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Author Topic: Gray cast in digital blending  (Read 2022 times)

RadicalDad

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Gray cast in digital blending
« on: January 15, 2007, 06:52:21 am »

I've tried the digital blending technique (layer mask version) described by Michael on this web site.  When I try it, I get a gray cast in the end result.  It looks like the photo has been slightly desaturated or a gray film has been placed over it.  I notice that the examples shown also have this problem.  Its easy to spot compared to the original photos.  It looks like the photo was shot through a dirty window or a window with a slight glare reflection.

To the degree that one is trying to reduce contrast with this technique, it isn't surprising that contrast is reduced even in places where you don't want that to happen.  Being a newbie at digital and color (last time I shot seriously, I was shooting Zone System on B&W film), I can imagine that this techique would introduce a gray cast.  The problem is getting rid of it.  The amount of desaturation or gray-ness doesn't seem to be uniform.  Adding an adjustment layer to change the saturation levels creates unwanted wild colors in some places.  I've also tried curves and contrast adjustments without success.

How do others deal with this problem when using digital blending with a layer mask as Michael describes?

I also notice that the Gaussian Blur added to the layer mask creates some unwanted artifacts.  In the photo I am working with, the Gaussian Blur in the mask creates unwanted luminance artifacts in both a snow patch and a cloudy sky located near some dark trees.  You can see a similar effect in Michael's first example (the "lake and flower" photo) where the area of the flower near the roots has an unnatural bloom of luminance and saturation (lack of the gray cast I noted above).  Eliminating the Gaussian Blur step fixes the problem for me.  I realize the amount of blur applied to the mask might need to be adjusted according to the needs of the photograph, but I'm wondering why any blur would ever need to be applied to the mask in this particular technique?  (I can understand mask blur with other techniques, but not this one).

Sorry for the long post.  Hope its not too technical.

--Bruce Morris
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brianchapman

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Gray cast in digital blending
« Reply #1 on: January 15, 2007, 09:47:02 pm »

Hi Bruce,

I would start by playing with varying amounts of blur on the mask.  This is probably what is causing the gray cast (reduction in overall contrast).  Have you tried increasing contrast using a curves layer or using local contrast enhancement to bring the image back in line to where you want it with regards to contrast?

Alternatively you can paint on the mask directly to fix problem areas - for example, in Michael's example, there is probably no reason to use any part of the dark image for the flower area so you could make sure that area is black in the mask.  This can lead to other problems when you approach areas that required a lot of blending but it's just something that you have to play with to see what works the best.  

The discoloration in the root area of the plants in Michael's example shows slightly in the bright image in the "before" set so I assume it is in the dark image but just not visible.  The mask accentuates this halo because it falls in to the area that is being masked in the brighter image - so the dark image is showing through in that area.  While we can't see the mask in the tutorial, I expect that it is lighter in that area than the area around it.

Hope this helps!  

Brian
http://www.brianchapmanphotography.com
« Last Edit: January 15, 2007, 09:48:02 pm by brianchapman »
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Brian Chapman
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RadicalDad

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Gray cast in digital blending
« Reply #2 on: January 16, 2007, 06:03:24 pm »

Thanks Brian!

I noticed the gray cast even when I blurred the mask.  Plus, the blurred mask created problems - a mottled look - in the snow and sky areas near darker areas.  I fixed this particular photo by directly painting on the mask instead.

I wasn't able to eliminate the gray cast using Curves (or any other tool) in Elements 5.  That's why I was wondering if others had noticed the gray cast and how they handle it.  Maybe I need to get the more controllable Curves command in the full PS, but I want to see if that will really solve the problem before I spend the bucks.   So far, anything I have done with Curves hasn't really touched the problem.

I'm still hoping for a digital blending solution that is quick and easy and renders something more useable than what I seem to be getting right now.

--Bruce Morris

(Did it snow in Seattle?  Its crazy in Portland - and it knocked out my Internet service at home.)
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brianchapman

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Gray cast in digital blending
« Reply #3 on: January 16, 2007, 10:10:01 pm »

Bruce,

Yeah, it snowed, but it wasn't as bad as Portland - check out this video!

Would you mind posting a screenshot or something showing what the before and after blending looks like so I can see the gray cast?  You can also send me a "personal message" and I can give you somewhere to upload it.  

Brian
http://www.brianchapmanphotography.com
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Brian Chapman
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