Date   

Shadow detail loss on press....

J Walton <jw@...>
 

(Note: I sent this earlier to the original listbot address, and got it
kicked back. Hopefully it doesn't double-send.)

Chris,

Here's what I think. Just be aware that Dan will comment later and
completely contradict my reasoning, so if you have to choose between the two
of us pick his comments. He'll pay for the next run if it's wrong. ;-)

1. I agree that the black limit is too high, but without seeing the image
it's awfully hard to say. In the context of the heavy coverage surrounding
the face, a higher-than normal Black limit will kill subtle detail.

2. In terms of photoshop, too much UCR won't really put too much detail on
the black plate. It is like a light-medium GCR, definitely a skeleton
black. I don't really see that as the problem either, although I'd rather
have a longer black in this case if I didn't trust the pressman.

It seems to me that the press is gaining a lot more than you expected. One
reason for this is that they are laying a pretty solid black down in that
background, and this dark dark color (65/52/51/100) "makes up most of the
background," as you mention below.

It's difficult to account for a rogue pressman who really opens the
floodgates on a piece, and that may be what you have. "Lots of ink and lots
of squeeze," as they say. They like it because you won't get as many
hickeys on that heavy coverage piece, but it also kills detail.

I would do this:

Reseparate with a long black and do a nice midtone pull. Then, depending on
whether or not the 65/52/51/100 has any detail or not, I'd make sure and
open that area up. If it is indeed supposed to be a flat tint, you should
definitely consider another midtone pull in the black channel only.

Now, let's give this a few more hours and Dan can show everybody what you
_really_ should do.

J

----- Original Message -----
From: "Chris Murphy" <lists@colorremedies.com>
To: "Color theory" <ColorTheory@listbot.com>
Sent: Tuesday, December 12, 2000 12:02 PM
Subject: [ColorTheory] shadow detail loss on press, but not on proof

I have a question. A close-up shot of a black person on a proof shows up
with really good detail. On press, there is no detail in the skin - it's
gone. I haven't seen the separations yet, but they describe what sounds
like a lot of detail on the black plate. To me it sounds like two things,
let me know if you think that sounds about right:

1.) Black ink limit too high. Black gains more than anythingn and it's
possible black ink limit needs to be 90% for an image like this, maybe as
low as 80%.

2.) Too much GCR or UCR which put too much detail on the black plate,
which gained too much and all detail was wiped out. What's needed is a
light GCR, maybe just a skeleton black, in order to retain more shadow
detail.

cheek bone: (CMYK) 30/29/32/5 (96)

eye socket shadows (where it looks good on proof and much too dense on
press): 62/51/49/65 (227)

lowest value on piece (comprises most of the background):
65/52/51/100 (266)

shadow detail on a building (lost on press):
66/52/45/75 (238)

adjacent darker part of building (melds into bkg):
63/52/51/89 (255)

One possible clue is they are printing the black plate FIRST. So maybe
those black dots are getting smashed and are gaining a lot more by the
time they get through CM and Y.

A side question. If press dot gain were controlled and accounted for
during separation really well, wouldn't it be OK to use a medium black
generation as long as the black ink limit were suitable? Or is it better
with dark images with lots of shadow detail that needs to be retained to
keep black generation lower?

Chris Murphy


SWOP TR001 profiles posted (free)

Steve Upton <upton@...>
 

Greetings all,

I have just posted 9 profiles build on the standard SWOP TR001 dataset to profilecentral.com

The TR001 data set is one of the most accurate SWOP data sets produced to date. The data were collected using multiple measuring devices from a SWOP-compliant press run in 1993.

After some deliberation I produced the profiles based on the following settings.

- Black level (max black): 90
- Black generation: UCR, Light GCR, and Medium GCR
- TAC (Total area coverage or "ink limit"): 280, 300, 320

The profiles are available individually or in 3 packages (for 280, 300, and 320 levels). If these do not cover enough possibilities I could be persuaded to create additional profiles with different parameters.

These profiles are offered free of charge to the color management community. Please give them a try and then send us your feedback. They are suitable for RGB to CMYK conversions as well as proofing CMYK on screen or a printer. You should find that they all produce the same proofing effect and you need only download the different flavors for the purposes of creating different separations. If you unsure which set to use I would suggest the 300 set.

I have received some feedback concerning conforming to the new ICC spec as well as the CGATS.12/1
(PDF/X-1) header characterization data identification. I am eager to conform to both of these standards and will be update the profiles some time in the future. I will be in contact with the specific parties concerning these standards.

I hope you are able to find these profiles useful.

You will find them at:

<http://www.profilecentral.com/>

Click on the search link and then select "Offset Lithography" in the Press area.


Regards,

Steve Upton

+--------------------------------------------------+
CHROMiX / Profile Central
www.chromix.com www.profilecentral.com
+--------------------------------------------------+


shadow detail loss on press, but not on proof

Dan Margulis <76270.1033@...>
 

Chris writes,

A close-up shot of a black person on a proof shows up with really good
detail. On press, there is no detail in the skin - it's gone. I haven't
seen the separations yet, but they describe what sounds
like a lot of detail on the black plate. To me it sounds like two things,
let me know if you think that sounds about right:>>

Given the numbers you describe, they have three problems: they are
underestimating dot gain at least in black, but probably overall as well;
they have too high of a black ink limit; and they don't realize that
Photoshop's built-in monitor preview overstates the power of black ink.

This is a CMYK-specific problem, an effect that isn't well known.
Regardless of sep settings, at some level of darkness the CMY channels max
out, and all the detail goes into the black. The CMY will look blurry or
even ghosted out. This point comes earlier as the total ink limit goes down
and also as the black ink limit goes up.

The numbers you quoted indicated that once they get to 60c50m50y that's
about it for the CMY. A shadow of
62/51/49/65 like you quoted is asking for a problem. It should be something
more like 75c65m65y50k. That way the detail's in all four channels, the
impact of misstating black dot gain isn't as severe, and the monitor won't
seem to lie so much.

A side question. If press dot gain were controlled and accounted for
during separation really well, wouldn't it be OK to use a medium black
generation as long as the black ink limit were suitable?>>

On a nonimpact printer, yes, on a press, no. On press, black is 1) the ink
with the highest dot gain; 2) the one where the density is most likely to
be something unexpected, because the pressmen are prone to judge the black
by the appearance of the type and not the pictures, and because the
presence of large black areas on the form (such as headline type) can alter
densities by themselves; 3) the one that has as much weight as the other
three put together, so that any error appears grossly magnified.

All this are true no matter what the black generation, but if you use light
generation the picture may well look *better* if the black density is too
high. Shadow detail will be lost but otherwise the picture will seem to
gain contrast. OTOH, if you use medium generation, there will be a modicum
of black ink in the fleshtones and other semisaturated colors, and these
will get muddy rapidly.

The cases where a heavier GCR is appropriate are usually those where the
subject is distinctly neutral or where for some reason you don't like the
idea of bright colors.

Or is it better with dark images with lots of shadow detail that needs to
be retained to keep black generation lower?>>

In images with critical shadow detail one normally has to exaggerate the
tail end of the black a bit. CMYK is too low-contrast to do nothing, and
the CMY channels have no detail in the shadows. Therefore, it's a major
hindrance to have more non-shadow detail in the black than necessary,
because we're apt to wipe it out in fixing the shadows. So, yes, you want a
lighter black generation in this case.

Dan Margulis


End Epson 5000 thread

Dan Margulis <76270.1033@...>
 

Chris, Ralph, David:

Please end this thread or take it off-line. No doubt both Epson and EFI are
major players and we should hear about the issues you've been discussing,
but the thread is still basically about only a single model of a single
vendor, and therefore isn't relevant to the vast majority of the group,
IMHO. I have no problem with anything written so far but in view of the
length of the thread I think it should go off-line at this point.

Dan Margulis


Re: Shadow Detail

Dan Margulis <76270.1033@...>
 

Chris writes,

A good separation is necessary as well, but an understanding that any
kind of profile may misjudge the ability of a press to hold detail. That
is, the profile is going to try to squish the image into the press's
dynamic range, which in theory solves the problem. In reality, the profile
can't know that so many CMYK dots in such close proximity will fill in and
shadow detail will be lost. Separation methods work with pixels, not
dots.>>

Right. This is a major limitation of machine-generated profiles. Whether
detail is being held in deep shadows is a highly subjective decision.

So a human is going to have to recognize that the image needs editing.
Either as an RGB image that needs to have these areas lightened before
separation, or separated and then lighten the CMY areas as you describe;
and in this case it's likely a CMYK editing process will yield much better
results because what needs to be reduced is the CMY portion - not just a
universal lightening of the image (which is what would happen in RGB.)>>

Yes. In images with critical shadow detail, CMYK has an enormous advantage
over either LAB or RGB correction because all the detail ends up in a
single channel that can be tweaked extensively without major damage to the
rest of the image. This is the only class of images that I would recommend
working on in CMYK even in an all-RGB workflow, that is, I'd go
RGB>CMYK>correction>RGB if necessary in preference to trying to fix the
problem either in RGB or LAB.

Dan Margulis


Re: SWOP ink limit

Dan Margulis <76270.1033@...>
 

Several people have queried what the SWOP standard is for total ink, what
the reasoning for the limit is, and how strictly it is enforced.

SWOP calls for a maximum ink limit of 300% in any area of significant size
and 325% in tinier areas. The reason for the limit is to prevent drying
problems, poor ink trapping, and possible ink contamination.

Most magazines knock this limit down to 280%. AFAIK, the reason they do so
is for bargaining room in case the printer rejects the film. Most magazine
prepress houses and printers offer SWOP ad inspection as a service. At the
time I was active in the field the inspectors were looking for an area the
size of a dime or bigger, in which the total ink was 305 or higher. They
ignored smaller areas altogether.

So, I think the request for 280 is to make it more palatable when the
printer rejects 305. In practice nobody is going to reject for 300 for a
magazine printed on coated stock.

Dan Margulis


Re: what would cause this

Preston Earle <PEarle@...>
 

Chris writes:
So the explanations for why the proof isn't predicting this might be:

2.) Perhaps printing K first is factor contributing to excessive black
ink gain compared to what the proof is predicting.

Preston responds:

I don't believe the order of the ink laydown will have a significant effect
on dot gain. It could well have an effect on ink trapping, which could
effect the final print appearance. Normally, black is printed as the first
down color because it is usually the lightest form and thus gives fewer
problems with wet-ink trap.

3.) A laminate proof allows 400% ink and can still retain detail; unlike
a press. The shadow area needs to be lightened in order to reproduce
effectively on press.
As to the laminate proof, what kind of proof is it? Was it made from film
(Matchprint, Color-art, Waterproof)? In that case, it should have the same
dot characteristics as the image on the plate: Total ink limit, maximum
black, etc. The problems in not matching the proof would be in the press
or platemaking. If the proof was a digital proof (Iris, Approval, etc.),
wouldn't it have been made from the same CMYK file as the film/plate, such
that it showed the same separation characteristics as the printing
film/plate? The fact that it might show more detail for a 400%TAC file is
not relevant since the file from which it was made should have the same dot
values as the printing film/plate.

If the proof was from some other proofer, perhaps one that used an RGB
file, then certainly the color separation issues of RGB > CMYK could cause
the printed image not to match the proof, but wouldn't this simply indicate
that the "proof" wasn't really a "Proof", but rather a different
representation of the same image?

So this is one of those examples of the limitations
of these kinds of proofs. Interaction between inks (such as tack and
print sequence) is not predicted with pretty much any kind of proof
except a press proof.
Pre-press proofs should predict the interaction of the various elements
under "standard conditions". It's when the conditions fall outside
standard that a press proof might be required.

This isn't to say that the solution to making the printed image better
isn't in the RGB>CMYK conversion. As Dan points out, different images may
need different set-ups. However, if you adjust the conversion to take into
account the abnormal dot-gain due the particular print conditions, then the
proof won't match the original, but that's a different problem.



------------------------------------------------------------
I've tasted watermelons honestly come by, and I've tasted watermelons
acquired by art. Both taste good, but the experienced man knows which is
better.--Mark Twain


Re: SWOP ink limit

Dave Balderstone <dave.balderstone@...>
 

At 1:36 PM -0500 12/13/00, Dan Margulis wrote:
So, I think the request for 280 is to make it more palatable when the
printer rejects 305. In practice nobody is going to reject for 300 for a
magazine printed on coated stock.
We've run 300 on newsprint if we've had to, even though our spec is 240. We've even run higher than that on occasion after the agency has been informed, has told us they can't get new material to us in time, and has accepted that color is going to shift when the press crew works their magic. But you've seen our operation, and I'm sure little we do would surprise you. <s>

Since acquiring our newest scanner a couple of years ago, though, we prefer to scan the film, descreen, then re-separate.

Dave Balderstone
Director, Technical Services
Western Producer Publications, Saskatoon, Canada


Re: Need help with web press cmyk

Dan Margulis <76270.1033@...>
 

John Sweeney writes:

<<If the plates are "curved" at the CTP device (that is, non-linear), is
the color bar being changed ? For example, if the color bar has a nominal
50%, BUT is curved to 52%, (in this example, weight added to CTP curves to
closer match conventional) then we are understating the dot gain, if the
assumption is the original was 50%.>>

A solid color bar won't change, but semisaturated colors certainly
will--they'll get dirtier. It's OK to adjust the color settings of a
digital proofer to chase another output device, or with the color settings
of a monitor to chase a proof. Trying to adjust a press to chase another
press is considerably more difficult.

Dan Margulis


Unsharp Masking at 50%?

Russell Proulx
 

I realize that it's generally recommended to perform Unsharp Masking with
an image viewed at 100%. But if the image's resolution is 2x the screen
frequency (for offset) then what's wrong with making USM decisions
based on viewing at 50%? Even Dan's most recent version of Professional
Photoshop leaves this issue ambiguous, admitting that the amount
required at 100% viewing is generally less than what the printed image
requires. Wouldn't judging the appropriate amount while viewing the image
@ 50% (with a very good monitor) be a better workaround?

Russell Proulx
Photographer
Montreal, CANADA


Monitor Profiles

Dave Badger <dbadge@...>
 

I've been spending days trying to figure out why my previews in PS6 don't
match my previews in PS5 despite loading identical RGB & CMYK working spaces
and making sure I was viewing untagged files so they would we forced to use
those working spaces and not any embedded profiles within them. It didn't
matter which set of working spaces I used. The relative differences were
always there; the PS6 preview was significantly more saturated. I did a
RGB>CMYK conversion of the same file through both versions and ran it to the
Iris; they were identical and confirmed the PS5 preview was correct. (Along
with the numerical values).

I then went back to PS5 and started switching my ColorSync profile between
ColorMatch RGB, Abobe 98, and Wide Gamut. The preview changed; which makes
sense as your telling PS5 to run the color through different monitor
profiles which should change they way they look. There was no change
toggling between "ColorMatch RGB", "Pressview XL", and "Display Pressview
XL". I figured this was because all are generate by the Pressview
calibrating software and are identical profiles. (?)

I then went back to PS6 and ran the same experiment. But this time there was
no change in preview regardless of which profile I pick in the ColorSync
control panel (v 2.6.1).Only if I went to View and picked "Monitor RGB" in
the proofing list, did it matched PS5 (This is only available with RGB
subjects opened). This tells me maybe PS6 is not getting its monitor profile
from the ColorSync control panel. So I opened the Monitor Control Panels and
switched it from "Pressview XL" to "ColorMatch RGB" and while the display
lightened a bit, the previews now match.

1) I thought I read that PS6 was compatible with ColorSync 2.6.1 & OS 8.6,
but is it picking the monitor profile through the Monitors Control Panel as
if it was using ColorSync 3? If so, it seems to be ignoring the system
profile I choose in ColorSync.

2) ColorSync 3 would not install; is it compatible with OS 9 only?

3) What is the difference between "ColorMatch RGB", "Pressview XL", and
"Display Pressview XL" AND the "ColorMatch RGB" installed by PS. (Two
"ColorMatch RGB"s show up in both control panels.)

This is not a problem unique to Pressview as I went to my LaCie calibrated
with OptiCal and changed the Monitors Control Panel from "electra22" to
"LaCie 12/8/00" (My latest OptiCal profile) and solved the same problem
described above.


Dave Badger


Unsharp Masking at 50%?

Dan Margulis <76270.1033@...>
 

Russell writes,


<<I realize that it's generally recommended to perform Unsharp Masking with
an image viewed at 100%. But if the image's resolution is 2x the screen
frequency (for offset) then what's wrong with making USM decisions based on
viewing at 50%?>>

You would then be looking at a crude RGB downsample to predict a very
complicated CMYK averaging process.

When you ask for a screen preview at 50% you ask Photoshop to present a
preview where one screen pixel is based on an average of the RGB values of
four actual pixels. This is loosely similar to what would happen in print,
where each dot is produced from, approximately, an average of four pixels.
However, it's quite inaccurate, because,

1) In print the averaging is done per channel whereas on screen it's done
in composite mode;

2) On screen we are likely to see brighter colors as a result of the RGB
averaging, causing us to believe that the image has been oversharpened;

3) On screen the RGB averaging is likely to suppress mild patterns of noise
that would be visible in print, especially if they occur in the black
channel, causing us to believe that an oversharpened image is OK;

4) Any kind of monitor preview is going to be deceptive because it hits our
eyes with continuous color, as opposed to print, where the white space
between the dots has a significant softening effect. That deceptiveness is
magnified at a lower resolution.

While 50% is probably better than 66.7%, 100% is much better, but far from
perfect.

The above goes for sharpening/graininess issues only, obviously, not for
overall color evaluation.

Dan Margulis


Re: Unsharp Masking at 50%?

Russell Proulx
 

On 19 Dec 2000, at 9:49, Dan Margulis wrote:

Russell writes,
what's wrong with making USM
decisions based on viewing at 50%?
You would then be looking at a crude RGB downsample to predict a very
complicated CMYK averaging process....

...While 50% is probably better than 66.7%, 100% is much better, but far
from perfect.

The above goes for sharpening/graininess issues only, obviously, not
for overall color evaluation.

Dan Margulis

Sigh....ok then. I was hoping for a better approach than guessing how
much "too much" is enough.

Russell Proulx
Photographer
Montreal, CANADA


Dan Margulis MADE me rad the User guide

psthree@...
 

In Dan's most recent Makeready column there is a screen shot of a repositon
and resize. I wanted to know where its was so bad, i ripped the shrink wrap
off the user guide and tried to look it up!


Re: Dan Margulis MADE me rad the User guide

jonathan clymer <jeclymer@...>
 

psthree@aol.com wrote:

In Dan's most recent Makeready column there is a screen shot of a repositon
and resize. I wanted to know where its was so bad, i ripped the shrink wrap
off the user guide and tried to look it up!
i rad this three times and couldn't figure it out! Is there an editor in the
house?

Jonathan Clymer


List FAQ

Dan Margulis <76270.1033@...>
 

Folks,

We've gotten several requests for an Applied Color Theory list FAQ.
Sterling and I have agreed on the following as a start. We'll probably post
it monthly. Like any other FAQ, it will change, so comments and suggestions
are welcome--nothing's set in stone. If you'd like to comment, please do so
to me or to Sterling privately.

Dan Margulis

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Last revised: 12/13/00


Dan's "Black Hole" image

Ron Bean <rbean@...>
 

I finally got a chance to see the digital photo of the "black
hole" that appears in Professional Photoshop 6. Interestingly,
the "before" version did *not* print as solid black-- if I hold
the book at an angle to the light (to avoid glare), I can
actually see most of the detail that shows up in the "after"
version. It's very dark, but it's there.

Could the original have been improved by using a longer exposure?
(And maybe a tripod to keep the camera steady?)

I'd like to see reviews of digital cameras (either in print or on
the web) that use images as challenging as this one.


Dan's "Black Hole" image

Dan Margulis <76270.1033@...>
 

Ron writes,

I finally got a chance to see the digital photo of the "black hole" that
appears in Professional Photoshop 6. Interestingly, the "before" version
did *not* print as solid black-- if I hold the book at an angle to the
light (to avoid glare), I can actually see most of the detail that shows up
in the "after" version. It's very dark, but it's there.>>

Well, *something* has to be there; even I can't fix an image that's 0,0,0
throughout. But I thought that the result when the range was opened up was
astonishing. I expected it to be full of noise. In fact, the result was a
lot better than one would get with a drum scan of a similarly dark piece of
a film--the scanner would have latched onto the film grain.

That particular image really should give pause to people who are obsessed
with extra bits. It's quality, not quantity, of data, that counts. That
corrected image can be expressed in 5 bits per channel.

Could the original have been improved by using a longer exposure?
(And maybe a tripod to keep the camera steady?)>>

Certainly, but that wasn't the point of the exercise, which was to get
something nearly hopelessly black and see what was actually there.

I'd like to see reviews of digital cameras (either in print or on
the web) that use images as challenging as this one.>>

Good luck. First of all, the technology is improving so rapidly that almost
any review is obsolete by the time it appears. Second, you don't often see
reviews of either cameras or scanners written by people who are
particularly knowledgeable about the subject. Third, few if any reviewers
see these cheap digitals as the revolution that they are, and the rest
insist on comparing them to previous film-based products.

Dan Margulis


Color settings and upgrades

gowens01@...
 

I'll start with a question. I just upgraded my Mac to OS 8.1 (I've
hesitated upgrading to 8.6 and 9.0 because I read that there were
conflicts with Photoshop). I have both 5.0 and 5.5 in the computer
and have set them to emulate the color settings for Photoshop 4.0. If
I calibrate my monitor with Colorsync will I have a conflict with my
photoshop settings?

I've just read Mr. Margulis article in the December 2000 issue of
Electronic Publishing about upgrades. I would like to upgrade to
photoshop 6.0 but as I mentioned before I'm still operating on 8.1
and if I would upgrade to 9.0 come January it will be time to upgrade
to OS X. I'm running a 7100/80 Mac. I will have to buy a new computer
to use OS X. And if I upgrade to Photshop 6.0 it will not be native
to OS X. And Photoshop hasn't said anything about a native upgrade
for OS X.

Thank you for your articles in Electronic Publishing Mr. Margulis. I
did follow your instructions to get Photoshop 5.0 to emulate the 4.0
color setting.

Gary Owens


Re: Dan's "Black Hole" image

Ron Bean <rbean@...>
 

Dan Margulis <76270.1033@compuserve.com> writes:

I'd like to see reviews of digital cameras (either in print or on
the web) that use images as challenging as this one.>>

Good luck. First of all, the technology is improving so rapidly that almost
any review is obsolete by the time it appears.
That's why I suggested a website.

Second, you don't often see
reviews of either cameras or scanners written by people who are
particularly knowledgeable about the subject.
True, but it only takes one...

Third, few if any reviewers
see these cheap digitals as the revolution that they are, and the rest
insist on comparing them to previous film-based products.
Well, there are a couple of magazines devoted to consumer-level
digital cameras, and they don't give a flip about film.
The photos they've published in the past aren't that impressive,
but that could change as the technology improves-- especially if
a few of them would read your book...

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