Dan Margulis Applied Color Theory

Correcting Flare

   Date: Sun, 5 Jun 2005 16:29:04 -0400
   From: John Castronovo
Subject: Re: correcting flare

I believe this has been discussed before, but does anyone have a suggestion for correcting an image that has been badly affected by image flare due to stray light from entering the lens that should've had a hood or gobo? The obvious thing would be to use levels and a generous 's' curve to replace the missing contrast, but I'm thinking that layering a duplicate channel in multiply mode might do it better, but I'm not sure why.
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   Date: Sun, 5 Jun 2005 14:46:05 -0700
   From: J Walton
Subject: Re: Re: correcting flare

Why not post the image and let us try our hand at it?

J
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   Date: Sun, 5 Jun 2005 18:34:46 EDT
   From: Dan Margulis
Subject: Re: Re: correcting flare

John Castronovo writes,

does anyone have a suggestion for correcting an image that has been badly
affected by image flare due to stray light from entering the lens that
should've had a hood or gobo?

The following is obviously changeable depending on the character of the image.

1) Locate the darkest RGB channel, usually the blue. Copy it into a fourth channel.

2) Open this fourth channel and Gaussian blur 15.0 pixels.

3) Invert this blurred fourth channel.

4) Make duplicate layer.

5) To duplicate layer (composite color visible), Image: Apply Image, Source=the fourth channel, Mode=Overlay.

6) Change mode of the duplicate layer to Darken.

Dan Margulis
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   Date: Mon, 6 Jun 2005 07:53:01 -0400
   From: John Castronovo
Subject: Re: Re: correcting flare

As you like. I've uploaded a jpeg called bluebird.jpg if anyone would like to give it a try. Thanks for the offer.
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   Date: Mon, 6 Jun 2005 23:13:28 -0400
   From: John Castronovo
Subject: Re: Re: correcting flare

If you don't mind Dan, could you elaborate on step 5? Apply image isn't giving me a source choice for the fourth channel.
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   Date: Mon, 06 Jun 2005 23:58:14 -0400
   From: Dan Margulis
Subject: Re: Re: correcting flare

"Source" refers to the name of the image. "Channel" is the field you're looking for.

The Apply Image command lets you blend with any channel of any image that's currently open that's the same size as your image. The source field tells you the name of all open images that meet that requirement. If you make a duplicate image it will show up as an alternative source, and then you can specify what channel you want out of it.

Currently, though, you only have one choice for source because your own image is the only one that's open. So, what you should be telling Photoshop to do is: blend in Overlay mode, Source=this same image; Channel=the blurred inverted copy that you just made.

Dan Margulis
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   Date: Mon, 6 Jun 2005 21:37:00 -0700
   From: Lee Varis
Subject: Re: Re: correcting flare

Dan, this sounds suspiciously similar to your manual steps for the "Shadow/Highlight" command in PSCS and would result in darkening the edge flare from a light background. Could one utilize the darken "Highlights" portion of "Shadow/Highlight" to achieve something similar?

regards,

Lee Varis
http://www.varis.com
888-964-0024
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   Date: Mon, 6 Jun 2005 23:03:01 -0700
   From: J Walton
Subject: Re: Re: correcting flare

I took a few minutes tonight and gave it a shot.  The result is posted, bluebirdJW.jpg.

I did not use any automated techniques, just converted to LAB and fixed the L and B channels.

J
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   Date: Wed, 8 Jun 2005 11:19:20 EDT
   From: Dan Margulis
Subject: Re: Re: correcting flare

Lee Varis writes,

Dan, this sounds suspiciously similar to your manual steps for the  
"Shadow/Highlight" command in PSCS and would result in darkening the  
edge flare from a light background. Could one utilize the darken  
"Highlights" portion of "Shadow/Highlight" to achieve something similar?

Something similar, yes, and definitely quicker. But this way is more flexible. We're finding the channel that's most suitable to blend with, rather than the S/H approach, which uses a grayscale conversion to determine what's a highlight.

If we're talking about a flare, it's probably much better defined in the darkest channel than it is in a grayscale. That's particularly so if, as usual, the darkest channel is the blue, which is hardly taken into account at all in the grayscale version.

So, there is better control of how to limit the change to the defective area, not to mention the ability to edit the extra channel further before applying it. In S/H there is a Tonal Range slider that is helpful, but it won't be able to isolate the damaged area as well as a single-channel move will.

Dan Margulis
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   Date: Thu, 09 Jun 2005 10:15:16 -0400
   From: Lee Clawson
Subject: Re: Re: correcting flare

John,

Tried Dan's method and got confused by step 5 too. What I came up fixed some of the flare but with an un-life-like bluebird. Here's another approach. I made a loose selection of the bird and used "selective color" to add blue back into the white/highlights and later added a bit of contrast; then inverted the selection and added green to the foliage. Letting the the green be a bit warm helped enhance the cool blue of the bird.

Lee  
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   Date: Thu, 09 Jun 2005 19:57:21 -0000
   From: "kuhammer2004"
Subject: correcting flare

Tried Dan's method and got confused by step 5 too.

In the apply image command. where it says "channel"(for the Source Image),...click on the drop down box...and select..."Alpha 1"(or whatever you named that channel). Below the "Target" should read,"background copy"(or whatever you named that layer), "RGB". OH! One other thing make sure you have the preview box checked, optional (a preview before the correction takes place). When this box is unchecked, some think that they done something wrong, somewhere.

     John Opitz
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   Date: Wed, 15 Jun 2005 10:27:39 -0700
   From: Rick Gordon
Subject: Re: Re: correcting flare

Dan,

This is a great suggestion! Works well with multiple iterations, too.

How do you determine the optimal blurring radius for this (or other related techniques)?

Thanks.

Rick Gordon
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RICK GORDON
EMERALD VALLEY GRAPHICS AND CONSULTING
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WWW:   http://www.shelterpub.com
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   Date: Thu, 16 Jun 2005 12:24:54 -0000
   From: Stephen Marsh
Subject: Re: correcting flare

Rick, I think this method provides an interactive blur for you, but uses more memory as a trade off.

From the top down, three layers:

Upper layer: The inverted blue channel, grouped with the previous layer in overlay blend mode.

Middle layer: The dupe of the flat background layer in darken mode, this is the target for the grouped overlay blend of the upper layer.

Bottom layer: The flat background original image.

Then blur the upper overlay blend mode layer that you copied/pasted
the darkest channel data into.

The whole process should be the same end result as Dan's method, providing an interactive blur but using more memory due to the
extra layer.

Hope this helps,

Stephen Marsh.
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   Date: Thu, 16 Jun 2005 22:49:26 -0400
   From: Dan Margulis
Subject: Re: Re: correcting flare

Rick Gordon writes,

Dan,
This is a great suggestion! Works well with multiple iterations, too.
How do you determine the optimal blurring radius for this (or other related
techniques)?

The technique is used to darken relatively large areas. Often there is some fine detail in these areas that isn't nearly as light as the surrounding area. The blur has to be just big enough to obliterate that detail so that the whole area will darken as a unit.

Dan Margulis
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   Date: Fri, 17 Jun 2005 01:37:38 -0700
   From: Rick Gordon
Subject: Re: correcting flare

Thanks, Stephen.

... Or to translate to the new CS2 vocabulary (which gave me a bit of confusion), "put into a clipping group" (I guess). Now that Adobe has, in its infinite wisdom, started referring to Layer Sets as Groups, and referring to the verbs "group" and "ungroup" as "create clipping group" and "release clipping group". (And changed the keyboard shortcuts, to boot.)

What is the new Adobe-approved way of referring to these things, anyway?

Rick Gordon

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RICK GORDON
EMERALD VALLEY GRAPHICS AND CONSULTING
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PHONE: 415-663-8652

WWW:   http://www.shelterpub.com