Date   

Freelance photography fees

Dan Margulis <76270.1033@...>
 

Folks,

For a forthcoming column that touches on the state of the economy for
professional photographers, I'd appreciate comments from the photographers
on this list


More Archives Posted

Dan Margulis <76270.1033@...>
 

Folks,

In response to requests, we've posted eight more edited threads at
www.ledet.com/margulis. You need to click on the "articles" option.

Also, we've posted a PDF of my millennium column, The Age of the
Enlightened, translated into Spanish.

Topics of the new threads include Total Ink, Wide-Gamut RGBs, Color
Proofing, Monitor Recommendations, Moire avoidance, color settings for
newsprint, handling of cartoons, and the color settings of Photoshop 6.

Further such postings depend on expressions of interest from the group, so
if you are making use of these or would like to see specific other threads
posted, please let me know privately.

Dan Margulis


Re: Optimal TAC, dotgain for b&w newsprint

Dan Margulis <76270.1033@...>
 

Stephen writes,

I originally started with light GCR settings, but due to registration
problems the newsprint images would get very blurry and out of focus.
I know that web presses can't hold rego as well as flat sheet, so
this is something that I will just have to accept. I originally tried
light/med. black generation, but was not happy with the inconsistent
results - so more black and less neutral CMY seemed to be the other
logical extreme to try...oh well.>>

There is a lot of merit in this position. This is why I said that Heavy GCR
is nonstandard, and not that it's bad. The pluses of more GCR are better
registration and less color variation. The big minus is that you are at the
mercy of the black plate, and if it prints too heavily (or if you
underestimate its dot gain) this can ruin the image fairly easily.

You also mention higher dot gain in the black plate. Would you
suggest setting this as a custom dot gain curve, or pulling down the
curve manually in the K channel?>>

The dot gain curve. Why go to the extra work of doing manually it each
time?

I also have the same question, in regards to max K limits...Generate
a file with 100% K and hand tweak the K plate with curves, or set the
CMYK setup for K: 80%, 70% etc.>>

Same answer, but stronger: if you have a 100% black ink limit, the shadow
value in CMY will be artificially low, which causes difficulties in the
correction process later on.

Personally I would trust Photoshop's conversion of black dot gain and
max black limits, over my hand tweaking with curves - but from
reading your 'by the numbers' approach it seems that I should put
more trust in myself - if I follow the info readout and keep the
balance of C to MY slightly higher.>>

Keeping that balance has nothing to do with black generation. If it isn't
balanced in RGB, you're going to have to correct it sooner or later no
matter what kind of GCR you use, and if it is balanced in RGB, nothing you
can do with the black channel will unbalance it.

So if I understand you correctly, using a 'skeleton' black as in
Light GCR or as found in a UCR separation - you can confidently
change the black plate for the extra expected dot gain, without
concern for altering the neutrality of the image, which is mostly
made of CMY inks.>>

Same as above. GCR or lack of it will not alter the neutrality of the
image. You can be confident that black dot gain is heavier than the other
three in newspaper printing. You should correct that no matter what kind of
GCR you use, and you should correct the Photoshop error that has cyan with
more dot gain than the others.

While increasing the black dot gain setting will surely improve things, it
will improve things *less* if you use a skeleton black. The black channel
will be lighter by nature, so the impact of any mistake, either in printing
or prepress, will be less.

The thing to do now is assemble some images that have printed already, and
view them on the screen. Reduce the black midtone in all of them by four
points. This will presumably give a more accurate preview. Once having
saved this change, also reduce the CMYK master curve by two points and ask
yourself whether this has made most of the images more accurate. If it
hasn't, this suggests that your 30% dot gain figure is correct. If it has,
you need to adjust your overall dot gain up by at least two points. One way
or another, when you choose your final dot gain figure, you should start
with C=M=Y=(K-4).

Dan Margulis


Re: Photoshop 6 question

Dan Margulis <76270.1033@...>
 

Andrew Engelhardt writes,

Regardless, this is a problem for us and I think we'll stick with 5.5 for
the time being. I'd be interested to hear if anyone else encounters this in
the coming months, perhaps this is a Windows specific problem as Dan was
unable to replicate the problem.>>

I would now like to amend that, and offer what seems to be the actual
solution.

When I originally wrote, I had tested it by embedding in PS 5.5 a couple of
setups that I had generated from built-in and had previously used in live
jobs. When I loaded those setups as CMYK working spaces in PS 6, no
mismatch messages.

Yesterday, Chris wrote,

*There is no way to change this.* You cannot come up with your own custom
naming convention for Photoshop 5 profile embedding when using
*built-in*. The way around this is [long and tedious methodology snipped]>>

Not so. You *can* name your setup anything you want, right in the built-in
box. So, starting from scratch in PS 5.5, I created a setup that was just
SWOP Coated with a one-point change in dot gain, and saved it out under the
name "Chris is a Cretin". Then I embedded it into a CMYK file, and with
Image Info, a third-party utility, analyzed it and got the desired message,
"ICC Profile found: Chris is a Cretin." I pasted that message into an
e-mail file and prepared to flame Chris. But before doing so, I said, what
the heck, I'll load that profile into PS 6 and open the file.

You guessed it--a profile mismatch. So I tried it again, with different
settings, with different inks, with different dot gains. Same result. And
yet my live-job profiles did not provoke the message.

After considerable headscratching, the correct explanation seems to be, dog
my cats if this isn't a Photoshop 5.5-specific problem. If the ink setup
was *originally* written earlier than PS 5.5--I've tried 5.02 and 4.0, and
assume it works for others--PS 6 recognizes a document written in PS 5.5
using that setup. If the setup was originally written in PS 5.5, it
doesn't. If the setup was originally written in an earlier version, and
then modified and saved under a new name in PS 5.5, it still works properly
and doesn't provoke the mismatch message.

So, it probably isn't a Windows-specific problem, but rather that the
setups I was using happened to antedate Photoshop 5.5. Of course, I hadn't
encountered the problem before, since I don't embed profiles in CMYK files,
because I believe that there are too many surprises and unexpected screwups
involved with such a little-used and ill-tested technology, and you have to
take a lot of time trying to figure out nonsense like this. Some, I know,
assure us that it's very stable.

Dan Margulis


Wavelengths to RGB -thanks

alanmartin@...
 

Thank you all for your helpful answers.
You gave me all I needed to shoot ahead.
For this project CIE Lab is obviously the
color space to work in, and the various links
you provided are great.
Thanks again - Alan


Re: Mixed questions on ICC Profiles, Rendering Intents & LAB Mode

Horacio Pe鎙
 

Horacio Pea wrote:
But if you open this on a Adobe RGB setup, with a 2.2 gamma, you get
a different RGB value (I can't remember off hand what the exact value
is).
Right, different color !
OOps, wrong answer ... thanks for playing !

It's still the same color, but different readings, due to different RGB
workspace.


Best regards,
Horacio Pea

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Re: Mixed questions on ICC Profiles, Rendering Intents & LAB Mode

Horacio Pe鎙
 

samarsh@ozemail.com.au wrote:

i) LAB is touted as 'device independent' and that it can include a
wide colour gamut. If LAB can hold both RGB and CMYK values, why is
there a small amount of error when converting from RGB > LAB > RGB?
The same goes for CMYK > LAB > CMYK. This is using the same workspace
settings and with no other settings changed, except for the mode
conversions.
I guess rounding errors ...

Besides, RGB has three 256-level channels (64K colors) while Lab has two
256-level channels but L channel is 100-level (less than 64K colors)...
so there is no point-to-point correspondence.
At least, that's what you can type in the Color Dialog ... and what you get
with eyedropper.

ii) How can LAB be 'device independent' if it is changed by the RGB
workspace setup?
Lab is not changed by the RGB workspace but *the color you are measuring
is* !

Same combinations of different RGB primaries give different results, and
thus, different Lab values. Eg:
r255g0b0 with Barco Phosphors is a certain Red, but different to Trinitron
r255g0b0.

If you convert a 128RGB tone in ColorMatch 1.80 gamma to LAB, then
open the file on another computer with the same RGB work space and
convert from LAB to RGB then you get a 128RGB value.
Right, same color.

But if you open this on a Adobe RGB setup, with a 2.2 gamma, you get
a different RGB value (I can't remember off hand what the exact value
is).
Right, different color !

In APS4 different monitor setups or ambient lighting settings would
change colour values - even for LAB mode. Once again this does not
sound very 'device independent' to me. So what gives? Should the RGB
setup affect how LAB mode converts colour values? If all colour
working spaces are expressed in gamma, white point and RGB XY
values...what is LAB? Does it matter? Am I
worried over nothing? Or is this more for CMYK values over RGB
values?
That was the greatest pain in the *** with PS4 ... monitor setup altering
not only what you see but color conversions too.

iii) One final question (for now) - I know that editing in LAB mode
offers some advantages for some special situations, but I also know
that it is dangerous for colour editing, and most editing of curves
is done to the Lightness channel rather than the AB.
RTFM ... I mean, Dan's book :) ... you can do very interesting things
with color in Lab mode.

Best regards,
Horacio Pea

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Re: old monitor

gowens01@...
 

--- In colortheory@egroups.com, Dan Margulis <76270.1033@c...> wrote:
Kenji writes,

My older Mitsubishi Diamond Pro monitor seems as if I can't get it
calibrated anymore. The problem is that there is a magenta/red cast in
the shadows and little bit of artifacting in the shadows. The overall
gamma and brightness doesn't allow me to get anywhere near calibrated
these days.It won't go dark enough...it feels too flat and washed out
in the shadows.>>

So?

If you're interested in quality color, you can't rely on your *perception*
of neutrality, which is affected by too many variables. If you look at a
single image, and the shadows seem to you too red, perhaps they in fact are
too red, or perhaps there is something else in the picture that's causing
you to *perceive* that they're too red. So, you don't trust your
perception, you look at the Info palette and find out whether it's really
neutral.

As for the contrast, obviously you are seeing less of it on this monitor.
But the whole purpose of calibrating a monitor is to be able to predict
what an image will eventually look like. Whether it's going to become a
chrome or print on newsprint, it won't match the contrast you see on your
monitor, no matter how good your monitor is. So, everybody makes a mental
adjustment.

So I have two questions. Is it maybe a problem with the video card, or
is it probably the monitor? And is it worth taking it in to a repair
shop? Can they get it anywhere near to being able to use it for digital
photography needs?>>

Based on your description, it seems usable now. Such problems typically are
with the monitor and not the card. As for repairing monitors, this is
generally a losing proposition unless they are under warranty. Monitors are
like people, as they get older more and more things start to go wrong.
I just picked up my test pritn form the photo lab. Two weeks back I
asked if recalibrating my monitor after upgading to OS 8.1 would effect
my PS color settings. The answer was no. So I changed my workspace to
RGB (1998) which gave me a white point of 6500; gamma 2.20. Then I
calibrated the monitor withcolor sync. It set the white point at 6500
which gave me a ghastly white so I changed the setting to 9300.

Then I scanned a negative with the Sprintscan and used the white,
black, and gray eyedroppers in the scanner software. This gave me a
monitor image where I was preceiving more red.

then I read a article in PEI about the 90% method of color correction.
I decided to use this method on the above print. After I had done this
I thought that worked pretty good (on the monitor). I could see the
difference.

So I took it to lab to be printed. Now I'm preceiving green. I've
looked at it outside; comparred it to the original proof; and comparred
it to the monitor. Outside (we are overcast today) the green is
obvious. Compared to the original proof you can see that the red is
gone and the subject (a bay horse) is darker. comparred to the monitor
it looks like a perfect match (knowing that is not true, but it is
close).

I will ask these questions:

If you have used one method of color corrrection and decide to try
something else; is it best to scrap the file and start over?

Can the white point setting in Color sync be different from the white
point setting in Photoshop?

I have a clue as to how this problem may be corrected. When using the
color sample tool in RGB I noticed that there were two areas out of
gamut in cymk. Thee areas were the shadow under the horse and the
horses' halter. Can these areas be corrected in RGB to bring them into
gamut in CYMK?

I felt this was a good exercise. It made me try some different
techniques and showed that if my corrections are correct what I get
back from the lab will be close.

Before I close I have a suggestion: Would it be possible to list posts
in the digest by the message list number or as 1-26; the second number
being the message list number. This would make it easier to find posts
on the list to save or respond to at a later date.

Gary Owens

Dan Margulis


Re: Printing Overseas

John McKercher <john@...>
 

I know it can be done, but no one in town seems to stock the material and we
don't do enough volume that it would make sense for these shops to stock it.
On to digital proofing, I guess...

John
john@hartleyandmarks.com

-----Original Message-----
From: mact@adcomgraphics.com [mailto:mact@adcomgraphics.com]
Sent: Friday, January 12, 2001 8:56 AM
To: john@hartleyandmarks.com
Subject: Re: [colortheory] Printing Overseas


<<positives for them to print from but there is
no one here in town that can make matchprints from positive film and we
don't really have the experience with other proofing methods that we could
be sure to trust them.>>

Imation DOES have film positive matchprint materials. It's new (last year or
so I think). Ther are several different materials depending on dot gain. I
believe they use the same processing, so there's no problem there.



Mac Townsend,
Adcom Graphics, Fairfield, CA:
Electronic Prepress
www.adcomgraphics.com


proofer

mact@...
 

Which low-cost digital proofer seems to be the leader of the pack these
days? BestColor with Canon 8500, HP GAPro with Imation software, Compose rip
with Canon 8500? Something Rip with Epson 3000/5000? Total price has to be
in the under $5,000 range.

The device would be plugged into an NT box so the software would have to be
NT usable. It would be used to provide hardcopy "feedback" for adjusting
color before committing to film. It should be able to generate a proof that
will look awful darn close to what a ColorKey from the same file would look
like.


Mac Townsend,
Adcom Graphics, Fairfield, CA:
Electronic Prepress
www.adcomgraphics.com


Re: Printing Overseas

John McKercher <john@...>
 

The 12% figure is the figure that was given to us by the printers in Hong
Kong, knowing they would be printing from negatives. The latest print job we
got back from them was acceptable using this figure. This was the first job
we had done with them using this figure (and the first one I was involved in
as far as the colour correciton goes). I believe in the previous jobs, we
were probably just using 20% (and standard Photoshop settings). So our
results are getting better. We're just a little worried about going to CTP
but I'll explore our proofing options with our overseas printers and see
what they have to say.

John McKercher
john@hartleyandmarks.com

-----Original Message-----
From: Chris Murphy [mailto:lists@colorremedies.com]
Sent: Thursday, January 11, 2001 10:14 PM
To: Color theory
Subject: RE: [colortheory] Printing Overseas


Dan writes:
12% is ordinarily too low for printing from negs, and usually results in
muddy-looking reproduction. However, with fine paper and good printing
conditions, it is possible that it's right.
I'm suspicious. It's possible, but if it's really this low, and the
separation was made with this in mind, and yet the result wasn't
satisfactory (sounds like it wasn't at all satisfactory) makes me think
it's not right. And the fact it's in Hong Kong, and that they don't have
a lot of experience with negative platemaking are contributing factors.


Re: Photoshop 6 question

Andrew Engelhardt
 

Sorry, I should have clarified. "Embedded: test_table, curves" is the text of the message that PS showed in the profile mismatch dialog box. The table in use was named simply "test_table". Regardless, this is a problem for us and I think we'll stick with 5.5 for the time being. I'd be interested to hear if anyone else encounters this in the coming months, perhaps this is a Windows specific problem as Dan was unable to replicate the problem. Thanks for all the input.

 - Andrew Engelhardt

-----Original Message-----
From: Chris Murphy [mailto:lists@...]
Sent: Thursday, January 11, 2001 7:49 PM
To: Color theory
Subject: RE: [colortheory] Photoshop 6 question


>That's exactly what I did but I guess PS 6 just doesn't like it.

Well they are different because if they are the same then Photoshop 6
doesn't give a profile mismatch warning. So something about them is
different. In you previous posting you wrote:

>>Same thing
>>happened when I opened an image, the profile mismatch pops up saying>
>>Embedded: test_table, curves >Working: test_table. Am I doing something
>>wrong in my color settings set-up? Is this possibly a Windows bug ?

You state Embedded: is "test_table,curves"  and then you state Working:
is "test_table". These are two different names. They must be identical.
It's possible there is a hidden character or something else in the
internal file name of the profile that is causing this.

I think the problem is you are saving a separation table. Don't save a
separation table directly from built-in. Go into the Tables portion of
CMYK Setup in Photoshop 5 and save it out from there. That saves an ICC
profile. Saving from Built-In does not.


Chris Murphy



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Mixed questions on ICC Profiles, Rendering Intents & LAB Mode

samarsh@...
 

Hello list members, Firstly I am sorry if I am repeating previous
posts, but I have not seen answers to these questions before.

A) APS 5.x Profile Mismatches & Profile embedding:

This is a two part question.

i) I am just starting to experiment with using the CM settings in
APS5.5 so that we can have a better idea of the images workspace. The
workspace will usually be a 'built in' CMYK setting, or one with a
custom name saved as a ICC profile from the tables section.

This question is related to standard, 'built in' CMYK settings - but
it probably applies to custom named profiles as well.

Recently I received a CMYK file. The profile was 'SWOP Coated, 20%'
indicating the 'default' Photoshop configuration. Fine. So to match
the working space, it was a simple matter to turn the ink set to SWOP
Coated and the dot gain to 20%. The file opened without a problem.

But to me this seems too simplistic. What about the separation method
(GCR/UCR), the max amount of black and total ink limit?

The image has 100% black in it, but my CMYK setup has 80% max black -
but there is no profile mismatch, it opens without any errors.

From a recent post on APS5 > 6 profile mismatch issues, it seems that
APS5.x only embeds a simple file name based on ink set/dot gain.

I would have thought that many more factors contribute to a CMYK
working space than just these variables.

So is this just a 'blind spot' in ICC profiles, or in Adobe's
use of them? Have things changed for the better in ver6?

If profile handling is based on names, rather than actual separation
methods and the data in the file - then this seems to be quite an
issue with the correct handling of tagged files from an unknown
source. It seems that if users blindly follow the ICC tag, then they
are not getting the full story!

So I will still have to read total ink densities to try to guess the
other separation setup data, so that my workspace is more 'correct'.
Since I don't change 'actual colour values' and judge things 'by the
number' this is not *too* much of an issue, but it does raise a good
point.

We use an action to convert to CMYK, and this action enters 'file
info' stating the separation settings used, but I thought ICC
profiles would not need this extra manual management.

ii) From a previous question of mine regarding rendering intents and
ICC profiles generated from the 'built in' CMYK setup, it seems that
Photoshop only uses a simple ICC profile without any rendering info
in the profile.

So if all render intents result in the same separation, in regards to
'built in' CMYK settings saved as profiles from Photoshop - what
common method are they all using, and is it the same as a standard
mode conversion using 'built in' settings?

I thought render intents were part of the CMM, rather than the
profile itself. I don't know much about the 'nuts & bolts' of ICC
profiles - are there any good links out there with some info so that
I can get a better grasp of this 'new' technology?

It seems that I am taking certain features for granted or as default,
when they are custom or not applied to all profiles. I understand
that there are many different profiles, but I am talking about RGB &
CMYK output profiles here.

How does one know what rendering intents are applicable to that
particular ICC file? The Kodak ICC PCD plug-in in APS has an info
window with some stuff about the selected profile. Is there a clue
here somewhere? How can you trust the profile in other ICC aware
applications, if Photoshop does not save any rendering info?

B) Render Intents & 'Built In' CMYK mode conversions:

Related to the above second part question, so what 'render intent' or
colour conversion method does the standard 'built in' or 'built in'
saved as an ICC profile use?

I seem to remember hearing that APS4 used Relative Colorimetric
rendering in it's RGB > CMYK conversions (this was before ICC profile
were used).

I can't remember if it was in the change over from 2.5 to 3, or 3 to
4 - but there used to be major out of gamut shifts in RGB to CMYK
conversions. Now there is much less visual change to images when
converting between RGB and CMYK. Any ideas?

C) LAB Colour Mode Questions:

i) LAB is touted as 'device independent' and that it can include a
wide colour gamut. If LAB can hold both RGB and CMYK values, why is
there a small amount of error when converting from RGB > LAB > RGB?
The same goes for CMYK > LAB > CMYK. This is using the same workspace
settings and with no other settings changed, except for the mode
conversions.

I understand that this is only a minimal shift, and only in some
colours - and that of all the colour mode conversions LAB is probably
the least 'destructive' to precise colour break up values...but small
value changes are still value changes - this is not a 'perfect'
colour conversion.

Is this related to 8 bit data? If Photoshop used 16 bit or higher for
all operations, would this change?

What if you used the Profile to Profile command and the Photoshop LAB
ICC profile? Would this differ from a simple mode/LAB change?

I hear that Photoshop uses 16bit for mode conversions, and 20bit for
ICC profile conversions...is this only in APS6? I have not heard
about this until recently.

ii) How can LAB be 'device independent' if it is changed by the RGB
workspace setup?

If you convert a 128RGB tone in ColorMatch 1.80 gamma to LAB, then
open the file on another computer with the same RGB work space and
convert from LAB to RGB then you get a 128RGB value.

But if you open this on a Adobe RGB setup, with a 2.2 gamma, you get
a different RGB value (I can't remember off hand what the exact value
is).

I have often heard that if you were unsure of the other end's setup,
to supply the file in LAB, then when they open it, it will be the
same as on your system. But what if their workspace is different? Is
this why ICC profiles can be embedded into LAB? I thought LAB was the
'all seeing, all knowing' colour space which was 'standard' and
recognised by all systems - so why does it need a profile? This must
be related to the RGB workspace.

In APS4 different monitor setups or ambient lighting settings would
change colour values - even for LAB mode. Once again this does not
sound very 'device independent' to me. So what gives? Should the RGB
setup affect how LAB mode converts colour values? If all colour
working spaces are expressed in gamma, white point and RGB XY
values...what is LAB? Does it matter? Am I
worried over nothing? Or is this more for CMYK values over RGB
values?

Do I have an incorrect understanding of 'device independence' or LAB
mode?

iii) One final question (for now) - I know that editing in LAB mode
offers some advantages for some special situations, but I also know
that it is dangerous for colour editing, and most editing of curves
is done to the Lightness channel rather than the AB.

I once read in APS4 that the LAB mode used a gamma response of '3' -
which is far from the linear response new users would expect. I guess
this means that a small tweak in the shadows can severely alter the
mid tones?

Once again, are there any thoughts out there on the hazards of LAB
mode editing?

Thanks for taking the time to read these many rambling questions.

Stephen Marsh.


Re: Digest Number 18

Gary W. Owens <gowens01@...>
 

Message: 5
Date: Thu, 11 Jan 2001 02:59:36 -0000
From: alanmartin@one.net.au
Subject: Wavelengths to RGB

I am trying to find a link between the view of scientists
(the physics of light and the biology and psychology of human
perception of color) and the expertise your members have in
color matching.

More specifically, I am hoping to find a way of matching
physical Hue values (ie the frequency or wavelength of a color)
to the rgb values of a typical monitor.

The Problem
In Photoshop's (and other software's) color pickers, hue values
come in a circle from 0 to 359 "degrees" through 0 again.
From this one can create a linear rainbow spectrum image,
say 800 x 100 pixels, red on the left, violet on the right
and no change vertically.
In the physics lab one can also create a rainbow spectrum of
the range of visible colors.
If you scale these two so their colors match at each end, the
colors in the mid range will not match.
This is like an analogy, in hue, of a gamma matching problem
in brightness.

Here's another way to describe this mismatch:
I am 55 years old so I learned "color theory" at art school
long before desktop computers and Photoshop even existed.
We learned that if you arrange the spectrum in a circle,
green is opposite red, etc.
But in image editing software, cyan (180 degrees) is opposite red
(0 or 359 degrees). The first of these seems truer to my perception,
with green offering the strongest contrast in hue to red.
This may just be early conditioning rather than unbiased perception,
but I doubt it because of what I will term "the Op Art experience":
if you paint equal width stripes of two fairly saturated colors,
with equal brightness, they jazz the eyes (appear to jump around)
most when you choose two colors that are opposites in the
traditional theory rather than the current software model
(ie red-green and orange-blue rather than red-cyan and
green-magenta).

It seems that current software uses this model because it fits
in with the technology: monitors use rgb so they space the pure
r,g,b colors equally round the circle.

That's the background problem.
Here is the practical need I am seeking help with:

For some experiments in human color perception (both normal and
various types of color-blind), I want to create a number of images,
with colors defined in 24bit rgb (the human subjects will see them
on a monitor). Later I shall also make printed images, but that
translation from rgb to cmyk will be less difficult - I shall be
aided by reading the messages in this eGroup no doubt.

The images will include some gradual spectra and also some images
with single-color juxtaposed blocks. In both cases I need to
translate from wavelength or frequency numbers to rgb numbers.
That way I can juxtapose colors which are true harmonics of each
other, in the same way that a major chord in music uses frequencies
with a simple mathematical ratio.
I am not fussy as to the form... it could be just a lookup table,
or an rgb image of a spectrum with markings and wavelength numbers
along the bottom, or even (best of all) a tiny program where you
enter a wavelength or frequency number and get your rgb numbers
as an answer.
So far my searches on the web have been fruitless. I found an image,
as described, but it was an 8 bit indexed gif (yuk) with only three
wavelengths marked (too crude).

In technical terms, I'd prefer the spectrum images to be logarithmic
rather than linear. But don't worry if that sounds too complicated;
almost any source would be better than what I have found so far!

Sorry to bother you with a query that's way off your usual subject
matter!

Alan Martin alanmartin@one.net.au
Hi Alan,

Interesting project. Eyewire catalog #42 for January (www.eyewire .com) has a center spread
dealing with color theory. There is a color wheel and mention of a company; Colorfield Digital
Nedia, Inc. These people have developed "a plug-in that allows designers with normal vision to see
images the same way people with color-deficient vision see them." there URL is www.colorfield.com

Godd researching,

Gary Owens


Re: Wavelengths to RGB

Dan Margulis <76270.1033@...>
 

--------------- Forwarded Message ---------------

From: "IronWorks", INTERNET:ironworks@ameritech.net
To: Dan Margulis, 76270,1033
Date: Thu, Jan 11, 2001, 3:58 PM

RE: Re: [colortheory] Wavelengths to RGB


My deepest thanks for this - an excellent site. I'm just learning all this
and the ColorFAQ and the GammaFAQ I also found there are invaluable.

I use Corel Photo-Paint so many of these discussions don't apply but many
do.

Thank you once again.

Maris Lidaka

----- Original Message -----
From: "Dan Margulis" <76270.1033@compuserve.com>
To: "Color Theory" <colortheory@egroups.com>
Sent: Thursday, January 11, 2001 1:26 PM
Subject: [colortheory] Wavelengths to RGB

[snipped]

| Another argument for the L*a*b* method. A good source of information on
| this, with a lot of links to esoteric stuff, is
| http://www.inforamp.net/~poynton/ColorFAQ.html


Re: Optimal TAC, dotgain for b&w newsprint

samarsh@...
 

Thanks, Dan.

So it seems that by trying to cure one problem, I was creating other
problems.

I originally started with light GCR settings, but due to registration
problems the newsprint images would get very blurry and out of focus.
I know that web presses can't hold rego as well as flat sheet, so
this is something that I will just have to accept. I originally tried
light/med. black generation, but was not happy with the inconsistent
results - so more black and less neutral CMY seemed to be the other
logical extreme to try...oh well.

So it seems that I will need to look at slightly higher total ink
limits and either Light GCR or UCR. Some papers quote 220-240%, so I
was striking a happy middle ground with 230%...but you're correct,
this can be run slightly higher - I was just playing things safe.

You also mention higher dot gain in the black plate. Would you
suggest setting this as a custom dot gain curve, or pulling down the
curve manually in the K channel?

I also have the same question, in regards to max K limits...Generate
a file with 100% K and hand tweak the K plate with curves, or set the
CMYK setup for K: 80%, 70% etc

Personally I would trust Photoshop's conversion of black dot gain and
max black limits, over my hand tweaking with curves - but from
reading your 'by the numbers' approach it seems that I should put
more trust in myself - if I follow the info readout and keep the
balance of C to MY slightly higher.

So if I understand you correctly, using a 'skeleton' black as in
Light GCR or as found in a UCR separation - you can confidently
change the black plate for the extra expected dot gain, without
concern for altering the neutrality of the image, which is mostly
made of CMY inks.

I am not 'new' to print, but I am new to the 'science' and the
practical side of colour separation (my typesetting background has
evolved into broader pre press, but I sadly lack the formal trade
training in graphic reproduction).

Thank you for your thoughts and experience.

Stephen Marsh.


Re: Printing Overseas

Chris Murphy <lists@...>
 

Dan writes:
12% is ordinarily too low for printing from negs, and usually results in
muddy-looking reproduction. However, with fine paper and good printing
conditions, it is possible that it's right.
I'm suspicious. It's possible, but if it's really this low, and the
separation was made with this in mind, and yet the result wasn't
satisfactory (sounds like it wasn't at all satisfactory) makes me think
it's not right. And the fact it's in Hong Kong, and that they don't have
a lot of experience with negative platemaking are contributing factors.


You can use their profiles on a PC (you just have to give them an .icm
suffix), but the problem is you would then have no method to generate a
proof for yourself.
If the profile is valid for the press (if if if if if), and yet more ifs
for having a profile for a suitable inkjet printer, this would be
possible. I'd be more interested in finding a contract proof everyone can
agree regardless of whether their profile is used or not; but if it's a
good profile there's no reason not to use it. More ifs.

Also, if this printer isn't even able to cope with
supplied negs expecting them somehow to have an accurate profile is
somewhat like expecting a fifth-grader to have an accurate understanding of
calculus.
I disagree with the analogy. Just because they seem to have low
experience with negative platemaking doesn't mean they don't have
adequate profiles for their positive platemaking and printing process -
which is afterall their normal workflow.

Just like here in the U.S. Just because most printers here would have a
problem dealing with positive platemaking and have an equally low
experience with it, doesn't mean they can't come up with good profiles
for negative platemaking and printing.

So I think it's premature to say the profile isn't accurate. It is
absolutely fair to say it's probably only accurate for positive
platemaking (just like if you make one for negative platemaking it's not
going to work for positive platemaking).



The preferable method is to become more comfortable with digital proofing.
Modern proofers can be configured to match almost any output. This way, you
supply a digital proof with your negs. You are going to need to go through
this education process anyway if you ever go CTP.
Yes, yes, yes. I concur.


Chris Murphy


Re: Photoshop 6 question

Chris Murphy <lists@...>
 

That's exactly what I did but I guess PS 6 just doesn't like it.
Well they are different because if they are the same then Photoshop 6
doesn't give a profile mismatch warning. So something about them is
different. In you previous posting you wrote:

Same thing
happened when I opened an image, the profile mismatch pops up saying>
Embedded: test_table, curves >Working: test_table. Am I doing something
wrong in my color settings set-up? Is this possibly a Windows bug ?
You state Embedded: is "test_table,curves" and then you state Working:
is "test_table". These are two different names. They must be identical.
It's possible there is a hidden character or something else in the
internal file name of the profile that is causing this.

I think the problem is you are saving a separation table. Don't save a
separation table directly from built-in. Go into the Tables portion of
CMYK Setup in Photoshop 5 and save it out from there. That saves an ICC
profile. Saving from Built-In does not.


Chris Murphy


Re: Color Correction on LCD displays

Chris Murphy <lists@...>
 

Is anyone doing serious color correction on laptops or LCD displays?
Only if you talk to Apple Marketing. They will tell you to get an Apple
Cinema Display and to calibrate and profile it with a $3000 instrument
and it's GREAT for color critical soft proofing. It's a bunch of bovine
excrement. Actually it's so full of excrement you can choose the genus
and species of animal you prefer.


I
have found the color gamut of all LCD displays to be smaller than that of
a quality CRT.
The Cinema Display has a gamut nearly identical to a conventional CRT and
has primaries that are also very much the same. But that's not the real
problem. The real problem is the viewing angle problem, which in addition
to a luminoscity variation causes a gray balance shift depending on
whether you look to the left side of the screen or the right side of the
screen and if you move your head a couple inches left or right from
center.

So unless you get a neck brace (or my preference, a full body cast) along
with your Cinema Display, I think it's pointless. Interesting certainly
because there are great benefits to flat panel viewing (crisper, no
flicker, less radiation, less eye fatigue, etc.), but still pointless as
this point.


Chris Murphy


Re: Wavelengths to RGB

Chris Murphy <lists@...>
 

No, the strongest contrast would be a blue-green.
I think it would be blue-yellow. The cones that are sensitive to short
wavelengths, closely approximating blue (but not exactly blue) are as
sensitive to blue as they are sensitive to the abscence of blue light
(unlike the other primaries, for example green and red, there is no
corresponding sensitivity to the abscence of such light). Hence why some
argue that yellow can be seen as a quasi-4th primary color.


Chris Murphy