least as much width as the eye is capable of seeing, if not a greater left-to-right field of view than we can ever see: 'behind you' as well as 'in front'. Movies use wide images which fill more of the viewer's peripheral vision in order to enhance the immersive effect when viewed on screen. Today, panoramic images are also used for virtual reality (VR) and increasingly, in other simple roles such as navigation on a website. 2

3 Conventional photographs may be described as "flat" or "planar", meaning that they are intended to be viewed as is without any perspective correction. It is common today to represent panoramas in this form covering a FOV of 120 or less. If the FOV is wider specialized software will more than likely ask you to stitch it as a cylindrical panorama... A cylindrical panorama is intended to be viewed as if curved around the inside of a cylinder. If you view the image flat, you will see curves in the horizontal axis. There are many Java applets and other viewers for displaying panoramic images on the Internet which are designed to display cylindrical panoramas as flat, i.e. without correcting perspective by displaying the image as if you are looking at it inside a cylinder. These viewers display the horizontal curves. 3

4 Spherical images are typically represented in equirectangular projection format image files, which represent exactly 360 degrees on the horizontal axis and 180 degrees on the vertical. These images are intended to be viewed as if projected using a special slide projector onto the inside of a sphere. Like cylindrical images, horizontal curves can be seen in the flat image, but unlike cylindrical images, the very top and bottom of the image will seem squashed. For panoramas with a large vertical field of view, the equirectangular (spherical) image format is far more efficient than cylindrical. Cubic images were made popular by QuickTime 5, which introduced the possibility of cubic panoramas in which the viewer can look straight up and straight down at the floor. Unlike cylindrical and spherical images, cubic images contain 6 separate cube faces, which are in themselves planar (flat) images, which look normal to the human eye (no horizontal curves or perspective distortion). Cubic is the most efficient format for panoramic images with a vertical field of view in excess of 140 degrees, and because each of the cube faces looks "normal" these images can be easier to edit or modify with image editing software. 4

5 How to make a panoramic image Hand held shots are OK, but, you will soon find out what your first mistakes are... Not level: Cropping will waste useful space Parallax error: Each image may not fit to the next one 5

6 There are 3 major flaws in this ʻpanoʼ...? 6

7 It's really easy to see the effect of parallax: hold up your index in front of you, close one eye and line up your finger with something further away such as a door, piece of furniture, window, whatever. Now, without moving your finger, rotate your head from left to right, your finger will seem to move slightly as you turn your head. Voilà! you are seeing parallax. FINDING THE NO-PARALLAX POINT Entrance Pupil Database - PanoTools.org Wiki 7

8 To fully avoid parallax errors you must do this: 1- Find the nodal / no-parallax / pupil entry point of your lens, 2 - Use a tripod, 3 - Use a panoramic head, a philipod or plumb line method set to that nodal point. 8

9 Then, you need to set yourself up with a good organized filling system: 9

10 Planning the composition Choose the right lens, Position the camera, not too high and not too low, Level the camera, Keep windows whole, spot lights and sun undivided, Beware of your own shadow...! 10

11 Recommended shooting method: - Always in manual mode, - Fixed W.B., daylight preferred when in doubt, - Manual focus, - JPEG OK but RAW is far better for best results, - Use a tripod, a panoramic head or the philipod technique... - Hang your camera bag to the centre column! 11

12 Good software available for panorama creation: 1. Photoshop, expensive but versatile Hugin, very good and free but, a bit complicated PTGui or PTGui pro at $150, HDR capable Photomatix better for HDR... but others also...? 5. and many more, of course... 12

13 Photoshop solution for panoramas: 13

14 PTGui pro solution for panoramas: 14

15 A 6 image panorama out of the 13 previously shown: 10161x3284 or 33 x11 15

16 PTGui uses a control point system to align images: 16

17 This pano is the result of 18 frames shot in vertical mode stitched together in PTGui. The size is 38905x4967 pixels or 11x1.3 feet at 300 ppi. You could print that at 150 ppi and the pano would be 21 feet wide and still have good definition... The next image is the100% view of the centre of the pano: 17

18 18

19 This panorama is made up of 45 vertical images: 6 sectors around (6x60 ), each one is 5 bracketed shots spaced at 2 E.V., 1x5 bracketed vertical (zenith) shots and 2x5 bracketed down (nadir) shots. 19

20 St. Patrickʼs Catholic Church in Halifax 20

21 An unsuccessful example: Missed High Dynamic Range Wrong focusing Unstable tripod Abandonned saw mill around Mahone Bay Nova Scotia 21

22 A High Dynamic Range example solved: St. Johnʼs Anglican Church Lunenburg 22

23 Make a panorama to work on your family tree...? 23

24 Thatʼs another way to show a panorama...? 24

25 Useful links cities cities Equirectangular projection - Wikipedia, the free encyclopedia The Panosaurus Panoramic Tripod Head Home Page PanoTools.org Wiki 25