Dan Margulis Applied Color Theory - Standard Color Viewing Temperature

Date: Tue, 26 Nov 2002 14:29:45 -0500
From: Bruce Fellman
Subject: Re: Printing to inkjet--from a lurker

Maris, this raises a calibration question I've had for years. Just what is the proper monitor temperature setting to use when calibrating with Adobe Gamma, and or any other calibration tool, for that matter? FYI, our images at the magazine are destined for CMYK and a four-color press, but I'm now wondering, if the output is, say, an ink-jet or the web, should we be calibrating with a different-from-the-Mac default, which, in our case, is 9300 degrees?

Bruce Fellman, Managing Editor and resident colorblind color-correction maven
The Yale Alumni Magazine
203-432-0650
PO Box 1905
149 York Street
New Haven, CT 06509-1905


Date: Tue, 26 Nov 2002 15:04:12 -0600
From: "Maris V. Lidaka Sr."
Subject: Re: Printing to inkjet--from a lurker

Disclaimer: I am not an expert, though I have studied color management seriously. I believe the consensus is 6500K, though it used to be 5000K for print. I would calibrate once and leave the color temperature and calibration alone, whether output is then for press or for web.

I think Chris Murphy, Andrew Rodney and Stephen Marsh could respond more expertly, and you might check their respective websites at

http://members.ozemail.com.au/~binaryfx/PSTV_links.html#D and

http://digitaldog.net/ respectively.

Maris

From: "Bruce Fellman"
.
> Just what is the proper monitor temperature setting to use when
> calibrating with Adobe Gamma, and or any other calibration tool, for
> that matter? FYI, our images at the magazine are destined for CMYK
> and a four-color press, but I'm now wondering, if the output is, say,
> an ink-jet or the web, should we be calibrating with a
> different-from-the-Mac default, which, in our case, is 9300 degrees?


Date: Tue, 26 Nov 2002 15:58:27 -0800
From: "Steve Wojno
Subject: RE: Printing to inkjet--from a lurker

Bruce:

You should set your monitor to 6500K which is the temperature of daylight and is the basis for judging color. Most print shops have a neutral gray booth with 6500K lights for proofing press proofs against your match print.

Steve


Date: Tue, 26 Nov 2002 16:10:59 -0700
From: Andrew Rodney
Subject: Re: Printing to inkjet--from a lurker

I1d suggest a 6500 white point and a gamma setting like 1.8 for Mac users (who care about previews outside ICC savvy applications) and 2.2 for Windows users. The calibration aim point of the display has nothing to do with the final output (ink on paper to inkjet). The display profile is only used for preview purposes (it1s totally independent of the file or the method of output). Logic would say we should calibrate to 5500 (to match the color temp of our viewing boxes) but that usually doesn1t work as well as using a 6500 white point (depending on the display).

Andrew Rodney


Date: Tue, 26 Nov 2002 21:09:15 -0500
From: "john c."
Subject: Re: Printing to inkjet--from a lurker

It's best to stick to the D50 ANSI standard which, among other things, calls for 5000K lighting throughout the shop. Print shops only use 6500K because the bluer light makes it easier to view yellow dots on press output.

john castronovo


Date: Tue, 26 Nov 2002 23:38:06 -0500
From: Lee Collins
Subject: Re: Printing to inkjet--from a lurker

Most light booths have 5000K temperature lighting. I've never seen one with 6500.

Lee Collins
--

> From: "Steve Wojno"

> You should set your monitor to 6500K which is the temperature of daylight and
> is the basis for judging color. Most print shops have a neutral gray booth
> with 6500K lights for proofing press proofs against your match print.


Date: Tue, 26 Nov 2002 21:52:56 -0800
From: Jan Steinman
Subject: RE: Printing to inkjet--from a lurker

> From: "Steve Wojno
>
>... 6500K which is the temperature of daylight...

Actually, direct sunlight is closer to 5000K. You'll get closer to 6500K in "open shade," where the primary illuminant is the blue sky, rather than the yellow sun.

--
: Jan Steinman -- nature Transography(TM):
: Bytesmiths -- artists' services:


Date: Wed, 27 Nov 2002 14:24:37 +0000
From: Steve Bradshaw
Subject: viewbooth colour temp.

Lee Collins wrote:

> Most light booths have 5000K temperature lighting. I've never seen one with
> 6500.

Our booth (made by DW Viewboxes) has both 5000K and 6500K lightsources.

Steve Bradshaw
Photographer

p ++44 (0)161 273 7551 . f ++44 (0)161 274 3326 . isdn ++44 (0)161 272 7166

http://www.photolink.co.uk .


Date: Wed, 27 Nov 2002 10:16:42 EST
From: Solux Lamps
Subject: Re: viewbooth colour temp.

A bit of education: Color Temperature and Color Rendering Index (CRI) are not the most critical aspects of lighting for viewing colors. In fact they can give a false sense of security. What is important is the Spectral Power Distribution. (SPD)

The more accurately the light source models the SPD of the standard - assumed here to be either D50 or D65 - the better.

In theory, the CRI would give you a measure of this ability to model the SPD of D50 or D65 but I am dubious of claims by lighting companies that make "daylight" fluorescent tubes and claim CRI's over 93 or 95. Their spectrums are spikey and the SPD of D50 and D65 are not.

In my opinion, it is best to look at high resolution SPDs and compare them to the SPD of D50 and/or D65.

Philip Bradfield, Ph. D.
VP-Tailored Lighting Inc.
Where SoLux was invented
SoLux home page (solux.net)
800-254-4487


Date: Wed, 27 Nov 2002 10:42:34 -0600
From: "Henry Segalini"
Subject: Standard color

We use 5000K only.

GATF sells a "RHEM Light Indicator" These are self adhesive strips which can be applied to proofs, etc. They show if the ambient light is 5000K or not.

Henry Segalini
Universal Printing Co
St. Louis MO USA


Date: Wed, 27 Nov 2002 12:00:07 EST
From: Solux Lamps
Subject: Re: Standard color

Henry Segalini writes:

> GATF sells a "RHEM Light Indicator" These are self adhesive strips which
> can be applied to proofs, etc. They show if the ambient light is 5000K or
> not.

There are an unlimited number of spectrums that can be 5000K and they can render color very differently. One cannot determine how well a light renders color if you only know the color temperature of the light.

The SPECTRUM is the standard. NOT the color temperature.

Philip Bradfield, Ph. D.
VP-Tailored Lighting Inc.
Where SoLux was invented
SoLux home page (solux.net)
800-254-4487


Date: Wed, 27 Nov 2002 17:25:15 -0000
From: "Tom Andrews"
Subject: Re: viewbooth colour temp.

Hi Steve,

Here's another perspective. I use Solux 3500K bulbs in my print viewing booth. Reasoning: I make fine art color prints on an Epson 10000 with pigment inks that will usually first be displayed in galleries or at art shows under halogen lamps. Although my custom profiled 10000 doesn't show near the metamerism that my 2000P printer did, it is still there. I found that when I print to look best under halogen, the daylight (~6500K) view is too color shifted (toward green) for my taste. Conversely, printing to look best at 5000K makes them look too red under halogen. I tried the 4100K Solux bulb, but found the 3500K a better compromise. Prints made to look best under 3500K look great under halogen (slightly warmer) and show minimal metamerism under daylight lighting. Also, I find that the quality of the light from Solux bulbs (and I am not talking numbers, but my perception of print appearance) is quite outstanding. I am putting Solux track lighting in my studio for this reason. And I have no connection to Solux other than being a satisfied customer.

Tom Andrews
http://www.wildlandart.com


Date: Wed, 27 Nov 2002 11:25:12 -0800
From: David Barr
Subject: Re: Re: viewbooth colour temp.

I too see this same behavior on Epson pigmented archival inks (appearance shifts towards green under skylight, and to a lesser extent under fluorescent lighting). If these prints are displayed near windows (sometimes unavoidable), their appearance shifts significantly during the day. Besides the compromise Tom describes below, does anybody know of alternative solutions? Do dye-based or aftermarket inks exhibit similar behavior? Could the paper choice have some impact in this regard?
Thanks.
-Dave

Tom Andrews wrote:

> Here's another perspective. I use Solux 3500K bulbs in my print viewing
> booth. Reasoning: I make fine art color prints on an Epson 10000 with
> pigment inks that will usually first be displayed in galleries or at art shows
> under halogen lamps. Although my custom profiled 10000 doesn't show near
> the metamerism that my 2000P printer did, it is still there. I found that when
> I print to look best under halogen, the daylight (~6500K) view is too color
> shifted (toward green) for my taste. Conversely, printing to look best at
> 5000K makes them look too red under halogen.


Date: Wed, 27 Nov 2002 15:36:38 -0500
From: David McDowell
Subject: Re: Standard color

Phil is right, color temperature is not enough.

There is an ISO standard on viewing conditions - ISO 3664, Viewing conditions - Graphic technology and photography.

It is available from ISO, ANSI or NPES (http://www.npes.org/standards/iso.html)

It uses chromaticity (Color temperature), color rendering index (both general and special) , and both the visible and uv metameric index to establish a defined set of viewing condition for both graphic arts and photographic viewing applications.

David Q. McDowell
Standards Consultant
51 Parkwood Lane
Penfield, NY 14526
Tel: 585-383-1706, Fax: 585-385-3828


Date: Wed, 27 Nov 2002 14:24:14 -0700
From: Les De Moss
Subject: Re: Standard color

Philip Bradfield, Ph. D. Writes:

> The SPECTRUM is the standard. NOT the color temperature.

I continue to find this confusing even after many years in the business. You appear quite qualified to provide a basic definition of the following and how they relate (or not) to each other. There is an anology for electricity (voltage, amperage, wattage) using a water spigot... is there anything similar you can toss out that helps to visualize these relationships?

CRI
Color Temp
Spectral Power Distribution

Regards,
Les De Moss
DigiGraphics
www.digi-graphics.com


Date: Thu, 28 Nov 2002 00:48:16 -0500
From: "john c."
Subject: Re: Standard color

> GATF sells a "RHEM Light Indicator" These are self adhesive strips which
can be applied to proofs, etc. They show if the ambient light is 5000K or
not.
>
> Henry Segalini

Not to argue, but these strips are not designed to reveal color temp. They work as well at any color temp to indicate if a light source is low in CRI or deficient in some part of the spectrum. Such lighting will produce metamerism effects.

john castronovo


Date: Thu, 28 Nov 2002 12:41:41 -0500
From: David McDowell
Subject: Re: Standard color

Les writes:

"I continue to find this confusing even after many years in the business.You appear quite qualified to provide a basic definition of the following and how they relate (or not) to each other. There is an anology for electricity (voltage, amperage, wattage) using a water spigot... is there anything similar you can toss out that helps to visualize these relationships?

CRI
Color Temp
Spectral Power Distribution"

I'm not Phil but let me jump in.

After helping prepare ISO 3664 (Viewing condition - Graphic technology and photography) and struggling with these concepts and how to explain them I arrived at the following general definitions and concepts that I find useful:

Spectral power distribution - wavelength by wavelength plot of the RELATIVE power emitted by a source of energy (we usually only care about the wavelengths in the visible spectrum)

Blackbody - often thought of as a heated iron ball or hollow heated chamber whose spectral power distribution and color only depends on their temperature.

Color Temperature (correlated color temperature) - Temperature of a blackbody radiator that most closely resembles the color of a stimulus of equal brightness

Color rendering index (CRI) - a measure of the difference in appearance (measured in CIELAB values) of selected reflectances when illuminated with a test illuminant vs a reference illuminant (e.g., D50 simulator vs D50 as define by CIE)

CIE Publication 13 provides a set of selected reflectance curves and an evaluation procedure. The General CRI is an average value for a series of reflectances while the Special CRI is related to the individual curves. Typical specification is that average must equal X but no value may be less than Y.

Metameric Index (MI) - Specified in CIE Publication 51 - A more sensitive test of the spectral power distribution of a specific illuminant that CRI. Sets of reflectance curve pairs are provided that are perfect metameric matches (Delta E = 0)under D50, D55, D65 and D75 (different sets for each). The color difference (Delta E) between these reflectances under the test illuminant that is supposed to match the reference illuminant is the input to computing the metameric index. There is one for only visible light (no UV) and one that considers UV Therefore a MI(Vis) and a MI(uv).

Simple analogy

Color temperature is a measure of what it looks like CRI is a measure of the effect it has on objects it is used to illuminate MI is a measure of how much its SPD differs from a reference SPD is a measure of what it really is

Bottom line is that if we compare two spectrums (SPDs) they will differ unless they are black bodies. How do we evaluate the difference. CRI and MI are two tools that CIE has developed to help try to evaluate the difference.

Perfect - no, useful - yes.

David Q. McDowell
Standards Consultant
51 Parkwood Lane
Penfield, NY 14526
Tel: 585-383-1706, Fax: 585-385-3828


Date: Thu, 28 Nov 2002 11:51:11 -0700
From: Chris Murphy
Subject: Re: Standard color

David McDowell wrote:

> Phil is right, color temperature is not enough.
>
> There is an ISO standard on viewing conditions - ISO 3664, Viewing
> conditions - Graphic technology and photography.

I have a copy around here somewhere, and if I remember correctly it seems to loosely imply that fluorescent light sources aren't ideal for the purpose of producing the reference standard which is D50, NOT 5000 K. 5000 K is merely color temperature. You can have something that has a balanced white, but actually contains a whole lot of green that just can't be seen until it hits something sensitive to those wavelengths.

Also, the standard does require CRI be applied collectively across the spectrum (the misleading value Phil Bradfield is referring to), but also requires CRI be applied across sections of the spectrum. But I feel those sections are wide enough to allow "averaging" within some of those sections, such that the CRI ends up higher than the minimum acceptable value. If the sectioning were narrowed, fluorescent would totally fail to produce the minimum sectional CRI for this standard.

The problem with failing fluorescent for ISO 3664 is that it's easy to manipulate the brightness of a fluorescent light source, so that it more closely matches up with the luminosity of the display, and that's more important than color temperature.

Chris Murphy
Color Remedies (tm)
Boulder, CO
www.colorremedies.com


Date: Thu, 28 Nov 2002 12:03:05 -0700
From: Chris Murphy
Subject: Re: Standard color

john c. wrote:

> Not to argue, but these strips are not designed to reveal color temp. They
> work as well at any color temp to indicate if a light source is low in CRI
> or deficient in some part of the spectrum. Such lighting will produce
> metamerism effects.

Two things I'd like to point out with the RHEM light indicator from GATF:

1. Their purpose is really to fail a given light condition, not to approve it. Metamerism isn't defined as not occurring in ONE lighting condition, but then occurring in ALL OTHER lighting conditions. It is possible for a light source to produce an SPD that will not cause metamerism to occur between two metamers.

2. The metamers making up the indicator are purportedly targeted at a particular vendors 5000 K fluorescent light source, NOT D50. So it's possible for them to lightly band in lighting conditions produce by competing 5000 K fluorescent bulbs, and even under near D50 lighting conditions such as daylight or with SoLux light bulbs.

The bottom line is that the indicators should only really be used in two ways in my opinion: first as a demonstration of metamerism, second if there is strong banding, to do something to improve the lighting. I would not use it to validate lighting conditions, nor would I use it with light banding to absolutely fail a particular condition.

Chris Murphy
Color Remedies (tm)
Boulder, CO
www.colorremedies.com


Date: Thu, 28 Nov 2002 22:56:26 EST
From: soluxlamps
Subject: Re: Standard color

I won't argue with what David McDowell wrote about the definitions of color temperature, spectral power distribution, and CRI. More could be said, but he boiled it down pretty well.

Chris Murphy wrote..
"The problem with failing fluorescent for ISO 3664 is that it's easy to manipulate the brightness of a fluorescent light source, so that it more closely matches up with the luminosity of the display, and that's more important than color temperature."

I would somewhat disagree with the final part of this sentence. I think that getting the spectrum correct is the most important aspect. Once you have that done right, the intensity is next in importance. A poor spectrum is a poor spectrum regardless of how intense it is.

My $0.02.
Philip Bradfield, Ph. D.
VP-Tailored Lighting Inc.
Where SoLux was invented
SoLux home page (solux.net)
800-254-4487


Date: Fri, 29 Nov 2002 01:23:01 -0700
From: Chris Murphy
Subject: Re: Standard color

Philip Bradfield wrote:

> I would somewhat disagree with the final part of this sentence. I think that
> getting the spectrum correct is the most important aspect. Once you have
> that done right, the intensity is next in importance. A poor spectrum is a
> poor spectrum regardless of how intense it is.

That's why I said color temperature and not spectrum. :) If the SPD is generally correct, but the color temperature isn't perfect, our eyes+brain can compensate for that, but they aren't good at compensating for differences in luminosity. Our eyes can't compensate for an insufficient SPD.

Chris Murphy
Color Remedies (tm)
Boulder, CO
www.colorremedies.com


Date: Fri, 29 Nov 2002 09:33:35 EST
From: soluxlamps
Subject: Re: Standard color

Chris Murphy writes:

> That's why I said color temperature and not spectrum. :) If the SPD is
> generally correct, but the color temperature isn't perfect, our
> eyes+brain can compensate for that, but they aren't good at
> compensating for differences in luminosity. Our eyes can't compensate
> for an insufficient SPD.

Chris,

Thanks for the clarification. :-)
Hope you had a good Thanksgiving!

Phil
Philip Bradfield, Ph. D.
VP-Tailored Lighting Inc.
Where SoLux was invented
SoLux home page (solux.net)
800-254-4487


Date: Fri, 29 Nov 2002 16:50:11 -0500
From: John Castronovo
Subject: Re: Standard color

Thanks to everyone for their input. These questions will plague everyone in this business forever because we see in our brains, not our eyes and not with spectrophotometers. Therefore, color vision is very changeable and everything from caffeine to Viagra can have an effect, so the more we standardize what we can, the better.

One thing I'm confused about in the new specs is the difference between what we're supposed to view transparencies by (D50 with 5000k) vs. the white point of the monitors (6500k). While this isn't a drastic difference, it is significant and the two white points don't match. As I understand it, the 6500k for monitors was chosen as an expedient way of getting around monitor brightness deficiencies in red rather than going for an ideal.

In our scanning lab, the entire gray room is lit with indirect Solux 4700k lights, we calibrate our monitors using a 5000k white point and we illuminate originals with GTI dimmable boxes using 5000k tubes. The white point of the lightbox is adjusted to visually match the white of the monitor for brightness. I've also checked with a spectrophotometer to be sure that dimming the box doesn't change anything but the amount of light. This all seemed good at the time, but given the new specs, should we change what we're doing, and if we do, won't the resulting scans be bluer?

John Castronovo


Date: Sat, 30 Nov 2002 09:53:26 -0800 (PST)
From: Mike Bevans
Subject: Re: Standard color

John Writes:

>Therefore, color vision is very changeable and
everything from caffeine to Viagra can have an effect, so the more we standardize what we can, the better.

I see this reasoning a lot, particularly from the calibrationists.

I wonder, though, if this is the case, how do we know if our prints look right?

-Mike Bevans


Date: Sat, 30 Nov 2002 13:16:09 -0500
From: "John Castronovo
Subject: Re: Standard color

From: "Mike Bevans"

> I see this reasoning a lot, particularly from the calibrationists.
> I wonder, though, if this is the case, how do we know if our prints look right?

The point I make is that our vision is extremely poor at maintaining itself at one point. Human evolution has used this to great advantage as our eyes and brain constantly adapt to the conditions at hand. By comparison, the sense of hearing is much more absolute. In fact, there are those who have perfect pitch while there is no such thing as perfect vision! I'm already prepared for the responses on this one ;-)

On the other hand, our vision is excellent as a comparing tool, so we establish standard viewing conditions that don't distort color on their own, then we compare and finally decide if what we got is pleasing. Sometimes, matching an original is the wrong thing to do, but we should at least know that we're not.

john castronovo


Date: Sat, 30 Nov 2002 10:33:00 -0800
From: Stuart Larson
Subject: Re: Standard color

john c. wrote:

> By comparison, the
> sense of hearing is much more absolute. In fact, there are those who have
> perfect pitch while there is no such thing as perfect vision!

This is not a good analogy. Perfect pitch is the ability to recognize or play a specific musical note without hearing a reference note. It has little, if anything, to do with hearing.


Date: Sat, 30 Nov 2002 17:17:53 -0500
From: John Castronovo
Subject: Re: Standard color

From: "Stuart Larson

> This is not a good analogy. Perfect pitch is the ability to recognize
> or play a specific musical note without hearing a reference note. It
> has little, if anything, to do with hearing.

My point is that we don't have the ability to remember or identify color the way we do other senses. Color vision is a comparative sense more than an absolute one. While I don't have perfect pitch, I can hum a note of my choice without a reference and be within a few cycles of the correct pitch. Many people would be able to with little or no training. There's nothing like that in vision. We might think we know what the color pink is, but change the room light or the surroundings and we're way off. Optical illusions showing this effect abound. Without the ability to measure and standardize we're dead in the water in the reproduction business.

john castronovo

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