Dan Margulis Applied Color Theory

General Questions on Shadow Setting

General question on shadow setting and incrementing 255
Posted by: "Sagers, Pat"
Fri Dec 8, 2006 3:18 pm (PST)

If an image is artwork and neutrals are non-existant, at least nothing close could be found after searching for about 30 minutes, I want to set a shadow according to the darkest area with channel values of R=19, G=12, B=3. I want to lighten the image without changing it at all, but I'm uncertain how to increment the 0-255 scale. Would I double each number or use a percentage of 255 with respect to the value of each channel? or neither and use something like R=30, G=30, B=30. I've experimented quited extensively and I've come to the conclusion that that my last suggestion is not the way to go.

Thanks for all your input to what I am sure is a very basic question.

Pat Sagers

ITS Systems Support
MS MCSE
Alliance Data
___________________________________________________________________________

Re: General question on shadow setting and incrementing 255
Posted by: "Stephen Marsh"
Sat Dec 9, 2006 5:37 am (PST)

Pat,it sounds like you wish to adjust range without greatly altering hue and saturation.

In RGB, perhaps try the level/curve in luminosity blend mode (adjustment layer or fade) or convert to LAB and adjust the L channel, which does not contain hue/saturation information.

Regards,
Stephen Marsh.
___________________________________________________________________________

Re: General question on shadow setting and incrementing 255
Posted by: "Lee Clawson"
Sat Dec 9, 2006 8:05 am (PST)

Pat,
I'm not sure either what you're asking.

What I think you want to do is use "curve" to edit but instead of creating a curved line use a straight line. This will lighten the entire image.

Lee Clawson
2/\V/\7 Studio
___________________________________________________________________________

Re: General question on shadow setting and incrementing 255
Posted by: "Paco Marquez"
Sat Dec 9, 2006 3:47 pm (PST)

Pat,

you are asking for two things:

1-set shadow values
2-lighten your image

1-Right now your shadow values are describing a reddish black which  is so dark that there is no way it would print as anything but black.  Making them 15-15-15 would still leave you with a color so black that  it would not print any different than the 19-12-3 you are starting from. Nevertheless it would make it neutral and comply with the suggested values for setting your shadow point.

2-Supposing that the values are correct as to the color you are trying to reproduce, but you want to lighten the image over all...

1-duplicate your BG layer TWICE so that you have 3 equal layers (BG, BG copy and BG copy 2)

2-set the blending mode of BG copy 2 to Screen and merge BG copy 2 and BG copy

3-to recover your lighter tonalities, if need be, use Blending Options so as to combine the darker tones from the BG copy layer and the lighter tones from the Background layer.

Of course, not having seen your image, this is just a suggestion as to how to approach the solution to your problem.

All the best!

Paco Marquez
661 McKinley
San Juan, PR 00907
787-721-8554 Studio
787-587-7384 Cel.
http://www.pacomarquez.com
___________________________________________________________________________

Re: General question on shadow setting and incrementing 255
Posted by: "Sagers, Pat"
Sun Dec 10, 2006 10:02 am (PST)

Thanks for the help so far,

My original question

I want to lighten the image without changing it at all

does seem very contradictory as I reread it.

It made perfect sense to me when I wrote it, though ;).

OK, the image's shadow areas are overly dark for the rest of the image. The artist went over much of the shadow area in a black pencil and then used watercolor over the top of that to "save" the piece. I got the tranny and the rest of the image looks really good, but the shadows are so dark, but there is color that must be preserved in the shadow detail. This led to my questions about raising the values in the shadows but preserving the numeric values as there is color.

This led to 2 questions:
1) Can a shadow be anything other than 3 equal values, when using the "set shadow" tool in curves in normal mode?
2) How does one work with the 0-255 scale, exactly. Is there a resource somewhere that explains this?

Thanks
Pat
___________________________________________________________________________

Re: General question on shadow setting and incrementing 255
Posted by: "Lee Clawson"
Mon Dec 11, 2006 11:20 am (PST)

on 12/10/06 1:41 PM, Sagers, Pat wrote:

It made perfect sense to me when I wrote it, though ;).

Mine do that too.

This led to 2 questions:
1) Can a shadow be anything other than 3 equal values, when using the "set
shadow" tool in curves in normal mode?

Yes. Especially in the shadow areas, those tones between the 3/4 tones and what you see as black. It would be any dark area that maintains a color cast. A more common one would be warm or cool dark tones.

2) How does one work with the 0-255 scale, exactly. Is there a resource
somewhere that explains this?

I don't know what you're asking here. I'd expect that of books on editing digital images start out by explaining this. The scale represents the 256 tones/colors in an 8bit RGB digital image. You can use a couple of tools in Photoshop to adjust these. When the RGB numbers are the same (or close) you have neutral colors (whites, grays and blacks).

Lee Clawson
2/\V/\7 Studio
___________________________________________________________________________

Re: General question on shadow setting and incrementing 255
Posted by: "Rich Wagner"
Mon Dec 11, 2006 4:40 pm (PST)

On Mon, December 11, 2006 8:11 am, Lee Clawson wrote:

The scale represents
the 256 tones/colors in an 8bit RGB digital image. You can use a couple
of tools in Photoshop to adjust these. When the RGB numbers are the same
(or close) you have neutral colors (whites, grays and blacks).

True, as long as you're working in a normalized RGB "working space" and not with RGB device profiles - e.g., scanner profiles and printer profiles.

--Rich Wagner
___________________________________________________________________________

Re: General question on shadow setting andincrementing 255
Posted by: "Sagers, Pat"
Mon Dec 11, 2006 4:44 pm (PST)

Great,

So if I wanted to keep the same color of R=22 G=14 B= 6 as my shadow point, BUT make it much lighter where R is in the 35-40 range, how do I determine the G and B values?

Thanks

Pat Sagers

ITS Systems Support
MS MCSE
Alliance Data
(541) 389-0120 x1554
___________________________________________________________________________

Re: General question on shadow setting and incrementing 255
Posted by: "J Walton"
Mon Dec 11, 2006 9:00 pm (PST)

I think this has been suggested before, but you could either set your adjustment layer to be "Luminosity" in RGB, or do the correction in LAB.

That will keep the cast but change the contrast.
-----
J Walton
___________________________________________________________________________

Re: General question on shadow setting andincrementing 255
Posted by: "Andrew S. Webb"  
Mon Dec 11, 2006 9:01 pm (PST)

Lock down the curve with points where you want it to stay, and use shift-click to set points in the areas you want to change. Then move those new points. If you want the RGB to stay in the same numerical relationship, move them by identical amounts. You could also do that via the composite channel.

If you're wondering what the RGB relationship is in a given area of the picture, look at the Info palette.

This is very basic Photochop Curves info that you can get from any book that includes a Curves section.

Cheers,

_andrew webb
___________________________________________________________________________

Re: General question on shadow setting and incrementing 255
Posted by: "George Harding"
Mon Dec 11, 2006 9:07 pm (PST)

Pat,

It's possible to set the color produced by the set shadow eyedropper in Curves. Click on "Option" in the Curves box. In the box that pops up, click on the Shadow patch under "Target Colors & Clipping". The Color Picker box will appear and you can set the desired color.

With regard to on-line resources to explain the 0-255 scale, if you search under "Photoshop Curves" you'll get a plethora of sites that will help explain it. As far as books go, Dan's "Professional Photoshop 5th Edition" gives a good explanation of the concepts. It also has some powerful but more complicated techniques for pulling color and details out of overly dark shadow areas that would be useful in solving your problem using false profiles and luminosity masks. "Real World Photoshop" by Fraser & Blatner and "Photoshop Studio Techniques" by Ben Wimore are also good on the basics, but don't have some of the more exotic techniques.

George Harding
Marlborough, MA
___________________________________________________________________________

Re: General question on shadow setting and incrementing 255
Posted by: Jeff Natrop

Pat,

Another option is simular to Paco Marquez, but just make one dupl.layer of the background and change the blend mode to screen. Then add a layer mask, hide all. Then use the brush tool using blank and white to revel or hide the screen layer. This will allow you to selectly paint in the detail in the shadow areas.

Another option is to try the shadow/highlite adjustment layer to open up the shadows. The same layer make technique can be used to selectively control its effect.

Jeff Natrop
___________________________________________________________________________

Re: General question on shadow setting and incrementing 255
Posted by: "Pajuaba Gmail"
Fri Dec 15, 2006 10:30 am (PST)

jeff090756 escreveu:

Another option is to try the shadow/highlite adjustment layer to open up the shadows.
The same layer make technique can be used to selectively control its effect.
Unfortunately, there is not such a thing. A workaround is to duplicate the layer and apply a S/H adjustment, and use it instead. I hope in CS3 they managed to make it available.

Regards,

Rodolpho Pajuaba
___________________________________________________________________________

and three weeks later...

Setting Shadow values
Posted by: "mfedecky"
Tue Jan 9, 2007 10:29 pm (PST

Can someone clarify how to set shadow values if starting in RGB and then converting to CMYK.

Say the conversion settings are for SWOP coated, dot gain 20%, GCR=Light, TIL=300 TBL=95%. When in RGB should I make my shadow R= 0 G=0 B=0 for maximum contrast? This would convert to 75,65,65,93 in CMYK and these values don't jive with the usual recommended values of 80,70,70,70 for a neutral shadow in CMYK. Is it really necessary to aim for these shadow values? Why not just trust Photoshop's conversion from RGB and leave it at that (as long as thet Total ink is not exceeded).

Thanks
Michael Fedecky
Fedecky Design
___________________________________________________________________________

Re: Setting Shadow values
Posted by: "Lee Clawson"  
Wed Jan 10, 2007 9:35 am (PST)

on 1/9/07 9:13 PM, mfedecky wrote:

Say the conversion settings are for SWOP coated, dot gain 20%, GCR=
Light, TIL=300 TBL=95%. When in RGB should I make my shadow R=0 G=0 B=0 for
maximum contrast? This would convert to 75,65,65,93 in CMYK and these values
don't jive with the usual recommended values of 80,70,70,70 for a neutral shadow in CMYK. Is it really necessary to aim for these shadow values? Why not just trust
Photoshop's conversion from RGB and leave it at that (as long as thet Total ink is not exceeded).

Michael,

As long as you have good separation in the shadow tones up to the "true" black I see no problem here. In one you have lower CMY and higher K with the opposite in the other.

Lee Clawson
2/\V/\7 Studio
___________________________________________________________________________

Re: Setting Shadow values
Posted by: Dan Margulis
Thu Jan 11, 2007 7:37 pm (PST)

Michael Fedecky writes,

Say the conversion settings are for SWOP coated, dot gain 20%, GCR=
Light, TIL=300 TBL=95%.

I do not recommend setting the black limit that high. I would set it at 80% or 85%, reserving the possibility of increasing the black after the conversion.

When in RGB should I make my shadow R=0 G=0 B=0 for maximum contrast?

Only if you are never planning to convert to CMYK at all, or if you absolutely refuse to work in CMYK after the conversion, or if there is no shadow detail at all and you don't care if it plugs.

One of CMYK's biggest advantages over RGB and LAB is that the black channel is rich in shadow detail while the CMY are worthless. If you know you will be able to work on the file in CMYK, then you should be quite conservative with the shadow while in RGB or LAB. If the shadow is temporarily too light, steepening the dark half of the black curve will darken it *and* add detail in a way that can't be matched in RGB or LAB without a lot of difficulty, if at all.

This would convert to 75,65,65,93 in CMYK and these values don't jive
with the usual recommended values of 80,70,70,70 for a neutral shadow in
CMYK.

As long as the CMY component is balanced (roughly, M= Y and cyan ten points higher than either) the shadow is acceptable provided that it's both dark enough and within the total ink limit. So both of these formulations work. If you're absolutely committed not to touch the file once it enters CMYK there's a case to use the first value. If you're willing to do some work to preserve and enhance shadow detail when necessary, set the black ink limit to 80% or 85%, use a more conservative shadow value in RGB, and you'll get close to 80c70m70y70k on conversion. Then you can decide what to do next.

Dan Margulis