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Thread: Getting PS to replicate precise stitching on different sets of files

  1. #1
    Senior Member Ed Hurst's Avatar
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    Getting PS to replicate precise stitching on different sets of files

    Hello all,

    I recently took a sequence of shots at sunrise for the purpose of stitching. However, due to the contrast in the scene, every position in the sequence was also taken at 5 different exposures to allow me to use the manual HDR technique in which I layer the differently exposed files and then manually apply layer masks to get the precise effect I want. I do not want to use conventional HDR as I dislike how it looks and want to control it all.
    My original intention had been to get PS separately to stitch together all of the files at a given exposure, layer those stitched files, then do the mask work at that point (i.e. on the layered set of stitched panorama files, each of which is at a different exposure). So, in other words, all the files taken at 1/125 would be stitched; so would all of those at 1/250 as a separate file, etc.; they would then be layered and align perfectly. Trouble is, due to the different detail visible in the files taken at different exposures, the stitching was not produced identically for the differently exposed shots. So the 1/125 stitched file did not match the shape and geometry of the 1/250 stitched file, etc. - which of course made simply layering those separate panoramas impossible, as they would not align.

    So I then decided to do the laborious process of doing the layering and mask work on each set of identically framed (but differently exposed) shots, then flattening those files - to give a single sequence of shots that could be stitched. The trouble is getting those shots to have compatible density so that the stitching would work. That proved next to impossible. I could not simply match the opacity of the masks because the differently lit parts of the scene demanded different opacities of mask - but stitching them looked messy. The function within the stitching process that smooth out transitions still left banding/blotches, etc..

    I can tidy all of that up, but it's a terribly slow and imperfect process.

    So...

    What I would like to do is to find a way of forcing PS to do it the way I originally intended. In other words, to take one sequence of the shots all exposed the same, stitch them, then get PS to stitch the other sequences of shots identically, so that I can layer the identically aligned panoramas (which will have different exposures) and simply work on one set of masks. As I said above, normally stitching the differently exposed sets of files does NOT have this effect - presumably because the dark and light files lack the detail in parts of the scene to make the algorithms work in an identical way and you end up with quite different (and hence not aligned) stitched panoramas.

    Does anyone have any ideas how to get PS, having stitched one set of files, to apply the EXACT same geometry to another set of files so they perfectly line up (given that the files at the different exposures are perfectly aligned)?

    Hope this all makes sense!

    BTW - I am using PS CS5 (in case that makes a difference).

    Thanks in advance for any advice.

    Ed

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    Re: Getting PS to replicate precise stitching on different sets of files

    Ed, Without such a set of files to work with, I can only make the following recommendation and see if this is what you did or not.

    Assuming all the images are open and on separate layers and all layers are selected. I would choose Edit -> Auto Align Layers -> Collage. This will disable any perspective/geometric correction but can still resize images if necessary (if that's not necessary then perhaps reposition would be better). If you're using a wide angle lens, this may not work. In that case I think the only choice would be to use something like Kolor Autopano which deals with this sort of problem gracefully if not entirely perfectly.

    Hope that may be helpful

    Paul

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    Re: Getting PS to replicate precise stitching on different sets of files

    PTgui is what you need. With PTgui you can select custom merge points. These merge points are what Ptgui uses to calculate the stitching merge. You can then apply these custom points to any number of file sets (batch i believe it is called in PT, it's been a while). This allows for "repeatable" stitches. With PT, stitched exposure brackets are fairly easy.

    Also, I would not give up on PS HDR. PS provides a great deal of control over how the merge is done. HDRs that don't have that typical plastic HDR look are very possible. Google something like "PS 32-bit HDR merge", that should start you in the right direction. The step where you convert the 32-bit to 16-bits is where you adjust the HDR look to your satisfaction. Again it's been a while...
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  4. #4
    Senior Member Ed Hurst's Avatar
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    Re: Getting PS to replicate precise stitching on different sets of files

    Thank you guys - much appreciated. I'll look into those methods and report back! I have already tried the HDR tools in PS and come to the conclusion that I would rather use my layering methods, so I'll first of all try the suggestions based on the stitching.

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