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Hello all...

I tried something today in LAB and eventually got it working OK, but I wonder if any of you have an easy way to get this done. (I'm also hoping that it's not somewhere in Dan's LAB book. THAT would be awkward...)

When correcting grays it would be nice to be able to get a mask for all things that aren't saturated. My first thought went back to HSB mode, which I think I remember converting to in some version of Photoshop. Then I remember Heidelberg had an LCH mode on it's color software, which would work too. Steal the S or C channel and go.

1. Does anybody know of a way to easily convert to HSB/LCH? I seem to remember a Photoshop plugin a while ago. 2. Any slick way to do this in LAB or some other method in Photoshop?

I ended up blending A to B using Hard Light, selecting it, inversing, selecting it again with Com-Opt-Shift and tweaking the resulting channel. It worked OK but not great.

Thanks in advance if you have any suggestions.

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J Walton

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Not sure how "slick" it is but I would work on a copy of the layer and use "blend if underlying layer" with a/b at 0.

Regards,

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Francis Corvin

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on 6/14/06 11:07 PM, J Waltonwrote:

I had a HSL&HSB filter made by John Knoll. Don't know if its been updated.

Lee Clawson

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Another related technique I use for creating a saturation mask is the following:

1) Duplicate the a channel.

2) Run a 3-point pencil curve (to create straight line segments) of 0->0, 128->255, and 255->0 on the duplicated a channel.

3) Duplicate the b channel.

4) Run an identical 3-point pencil curve of 0->0, 128->255, and 255->0 on the duplicated b channel.

5) Run Calculations on the copy of a and the copy of b in Linear Burn blending mode (or Multiply or Darken for slightly different effects), putting the result into a new channel.

7) Use the resulting channel as the mask channel for a straight-line curve adjustment to a and b (or as the mask channel for a Hue/Saturation adjustment)

8) Run a curve on the mask channel to tailor the effect as desired.

I find this approach, which I have set up as an action, invaluable for doing things like boosting saturation on low-saturation areas of an image without oversaturating areas of higher saturation. The calculated channel can be inverted to affect things the other way around.

Rick Gordon

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You could have your Lab image on a Layer, and set Blend-If for this layer for both the a and b channels to [128/128 ... 128/128] or [124/126 ... 130/132], or whatever tolerance suits you.

Underlay that with another layer filled with very high-saturation color (like a=127, b=127). Then make a magic wand selection of the high saturation color with a tolerance of zero, non-contiguous, and sampling all layers. The inverse of that selection will be your low-saturation selection.

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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There are miscellaneous techniques and actions here:

<http: //www.thelightsrightstudio.com/photoshop-tools.htm>

and a saturation mask action and usage description here:

<http: //www.thelightsrightstudio.com/TLRSaturationMask.htm>

Hope that helps,

_andrew webb

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WebbWorks Words & Pictures

http://www.webbwork.com

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Lee--

Andrew Webb sent along a link to a website:

http: //www.thelightsrightstudio.com/TLRSaturationMask.htm

They have a PDF called ""Restore Those Clipped Channels: Using a Saturation Mask to Fix Severe Saturation Problems" at http: //www.thelightsrightstudio.com/tutorials/RestoreThoseClippedChannels.pdf

On page 3 of the PDF is the following paragraph:

"Adobe Photoshop CS does not natively support conversions to the HSB space in the same way it supports L*a*b and CMYK conversions. There is a plug-in tucked away on the Goodies directory of your Photoshop CS disk that converts images between RGB, HSB, and HSL color spaces. To use it, you need to copy the plug-in to the Adobe Photoshop Only folder within the Plug-Ins folder on your Photoshop CS installation. This will add the HSB/HSL filter under the "Other" filter menu item."

Is this the plug-in that you were talking about?

I haven't tried this yet. Hope this helps.

--Herbert Ripka

Greendale, WI

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on 6/21/06 11:02 AM, Ripka, Herb wrote:

It certainly is. But it wasn't for my needs I think J. Walton was asking. Thanks anyway...

Lee Clawson

2/\V/\7 Studio

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Perhaps I can provide some closure on this topic. The plug-in is *exactly* what I was looking for, and is pretty much what I remember it being.

I've found that converting to HSB and then tweaking the S channel provides a very good mask. It's an interesting way to use the Hue/Saturation tool - only desaturate things that were pretty close to nuetral but not close enough. In outdoor shots think sidewalk, street, concrete building; indoor shots would be wall, tile ceiling, gray desk.

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J Walton

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