Photomerge having problems stitching images that are mostly black/block colours

[Anna2781240282k4]

I work in a museum, and our team is working on digitising large-scale posters. We scan sections of the posters, usually 2-3, overlapping significantly, which usually results in images that easily stitch together when photomerged in Photoshop. We have come up against a few problems when trying to stitch together/photomerge images which have a lot of black in them or are block colours.

Does anyone know if there's a way around this? Does Photoshop need lots of images/sections so it will stitch properly? I have tried a few ways of manually stitching them in Photoshop after reading some tips online but they didn't blend/stitch very well.  Would you recommend any plugins that work? I read about one called Hugin, but I'm thinking it could be risky to download an unknown programme onto our computer/is something I need to run past our IT team. 

If anyone has any advice or resources they know of, it would be greatly appreciated.

Thanks!

[c.pfaffenbichler]

Can you post a set of sample images that don’t process well? 

The overlap is not the only thing – if the imges technically have overlap but lack detail Photoshop may not be able to determine the intended positions. 

[Anna2781240282k4]

         

Thank you for all the responses so far, and there's definitely some things I can try out already. Just attaching some examples - as you will see, and as I should have mentioned, the images I am having problems with contain text/are text-based. It might look like they could easily blend together manually, but as I mentioned below my results looked a bit messy, though perhaps that's down to my Photoshop skills! I 'm feeling that I want to avoid 'touching up' the image to keep it as close to the original as possible... but perhaps it is necessary. 

[c.pfaffenbichler]

I have to admit that was surprised that the apprent clear detail would not suffice … but technically the overlap is less than the recommended 40%. 

[D Fosse]

I don't think it's strictly the % overlap that matters here. I think it's the lack of structure, so that the pattern recognition doesn't have anything to work with.

I've seen less overlap than this work with "normal" photographs. 40% is just a rough guide for normal circumstances

[c.pfaffenbichler]

What surprised me with the grey pair of images was that there seem to be unequivocally recognicable details (the letters) present in both images but they don’t suffice.

But I suppose they are pretty small in terms of area and the images are otherwise pretty flat. 

[Anna2781240282k4]

So do you think it's best to make sure there is a 40% overlap? And then manually arrange and blend, as suggested by another commenter,  rather than Photomerge? Or it might be possible to merge with a 40% overlap? Thanks!

[c.pfaffenbichler]

My current suspicion is that 40% overlap should make Photomerge »work«. 

If you manually arrange any meaningful overlap would suffice, 40% would not seem necessary in principle. 

[Lumigraphics]

I find that manual stitching is easier and more effective than using automated merges. Just my opinion 🙂

[D Fosse]

The problem is that Photoshop's Auto-Align (or the derived combo Photomerge) uses pattern recognition. If there are no patterns, it doesn't work regardless of how much overlap you have.

I agree with the above; in these cases manual alignment should work well. You will need a setup to move the camera along the original to avoid scaling differences! That's normally a no-no because of parallax error, but for a flat original that's not an issue.

Once moved into position, Edit > Auto-Blend will merge them seamlessly.

Remember to set Blend Method to Panorama, not Stack! (important, easily missed).

[Lumigraphics]

You can also add registration marks (outside the content area, something like gaffer tape that won't leave residue) and use those for alignment.

[Anna2781240282k4]

This sounds like a good method to try, and I'll give it a go!

[allenc26953525]

I'm preparing to do a similar project, involving a large painted mural on a curved concave surface, 12 feet high, and 18 feet in diameter. It will be shot in tiles for merging. The file needs to be at a 'reasonable' print resolution.

Photoshop Photomerge works well for me in many instances, but can be cranky with large numbers of big image tiles. You may know that Camera Raw can now (attempt) to make panoramas by right clicking a group of selected overlapping images and selecting Merge to Panorama. It makes a DNG.

HOWEVER

If I get too deep into stitching issues I use Hugin. It is a popular, long-time, open source User Interface based on the Pano Tools routines.

It allows manual feature matching, (among MANY other tools) to help with difficult auto stitching. Very useful tool to have in your 'kit'...

Do have your IT folks check it out. I've used it for more than a decade (and I'm still not anywhere near an 'expert"). Never caused any system problems at all.

Keep us posted on your adventure.

[c.pfaffenbichler]

I did a test (manually arranged the two images, then split them into two images 10/16th of the new width) and with that 40% overlap it seems to work fine. 

Like I said, I would have expected the available overlapping details to suffice, but they are less overlap than recommended.