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Old Jun 25, 2005, 11:27 PM   #1
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I recently took a 7-shot series at a nearby lake. While my previous Autostitch panos came out very nicely (usually 3- or 4-shot series), this one had trouble with the sky.


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Old Jun 25, 2005, 11:28 PM   #2
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Autostitch failed to blend the variations in the sky. Here's a 4-shot portion of the same series.


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Old Jun 26, 2005, 3:49 PM   #3
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It looks like there is a difference between the exposure between "frames". I assume that you had your exposure fixed (f/stop, shutter speed, ISO), so a likely problem is clouds changing the light level as they pass in front of the sun. Take a look at your EXIF data to see how fast you were shooting - the longer the time between "frames", the more likely a light level change.
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Old Jun 26, 2005, 6:40 PM   #4
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Hi Walter;

Autostitch can adjust this to a certain extent, though I am sure you have experimentis with it already. Make sure GAIN COMPENSATION is on and try adjusting GAIN SIGMA and/or GAIN MEAN. If that fails, you can always edit the offending panel in Photoshop to match it to the other frames. That being said, there is only so much you can do to compensate for differences in exposure, white balance, etc.

I don't necessarily mind that much when Photoshop or Autostitch (or any program) throws a little challenge at me. It gives me an excuse to try things in a way I hadn't thought of before. When I was a much younger man and a recreational skier, my motto was "If you're not falling down, you're not learning.":roll:

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Old Jun 26, 2005, 11:03 PM   #5
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Bill and Tom

Thanks for the tips. Much appreciated. I'll try them as soon as I have some free time.

Walter
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Old Aug 6, 2005, 2:15 PM   #6
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Hi Bill,

Does it mean that i will have to take the pics real quick and standing at same position?
Shud i also put camera in manual mode so that every setting is identical ?

I have 4 pics of sky but taken with a time idfference of abt say 1-2 mins each + from different positions. I thought still it was the sky itself but didnt work stitching.

Thanks
Kaz.
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Old Aug 6, 2005, 7:30 PM   #7
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Yup, fix the exposure - manual or some cameras have a "panorama" mode that does it. Shooting quickly will help with light level changes. Spend a bit of time figuring out where you want to stand, "dry shoot" over the pano you are thinking about to get a feel for how many shots and what kind of motions you might have to make, think about it a bit more, practice a bit more, then set the camera for the right exposure and shoot quickly.

You don't have to stand in the same position, but the camera does. It should be rotated about the nodal point without sideways motion. The further your subject is, the less critical.

Shooting the sky likely means your camera was well off level, pointing upwards. Some stitching software doesn't deal with that very well.
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Old Aug 6, 2005, 8:48 PM   #8
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kazaan wrote:
Quote:
Hi Bill,

Does it mean that i will have to take the pics real quick and standing at same position?
Shud i also put camera in manual mode so that every setting is identical ?

I have 4 pics of sky but taken with a time idfference of abt say 1-2 mins each + from different positions. I thought still it was the sky itself but didnt work stitching.

Thanks
Kaz.
Matt Brown states in his research regarding one of his examples, "This sequence was shot using the camera's automatic mode, which allowed aperture and exposure time to vary, and flash to fire on some images. Despite these changes in illumination, the SIFT features match robustly and the multi-band blending strategy yeilds a seamless panorama."

It is certainly my experience that AutoStitch, using the blending options can diminish practically any seam, if the exposures are reasonalbly close. For example, check out this example: Detroit Panorama This is a two-layer panorama (upper and lower) comprising 12 images shot across a late-eveing sky. Shot in shutter priority, the light levels vary quite a bit. AutoStitch handled the exposures with ease. This is not a perfect example, but it demonstrates how the blending function of AutoStitch handles difficult situations. (I know one frame in the middle is blurry - my light-weight tripod couldn't handle some gusts of wind.:roll

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Old Aug 7, 2005, 5:59 PM   #9
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It is cerianly true that a fair degree of exposure compensation can be dealt with, but at a price. The same price you will pay if you adjust the exposure in any editing software instead of getting it right in the first place. Typically blown highlights or blocked shadow areas and less dynamic range in the image.

Shooting panos isn't really much different than shooting any other photo. You will get the best results if you have the exposure set right in the first place.
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Old Aug 7, 2005, 8:10 PM   #10
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Agreed, agreed and agreed.

Cheers,

Tom, on Point Pelee, Canada
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