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Mysterious hairline shadows
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johan



Joined: 06 Sep 2011
Posts: 961

PostPosted: Thu Mar 29, 2012 1:51 am    Post subject: Mysterious hairline shadows Reply with quote

Hello,

Just wondering if this is a common problem or something peculiar to the eq I use or lighting inadequacy or zerene incompetence or...?

I use a smallHD field monitor (think small computer screen) as a background; I pipe PC output into it and with a blank canvas open in photoshop, I can get any gradient I want as background. Which is nice, but it's not without issues, one of which I don't see in other people's work, namely hairline shadows in the output on a plane where there shouldn't be any. Ie the monitor is quite far back so it's not a reflection, it's a "shadow in space".

Example: - taken from pic here

Thank you
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Cactusdave



Joined: 09 Jun 2009
Posts: 1523
Location: Bromley, Kent, UK

PostPosted: Thu Mar 29, 2012 2:10 am    Post subject: Reply with quote

Is the large bright background perhaps causing an internal reflection in your setup, maybe in an extension tube, and that way picking up detail from outside the field of view? See this link posted coincidentally on another thread http://www.eoshd.com/content/7415/revealed-metabones-ef-sony-e-mount-adapter-optically-defective
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rjlittlefield
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Joined: 01 Aug 2006
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Location: Richland, Washington State, USA

PostPosted: Thu Mar 29, 2012 9:50 am    Post subject: Reply with quote

I assume you mean the dark line on the right side of the antenna. I do not recognize that problem. Does it appear in the original input images, or is it an artifact of the stacking?

--Rik
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johan



Joined: 06 Sep 2011
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PostPosted: Thu Mar 29, 2012 10:51 am    Post subject: Reply with quote

Thank you. Yes - I just saw it's in the originals, so I assume it's something to do with my backlit methodology. Anyone seen this before?


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DQE



Joined: 08 Jul 2008
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Location: near Portland, Maine, USA

PostPosted: Thu Mar 29, 2012 12:15 pm    Post subject: Reply with quote

My comments will probably be not helpful, but I have seen such artifacts if one applies a commonly used image enhancement method. In ACR it is called "clarity", and is on the main page of Bridge as a slider.

Similarly, Photoshop has unsharp masking and/or the "shadows/highlights" modules that can sometimes create similar artifacts, IMO.

Basically, I believe it is possible to tune USM (unsharp masking) and most other sharpening filters, modules and packages to create this type of artifact. From distant memory I think a large radius in USM is often a part of creating such an artifact.

I believe the left side of the structure is too blurred out to be vulnerable to this possible sharpening artifact, whereas the right side may be vulnerable.

Hope these ad-hoc thoughts help. I realize that they may simply be irrelevant.
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johan



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PostPosted: Thu Mar 29, 2012 12:19 pm    Post subject: Reply with quote

Thanks... though that second image is unsharpened, the JPG as shot (I have +0 as the incam setting)
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lauriek
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PostPosted: Thu Mar 29, 2012 12:24 pm    Post subject: Reply with quote

Do you get the same effect if rather than the LCD screen you use a bright coloured piece of paper as backdrop with a decent amount of light going onto it?

I'm suspicious it might be something to do with some of the funky materials that make up a modern LCD screen, but I could be way off!

This is very interesting, I had considered using my iphone/ipad as a backdrop in the same way but never got round to trying it out. Hope we can work out what's causing this..
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DQE



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PostPosted: Thu Mar 29, 2012 12:25 pm    Post subject: Reply with quote

Thanks for the reply.

Now I'm really convinced that my thoughts were off-track.

One last thought along this line - Is there any credible possibility that in-camera sharpening or other image enhancement could have done this? I've often been surprised at some of the things the built-in in-camera image processing "styles", etc, do to photos, although they may helpfully enhance general photography images. Same concerns apply to the vendor's software, including some features of Canon's DPP, and Nikon's equivalent.
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lauriek
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PostPosted: Thu Mar 29, 2012 12:39 pm    Post subject: Reply with quote

Have you got any raw processing software available?
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PRC



Joined: 05 Jan 2012
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PostPosted: Thu Mar 29, 2012 1:21 pm    Post subject: Reply with quote

The lit card would be interesting as it may well be a synch issue with the scan update of the screen and the shutter on the camera.

Paul C
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johan



Joined: 06 Sep 2011
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PostPosted: Thu Mar 29, 2012 1:24 pm    Post subject: Reply with quote

First of all thank you very much for the responses, much appreciated.

I'm fairly convinced is something to do with the interplay between bright screen (smallHD) and subject lighting (flash). The reason I say this, is because I'm ashamed to say I've never used card - I wanted to make this method work (being a "koppig" Dutchman) - and I've never seen it in other people's stuff that does use card.

More rationally though, here's a link to a pic that I was too ashamed to post because this flaw is SO OBVIOUS on the top left and just ruins it for me. This was shot with 1 flash from the top left and the shadow is below right. The pic above in the thread at the top, that had stronger light from the left but was with 3... yet similar thing again, hairline shadow on opposite side. Ie in both cases the flash strength clearly has something to do with it.

But what I don't get is where this shadow actually is physically or how to avoid it, as this dark shadow doesn't actually seem to be 'on' anything. The clearest example is I think this - at the tip of the tongue in the second pic - the shadow "hangs" in some non physical space between the subject and the monitor, ie below and to the right of anything physical. Which I'm just not grokking because the monitor was 10cm away and at an angle?



I'm sure it must be me being silly and it's probably some really obvious thing and perhaps I can get rid of it by playing with flash direction or light but... it's cramping my style! Annoying!

I do have RAW processing software and used to use it religiously before starting macro here a few months ago but nowadays I just use jpegs out of cam -- it already takes my puter ages to run through zerene, making it convert 200 RAWS to jpegs would make it take industrial action and go out on strike I think.

The exposure in the top shot was 1s, on the linked one 2s - flash at 1/n so likely extremely extremely fast.
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Last edited by johan on Thu Mar 29, 2012 3:29 pm; edited 1 time in total
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DQE



Joined: 08 Jul 2008
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PostPosted: Thu Mar 29, 2012 3:01 pm    Post subject: Reply with quote

Yet another ad-hoc and probably useless suggestion:

Due to the color contrast between your novel background and the primary subject, is it possible that you've somehow excited an unusual form of something like chromatic abberation in the lens/camera assembly? Normally we look for such things with a fine neutral or black subject against a lightly tinted background. A typical example might be fine tree branches against a light blue sky.

Again, just grasping at straws, with a faint hope that this line of thought might stimulate someone else to propose a useful hypothesis.

If it's not an artifact due to in-camera or in-computer image processing and it's not a common optical abberation, I'm personally at a loss.
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lauriek
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PostPosted: Fri Mar 30, 2012 11:15 am    Post subject: Reply with quote

Have you tried rotating the screen to see if the shadow moves?
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TheLostVertex



Joined: 22 Sep 2011
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PostPosted: Fri Mar 30, 2012 2:56 pm    Post subject: Reply with quote

lauriek wrote:
Have you tried rotating the screen to see if the shadow moves?


This is the first thing I thought as well. LCD screens have linear polarizers in them, so if it is only occurring on edges that are in certain areas/angles perhaps this could be contributing to it. Id trying and get it to produce the issue, then rotate the lcd 45º and 90º to see if it changes at all.
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ChrisR
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PostPosted: Fri Mar 30, 2012 3:38 pm    Post subject: Reply with quote

Am I seeing things or is there a rather odd complementary light "atmosphere" too?:
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