My stitching technique

[iangreenhalgh1]

Hi folks

A few people have asked me to explain how I do my HDR stitches. It's not very complex. Eqipment used is very basic - NEX-3 with Industar-61 2.8/53 mounted on a Velbon Sherpa tripod with 157Q pan/tilt head. I recommend a 50-ish lens because they have the least distortion and gives you a large image in mp terms that allows for much editing and tweaking. In this example I used f11, which is around the diffraction limit for APS-C and gives a nice deep dof.

Due to continual rain, I had to do this indoors.

It's a 9 shot stitch - 3x3. Each HDR frame is composed of 4, 5 or 6 exposures. I usually do 5, but it's really not critical, as long as you have at least 3. I space them 1 stop apart, being indoors on a dark day, this used 10 secs, 5 secs, 2.5 secs, 1.3 secs and so on.

This picture shows the exposures I shot, they overlap a fair bit, which is important:



I use Photomatix 4 to create the HDRs, 9 in total:



Once I have the HDRs, I load them into Autopano Giga to be stitched together:



After creating the stitched image, I load it into Photoshop so I can correct the distortion, crop it and retouch any flaws. First step is to use the Warp tool to correct any perspective problems:



I only had to make very slight changes to this one:



After warping and cropping, there is a small piece at the top missing, which is due to user error:



Because I want to keep the ceiling rose and light fitting in the frame, I chose to use the clone stamp tool to fill in the missing bit:



Almost done, just sharpening and a slight tweak of curves to brighten the dark areas. The finished image is 12107 x 7763, which is 89.6mp:



Et voila, the finished image:



I hope that makes sense. Any questions, fire away!

[RSalles]

Ian,

Simple, effective. I have some questions:

What kind of image I have a chance to anticipate that it will result in a good HDR: a flat one, a bright one, an image with lot of contrast, or little. What kind of light give me the more natural HDR result?

What level of hardware - at least - is necessary to work with this amount of pics simultaneously, a Core2 duo with 8 GB with a GForce 1GB video card will be enough?

Thanks, I learned something useful today!!!



Renato

[iangreenhalgh1]

Glad to be of help.

HDR works in most light conditions, realistic is a matter of your tone mapping settings, Photomatix has many presets to experiment with. Where you really see the benefits of HDR are in less than ideal light or in a situation where you have a great difference n brightness between the light and dark areas.

There is such a huge difference between the light levels and conditions you will have in Brasil compared to up here at 56.4N in England that I'm not sure how to advise you when it comes to light and what will work best.

That spec PC will be easily enough to work on files upto 250mp without driving you mad. 250mp is somewhere around 25 or 30 images stitched if using a 12-16mp camera.

[mzzyhmd]

How do you take the shots? :/ I am confused with the parallax thing. Please advice

[iangreenhalgh1]

I'm not sure I understand the question, sorry. You just rotate or tilt the tripod head between each shot, making sure the shots overlap.

Maybe this graphic makes it clearer:

[mzzyhmd]

http://wiki.panotools.org/No-parallax_point

I thought you need to find nodal point to get the panorama correct. So the same object doesn't look different in multiple shots.

[iangreenhalgh1]

Never been an issue, the stitching software takes care of that.

[RSalles]

[David]

Do about a dozen of these, and the nodal point starts becoming second nature. Ian probably intuites it. THat's what I do. I go more for composition and then trust the software. That said, about 12% of my panoramas from the Japan trip are nusable due to the software distorting the image wildly.

More important then nodal point is a solidly pre-conceived composition. I managed a multi-shot stitch (that I SO WISH I could share because it's amazing, and FOUO until the government gives us the okay to release it) of scaffolding (I've already said too much -- just kidding) that's both vertical around columns and horizontal inside a large structure's circumference. So I stitched the shot from about 16 30-second exposures. But before I did that I took a minutes to plan the framing, the overshoot (you need to add about 15-20% of the image on to your final framing to account for image borders and to allow some composition correction in post,) and the perspective. I intuitively selected an off-center nodal point (lower right rule of thirds intersection) and from there structured the image's composition.

Were I to rank nodal point, composition, and horizon, I would rank them 1- comp, 2- horizon, 3- NP.

Anyway, stitching is like any photographic technique. Practice and screw up and learn from that. The mistake stitched I've made have all been more teaching than any instructions I've read and a few have turned out well and given me some ideas on how to intentionally create dramatic effects


For instance, here is one of my early stitches and it is SERIOUSLY flawed. But people love it because of the sky and the dramatic building warping. I learned from this that an idea stitch maintains a reasonable perspective and that if the stitched image covers too great a distance ratio from center to edge the 2-D-ification of 3-D space will make the final image appear to bend unrealistically. I actually gave a lot of thought in this shot to my image's nodal point (and couldn't get to the ideal location for it due to a crazy meth head, but the final result would have been similar.)


About 18 months later I shot this one, which by any measure is meaningfully better image. And it was also about 500 stitched images later, if not more. The difference is that the latter didn't use stitching to exceed a realistic perspective but to increase resolution while retaining a realistic but wide perspective. For this shot, I focused entirely on composition and horizon with no thought at all for the nodal point. Photoshop did that for me.

So, the point is that you just gotta do it and learn it and find out what technique works for you. Don't get trapped focusing on technical issues unless your images repeatedly have serious and similar flaws.

[hoanpham]

Great. Very informative and nicely done.

Regarding stitching,
I use handheld, stitching long focal to simulate wide fast none-existing-lenses,
no problem so far, but for HDR, tripod is needed. Stitching in PS is good, but needed 'manual guide' frame by frame for the best result.
Any distorsion should be corrected after each frame. It's a time consumption process.

otherwise, I use to stitch 2, or 3, or 4 or 6 frames in one with a 35mm shift lens to cover a cityscape, but never done HDR...

[Nordentro]

Skies can be difficult if they move to fast, also shadows from the sun might be a problem if you're not fast enough

[hasan]

Hi Ian,
I process almost the same way for my stitched panoramas

Only difference is, that I crop the image already in Autopano,
before I postprocess in Photoshop.

!! Great tutorial by the way


Regards
Hasan

[iangreenhalgh1]

Cheers guys, some great info there.

David, you really summed it up very well, I just intuitively have a good idea what will work and what is a bit too ambitious. I also find using a 50-ish lens solves quite a few problems I used to get with wider lenses, if the lens has very little distortion, then you get much less distortion in the final stitched image. I used to used 28mm lenses and even though the distortion they have is not great, it could add up across several frames width to quite a problem.

The point about just do it and learn by doing/failing is exactly how I feel about it. I also very much agree that having a clear idea in your head of what you're trying to achieve before you start is a good idea too.

Overall, it's a fun technique and I think it's best t just get out there and try it for yourself, have some fun and learn as you go. I deliberately kept things a little loose and vague in my tutorial because I think there's plenty of scope for trying different things and developing your own methods.

I really like both of David's samples, two pretty different approaches but both work for me, thanks for sharing.

I agree about the need for speed when conditions are changing, skies can be a problem if the clouds are moving, the angle of the sun can change too, especially in the golden hour before sunset.

Hoanpham's handheld technique is very impressive, using stitching to give a lovely 3D effect, I loved his thread about it. In fact, I shamelessly copied the idea to make this shot a few days ago; this one was HDR on a tripod, but hoanpham's work was in my head when I had the idea



Thanks for the kind words Hasan. I often crop in Autopano too, it just depends on the particular image and what I need to do to it.

[philslizzy]

[iangreenhalgh1]

Cheers Phil. I have only scratched the surface of what Autopano can do, I'm looking forward to exploring it further.

[philslizzy]

The editing window is interesting and you get wildly different effects using the projection settings.

And now, just a blatant plug for my own pano posts : http://forum.mflenses.com/viewtopic,p,1337312.html#1337312

[Attila]

many thanks Ian , great tutorial!

[iangreenhalgh1]

Nice Pano work Phil, I see some ideas there I can shamelessly steal! lol

I need to learn to use the tools in Autopano.

Cheers Attila.

I shot this one today at Eskdale Bridge. 32 HDR shots stitched into a 244mp image. Industar-61 on NEX-3.