The “Tilted Drum” Technique to for Vr Panorama

The “Tilted Drum” technique to for Vr Panorama Valerio Vendegna The “Tilted Drum” technique to for Vr Panorama wwwValerioAGNO’S VendegnaEQUIPMENT www.agnos.com General I like very much immersive panoramas. Looking around yourself in a 360° by 180° undistorted view is fascinating. I use them for my work, teaching and research in Applied Ecology, and as an hobby of mine. Several techniques are possible to get immersive VR panoramas, but for me is necessary to be as fast as possible in taking and as simple as possible in stitching the images to compose a full spherical view. Since I want to stay simple to use, light to carry, cheap in price and yet precise, a lot of compromise is necessary both in hardware and in software. I have a Nikon Coolpix 5000 equipped with a Nikon Fisheye Converter FC E8 and this lens is mounted (permanently, by my choice) on rotator Mrotator A made by Agno’s, a perfect tool precise and casting a very small nadir footprint. I use a Cullmann Magic 2 tripod. After using a very good Manfrotto, precise but bulky, I found Magic 2 the best possible compromise to fulfi ll my needs because even if is not the stiffest you can get, it is precise, reasonably steady and easy to carry since it is lightweight and very compact when it is folded fl at. This system, all included, is very handy and compact in packaging, weights only 3.5 kilos, including spare batteries, extra memories and assembling tools. To stitch my panoramas I use Easypano Panoweaver 4, a big improvement on release 3.1 I used previously, since release 4 is more precise and automatic. The Coolpix 5000, out of production now, is a very good digital camera. Its 2/3’’ sensor delivers high photo quality, but looking at the immersive panorama I obtained stitching 3 180° by 180° full circular fi sheye pictures the quality is far too low to compare with the “normal” photos by the same camera. They are good enough to share in internet and for classroom projection too, but they look “soft” and without details suffi cient for zooming in when I look at them on my computer screen. So the problem is: how to increase the resolution in a cost effective way. The key to solve the problem, obviously, is to optimise the use of the camera sensor surface, so to have a better and more usable equirectangular image and immersive panorama while retaining the fast 3 takes technique to produce a full 360° by 180° spherical panorama. Let’s have fi rst a little theory comparing different ways to take a fi sheye picture [modifi ed from: http://www.panotools.info/mediawiki/index. php?title=Special_issues_with_fi sheye_lenses] Fisheye lenses and adapters are very popular among the VR panorama photographers because they allow full-spherical immersive panoramas to be constructed from just a few images, minimum 2 in principle but in practice 3 to have a better stitching. Nikon Coolpix 990 and better camera models and Fisheye Convereters, FC E8 (compact) and FC E9 (bulky), match perfectly. Here you can see different ways how fi sheye use the sensor surface in your digital camera. The “Tilted Drum” technique to for Vr Panorama wwwValerio Vendegna www.agnos.com General The fi rst image, left to right, is full circular fi sheye, using an 8mm focal length equivalent 24x36mm frame on fi lm. The usable fov of this image is 180 degrees horizontal and 180 vertical. This is achieved choosing in the Coolpix 5000 a preset user setting F1 fi sheye lens. 3 full circular fi sheyes are enough to give good overlap, easy to stitch, but most of the sensor surface is wasted and thus the resolution is much lower than normal camera use could deliver. Thus let’s use the optical zoom to exploit the sensor surface more effi ciently. The second image is portrait cropped circular fi sheye. Cropped circular fi sheye is defi ned also a “drum” fi sheye image. Presetting the “Normal lens” user setting with my Coolpix 5000 I zoom in until the circumference of the fi sheye image touches the top and bottom sides of the LCD monitor. The usable fov of this image is only about 120 degrees horizontal by 180 degrees vertical. 4 portrait cropped circular fi sheyes are enough and stitching is comfortable. The third and fi nal image is a tilted cropped circular (or “tilted drum”) fi sheye. As before, I set “Normal lens” user setting and zoom in until the circumference of the fi sheye image touches the top and bottom sides of the LCD monitor screen., but now the camera has to be tilted to make an angle so the picture diagonal is vertically aligned. The usable fov of this image is about 145 degrees horizontal (equator) by 180 degrees vertical. 3 diagonal cropped circular fi sheyes, 120 degrees apart, are enough, but stitching is more critical. Adopting the technique of point 3, I was able to reach a striking resolution improvement with the same compact equipment and the very user friendly software I already have. The “Tilted Drum” technique to for Vr Panorama wwwValerio Vendegna www.agnos.com Setup “TILTED DRUM” , HOW DO IT Setup and taking For the “tilted drum” technique in Coolpix preset a user setting with: 1) lens as Normal; 2) image Size 2,560 x 1,920 always FULL and never 3:2, because 3:2 gives severe vignetting problems; 3) image Quality HI (to obtain a fi nal equirectangular image up to 8000x4000 in size) very good but slower in taking and in processing in Panoweaver and Photoshop, or FINE (to have a good fi nal 6000x3000 equirectangular) faster in taking and postprocessing. I usually use FINE to take more panoramas, in more dynamic situations, and to cut processing time, so being able to conclude the job on the same day leaving me the opportunity to repeat the day after the unsatisfactory, but important, ones; 4) exposure lock YES; 5) contrast LESS. The camera with FC E8 lens connected to Mrotator A is fi rst fi tted on the tripod, facing a vertical line (e.g. a doorway, a library). Then I precisely set Mrotator A to level and lift the LCD monitor. The Mrotator A connection to the fi sheye is loosened and the camera gently rotated, clockwise, until the vertical line runs from one corner of the frame to the opposite corner of the LCD screen. Then the connection is tightened in this position. Camera, rotator and lens assembly are ready now for the “tilted drum” VR panorama technique. They can be stored, assembled, in a compact camera bag. Ready to go. The assembled system is solid, compact, balanced and has a fi ne “professional” look. The “Tilted Drum” technique to for Vr Panorama wwwValerio Vendegna www.agnos.com Setup On location, snap the rapid connection on the ball head and extend the tripod at the desired height. I usually prefer chest level because so it is easier to check the bubble level on top of Mrotator A and it is easyer to frame the picture too, since Coolpix 5000 has a swivelling LCD monitor (a signifi cant advantage on the DSLRs!). Levelling very well on the fi rst picture pays, because it makes the stitching easier. To reach the chest level, I prefer to extend the central column and keep the tripod legs shorter, because this make them not to appear in the nadir footprint. Practically only the rotator is left, it is a small footprint and easy to remove in Photoshop. Sensor surface is effi ciently exploited and the overlap between the pictures is small but yet easy to recognize. In close portraits, composing may be more diffi cult than in “vertical drum” position. [San Cristoforo sul Naviglio, XIV century small church in Milano, after celebration.] The “Tilted Drum” technique to for Vr Panorama wwwValerio Vendegna www.agnos.com Stitching and processing Now let’s stretch Panoweaver 4 beyond its normal use. This very user friendly software smoothly supports “drum” (minimum 4 pictures) but it is not preset to support - not yet but I hope in future - any “tilted” technique. Anyway Panoweaver 4 proved to be robust enough even to help in the implementation of “tilted drum”. First you have to choose: Image type Circular 3. Then upload your pictures, using the suitable rotation. Since the image is not full circular, it is necessary to regulate the image select circle to fi t the drum image. This process is not as much automatic as it is for a preset technique and thus you have to help yourself. Do it carefully and then choose Apply to All button. If you want top quality and you got HI quality takes then you have now TIFF, RAW or NEF image fi le, chose image size Print (8000x4000). Instead, if you shot your pictures in FINE quality mode and your fi le is JPEG you chose image size CD (6000x3000). Most of the time I fi nd this the most prac- tical compromise, faster and yet good in results. The “Tilted Drum” technique to for Vr Panorama wwwValerio Vendegna www.agnos.com Stitching and processing When you launch the stitching action, in a short time, a message warns that mismatching points exist and ask if you want to edit them. Of cour- se you have to! After clicking the Yes button in the message window you see why you re- ceived the warning.

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