Dan Margulis Applied Color Theory - CMYK Shadow Value

Date: Mon, 29 Jul 2002 20:24:44 +0000
From: Christian Macey
Subject: RGB to CMYK highlight and shadows

Dan, this is my first posting after purchasing your book so I will try to make it a good one.

(Also no disrespect meant to Stephen Marsh aka Marshy Swampy ;-) by re-posting this question to a different list, who has already been more help than I could of hoped for on the Photoshop Discussion list.)

The question, I don't won't to be known as a sissy so what should I do when faced with an image that starts in RGB that I would like to correct in CMYK? I've been used to working in RGB mode thanks to people like Ben Willmore, and appreciate the advantage over CMYK where equal numbers=neutrals.

Also, In a few sentences from Ben Willmore's book he states "when calculating for shadow in RGB Mode we set it to Pure Black so P/Shop will adjust it for us when converting to CMYK Mode"; and "when calculating in CMYK mode you'll have to adjust it manually going by the settings in the custom cmyk or cmyk setup dialogue box". He also says that "if i reset the foreground colour to black and click on it to see how p/p created it, the numbers shown in cmyk will be what i need to use for my shadow setting. adding the cmyk numbers up will be my total ink limit set in the custom cmyk or cmyk setup dialogue box and the black should also be set at the more or less same setting used for the black ink limit>".

Stephen replies,
Yes, I agree that this is all SOP for many users - although I agree with
Jim Rich and would use RGB aimpoints that are slightly reduced from the
full 255/0 extremes. Perhaps ranges between 235-255 and 20-0 depending on
the image content and output.

Question number two,
I think I'm still missing something here, to do with CMYK custom dialogue box and setting the shadows. What are the Photoshop setting/s that directly affect these CMYK shadows? Will I need to learn more about TIL values.

Thanks
Christian


Date: Mon, 29 Jul 2002 23:35:35 -0000
From: Stephen Marsh.
Subject: Re: RGB to CMYK highlight and shadows

Christian writes:

> (Also no disrespect meant to Stephen Marsh aka Marshy Swampy ;-) by
> re-posting this question to a different list, who has already been more
> help than I could of hoped for on the Photoshop Discussion list.)

No disrespect taken - when you get serious about a CMYK concern you generally come here instead of other lists - well that's what I do. Now, depending on if using the Yahoo interface or email you will get different 'aliases' for me.<g>

> The question, I don't won't to be known as a sissy so what should I do
> when faced with an image that starts in RGB that I would like to correct
> in CMYK? I've been used to working in RGB mode thanks to people like Ben
> Willmore, and appreciate the advantage over CMYK where equal
> numbers=neutrals.

If it starts in RGB then I see two options - convert to CMYK right away and only concern yourself with the CMYK edits without any concern for the benefits to be found in RGB. The other option is to do as much work as necessar in RGB before going to CMYK and then honing things there (the third option which you are not using is to only work in RGB and convert with no post sep edits, in the belief that a ICC profile or LUT will be perfect).

> Also,
> In a few sentences from Ben Willmores book he states "when
>calculating for shadow in RGB Mode we set it to Pure Black so P/Shop
> will adjust it for us when converting to CMYK Mode" and " when
>calculating in CMYK Mode you'll have to adjust it manually going by the
> settings in the Custom CMYK or CMYK Setup dialogue box".

These are the previous list archive URL's that directly relate to this question (I think I told you to look at this list for this info):

http://groups.yahoo.com/group/colortheory/message/1941 (also messages 1944, 1957, 1959, 1961, 1962, 2112, 2113, )

> He also says
> that "if i reset the foreground colour to black and click on it to see
> how P/Shop created it, the numbers shown in CMYK will be what I need to
> use for my shadow setting. Adding the CMYK numbers up will be my total
> ink limit set in the Custom CMYK or CMYK Setup dialogue box and the
> black should also be set at the more or less same setting used for the
> black ink limit".

There are many ways to judge the TIL from a given LUT or profile - this is one way. I personally like the color palette/window with the gradient set to grayscale and the sliders to CMYK. Then it is a simple matter to drag the eyedropper through any gray tone in the gray ramp gradient and judge the profiles ideas of the numbers for that particular gray tone.

Even though I often follow a profiles aimpoints for gray balance (if I don't have number aimpoints) - when it comes to the endpoints I often use my own idealised aimpoints and not what the profile indicates. Perhaps the only time I would not adjust a conversions shadow point is in a four colour grayscale...and even then I might play with K but not CMY.

> Stephen replies,
> Yes, I agree that this is all SOP for many users - although I agree with
> Jim Rich and would use RGB aimpoints that are slightly reduced from the
> full 255/0 extremes. Perhaps ranges between 235-255 and 20-0 depending on
> the image content and output.

For readers of this list -- the above is taken from a message to another list, but is related to the ColorTheory archive links posted above -- which is the source of the question from Christian. What RGB values to use for working going to CMYK in your post acquistition edits...

> Question number two,
> I think I'm still missing something here, to do with CMYK custom
> dialogue box and setting the shadows. What are the Photoshop setting/s
> that directly affect these CMYK shadows? Will I need to learn more about
> TIL values.

For custom CMYK - look for total ink limit and K ink limit for a
start. If you are using GCR the UCA will affect the TIL too.

Regards,

Stephen Marsh.


Date: Wed, 31 Jul 2002 22:21:14 EDT
From: Dan Margulis
Subject: Re: RGB to CMYK highlight and shadows

Christian writes,

>>The question, I don't won't to be known as a sissy so what should I do when faced with an image that starts in RGB that I would like to correct in CMYK?>>

That basically is like asking, I would like to go outside, but the door seems to be closed. What should I do?

Now in view of all the misinformation and nostrums that circulate about this topic, it's unsurprising that people have to ask questions like this. One can only imagine what would happen if you asked it of the usual coterie of colorspace chauvinists, calibrationists, and color management vendors. Their advice would likely be,

1) Get somebody with a colorimeter to measure the door to find out whether you can fit through it.

2) When the measurement comes back showing that the door is only 3 microns tall, hire a consultant to come in and "tune" the measurement.

3) Note that the door does not have an ICC profile embedded, therefore you cannot accurately know what color it is and are likely to suffer irreversible data loss if you open it. This door is obviously stuck in another century. You should not do business with it, and find other doors that do have such profiles.

4) According to Photoshop 7, this door is actually a window, so you shouldn't go out through it at all. This is the fault of the door manufacturer, to whom we recommend that you complain.

5) You should get a physical checkup of your back first, since you will need to be carrying a characterized and calibrated monitor with you when you go through the door. Without a characterized and calibrated monitor, you can't go anywhere.

6) It's so much more comfortable to stay in where it's air conditioned; why do you want to go out at all?

Personally, I say if you want to get outside, open the door and walk through it, and I say that if you want to work in CMYK just convert the file and get on with it.

>>In a few sentences from Ben Willmores book he states "when calculating for shadow in RGB Mode we set it to Pure Black so P/Shop will adjust it for us when converting to CMYK Mode"

This advice makes sense if a person is determined to correct only in RGB. If, however, you've decided to take advantage of CMYK, and you start out with a shadow that's too light in RGB, you're better off leaving it alone until you get into CMYK. That way, you'll be able to apply a curve to the black that in the course of darkening the shadow, also emphasizes whatever you believe is the most important part of the image.

This doesn't apply to highlights or neutrals, which can be corrected as effectively in RGB as CMYK, but being able to tweak the black in a shadow is a big CMYK advantage.

>>I think I'm still missing something here, to do with CMYK custom dialogue box and setting the shadows. What are the Photoshop setting/s that directly affect these CMYK shadows? >>

Total ink limit and black ink limit.

Dan Margulis


Date: Fri, 02 Aug 2002 17:48:52 -0000
From: John Robinson
Subject: Shadow Aim Point

Dan:

Is the setting for the shadow area still 70/70/70/80?

Or have you found a better setting in cmyk?

John Robinson, Designer, and prostrate follower of the ColorGod.


Date: Fri, 02 Aug 2002 21:20:08 -0400
From: Jerry P'Simer
Subject: Re: Shadow Aim Point

John Robinson wrote:

> Is the setting for the shadow area still 70/70/70/80?
> Or have you found a better setting in cmyk?

John,

It's not 70/70/70/80 it's 80/70/70/80 and I have never liked these values because IMHO these numbers are to conservative. I prefer 78/68/67/87 for a standard SWOP 300 d-max condition. I'll even allow the black to go up from there depending on the image and adjust the CMY values accordingly.

Jerry P'Simer


Date: Sat, 3 Aug 2002 13:49:59 EDT
From: Dan Margulis
Subject: Re: Shadow Aim Point

John Robinson writes,

>>Is the setting for the shadow area still 70/70/70/80?>>

80c70m70y70k is a good all-purpose shadow aimpoint for those who don't know much about their printing condition and who are not trying to do anything special with the black channel to augment shadow detail. It is rather conservative and there are often occasions when a higher black is desirable, as Jerry indicates.

Dan Margulis




Date: Sat, 02 Nov 2002 18:01:45 -0500
From: Lee Collins
Subject: A questions (separation variables)

Hi everyone,
I'm a lurker who has found the conversations on this site very helpful at times. I have a question that I'm sure one of you could answer for me. I teach at a college and this came up in my class.

We set the CMYK Custom Color Settings in Photoshop 6 to SWOP Uncoated (25% dot gain), the GCR to light with 300 total area coverage and 100 for one ink. Then we proceed to correct color images with HL at 5,2,2 and shadow at 80,70,70,70. What effect does the color settings have on the image we have corrected with those end points? Where does the the dot gain setting have an effect on the RGB and eventually the CMYK image? If we adjust the curve, knowing that there will be dot gain on our press, what role do the original settings have in this process? I hope I was clear in my scenario. This question has nagged me before and I would appreciate any information to clear up this question.
Lee Collins


Date: Sun, 03 Nov 2002 01:10:10 -0000
From: Stephen Marsh
Subject: Re: A questions (separation variables)

> We set the CMYK Custom Color Settings in Photoshop 6 to SWOP Uncoated (25%
> dot gain), the GCR to light with 300 total area coverage and 100 for one
> ink.

Hi Lee, I guess you mean 100% K limit here?

> Then we proceed to correct color images with HL at 5,2,2 and shadow at > 80,70,70,70.

The beauty/curse of the info palette is that you can be working in one colour mode (say RGB), but be making your decisions based upon the numbers preview of the current colour settings and work space or proof space setups (say a CMYK WS or proof space). It can be very handy to judge one colour spaces edits via numbers other modes. Evaluating CMYK via HSB, LAB or even grayscale number readouts for example.

So what colour mode are you making these CMYK based numbers edits in - grayscale, RGB, LAB or CMYK? This has a huge effect on your next question...

> What effect does the color settings have on the image we have corrected with
> those end points? Where does the the dot gain setting have an effect on the
> RGB and eventually the CMYK image? If we adjust the curve, knowing that
> there will be dot gain on our press, what role do the original settings have
> in this process?

If a file is NOT in CMYK, then the separation variables WILL come into play when the gray/RGB/LAB source is converted to the CMYK destination.

If a file IS in CMYK, then the separation settings do NOT affect the current CMYK numbers in the file in any way - just the preview of those numbers (how they are described). If you convert out of the CMYK source to a new space, then yes the settings DO affect the outcome (the stock/inkset and dot gain data is used to describe the numbers in the file into LAB before conversion to the new space - hope I got that right.<g>).

So if you are in CMYK and are manually curving things to 'human' defined aimpoints - then the current CMYK setup (no CM) or ICC tag (CM on) for that image is for preview only or for when you make a conversion out of CMYK.

Hope I am making sense here.

> I hope I was clear in my scenario.
> This question has nagged me before and I would appreciate any information to
> clear up this question.

Perhaps look into this past list archive (copy and paste the full URL as the link will probably appear broken):

https://www.ledet.com/margulis/ACT_postings/SeparationIssues/ACT-dot-gain-resp.htm

Sincerely,

Stephen Marsh.


Date: Sun, 3 Nov 2002 08:04:57 EST
From: Dan Margulis
Subject: Re: A questions

Lee Collins writes,

>>We set the CMYK Custom Color Settings in Photoshop 6 to SWOP Uncoated (25% dot gain), the GCR to light with 300 total area coverage and 100 for one ink. Then we proceed to correct color images with HL at 5,2,2 and shadow at 80,70,70,70. >>

These settings are like mixing gasoline and matches. If the maximum black is 100%, then RGB files that have a heavy shadow will come into CMYK at around 70c60m60y95k. From this, it's quite difficult to achieve 80c70m70y70k. Far better to set the maximum black at 80% or 85%. Then, a shadow will convert to approximately the CMYK value you want. It's easy to make the black heavier later if you feel it's appropriate. It's hard to lighten it if you think it's too strong.

As to the other questions, I agree completely with what Stephen responded.

Dan Margulis


Date: Sun, 03 Nov 2002 17:30:26 -0500
From: Lee Collins
Subject: Re: Re: A question

Hi Dan and Steve,
I didn't realize how the 100%K in the CMYK setup made such a difference. No wonder it was so difficult to get the correct numbers for the shadow! When I set it correctly, the transition was almost right on the nose with very little tweaking to do!

I still am not clear about the SWOP dot gain settings. Can you verify what I think I know?

When I change over from RGB to CMYK, that is where the monitor shows the image as if it had the 25% dot gain and the film will reflect that difference as well. Bottom line is that nothing happens until I change the mode.

So we are correct using the curve in our grayscale images to compensate for dot gain (i.e. 5 and 85), but we let the CMYK setup take care of it for color images.

Lee Collins


Date: Mon, 04 Nov 2002 09:00:03 -0000
From: Stephen Marsh
Subject: Re: A question

> I didn't realize how the 100%K in the CMYK setup made such a difference. No
> wonder it was so difficult to get the correct numbers for the shadow! When I
> set it correctly, the transition was almost right on the nose with very
> little tweaking to do!

Looks like I gave you the wrong archive link - although the one I previously pointed you to went into some of the behind the scenes stuff that goes on when conversions are made. This link deals specifically with your situation of having to deal with shadow values which are too far from your own aimpoints:

https://www.ledet.com/margulis/ACT_postings/ColorCorrection/ACT-bynumbers-badshadow.htm

Listmember Jerry L. P'Simer introduced me to a better way to manually perform UCR than my previous method (using the K plate and the channel mixer and a quick mask) - So it is a pretty rare case that I have problems with any shadow build (thanks again Jerry).

I have mixed feelings on the default custom CMYK settings. They 'work' for many users when 'canned' with no tweaking - but these users would probably get better results with one of the v2 profiles from Adobe.

I think the major reason that custom CMYK is still used by the more 'hands on' users is that unlike a pregenerated profile - it allows for very flexible on the spot separating for the unique conditions of the particular image/output. I really like it for making a quick Heavy GCR four colour grayscale or for GCR on full colour images (as our drum scanner produces a UCR sep by defualt).

It is also great for flexible tonal value (dot gain) manipulation of one or more plates.

The legacy custom CMYK is also good for when you need to have a true 'black' black point (as proper profiles simulate visual ink density with a less dense L value than custom CMYK). Having the ability to have 100K that is also of a L value of 0 (zero) can be a good thing when you need solid black text. So most 'images' may not require 100K - but that is not to say that not all 'graphics' may not need this setting when converting or rasterizing etc.

> I still am not clear about the SWOP dot gain settings. Can you verify what I > think I know?

Since you are using the 'uncoated 25%' custom CMYK - then we probably should not call this 'SWOP dotgain'...but I understand that you are only following the less than ideal naming convention set down by Adobe all those years ago when the separation settings and ink settings were first formulated.

> When I change over from RGB to CMYK, that is where the monitor shows the
> image as if it had the 25% dot gain and the film will reflect that
> difference as well. Bottom line is that nothing happens until I change the
> mode.

Yes, if the original is NOT in CMYK, then when you convert to the new CMYK those separation specifics are used.

> So we are correct using the curve in our grayscale images to compensate for
> dot gain (i.e. 5 and 85), but we let the CMYK setup take care of it for
> color images.

Even though dot gain will affect your endpoints - dot gain is usually referring to the *midtone or near midtone* values and not the extreme whites/blacks (or what passes for white/black extremes in print).

Dot gain curves can be for any part of the tonal range - but the custom CMYK defaults are only affecting the 50% point in this case.

When converting to grayscale you would still use an appropriate profile or setting that factors in the dot gain for that process - setting the endpoints is independent of this. If you use 25% for colour work then grayscale on the same stock should at least use the same, or perhaps a little more gain could be factored in if you expect the K plate to run high (or just for safety).

Others may simply adjust the tones manually to accommodate any tonal value increase or decrease when making a grayscale. As with colour work - there are users who do it all in RGB and simply convert, those that do it all in the final device space by hand - or those like me who are often doing a little of both, depending on the situation.

Hope this helps,

Stephen Marsh.


Date: Mon, 4 Nov 2002 10:04:37 EST
From: Dan Margulis
Subject: Re: A question

Lee Collins writes,

>>So we are correct using the curve in our grayscale images to compensate for dot gain (i.e. 5 and 85), but we let the CMYK setup take care of it for color images.>>

You should be letting the color settings take care of both grayscale and color images. Your grayscale setup should match the setting for black in your CMYK. If you have set up your CMYK for 25% dot gain then you should set grayscale at 25% dot gain or even 30%, because black ink typically has considerably more dot gain than do CMY. Some people also tweak the CMYK dot gain curves manually, in which case the black curve should simply be duplicated into the menu accessed by Edit: Color Settings>Working Spaces>Grayscale>Custom Dot Gain.

Dan Margulis


Date: Mon, 4 Nov 2002 09:34:29 -0800 (PST)
From: faro mojahedi
Subject: Re: shadow build

Good Morning to all(from Los Angeles),
I need some confirmation on three issues that I think I already know.
1-
What is the difference betwwen a black point of 80C-70M-70Y-70K and 60C-40M-40Y-100K? The latter has a lower TIL and more of GCR meaning that colors will be less saturated.Am I correct? Would you recommend such a black point and why? Is it wise to have a 100K setting anyway and why, either way?

2- What does the term "super black" mean? It means 100K plus a second, third or a fourth color to enhance black in a logo or something like that. It is dictated by underlaying colors and trapping. Correct?

3- I want to create a D'tone with black and a color. One way to kep the blacks nuetral is to keep the color out of the blacks by using the D'tone curves.

Thank you in advance, Faro


Date: Mon, 04 Nov 2002 14:17:39 -0500
From: Jim Rich
Subject: Re: contract proof question

On 11/4/02 12:34 PM, "faro mojahedi" wrote:

> 1-
> What is the difference betwwen a black point of
> 80C-70M-70Y-70K and 60C-40M-40Y-100K?
> The latter has a lower TIL and more of GCR meaning
> that colors will be less saturated.Am I correct? Would
> you recommend such a black point and why? Is it wise
> to have a 100K setting anyway and why, either way?
>
> 2-
> What does the term "super black" mean?
> It means 100K plus a second, third or a fourth color
> to enhance black in a logo or something like that. It
> is dictated by underlaying colors and trapping.
> Correct?
>
> 3-
> I want to create a D'tone with black and a color.
> One way to kep the blacks nuetral is to keep the color
> out of the blacks by using the D'tone curves.

When you ask for the difference, I am assuming you are after the visual difference. We did a book last year showing the effects of various CMY and K combinations as well as black only. The black only swatch was visually and densitometerically less dense, but the other combinations of CMY and K were so slightly different. Another technical difference is that, if you build a color separation with too much max density (percent dots) for a press the ink does not dry. This can cause various press and drying problems in the printing.

Is it wise to use 100K? I personally think it is a small issue. Each printer will have there opinion and preferred way to create a black point in a color separation. I rarely use use over 98% in the k.

It has been my experience that Super black (in a CMYK workflow) is a way to build a better black that takes advantage of all the inks. Some printers use different percentages of CMY to achieve the super black. Usually the color build is something like 60%c, 40m+y. Others might use only 20c, to get a blue black. Mileage will vary.

GCR, the black point and color image areas. If I understand your post, you are suggesting that if you change the max ink values of your black point (so less ink with print in the shadows or images) that the colors will become less saturated (so that less ink is printing the color areas). This is not supposed to happen if the GCR option of your color separation program or scanner is working correctly.

What is theoretically supposed to happen is that the neutral shadows will be converted to the max ink values, but your color image areas should stay nice and saturated. In reality, the color image areas might visually show a change, but not dramatically. In some GCR and press situations the colors image areas have been known to printer cleaner, therefore looking less contaminated and visually more saturated. Of course this depends on the color separation program and the printing press variables.

Duotones? When you mean blacks do you mean shadow areas? If you do, then the answer is yes.

My .02

Jim Rich


Date: Mon, 4 Nov 2002 17:54:07 -0800 (PST)
From: Faro Mojahedi
Subject: Re: contract proof question

Jim,

Thank you for the feedback. Following is my respond. Please let me know if I understand this correctly.

> > What is the difference betwwen a black point of
> > 80C-70M-70Y-70K and 60C-40M-40Y-100K?
> > The latter has a lower TIL and more of GCR meaning
> > that colors will be less saturated.

One way that I see this is that 80C-70M-70Y-70K does less of a black replacement than 60C-40M-40Y-100K does. This would be similiar to light, medium and heavy black repalcemt settings in CMYK diaolog box. Heavy black replacement would desaturate colors more than light would. In other words , if I want to increase black replacement manually, I would, in a curve, increase black and decrease CMY proportionally to maintain the gray ballance. 60C-40M-40Y-100K would insure more nuetral blacks and grays since most of the colors get replaced by black(K) inkand at the same time it desaturates colors some.

Thanks,
Faro


Date: Mon, 04 Nov 2002 21:27:20 -0500
From: Lee Collins Subject: Re: A question

I have to say that this is the best listserv around! I have learned more specific information in the last couple of messages than I ever could by pouring through many books!
Thanks!!!
Lee Collins
--
> You should be letting the color settings take care of both grayscale and
> color images. Your grayscale setup should match the setting for black in your
> CMYK. If you have set up your CMYK for 25% dot gain then you should set
> grayscale at 25% dot gain or even 30%, because black ink typically has
> considerably more dot gain than do CMY. Some people also tweak the CMYK dot
> gain curves manually, in which case the black curve should simply be
> duplicated into the menu accessed by Edit: Color Settings>Working
> Spaces>Grayscale>Custom Dot Gain.
>
> Dan Margulis


Date: Tue, 05 Nov 2002 07:54:07 -0000
From: Stephen Marsh
Subject: Re: Shadow builds, 100%blacK, Super K & D/Tones

> What is the difference betwwen a black point of
> 80C-70M-70Y-70K and 60C-40M-40Y-100K?

The 100K shadow build is more dense in LAB terms and slightly more neutral when evaluated with SWOP v2 profile with AbsCol measurements. I would also expect the human eye to report the same thing.

> The latter has a lower TIL and more of GCR meaning
> that colors will be less saturated.Am I correct? Would
> you recommend such a black point and why? Is it wise
> to have a 100K setting anyway and why, either way?

I would say UCR here - since neutral shadows are the concern, there is no colour to consider so GCR would not enter into things. I like to use UCR as the term when K in neutrals is the topic, while GCR is used for when both neutrals and colours and K is the topic. However, these terms are used in different ways by different people - that is just how I like to think of things.

100K in custom CMYK does not always give 100K in the final sep - it depends on image content and the L value of the tone in question on how it maps to the K and CMY values that the profile asks for.

For common 'images' 100K would not be a common thing for a shadow. I often manually build 100K areas into seps (keylines, logos etc) but these are not the same thing as a shadow though.

For 'graphics' then 100K may be needed, such as text or logos or keylines or screen caps or for rich black panels etc.

It all depends and it is not easy to comment on shadow value aimpoints without knowing the final print conditions and the image content - and there are other things too which could change the decisoin on how the sep is built.

CMYK can be as simple or as complex as you care to make it.

Evaluating step patches which rise in CMYK values with each patch is very handy - you pick the patch one step back from where you can't see any density difference between one patch and the next (if this patch is with the TAC limit). The next, better step is to see what a real image which requires detail in dark areas does with different shadow builds.

You will find that a solid patch and an image are two differnt things, and you may need two different shadow builds depending on what type of conetent you are reproducing (on a given stock/press). Transition tones and shadow detail can be touchy when the goal is to increase density but still maintain the images shadow details.

> 2-
> What does the term "super black" mean?
> It means 100K plus a second, third or a fourth color
> to enhance black in a logo or something like that. It
> is dictated by underlaying colors and trapping.
> Correct?

Yes, 100K panels of large areas look weak. Traditionally 40C or some other nice value was added, but with digital you can easily build any super/rich/extended black you like.

I would not go for the full TAC in a graphics panel, if 300% was the limit I might aim for 200-250 TAC or whatever.

Performing spreads on the under colours is usually required for any text reversals (layout apps and trapping software usually takes care of this with a rich black hold away option setting). An amount that is two or three times more than standard trap value is probably good -
but not too much so that a density halo appears (which can be hard to do with web presses with less than ideal stock and press fit). CTP and good plate rego punching improves the fit accuracy on a decent flatsheet press and you can often get away with but fit (no traps) - but giving the press operator a little room to play can't hurt.

(links below may appear broken)

https://www.ledet.com/margulis/ACT_postings/SeparationIssues/ACT-Rich-Black.htm

https://www.ledet.com/margulis/ACT_postings/SeparationIssues/ACT-Ink-Limits.htm

https://www.ledet.com/margulis/ACT_postings/SeparationIssues/ACT-How-Harsh-Black.htm

https://www.ledet.com/margulis/ACT_postings/SeparationIssues/cartoons_and_linework.htm

https://www.ledet.com/margulis/ACT_postings/

> 3-
> I want to create a D'tone with black and a color.
> One way to kep the blacks nuetral is to keep the color
> out of the blacks by using the D'tone curves.

I would perhaps limit the 2nd undercolour to the three quarter tones and or only the shadows if this is a concern, with a lower than solid weight...that way you can boost the density a bit but not pollute the lighter tones. But yes, you also have the option of not putting any ink in the shadows and stopping at whatever tonal crossover point is naturally pleasing for that image.

If duotone mode does not offer the editing solution you require, you can convert to multichannel mode and then save out as EPS DCS 2 - this way you have the ability to hand craft the seps...but you can't go back to d/tone mode (so save a b/up or the settings and keep the original gray etc).

Hope this helps,

Stephen Marsh.


Date: Tue, 05 Nov 2002 09:52:18 -0500
From: Jim Rich >
Subject: Re: shadow build

Faro

Hmm, I might not be understanding what you are after, but let me reiterate my first comments about this and I will direct it toward how Photoshop works.

I looks like you are suggesting that if you change the max ink values and the curve in the Custom ink settings dialog box that the colors of your color separated image will become less saturated. This is not supposed to happen if the GCR option of your color separation program or scanner is working correctly. And in Photoshop it generally works that way.

When you change the curve in the custom CMYK dialog box you are not just changing one of the variables that control the RGB to CMYK conversion, you are changing the way the color separation creates cmyk values, say for different printing processes. When that curve in the Custom CMYK dialog box is changed, Photoshop does a number of calculations to try and make the any color separation you create based on those settings come out looking similar to the original image, that is if it is technically possible in your color printing process

When you adjust the custom CMYK settings you might be changing the percent dot values that come out on the color separation, but the appearance of the cmyk image should be very similar to the original. That is the way the Photoshop color sep engine was built. So when the custom CMYK settings is altered you would not desaturate or over saturate the resulting color separation.

Consider this. You were to copy an RGB image so you had two identical images. Then use the PS defaults to convert one image to cmyk. Then change the Color Setting to a Heavy K and convert the other image to CMYK using the Heavy K settings.

In this example, you will get different halftone dot values that create neutral gray, image contrast and color image areas, but if Photoshop has done its job correctly, both of the images appearances will be very similar if you printed them out in a reasonable printing process. I would not expect the colors of the two images to be dramatically different.

My sense is you are thinking that this dialog box works just like the Curves dialog box under the Image/Adjustments menu. It does not.

Good luck

Jim Rich


Adobe Photoshop training classes are taught in the US by Sterling Ledet & Associates, Inc.