Issue with Photomerge in CS5

[rlriii13]

I was fiddling around with CS5's Photomerge operation yesterday and ran across an issue. In Lightroom 3, I selected 6 RAW files from my 60D and chose Photomerge from the menu. CS5 opened up and I proceeded to kick off the operation. Once Photomerge was finished, I was left with something I didn't want, especially with the blending. You could clearly see where each image stopped and the next one began. It was as though the shots were taken at slightly different exposures, which is not the case. All shots were taken at the exact same exposure settings.



If I stopped there, there are a million questions you could ask me to try and diagnose this issue. But, the other big piece of evidence is that when I do the same exact steps with only 4 of the images, the Photomerge image looks great.



Things get slightly better if I run the test with the same 6 RAW files from within Photoshop (without using Lightroom), but still not acceptable.



And again even better if I use 6 JPEG files from within Photoshop, but no where near as good as the 4 shot image.



Does anyone know why doing additional images is limiting Photomerge's performance? I would initially wonder about scratch disk space and RAM. I've got about 70GB of empty SSD scratch space and I'm using 4GB of RAM on a 32-bit Windows 7 machine. Of the 4BG of RAM, Photoshop is allowed to use 1192 MB of the total 1633 MB available. I've read about people doing 60 shot merges in Photoshop. Why can't I get 6? Not enough RAM? Isn't that what the scratch disk is for?

Also, I did my usual Googling to see what I was doing wrong and I found this thread. The second post shows the results I'm seeing. The original poster's solution was restarting. I'm continuing to get that result even after a restart. It seems quite repeatable with either RAW or JPEG files.

http://forums.adobe.com/message/2903101

Anyone have any ideas?

[cls]

Hi, in the upper stitch, it's obviuos that the images are not equally exposed/white balanced. I've had similar problems myself and have learned a few error sources by experience. What's required for stitching is basically constant lighting and fixed camera settings (exposure time, aperture, ISO, WB).

Did you use manual WB setting? If you shoot RAW this can of course be easily adjusted in post.

When you say all images have the same exposure settings, I suppose this means you have shot in manual mode. Did you also remember to set ISO manually?

If exposure settings in the camarea are the same for all images, it must be the actual lighting that differs between the photos. Did you use any flash, or just the window light? If shot on a day with failrly rapidly moving clouds, it doesn't take much to get quite different exposure from one minute to the other. (If you used flash, it could be that the flash output isn't constant.)

If these things are already checked I'm afraid I can't be of any help.

(Edit: Forgot to mention that when I've had issuses with photomerge it hasn't been Adobes fault - it has been me messing with the exposures. There may be some photomerge issue I don't know, but I've stitched up to 10-15 images in photomerge on a modestly speced computer without problems.)

[neuroanatomist]

You show that the 4-image merge works and the 6-image merge doesn't. I wonder if the problem isn't the number of images, but rather the content. The difference that jumps out to me is that the 4-image merge doesn't include the window. That feature is overexposed relative to the rest of the scene, and that may affect the blending if PS is trying to compensate for different exposures. What happens if you try to merge the 4 images on the right, including the window image?

[rlriii13]

Did you use manual WB setting? If you shoot RAW this can of course be easily adjusted in post.

When you say all images have the same exposure settings, I suppose this means you have shot in manual mode. Did you also remember to set ISO manually?

(Edit: Forgot to mention that when I've had issuses with photomerge it hasn't been Adobes fault - it has been me messing with the exposures.)

All exposures were at f13, 0.8s, ISO 100. I was in auto WB though, which was then corrected in post. I'm interested in trying to reshoot this to run some more tests. If I do, I'll be certain to set the WB. I'm also convinced it's not Adobe's fault, I'm only interested in preventing it from happening again.

What happens if you try to merge the 4 images on the right, including the window image?

Here is 4 RAW files including the window. The color came out OK, but there are still minor misalignments at the layer edges (like where the green wall meets the white ceiling), which are a bit more evident when viewing a larger version.



Here's 5 RAW files excluding the window, which causes color issues to return.



The more I look at this, the more I wonder if there aren't several issues, one of them being distortion or perspective (having objects too close to the camera). No matter what ideas I have though, I keep coming back to the fact that I can make those 4 shots merge successfully.

[Sheiky]

Have you used any Lens correction before transferring to CS5? In my opinion this looks a lot like a vignetting problem on the individual photos. Also I assume that you used manual focus on all of the shots. No changes in between?

I don't know your exact method, but try this:

- All equal white balance.
- No lens corrections in Lightroom, apply them during the photomerge in CS5 if necessary
- Do not use the Auto layout in photomerge, use the cylindrical instead.
- Play with the photomerge settings. Try the 3 options separately from each other and see what the differences are. Then apply multiple settings to your liking.

You might also have quite some trouble with distortion. You could try avoiding the widest end of your lens and just zooming in a few mm's. That will help enormously with the distortion.

As far as scratch disk and memory. Your pc gives an error when trying the 6-shot panorama? Or does it just deliver bad results. If the panorama is too big, photoshop will mention that it doesn't have enough recourses to make the shot. Using JPEG instead of RAW could help. Using smaller photos could help as well. I've had TIFF-files up to 2GB in size. Panorama's up till 24 full size 21MP RAW files. It takes a while(15 minutes or so) but it worked for me.

Good luck,
Jan

PS: using auto WB never posed a problem in my shots. Just make sure you apply the same WB to all shots afterwards. Of course you're free to use manual WB

[DavidEccleston]

I'm not sure how CS5's PhotoMerge ranks for quality vs. everything else. A few years back I found that Microsoft Research's ICE (Image Composite Editor) did the best stitching by far of anything I had access to. It can't hurt to try it out.

[rlriii13]

Have you used any Lens correction before transferring to CS5? In my opinion this looks a lot like a vignetting problem on the individual photos.

No lens correction was applied. I have been using the Photomerge option to remove vignetting.

Also I assume that you used manual focus on all of the shots. No changes in between?

I was definitely in autofocus. If I get to reshoot, I'll do everything I can manually and keep them consistent through the shots. I've merged shots with autofocus before without issues though, so I didn't worry about it when I was shooting the first time. Could that be contributing to my problems?

Your pc gives an error when trying the 6-shot panorama? Or does it just deliver bad results.

No error, just subpar results.

A few years back I found that Microsoft Research's ICE (Image Composite Editor) did the best stitching by far of anything I had access to. It can't hurt to try it out.

Thanks for the recommendation David. I know there are other options out there, but I've been using Photoshop for panos for a while and this has never happened before, so I guess I'm just playing detective now. I want to know why! I'm fooleshly hoping someone else has gone through my pain and knows exactly one small, easy change that will solve everything. (Also, forums are a great historical troubleshooting guide. If a solution is found, it could likely help others in the future.)

[Sheiky]

I was definitely in autofocus. If I get to reshoot, I'll do everything I can manually and keep them consistent through the shots. I've merged shots with autofocus before without issues though, so I didn't worry about it when I was shooting the first time. Could that be contributing to my problems?

Yes, I really think this could be an important factor. I will not say that it's impossible with AF, but definitely at a higher risk of failure. Anyway everything that you can rule out would be nice. Differences in distortion and vignetting seem like the most likely problem in your shot.