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Snag with photos as backgrounds

 
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Beatsy



Joined: 05 Jul 2013
Posts: 1392
Location: Malvern, UK

PostPosted: Thu Jul 05, 2018 8:42 am    Post subject: Snag with photos as backgrounds Reply with quote

[Edit: oops - meant to put this in techniques - would you move it pls mods?] [done - Rik]

A couple of days ago, I mentioned that I'd hit snags using a small print as a backdrop for the "Evangelical Weevil" stack ( http://www.photomacrography.net/forum/viewtopic.php?t=37526 ). I've been investigating and solved the issue. It was an obvious thing, almost not worth reporting - but I said I would, so...

In the past, when not using plain backgrounds, I sometimes used small prints of blurred, low-contrast imagery as backdrops. For the weevil, I used a photograph of bright pink flowers against dark green foliage. The print wasn't blurred this time either. I positioned it about 30mm behind the specimen and relied on it being out of focus throughout the stack. But I got nasty dark smearing against some edges that overlapped the brighter flowers and coloured (pink) haze behind other features set against darker background. These are visible in the un-retouched stereo images at the link above.

Turns out, it's simply the bright "spots" (pink flowers in this case) acted just like small, directional light sources - creating exactly the same issues that entails when stacking (particularly with deep stacks). I won't go into detail on the aberrations seen (flares and coloured shadows that move as the stack progresses) as that's been discussed all over the forum.

The solution is a little restrictive - but not too bad. In printed background imagery, I will now keep high contrast details relatively large, or reduce their contrast, or print darker (or use less light on the background). Or any combo of these minor restrictions. Then the issue goes away! Couple of (very) quick test stacks attached, each with the "better" backgrounds and no retouching. I had no problems with these at all.

That was it. Apologies if it's obvious - but it caught me by surprise Shocked




Sorry for the "ransom note" layout of the images too. I was trying out macros in Affinity Photo to automate the creation of various border designs.
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naturepics43



Joined: 11 May 2015
Posts: 72
Location: Hocking County, Ohio , USA

PostPosted: Fri Jul 06, 2018 2:22 pm    Post subject: Reply with quote

Thanks so much for posting this information on backgrounds. I'm still strugling with backgrounds and this will be a great help. Being fairly new to focus stacking, I'm always looking for tips & tricks. Thanks again for posting.
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