Shooting/Processing Panoramas

While I was away at the weekend I took the time to grab a few photos that I wanted to turn into a panorama. I was not able to set everything up with a tripod etc, but thought it would be worth a try hand held. I was shooting with my 20D using a Sigma 20-40 2.8 EX DG at 20mm. I used Manual exposure mode but with a +-1 stop bracket shot in continuous mode incase I wanted to do an HDR with it as well. I did a 360 degree with a full frame of overlap at the ends, doing a total of 24 frames at each exposure setting. I ended up using f5.6 and 1/640s. As I shot quite late in the afternoon the sun was only just out of frame in the shots facing west, so I used one of those shots to set up the processing, in order to recover the highlight detail. As I had shot in manual, and made sure that I had only used the shots with the same settings, I then pasted the conversion to the other 23 images. I expected that this would give me a reasonably consistent conversion across all 24 images. Ithen sent them to CS5 and had them auto stitched. I then cloned / Content aware filled the "gaps" around the edges. This was the result.

IMAGE LINK: http://www.flickr.com/​photos/alan-evans/8723229268/

IMAGE LINK: http://www.flickr.com/​photos/alan-evans/8721723483/

If you used the frame with the sun in it to set your exposure adjustment, all of the frames with little direct sun presence (esp opposite to the sun) will be darker, because you are setting the exposure for the impossibly bright sun. If the sun were high in the sky and not present in your pano, then the sky would likely appear more uniform across the 360° FOV. This gets even worse when you use a polarizer, which responds to the direction of the sky you are shooting relative to the sun.

Maybe try setting your exposure adjustments for the sky, generally, and then make some additional compensation for the area around and including the sun to bring the sun into line with the rest of the image. You may want to try stitching two panoramas, one with the current exposure adjustments (for the sun) and one for the sky and then blending the two to even out the overall sky. The problem is that Photoshop does not permit you to save the stitch from one panorama and apply it to another, so you may actually get inconsistent stitches even if you use identical images with different exposures.

Another solution may be to merge each exposure set (3 images) into an EXR and then stitch those to a full HDR panorama. Then you can control the tonal range compression across the image and map the sky all at once.

Hugin is a free stitcher that, if memory serves, has an exposure tool that attempts to equalize exposure over the panorama for problems just like this.

Also, you may want to try PV 2010 instead of PV 2012 for raw conversion, to see if you get more consistent results from exposure adjustments.


kirk

Actually it was the shots at 90 degrees to the sun that were darkest (2/3rd stop) and down sun was only 1/3rd stop darker than the up sun shot. I guess what I failed to consider is that PV2012 is only giving an impression of producing a wider dynamic range, when what it is really doing is to compress the wider range into the same space that we can display. I think that given PV 2010 I would have ended up having to use a selection of the different exposure brackets to get detail across the whole DR that is represented in the image. I guess that I should be considering that I was working with a DR that is still impossible to represent from one single exposure/conversion. The option is probably the ability to use one exposure/conversion, maintaining the midtones and losing both highlight and shadow detail, or maintaining detail across the whole of the DR by differential processing.

Thanks for the help in realising what I now think the issue is.

Alan

BigAl007 wrote in post #15914087
Actually it was the shots at 90 degrees to the sun that were darkest (2/3rd stop) and down sun was only 1/3rd stop darker than the up sun shot.

That is exactly what you would expect when using a polarizer. It performs best (and thus darkens most) at 90 degrees to the sun.

Well now having had time to go back and do a little more work on this here are the brightest and darkest of the images, when done with the conversion to recover the highlights.

Dark

IMAGE LINK: http://www.flickr.com/​photos/alan-evans/8723750484/

IMAGE LINK: http://www.flickr.com/​photos/alan-evans/8722627279/

IMAGE LINK: http://www.flickr.com/​photos/alan-evans/8722626273/

IMAGE LINK: http://www.flickr.com/​photos/alan-evans/8722630263/

IMAGE LINK: http://www.flickr.com/​photos/alan-evans/8722628345/

If you remove the overlap, you can "fix" what's in the center of the frame.

With a 360-degree pano, you have complete control over what's in the center of the image, because all you have to do is fix the yaw of the virtual camera. In a more sophisticated stitching program, like Hugin (which, btw, is open source), it's a simple drag in the preview window to adjust.

1. Open the image in Hugin, and set the lens type to "Panoramic (cylindrical).
2. Click on the GL Preview button.
3. Click on the Move/Drag button.
4. Click the "Fit" button to rescale the image.
5. Drag horizontally, and the image's yaw will change (vertical will fix the pitch and straighten out curved horizons, right-drag will fix the roll/rotation). Hold down the shift key if you only want to adjust the yaw.
6. "Stitch" the pano.

Minor note 2: shooting with the camera in portrait orientation can give you some more vertical coverage.

Dan Marchant wrote in post #15914315
That is exactly what you would expect when using a polarizer. It performs best (and thus darkens most) at 90 degrees to the sun.

My guess as well.
Then again, on this image, I don't mind much (2nd version)

From what Al says in his OP, I'm under the impression that he shot in Manual mode with fixed exposure settings...is that correct, Al?

In that case, there would be no exposure "adjustments" taking place, but only how the sensor was capturing the scenes relative to the position of the sun, in other words, the "discrepancies" would be in the relative variation between highlights and shadows. As we know, our cameras don't always provide a consistent "interpretation" that matches our expectation when shooting facing the sun and with our backs to the sun...?

Just my two bits...

Tony, yes I shot in manual mode, actually I had the camera setup to do a 3 shot bracket, and picked out all of the minus shots for processing. That said all the images used were 1/640s f/5.6 ISO 100. I did not use a polarising or any other filter. I have considered getting a polariser for that lens, but as it is an 82mm filter thread, and would really need a slimline filter, it is afterall a 20-40 mm full frame constant f/2.8 zoom lens, the filter would cost me as much as I paid for the lens in the first place. For the amount of times I would need the filter it would not be cost effective.

My main error in initially processing the files was deciding that I needed to recover the highlights for the down sun images. Even with the great strides that PV 2012 has given us in DR recovery the difference between the highlights and shadows is such that a single set of conversion parameters cannot give us both ends at the time. When I processed the image that consisted mostly of the middle tones of the complete set of 24, and then applied those settings to both the bright and dark images the midtones are fine, although there is clipping of both shadows in the "darker" images and highlights in the "lighter" images, the midtones (mainly in the grass) in all three images is pretty damn close to the same across all three of the images with that set of conversion parameters.

I guess that if I want to be able to produce a finished image that recovers both the highlight and the shadow details, and keeps the midtones correct then I need to process each of the images individually and manually match the overall brightness across all the tones of the images. Which is of course what I ended up doing, without knowing why. I think I ought to sort out the vignetting as well as I think that is what is causing the odd that unevenness of the darker blue parts of the sky, where it is picking up the corners of some of the images.

When it comes to doing the stitching, as it is not something that I do a lot of I just wanted to be able to use the software that I had available. Actually the way the road moves across the image as PS produced it automatically is actually visually nicer than what I got when I tried to move things around manually. Overall I was actually very impressed by the way that the software did the stitching without any manual intervention. It was just a surprise that it did not attempt to put the first/last images as taken at the ends of the completed panorama. When I tried to move the ends to the middle of the finished panorama I was using the original version and there was a considerable difference in the brightness at either end of the image.

Thanks for all the suggestions.

Alan

I've had the easiest time stitching panoramas in Microsoft ICE, especially the HDR panos I have done. It's usually been a one shot deal.