Posted by Chris Ebright on January 15, 2007 at 1:02 PM
I have been playing around with stitched panorama's and I am having exposure issues that I can't figure out. I am shooting with a Nikon D70, manual mode with the same exposure for each frame. I am shooting in auto white balance, but shooting raw and processing for the same temp, so i didn't think that should matter. but when i am done processing the images, with the identical parameters, i still get widely varying exposures and colors, which makes stitching the pano very difficult. any ideas on what i am doing wrong?
Posted by Bret Edge on January 15, 2007 at 1:23 PM
Are you using a polarizer? Doing so can make it nearly impossible to blend the sky in a pano. Also, what software are you using? I had some difficulty stitching successfully w/ PS CS2, so I bought AutoPano Pro and it's made a world of difference. Aside from that, I have no idea what the issue might be. Sorry I can't be more help to you!
Posted by Nat Coalson on January 15, 2007 at 1:23 PM
I've found that Auto White Balance actually can affect the exposure, so as a general rule of thumb, never shoot in Auto White Balance.
What software are you using to process the raw files? There may be automatic settings in that software that are affecting the output.
For example, if using Adobe Camera Raw, make sure the Curve is set to Linear. The default is Medium Contrast, which will affect each image differently.
Posted by Chris Ebright on January 15, 2007 at 1:50 PM
I am not using a polarizer. Using PS2 for stiching and Adobe Camera Raw for processing. I will try shooting with manual white balance and see if that is the answer, but i will also try AutoPano Pro and see if that helps blend the exposured better. thanks for the advice Bret and Nat!
I'll second AutoPano Pro as an option for simplifying stitching!
Posted by Bret Edge on January 15, 2007 at 2:56 PM
Erik likes AutoPano Pro so much he had to recommend it twice!
Posted by Tony Bouchard on January 15, 2007 at 3:33 PM
If you are shooting RAW then the white balance setting should be applied only when the image is converted it has no affect on the RAW data itself. Can you link to your files so we can see the difference between them?
Posted by Nat Coalson on January 15, 2007 at 4:21 PM
Tony - you're correct - white balance is exif metadata that is attached to the raw file and doesn't directly affect the exposure.
However, I've found that I am able to make more accurate exposures by paying close attention to the white balance setting at the time of capture. At the very least, I use one of the presets, but if I have the time, I use custom white balance by either entering a kelvin temperature manually or shooting a white piece of paper to use for the custom setting.
The reason the exposures are more accurate when the white balance is correct has to do with the fact that the histogram on the camera is generated by the internal image processor, just as if you were shooting in JPEG. I am able to make more effective exposure decisions when evaluating the histogram if the colors in the image are correct to begin with. If the colors are off because of incorrect white balance setting, the histogram is affected, and it's harder to know how the actual raw data is being captured.
Posted by Tony Bouchard on January 15, 2007 at 4:29 PM
Nat,
exactly - this is why I don't go with the internal histogram when shooting 4x5 (using my Canon to meter) - I don't know the WB it used to make that histogram, unless I set the WB myself.
Posted by Todd Caudle on January 16, 2007 at 1:41 AM
Erik likes AutoPano Pro so much he had to recommend it twice!
And he even finally paid for it so he could get the AutoPano Pro logo to go away! Now THAT'S saying something!
Posted by Chris Ebright on January 18, 2007 at 12:21 AM
I went out and downloaded the trial of AutoPanoPro and did a comparison with Photoshop CS2. AutoPanoPro does do a much better job, and that is just with a quick default run through. Here is a post to show the comparison, with AutoPanoPro on top and Photoshop CS2 on the bottom. On both, I just used the default settings and did not do any post processing. thanks for the advice Bret and Erik, unfortunately, now i have something else to buy!
Posted by Bill Pelzmann on January 18, 2007 at 2:08 AM
Nat,
You claim that the ACR default medium contrast curve will affect each image differently. I then obviously don't understand the curves transform. If I have identical RGB values in two separate exposures, why would they be transformed differently using the same function? Same values in. Identical values out. No ?
In Chris's pano, it looks like the image on the far left does have a significantly different overall exposure. The others appear to be more of a light to dark gradient across each frame from left to right. Could this be due to a lens vignette effect?
Although AutoPano does a better job, I can still see the tonal variation in the sky at each seam, so the problem is still there. It would be great to understand the underlying cause.
Bill, the sensor doesn't give you RGB values. It's the raw converter that takes the readings from individual photo sites and decides what RGB value to assign to them. It does that based (partly) on the curve which allows you to increase contrast in select areas. A linear conversion means that a given increase/decrease in light read will result in the same increase/decrease in RGB values. This is not always desirable since it's not the way the human eye sees.
Guy
Posted by Arthur Lund on January 19, 2007 at 12:32 AM
Two more suggestions:
1. Your lens is probably darker in the corners. Try a different one, and see if that makes
your problem better or worse.
2. Download and try Panorama Factory. It does a very good job of blending.
Discussion
13 repliesWhat software are you using to process the raw files? There may be automatic settings in that software that are affecting the output.
For example, if using Adobe Camera Raw, make sure the Curve is set to Linear. The default is Medium Contrast, which will affect each image differently.
However, I've found that I am able to make more accurate exposures by paying close attention to the white balance setting at the time of capture. At the very least, I use one of the presets, but if I have the time, I use custom white balance by either entering a kelvin temperature manually or shooting a white piece of paper to use for the custom setting.
The reason the exposures are more accurate when the white balance is correct has to do with the fact that the histogram on the camera is generated by the internal image processor, just as if you were shooting in JPEG. I am able to make more effective exposure decisions when evaluating the histogram if the colors in the image are correct to begin with. If the colors are off because of incorrect white balance setting, the histogram is affected, and it's harder to know how the actual raw data is being captured.
exactly - this is why I don't go with the internal histogram when shooting 4x5 (using my Canon to meter) - I don't know the WB it used to make that histogram, unless I set the WB myself.
And he even finally paid for it so he could get the AutoPano Pro logo to go away! Now THAT'S saying something!
You claim that the ACR default medium contrast curve will affect each image differently. I then obviously don't understand the curves transform. If I have identical RGB values in two separate exposures, why would they be transformed differently using the same function? Same values in. Identical values out. No ?
In Chris's pano, it looks like the image on the far left does have a significantly different overall exposure. The others appear to be more of a light to dark gradient across each frame from left to right. Could this be due to a lens vignette effect?
Although AutoPano does a better job, I can still see the tonal variation in the sky at each seam, so the problem is still there. It would be great to understand the underlying cause.
Guy
1. Your lens is probably darker in the corners. Try a different one, and see if that makes
your problem better or worse.
2. Download and try Panorama Factory. It does a very good job of blending.
Art Lund