Stitching Shots With Perspective Distortion

[dje]

I had a situation the other day where I wanted to get a shot of our newly re-furbished City Hall but I couldn't get a vantage point that gave a wide enough shot or could avoid perspective distortion. So I had to opt for a 3 shot stitch in PS CS6. I was using my Canon G15 compact at it's widest view (28mm FF equivalent). The first image below shows a collage of the three shots I had to work with.



I figured I had two options - one to stitch the shots as they were and apply perspective correction on the stitched image and the second option was to apply some perspective correction on the three images separately before stitching. I tried both approaches but found the first option seemed to work the best (using the Automatic option in CS6's Photomerge). This produced the following results - the first of these two used only the image either side of the collage but not the centre image and the second result used all three images. The latter obviously worked best but interestingly none of the people in the foreground in the centre image appeared in the stitched version.


Two outer images stitched


All three images stitched



The final version with perspective correction applied (and some other editing) was as follows


I wonder could anyone comment on the best way of dealing with this situation. I was reasonably happy with the result but I fear this was as much good luck as good management.

Thanks Dave

PS : I hope I haven't made you feel dizzy looking at these shots.

[Colin Southern]

Dave,

I think you're on the right track, but you've made a rod for your own back by not keeping the horizon level to start with, which has impacted on your distortion correction in the final image (the right hand side is OK, but there are issues on the left).

[Colin Southern]

[Nigel]

Hi Dave
I overlap images by 25% & shoot in portrait. Shoot from left to right or right to left and shoot as many as you require (useing a pano head on your tripod if you have it will help). Use photomerge and only stitch 3 images at a time, then stitch final 3 stitch versions together and check perspective and correct if needed. On final merged image check people etc in shot are not duplicated. Looking at your version there is a man and woman duped (in the centre and the right) but apart from that a nice pano.
Nigel

[James G]

Hi Dave, I tend to shoot more landscape panoramas than architectural stitches.

I agree with Colin and Nigels's comments, shooting without a tripod can be tricky but with practice it does get easier. I wouldn't have been unhappy with your capture in similar circumstances.

My technique, if it helps, is as follows: -

1) particularly for architectural shots, get as 'central' to the shot as you can (I know obvious, but not always easy!)
2) As Nigel said shoot the sequence right to left or left to right making sure you get 20-30% overlap.
3) Take care with your horizontals as Colin suggests. I usually set a horizon line and then swing from my hips without changing stance. Being a contortionist helps, but watch out for your shoulder dropping as you turn because this will alter your midline/horizon as you take the sequence.
4) If I'm attempting a wide panorama I shoot parallel sequences above and below the main sequence, allowing plenty of overlap, and usually extend the additional sequences to create more marginal area for cropping capability after the image has been stitched.
5) I often choose to shoot portrait orientation and take more shots horizontally across the field. I find this works well for me with 'closer' scenes, eg buildings rather than with the wider landscapes.
5) I'd also suggest that you experiment with the different projection options rather than stick to Auto when you do the stitch. (Apologies if you have already tried this!) I have found that cylindrical and/or spherical projections work better than Auto in CS6, and in general, I tend to use cylindrical as the default to start from.
6) After I have completed a stitch there may still be perspective adjustments required and I use the 'standard' adjustments in CS6. More recently though I have been experimenting with the 'adaptive wide angle' filter in the filter gallery and have been impressed with its performance.

Shooting handheld does work well as I said, but if there is a big difference in lighting across the span of the image , it may be better using a tripod to make adjusting for lighting easier. Otherwise if this is not practical, try shooting bracketed shots if your camera allows. You can select the best sequence of images for the lighting conditions.

The attached link will take you to my Dropbox site and if you click on the Panorama and Stitch folder you will see a few examples of handheld stitches from a recent extended visit to Ireland.

https://www.dropbox.com/sh/agzncx4rmv3bzez/8wRXuQYv39

Good luck and have fun , James
ps you may need to copy and paste the link into your browser... :-)

[inkista]

This kind of thing is why I like PTGui.



Fed it the three images you had up top, added a few vertical and horizontal line control points, and also told PTGui to adjust for viewpoint. Did some perspective correction by dragging around in the preview, and done. Took about 10 minutes.

[dje]

Thank you Colin, Nigel, James and Kathy for your very helpful comments.

Colin I'd be interested to know what you did to produce your version. Mine has a bit of a bend in the main building whereas yours is straight. You've also been able to retain more sky.

Kathy the same comment goes for your version. PTGui seems quite impressive based on what you've done with this set of images. I've just had a very quick look at the web site but will have a closer look at the software. I do like the idea of having some input on how things are adjusted.

Nigel I take your point about the tripod and pano head. I don't have a pano head but I think using a tripod would help. This was not really a planned shoot. I should re-visit with my 600D and tripod and have another go at it. The light was good that day and hopefully I can get similar conditions again. It's also clear to me from your comments and those from James that I should take more over-lapping shots. I would think this would help when you have significant perspective distortion as the difference between shots will be more gradual. And yes point taken about the moving people - I did notice it in the final version but didn't even think about it when taking the shots!

James thanks for detailing your technique so well. I wasn't quite square on to the building or in direct line with the centre (clock tower) but I will look at that next time. I really need to do a bit more research on how the various Photomerge projection options work in CS6 as at the moment I have no understanding of this. I have tried a few of them before (but not on this shot) and found Cylindrical often works best for tricky situations. I'm not sure but I suspect Auto just selects one of the options for you (but doesn't tell you which one). I wasn't aware of the "Adaptive Wide Angle " filter but it does look like it could be useful. You have some very nice panos there on your website.

Dave

[jcuknz]

I have only done this once and I applied perspective correction in equal amounts prior to the stitch. I have only used a tripod once and it was such a problem setting up I have never done it before or since. I discovered that I can reduce the density of the upper layer to enable me to see the layer below to register hand held shots. In shooting with a generous overlap one can in an editing rather than stitch programme choose which version of reality one wants and can avoid shiowing people twice for example. In Paint Shop Pro, versions v.8 onwards, there is a tool called 'warp mesh' which places a grid of lines over the picture, you can decide how many you want either horizontally or vertically, and then move each intersecting point to correct or distort the image. One Photoshop advocate said it was worth getting PSP just for this tool, many of the PS Plug-ins cost as much and more back then when v.8 appeared PSP is much cheaper too these days.
The creature I 'found' with Warp Mesh, water coming out of a drainpipe into a local stream....

[dje]

I have only done this once and I applied perspective correction in equal amounts prior to the stitch. I have only used a tripod once and it was such a problem setting up I have never done it before or since. I discovered that I can reduce the density of the upper layer to enable me to see the layer below to register hand held shots. In shooting with a generous overlap one can in an editing rather than stitch programme choose which version of reality one wants and can avoid shiowing people twice for example. In Paint Shop Pro, versions v.8 onwards, there is a tool called 'warp mesh' which places a grid of lines over the picture, you can decide how many you want either horizontally or vertically, and then move each intersecting point to correct or distort the image. One Photoshop advocate said it was worth getting PSP just for this tool, many of the PS Plug-ins cost as much and more back then when v.8 appeared PSP is much cheaper too these days.

Thanks Photo Nut, a friend of mine has PSP so I'll have a look at that warp mesh feature when I see him next.

Dave

[GrahamH]

Hi Dave,
Bear in min that the wider angle of your lens the greater the distortion. Zoom in a little more (e.g. 50mm FFE or greater) and take as many shots as necessary (with the above stated overlaps). With less distortion, the end result should need less work (but some nevertheless).
Graham

[dje]

Hi Dave,
Bear in min that the wider angle of your lens the greater the distortion. Zoom in a little more (e.g. 50mm FFE or greater) and take as many shots as necessary (with the above stated overlaps). With less distortion, the end result should need less work (but some nevertheless).
Graham

Thanks Graham, I will be re-shooting this so I'll give that a try as well. It makes sense to me. It will require vertical as well as horizontal stitching ie with a matrix of shots.

Dave

[revi]

Less distortion would only apply to the lens distortion (barrel/pillow), not the perspective 'distortion'. Perspective only depends on viewpoint and view direction
(for the same final field of view), and is independent of the lens you use.

Also, I wouldn't correct any distortions before stitching: the program I use (Hugin) uses the lens information in its calculations. It can even calculate the distortion
parameters (for future use in e.g. lensfun).
Now, if I correct the distortions prior to stitching, there's a good chance I won't have the same correction in each image. But I still tell the program that the images
are taken with the same lens, and thus require the same correction. That is no longer correct, so I should expect a lesser result.
.

[Colin Southern]

Colin I'd be interested to know what you did to produce your version. Mine has a bit of a bend in the main building whereas yours is straight. You've also been able to retain more sky.

Basically,

Just chuck it into Photoshop and get it to spit out (warts and all) the composite (only needed 1st and 3rd images) then use the transform tool to "distort" the "distortion".

It saves having to over-crop the bottom, but does lower the resolution of the top bit. It also leaves dimensions a bit up in the air, so they need adjusting separately (I just did that but by eye).

[Colin Southern]

You need one of these:

http://www.bhphotovideo.com/c/produc...ic_Camera.html

[dje]

Also, I wouldn't correct any distortions before stitching:.

The tests I did using CS6's Photomerge also support that view.

[dje]

You need one of these:

http://www.bhphotovideo.com/c/produc...ic_Camera.html

Hmm, interesting but I won't rush into it !

[jounpla]

I used panorama software to do stitch staff~ however some professional photo editing software have this function
I tried PS and photostudio, PS may be inconvenient, Photostudio cheaper but not professional
http://www.arcsoft.com/topics/photo-...to-editor.html

[dje]

I used panorama software to do stitch staff~ however some professional photo editing software have this function
I tried PS and photostudio, PS may be inconvenient, Photostudio cheaper but not professional
http://www.arcsoft.com/topics/photo-...to-editor.html

Hi jounpla

I use PS for stitching and am quite happy with it. I do also have the Arcsoft Panorama Maker software which came with my Canon camera. It's quite good but I prefer PS.

Dave

[jounpla]

guys, i think the vertical stitch mode is great!
BTW. have you heared about Panorama Maker? It's a professional panorama photo maker.

[jcuknz]

Now, if I correct the distortions prior to stitching, there's a good chance I won't have the same correction in each image. .

I believe this is one of the advantages of PSP that it remembers the previous use of a tool so one can apply the same correction to any number of images ... but apart from an occasional use of Canon Stitch which came with my original P&S camera I don't use a stitch programme but my editor ... PSP of course
I have three stitch programmes which came with different cameras, Nikon, Canon, and Panasonic But I started with CanonStitch so stay with it. Though last time I used it for a quick job it put the right hand six frames on the left of the left six or so frames and I had to do it manually More haste less speed

As one person wrote years ago about Warp Mesh when it arrived with v.8 ... even if you are a confirmed Photoshop user it is worth buying PSP for the things PS doesn't do .. it is cheap enough, no more than the plug-ins that PS seemed to need back then.