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Author Topic: Pantone Huey for monitor calibration?  (Read 21103 times)
opgr
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« Reply #20 on: May 15, 2006, 08:33:31 AM »
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If we were referring to a true black body then yes, that point would be an exact point on the plankian radiator curve. Since virtually no device behaves this way, using CCT 6500K we define is a range of colors running perpendicular to that black body curve; the lines of correlated temperature. By using CCT, as you point out, I'm referring to a point on that line (the exact point isn't defined). But clearly one point on either end of that line of correlated color tempature isn't the same color of white. The illustration from the book is enclosed.

Nope, you're using reversed logic. The entire point of the exercise is exactly that: matching a light-source to its equivalent color-temperature. The color-temperature BY DEFINITION is ON the planckian locus.

The lines you call "lines of correlated temperature" are usually referred to as "iso-temperature" lines.

A CCT is not somewhere on these "iso-temperature lines", it is the exact point where the iso-temperature line crosses the planckian locus.
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« Reply #21 on: May 15, 2006, 08:50:14 AM »
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A CCT is not somewhere on these "iso-temperature lines", it is the exact point where the iso-temperature line crosses the planckian locus.
[a href=\"index.php?act=findpost&pid=65519\"][{POST_SNAPBACK}][/a]

Yes, agreed. The point is the exact color, no question. The question becomes, when a software product (or a color meter as an example) tells us we have 6500K, WHERE on that line does the point lie? If we get the chromaticity values, this is now defined. Without, it's a *possible* range of colors. My terminology (CCT6500 is a range of colors) wasn't well written.
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Andrew Rodney
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« Reply #22 on: May 15, 2006, 10:13:37 AM »
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when a software product (or a color meter as an example) tells us we have 6500K, WHERE on that line does the point lie?

I'm with you on that one. I would very much like the software to give me 2 options:
1. Use Exact Color, or
2. Use Daylight Equivalent (which for all practical purposes is the CCT).

That way I can measure my viewing-booth lights and be assured the software uses the exact color of the lights as opposed to using some daylight equivalent which most likely doesn't match the color of the viewing booth lights.

I presume this is what you are referring to?
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« Reply #23 on: May 15, 2006, 10:21:33 AM »
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I'm with you on that one. I would very much like the software to give me 2 options:
1. Use Exact Color, or
2. Use Daylight Equivalent (which for all practical purposes is the CCT).

That way I can measure my viewing-booth lights and be assured the software uses the exact color of the lights as opposed to using some daylight equivalent which most likely doesn't match the color of the viewing booth lights.

I presume this is what you are referring to?
[a href=\"index.php?act=findpost&pid=65541\"][{POST_SNAPBACK}][/a]

I don't know that we'll ever see this in the huey software (nor is it really appropriate for this audience). In Eye-One Match, you can specify any xy chromaticity values but I wonder how many users would do this. You can measure the light box/viewing conditions and build that into the profile in Eye-One Match and ProfileMaker Pro. For the later, it's a pretty serious audience so it's a good feature to have.
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Andrew Rodney
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Hermie
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« Reply #24 on: May 15, 2006, 01:49:09 PM »
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For those who want to read more about color temperature, see Doug Kerr's excellent article: http://doug.kerr.home.att.net/pumpkin/Color_Temperature.pdf

Herman
« Last Edit: May 15, 2006, 01:50:06 PM by Hermie » Logged
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« Reply #25 on: May 15, 2006, 02:05:18 PM »
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For those who want to read more about color temperature, see Doug Kerr's excellent article: http://doug.kerr.home.att.net/pumpkin/Color_Temperature.pdf

Herman
[a href=\"index.php?act=findpost&pid=65563\"][{POST_SNAPBACK}][/a]

Doug's articles are excellent (does he hang here?).

The part to zoom in on (in relation to this discussion):

"Does every chromaticity have a color temperature? Strictly speaking,
no. Only chromaticities falling on the Planckian locus (chromaticities
that could actually be emitted by a blackbody radiator) have true color
temperatures.
However, for chromaticities falling near the locus, but not on it, we
may usefully state a related property called the “correlated color
temperature”. This is the color temperature of the point on the
blackbody locus that is “closest in appearance” (chromaticity-wise) to
the chromaticity of interest".

Karl Lang (my tech editor) is even more 'brutal" when speaking of color temperature expressed in Kelvin/CCT. He calls it an "obsolete method of defining white illuminants"
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« Reply #26 on: May 15, 2006, 02:20:07 PM »
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> (does he hang here?)

Formerly RG I believe.
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« Reply #27 on: May 15, 2006, 03:44:45 PM »
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I don't know that we'll ever see this in the huey software (nor is it really appropriate for this audience). In Eye-One Match, you can specify any xy chromaticity values but I wonder how many users would do this. You can measure the light box/viewing conditions and build that into the profile in Eye-One Match and ProfileMaker Pro. For the later, it's a pretty serious audience so it's a good feature to have.
Here's what I want:

We already have monitors with adaptive lighting tech. Why not combine that with adaptive profiles, based on live measurement of the ambient light?
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« Reply #28 on: May 15, 2006, 09:45:31 PM »
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For those who want to read more about color temperature, see Doug Kerr's excellent article: http://doug.kerr.home.att.net/pumpkin/Color_Temperature.pdf

Herman
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Thanks for the link. It all makes sense now.

So to set a D65 when it's not explicitely available I can put  x0.3127   y0.3290 from what I understand (not in Huey obviously). I was wondering why I get a closer match in two monitors when I target xy values rather that the K number. Excellent. I guess D stands for daylight and it's on a daylight locus and not on a blackbody locus.

I suppose I can just forget the reciprocal megakelvin part...
« Last Edit: May 15, 2006, 10:08:16 PM by Serge Cashman » Logged
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« Reply #29 on: May 16, 2006, 02:04:32 AM »
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Optix XR Pro software lets the user choose either between 6500K or D65. Which one should I be using?
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« Reply #30 on: May 16, 2006, 07:41:20 AM »
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Thanks for the link. It all makes sense now.

So to set a D65 when it's not explicitely available I can put  x0.3127   y0.3290 from what I understand (not in Huey obviously). I was wondering why I get a closer match in two monitors when I target xy values rather that the K number. Excellent.[a href=\"index.php?act=findpost&pid=65613\"][{POST_SNAPBACK}][/a]

Not sure. The idea is first of all, when a software product asks for D65 versus 6500K, at least with D65, we know what illuminant it's aiming for.

Getting two monitors to match would involve not only aiming for the white point but also the luminance. You need to measure both and set them the same.
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« Reply #31 on: May 16, 2006, 10:58:57 AM »
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Getting two monitors to match would involve not only aiming for the white point but also the luminance. You need to measure both and set them the same.
[a href=\"index.php?act=findpost&pid=65641\"][{POST_SNAPBACK}][/a]
I know that.

x0.3127 y0.3290 are the coordinates for D65, aren't they? Is there another component to it?

From what I understand D65 is a better choice because it gives you more consistent results - it attempts to achieve the same chromaticity ("color" minus luminance) of white. While 6500K allowes many different chromaticities that are on 6500K "iso-temperature line" if I understand it correctly. D65 is one of the points on that line so if you aim for it every time you calibrate the results are more consistent.

<edited by poster>  Just wanted to make a note that later in this thread the above paragraph about D65 and 6500K as targets is proven to be completely wrong.
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« Reply #32 on: May 16, 2006, 11:06:24 AM »
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From what I understand D65 is a better choice because it gives you more consistent results - it attempts to achieve the same chromaticity ("color" minus luminance) of white. While 6500K allowes many different chromaticities that are on 6500K "iso-temperature line" if I understand it correctly.
[a href=\"index.php?act=findpost&pid=65681\"][{POST_SNAPBACK}][/a]

That's my take on it.
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Andrew Rodney
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« Reply #33 on: May 16, 2006, 11:09:08 AM »
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That's my take on it.
[a href=\"index.php?act=findpost&pid=65682\"][{POST_SNAPBACK}][/a]
That's what you said the first time, actually. But it was hard to understand without further reading...
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« Reply #34 on: May 16, 2006, 12:27:30 PM »
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While 6500K allowes many different chromaticities that are on 6500K "iso-temperature line"

There is no ambiguity in using 6500K as a data entry. The ambiguity arises when you tell software to calibrate a monitor to native white and it returns for example 5500K as the CCT. In this particular case the question becomes whether the software will use the actual color (thus R=G=B=max for white), or the true Blackbody co-ordinates for 5500K (thus max RGB will be adjusted).

If you are requested to enter a temperature as is then there is no such ambiguity because the software will use the exact blackbody co-ordinates. The difference between blackbody co-ordinates (the planckian locus) and daylight co-ordinates is negligible for practical purposes. So D65 and 6500K are practically identical.
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« Reply #35 on: May 16, 2006, 12:53:08 PM »
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Let's defer to an excellent post by Bruce Lindbloom (with permission I  quoted this in my book and point e is of interest in the context of our discussions):

a) D65 is a spectral power distribution (a certain amount of energy at each wavelength across the visible spectrum).
 D65 is a tristimulus value; the D65 spectrum, when viewed by the CIE standard observer, produces an XYZ triplet (or xyY if you prefer).
c) 6500K blackbody radiator is a spectral power distribution.
d) 6500K is blackbody tristimulus value; the 6500K blackbody spectrum, when viewed by the CIE standard observer, produces an XYZ triplet—similar to, but slightly different from, the one found in (.
e) Correlated color temperature takes a color's chromaticity coordinate (x,y) and finds the particular blackbody temperature whose chromaticity coordinate (d) is closest to it. Note that there are many different colors that have the same correlated color temperature. So a spectrum is very precise and unique. Its xyY is less precise and unique. Its CCT is even less precise and unique.
D65 is a unique SPD (there exists only one). A color whose CCT is 6500K is not unique (there are infinitely many different xyY and SPDs that share it).
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« Reply #36 on: May 16, 2006, 02:23:07 PM »
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x0.3127 y0.3290 are the coordinates for D65, aren't they? Is there another component to it?

Looks like it yes. Optix XR Pro shows x=.313 and y=.329 and a CCT of 6504.
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« Reply #37 on: May 16, 2006, 02:35:14 PM »
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x0.3127 y0.3290 are the coordinates for D65, aren't they? Is there another component to it?

You'll find the same chromaticity values for all the working space white points defined as D65 as well in Photoshop's custom RGB dialog (select sRGB, Adobe RGB etc).
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Andrew Rodney
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« Reply #38 on: May 16, 2006, 04:52:46 PM »
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There is no ambiguity in using 6500K as a data entry. ...
[{POST_SNAPBACK}][/a]

Do you mean to say that 6500K as a calibration target actually specifies the coordinates of the blackbody 6500K, as a point on the planckian (blackbody) locus? Spyder2 Pro specifies it's coordinates as x0.314 y0.324 for instance. Not the same as D65 but  a close point. I can't tell how close and if it's perceptibly different.

But in that case using either one as a target is OK I guess. In that case I suppose the only difference is if it's a point on a blackbody or a daylight locus  (on the intersection with a 6500K iso-temperature line). If it's negligible for practical purposes (like Oscar said)  you can use either one.

<edit> OK, here's from Colorvision's website, don't know if others use the same exact coordinates. So both are used as points it seems:
"...6500K is 0.314, 0.324 CIExy and D65 is 0.313, 0.329 CIExy..."
[a href=\"http://support.colorvision.ch/index.php?_m=knowledgebase&_a=viewarticle&kbarticleid=385&nav=0,16]http://support.colorvision.ch/index.php?_m...id=385&nav=0,16[/url]
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« Reply #39 on: May 17, 2006, 03:39:45 AM »
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Do you mean to say that 6500K as a calibration target actually specifies the coordinates of the blackbody 6500K, as a point on the planckian (blackbody) locus?

Yes, that is correct.

The daylight co-ordinates are positioned slightly above the planckian locus in the xy diagram, which means you should expect a slightly higher y value for daylight.

Would you see the difference between D65 and 6500K? Yes and no.

Yes, because it really is a 10 degree observer problem as opposed to the usual 2 degree observer upon which most theory and calculations are based. In addition it is on the neutral axis. We are extremely sensitive to comparative differences in the conditions above.

However, no, because there is no comparative difference. Your screen is either set to one or the other and you will immediately chromatically adapt to the difference. Even if there is something like an absolute perception, as a hypothetical equivalent to absolute hearing, you would not be able to discern the difference temporally.

More over, it is my experience that the stability of the measurement device in combination with the stability of LCD near white is simply not precise enough to measure the differences required to find the exact white point. This may explain why you get better results with one value as opposed to the other. The minute difference between the target whites may give a relatively significant difference in the graybalance after calibration.

With this in mind I would advice the following:

If you have a choice between D65 or 6500K, use the value that gives you the most pleasing, stable, and or comfortable result subjectively.

Have a slight preference for D numbers, because the ICC internals may have fixed values for these. For example, the ICC internals are based on a fixed D50 illuminant. Providing the exact same values for your device white will allow a CMM to skip Chromatic Adaptation calculations.

PS. The "experience" mentioned above is based on the original i1-display and relatively old LCD technology. The results may be different for a quality colori/spectrometer and a state-of-the-art, high-end eizo for example.
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