photo stitiching

[howard b. schwartz]

<p>i have included my first try at pano and stitching with cs5. as you can see, the image is distorted and has the scalloped edges. i am using a really right stuff pano outfit, with a canon 5d mark ii camera and 24 mm lens. i have adjusted my gear to adjust for parallax (i think). i am overlapping my images, going only 30 degrees for each shot on rotation. what i am doing wrong to not get a planar panorama?</p><div></div>

[acedigital]

<p>Hi Howard, based on my limited experience using PTGUI, you just need to crop the photo to remove the scalloped edges. You may have to do some more editing to adjust the curve effect on the pier if thats what you are referring to.</p>

[howard b. schwartz]

<p>the cropping i understand, but any help with the distortion?</p>

[garrison_k.]

<p>go into filter and lens correction?</p>

[lornesunley]

<p>I use Autopano and it has a thing that you can use to mark objects in the photos that are vertical or horizontal. The software uses that to correct for distortion. Perhaps CS5 has an equivalent. The scalloped edges are present, but Autopano suggests a crop to remove then.</p>

[robert lee]

<blockquote>

<p>... any help with the distortion?</p>

</blockquote>

<p>The field of view of the final stitched image is extremely wide. As such, the pano program chose to use a cylindrical projection. The boardwalk isn't distorted in the strictest sense. Print this image out. Wrap the print around a cylinder. If you then view print while standing in the cylinder axis the curves would straighten out.</p>

<p>Now, horizontal lines stays straight if you center it vertically in the stitch. Horizontals above the midpoint bows up and horizontals below the midpoint bows down. So to keep the boardwalk straight, take the exposures so that the boardwalk is in the middle (vertically) of the final composite.</p>

<p>By the way, a 50mm or longer lens is preferable in shooting panos. Wide angle lenses, such as the 24mm you're using, tends to have more distortion. The less source errors the pano software has to compensate for, the higher the quality of the final stitch.</p>

[francisco_disilvestro]

<p>Usually Photomerge (in Photoshop) defaults to cylindrical projection which gives the results you see. They are similar to what you get from a rotating lens panoramic camera like the widelux or noblex.</p>

<p>If you want straight lines you shoud use the "Perspective" projection in Photomerge. Anyway, since the images were taken with a 24mm lens on FF maybe you will run in other projection issues.</p>

<p>As Robert said, it would probably work better if you use a longer lens, like a 50mm.</p>

[Mattman944]

<p>I always shoot my panos with the camera vertical, no wider than 28 mm full frame equivalent. If the camera was horizontal, about 50 mm is about the widest you should use. Like Robert said, only horizontal lines in the middle will be straight, but don't tilt your lens trying to put the pier in the middle or you will have worse problems (for a one row pano you always want the camera level).</p>

<p>There are some scenes that just don't look good as panos (at least simple panos).</p>

<p>For this pier shot, the horizon is fairly straight since it was near the middle (the top has been cropped). The railing is seriously bowed, but who cares.</p>

<div></div>

[howard_m]

<p>definitely a problem w/ the chosen 'projection'.</p>

[howard b. schwartz]

<p>thanks for the help. i use a getright pano system, so the nodal point is fixed, and i keep the camera level. i shoot portrait mode. should i use a 28 mm or 50 mm lens? i will try stitching in perspective mode. thanks for the help and all responses are greatly appreciated.</p>

[howard b. schwartz]

<p>also, i forgot. is it okay to shoot 180 degrees, or should i go less, say 140?</p>

[Ed_Ingold]

<p>You have several choices in PTGui for the rendering of the results. The most useful are "Cylindrical", which you used in this example, or "Rectilinear". The scalloped edges are unavoidable, and must be cropped for a rectangular print.</p>

<p>Cylindrical projection causes horizontal lines to curve backward away from the center. Vertical lines remain vertical and straight. Stitches are always created using cylindrical (or spherical) projections, because that's the only way to blend horizontal lines one frame to the next without corners or steps. Sperical objects remain round, even at the extreme edges or corners.</p>

<p>Rectangular projections render all lines, vertical and horizontal, straight, like a standard wide-angle lens. Sperical objects (e.g., faces) get stretched if near the edges or corners, just like with a WA lens. It does this by distorting the cylindrical projection in a bow tie manner, then cropping away the wide ends. You can't create a rectangular projection spanning more than 180 degrees. In practice, you can't go wider than about 120 degrees. A cylindrical projection can be any width, including 360 degrees.</p>

<p>In your example, the beach does not appear level. This is usually caused by assuming the wrong focal length by PTGui, or the wrong cropping factor. The scallops appear even, which means you have leveled the camera properly. Failure to level the camera can produce useable results, but requires a lot more cropping to remove the rough edges. It's important to use manual focus, since the image size changes slightly if the focus is changed.</p>

<p>Failure to eliminate parallax (using a nodal point slider) causes doubling or ghosting in nearby objects. Again, this does not appear in your sample.</p>

[ellis_vener_photography]

<blockquote>

<p><em>i have included my first try at pano and stitching with cs5. as you can see, the image is distorted and has the scalloped edges. ...i have adjusted my gear to adjust for parallax (i think). i am overlapping my images, going only 30 degrees for each shot on rotation. what i am doing wrong to not get a planar panorama?</em></p>

</blockquote>

<p>I also use Really Right Stuff panoramic gear, specifically the RRS Ultimate-Pro Omni-Pivot Package, http://bit.ly/gv6BMe , as I sometimes create very high resolution 3 row panoramas. I use PTGui 9.0.x for stitching but also have extensive experience with the Photomerge tools in PsCS5.<br>

1) Do you have your camera body oriented with long side of format oriented vertically or horizontally, 30˚ of horizontal rotation with the camera oriented vertically as opposed to horizontally will have a great effect on much actual image over lap is created. This may sound crazy to some but for my work , with a camera oriented vertically, I get better results using a rotation angle of 7.5˚, even with very wide angle lenses. The tighter the rotation angle the less scalloping on top and bottom, What you are seeing when scalloping occurs is the result from a lack of overlapping data. One way to address scalloping after the fact in PsCS5 is to use the magic wand tool to select the areas where the scalloping occurs, click delete and then choose the Content Aware Fill option so that Photoshop can make a pretty good ( sometimes perfect, other times not close) guess as to what pictorial information you'd like to see there. <br>

But basically using smaller rotation step will save you a world of headaches. Also when you have decided where your start and stop points will be in the final image -- start and end at least one if not two steps beyond them. </p>

<p>2) The distortion comes from trying to cram an extremely wide angle of view of a three dimensional world into a two dimensional form. Essentially what is happening is that you are seeing is single point perspective ( think of parallel railroad tracks looking like they come towards a meeting point in the far distance ) applied to both the left and right ends of the photo. if you could make the print large enough that you could stand inside it the sense of distortion would be more natural looking. I agree with Mr. Ingold about the limit for a photo reproduced at a smaller size than that being about 120˚ of view, maybe a little less.</p>

<p> </p>

[howard b. schwartz]

<p>just so i am clear, you use about 7.5 degrees of rotation? my camera is vertical or portrait mode. what focal length lens? would 35 or 50 be ? also, you don't shoot greater than 120 degrees in rotation? do you ever aim your camera 10 degrees up or down to get even better coverage?</p>

 

[robert lee]

<blockquote>

<p>just so i am clear, you use about 7.5 degrees of rotation? ... what focal length lens? would 35 or 50 be ?</p>

</blockquote>

<p>Okay, rules of thumb:</p>

<ol>

<li>On your camera (5dii) use a 50mm prime. If you're after higher resolution from the final stitch, use a 85mm or 100mm prime.</li>

<li>If you want straight lines to stay straight regardless of orientation, shoot for a final composted image of no greater than about 120deg. Choose a rectilinear projection when rendering.</li>

<li>If you want straight lines to stay straight <em>and</em> maintain correct image aspect ratio, e.g., a soccer ball that doesn't get stretched into an oval toward the frame edges, then shoot for a final composted image of less than 90deg. Choose rectilinear projection when rendering.</li>

<li>Cylindrical projection renderings can be compelling too. Try a 360deg pano sometime.</li>

<li>Don't worry about degrees of rotation per shot. Just rotate enough for at least quarter frame worth of overlap on all sides.</li>

</ol>

<p>If you decide to get into pano photography even deeper, a robotics mount will dramatically quicken your workflow (I've been using a Gigapan for years.) This enables much higher resolution panos. More importantly, it effectively shortens the aggregate exposure time. It provides a better chance for capturing the more quickly changing scenes.</p><div></div>

[ellis_vener_photography]

<blockquote>

<p><em>just so i am clear, you use about 7.5 degrees of rotation? my camera is vertical or portrait mode. what focal length lens? would 35 or 50 be ? also, you don't shoot greater than 120 degrees in rotation? do you ever aim your camera 10 degrees up or down to get even better coverag</em>e?</p>

</blockquote>

<p>7.5 degrees is what I use even for extreme wide angle lenses or short telephotos. The longer the lens the less area covered of course so if you do multi rows you end up with a higher resolution photo once it is stitched.</p>

<p>I quite often create panoramas that quite often take in 180 to 360 degrees. If the angle of the scene is obviously wide enough people accept the distortion.<br>

Yes, sometimes I tilt the camera at an angle other than level, but that is where having a really well designed tripod head and shooting multiple rows helps.<br>

The head I prefer using for this is the Foba ASMIA (great if you can afford it as it is around $1600 new) to which I have added an RRS PCL-1 panoramic clamp to the top. Another excellent and expensive choice are the Arca-Swiss Cube (AKA C1) or forthcoming Arca-Swiss D4 heads. A more affordable and very good option is the Induro PHQ-3 head. The advantage of my ASMIA or P the PHQ-3 head is that they are 2 double tilt heads (l/r & fore/aft) so you have more control over getting the rig level to start with than you have with a ballhead. the key here is to have both a panning base AND a panning platform on top of the head,<br>

The larger of the two geared Manfrotto heads (the 405?) will also be very good in this regard as would any geared tilt tripod head.</p>

<p> </p>

[dbcooper]

<p>Scalloped or uneven edges after stitching is common. Just crop them off. You'll probably want to shoot panos a little loose, for cropping later. Don't worry about 180/140/whatever. If you use more frames, you'll have enough pixels to get resolution if you crop <em>before</em> resizing for export or printing. Let the subject, the light, and your envisionment tell you how much angle to shoot. When in doubt, shoot more angle of view (more frames) and crop later or use just less frames for the stitching. It beats going back and reshooting the scene if you wanted a wider view.</p>

<p>Nice first effort! It looks like you left the camera in some autoexposure mode or auto ISO switched on - the sand below the sun appears darker then the rest of the beach on my monitor. Ordinarily I'd expect it to look the same or brighter. That could explain the uneven transition in the sky around the sun that spans 3 frames. Otherwise, pretty doggone good IQ for shooting into the sun.</p>

<p>Looks like you got the parallax pretty right. If the scalloped edges aren't stairstepped or sawtoothed, and the stitching went well, the parallax is okay.</p>

[howard_m]

<p>Yes, the key is MANUAL everything (including white balance) and be wary of any polarizer usage.</p>

[whydangle]

<p>Try the "Reposition Only" button and that should work if you are using a pano system with a level camera. </p>

[bgelfand]

<p>Hi Howard,</p>

<p>I cannot help with the distortion (which I think adds to the image), but for the scalloped edges, you do not have to crop. You have CS5 with Content Aware Fill. Select the top, sky portion of the scallopes, the quick selection tool works well, expand the selection slightly, then EDIT > FILL and select Content Aware Fill. Do the same for the bottom. Clean up with the Spot Healing Brush in Content Aware mode. </p><div></div>

[BelaMolnar]

<p>Hi Howard. The biggest problem here with this panorama shot, you did it with APERTURE PRIORITY, witch is an absolute NO NO! It shown on you image the uneven exposures, on the sky, and on the shore. When you taking a panorama shots, you have to set you camera, to "M" MANUAL MODE. Set the exposure manually, then forget the light-meter and shoot the 10 or 20 images you my need. Otherwise, with "A" mode, the camera going to producing a slightly different exposures for each frame, as you moving in a bigger circle / angle. The lines witch is on the middle of a frame, going to be straight, and like a bridge or pier, it going to be curved / arched on a very vide angle panorama soots, the same as a very wide angle lens will distort too. Try to shoot more panoramas, with M mode and your images going to be mach better. Specially on the merged edges. You don't need a special panorama program, PH CS3 can do it too.</p><div></div>

[BelaMolnar]

<p>All of my panoramas where handheld, vertical frames, and MANUAL MODE! This image made up of 20-30 frames, at list. Lens 24mm if I remember right. Lazy to check the meta data.</p><div></div>

[Ed_Ingold]

<p><em>What you are seeing when scalloping occurs is the result from a lack of overlapping data.</em></p>

<p>The scalloped edges are a consequence of converting each frame to cylindrical projection, which shrinks the ends vertically. This is done so that horizontal lines blend without a sharp bend at the juncture. If the shots are spaced more closely, you get more scallops, but not necessarily less loss when cropped. If you have less than the recommended 25% overlap, the stitching will fail to complete, or create odd artifacts at the borders.</p>

<p>This conversion is dependent on an accurate knowledge of the effective focal length of the lens. If you use a zoom lens, it's nearly impossible to accurately determine the focal length manually. Even prime lenses usually vary from their nominal value. PTGui can detect the focal length from EXIF data in the exposure, and the cropping factor from data you enter. This is probably the reason the beach appears to undulate.</p>

<p>PTGui is able to rotate images that are not exactly level from frame to frame. This allows you to shoot panoramas without careful leveling or even a tripod. The uncropped borders will usually show steps in addition to scallops, which take more of the image area away when cropped.</p>

<p>This example is composed of 6 frames, taken with a base-leveled ball head, manually spaced to yield a 25% overlap, using the focusing brackets in the viewfinder as a guide. Each frame is composed of 7 bracketed exposures, rendered by fusion in Photomatix. It was taken with a Nikon D3 and a 28-70/2.8 lens at ISO 200. The final image is rendered by PTGui in cylindrical projection.</p><div></div>

[howard b. schwartz]

<p>thanks for all the responses. i have reshot the pier, using manual exposure, and a 24-70 lens set at 50 mm with the parallax point determined. i will upload this later, since it is now processing. i have yet one other question. if i have two panorama shots, say panorama 1 and panorama 2 that share thirty or fourty percent of one side in common, can i stitch those two together to get a wider image? so for example, i have four 90 degree pano images that share common views, can i stitch them together appropriately? thanks again. </p>

[Ed_Ingold]

<p>The individual frames have to be EXACTLY the same size (pixels), type and resolution (8 or 16 bit). That done, you can stitch them together using PTGui.</p>