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Author Topic: Profiling Monitor  (Read 12131 times)
digitaldog
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« Reply #40 on: June 01, 2010, 11:26:57 AM »
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In addition to device-dependent color spaces, there are also device- independent color spaces. These color spaces encompass all of human vision. The most common is called CIELAB (or L*a*b; often written as LAB, although technically the * should be used). Back in 1931, the CIE (Commission Internationale de L’Éclairage, also known as International Commission on Illumination), a group or color scientists, conducted a series of experiments and tests on humans to determine how they perceive color. The tests involved showing groups of volunteers a sample color under very controlled conditions whereby each subject adjusted the intensity of red, green, and blue lights until the mix of the three matched the sample color. This allowed the CIE to specify precisely the stimulus response of the human eye.
The CIE came up with the term standard observer to describe a hypothetical average human viewer and his or her response to color. Furthermore, the results of these tests produced a mathematical model of a color space formulated not on any real-world device, but rather on how we humans (the standard observer) actually perceive color. This core color model is called CIE XYZ (1931). This is the color model from which all other device-independent color models are created. Like the RGB color model with three additive primaries, CIE XYZ uses three spectrally defined imaginary primaries: X, Y, and Z. These X, Y, and Z primaries may be combined to describe all colors visible to the standard observer. Also in 1931, a synthetic space called CIE xyY was created, which itself is derived from CIE XYZ. In 1976, CIELAB and CIELUV were added to the mix of these device-independent color spaces. The CIELAB color space is a synthetic, theoretical color space derived from XYZ. Unlike the original, CIELAB has the advantage of being perceptually uniform (sort of . . .). That simply means that a move of equal value in any direction at any point within the color space produces a similar perceived change to the standard observer.
The XYZ color space is based on three quantities or stimuli. The geek term for describing this is tristimulus values (three stimuli). Technically the term tristimulus values refers to the XYZ values of the original CIE XYZ color model although you will often hear people describe tristimulus values when defining a color in RGB or CMY (or using any three values). This is incorrect. Since our aim is to keep the color-geek-speak to a minimum, it’s not important to know the differences in the various CIE constructed color models, but rather to recognize that a color space such as CIELAB is based on how we see color. What you should keep in mind here is that using a set of three values, any color can be specified exactly and mapped in three-dimensional space to show its location in reference to all other colors. This can be useful! There are no capture or output devices that directly reproduce CIELAB; however, this color space allows us to translate any color from one device to another.


Chromaticity Values and the Chromaticity Diagram: The CIE XYZ color space represents color using three imaginary primaries defined as X,Y, and Z—imaginary because the color of these primaries doesn’t correspond to a real-world light source. This is a three-dimensional color space. The CIE also defined a method in which chromaticity can be plotted in two dimensions (x,y). In this color space, the third component is luminance (Y). They named this CIE xyY. This color space allows you to plot hue and saturation, independent of luminance, two- dimensionally on a two-dimensional graph called the CIE Chromaticity Diagram. The x and y values used to plot a color on this diagram are referred to as the chromaticity coor- dinates or sometimes, chromaticity values.

IF you look closely at the diagram in the article, around the horseshoe shaped plot, you’ll see numeric values which are the range of frequencies from approximately 400nm to 700nm that is visible to the eye.
« Last Edit: June 01, 2010, 11:28:04 AM by digitaldog » Logged

Andrew Rodney
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« Reply #41 on: June 01, 2010, 12:28:53 PM »
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Quote from: digitaldog
IF you look closely at the diagram in the article, around the horseshoe shaped plot, you’ll see numeric values which are the range of frequencies from approximately 400nm to 700nm that is visible to the eye.
Thanks for the explanation, but I still don't see how those values relate to the XY scale and I am still totally confused how you plotted the black body and the corresponding Kelvin lines on the chart.
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digitaldog
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« Reply #42 on: June 01, 2010, 12:33:36 PM »
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Quote from: MarkPaulson
Thanks for the explanation, but I still don't see how those values relate to the XY scale and I am still totally confused how you plotted the black body and the corresponding Kelvin lines on the chart.

http://en.wikipedia.org/wiki/Black_body

Knock yourself out with any or all equations.
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Andrew Rodney
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« Reply #43 on: June 01, 2010, 01:55:21 PM »
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Quote from: digitaldog
http://en.wikipedia.org/wiki/Black_body

Knock yourself out with any or all equations.
Thanks for you patience, that answers my questions.

Mark
« Last Edit: June 03, 2010, 08:39:12 PM by MarkPaulson » Logged
BobFisher
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« Reply #44 on: June 03, 2010, 08:02:07 PM »
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BobD, how can you adjust the viewing conditions of your prints at your site to mimic the conditions under which the prints will be viewed?  Unless you're hanging them in your own house/office or know precisely what the conditions are, it's not possible.  We have no idea under what conditions someone who buys a print will be displaying it.  At least not in the majority of cases.  The best we can do then is get the best possible result in 'ideal' conditions and not worry about it after that.  No?
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BobD
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« Reply #45 on: June 06, 2010, 09:09:52 PM »
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Quote from: BobFisher
BobD, how can you adjust the viewing conditions of your prints at your site to mimic the conditions under which the prints will be viewed?  Unless you're hanging them in your own house/office or know precisely what the conditions are, it's not possible.  We have no idea under what conditions someone who buys a print will be displaying it.  At least not in the majority of cases.  The best we can do then is get the best possible result in 'ideal' conditions and not worry about it after that.  No?
Bob F:
I think I said “I try to match the brightness of the light in which the prints are to be hung.  If I don’t know the brightness of the “hanging light” then I try to attain a brightness of 250–300 lux (using the ColorMunki).
Granted it is not always possible to know the final hanging light brightness but when I am printing for a controlled hanging area like a corporate space, I will take my Munki to get an indication of the brightness.

I also said “…most people try make monitor adjustments and print evaluation in the same room under the same light brightness.
I think a general statement can be made that it is better to evaluate prints with a light duller than the hanging light.  If your print evaluation light is too bright then your prints will lose shadow detail when viewed in a duller light.

Also, let’s not lose sight of the prize here – a good photograph is more important than exactly matching evaluation and hanging light. Remember doubling the viewing light from 250 to 500 lux is only one stop and it can only help to show more shadow detail in the print.
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neil snape
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« Reply #46 on: June 07, 2010, 12:46:45 AM »
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I only red the last few posts. If I can add the fact the middle to high brightness retains a fairly constant appearance ,  whereas in low brightness it no longer holds true.

I am not saying at 300 lux, but just wanted to point out predicting print matching becomes iffy at low brightness and is outside of the viewing model of ICC profiles intentions. The more stable the colorants/pigments are the better the consistency will be in variable lighting scenarios.

I do agree if you can at least lower the viewing lights in the proofing station you'll be closer to the possible match. If you can use similar lights the same will also help or be as close as possible to the display conditions.

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digitaldog
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« Reply #47 on: June 07, 2010, 07:35:23 AM »
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Quote from: BobFisher
BobD, how can you adjust the viewing conditions of your prints at your site to mimic the conditions under which the prints will be viewed?  Unless you're hanging them in your own house/office or know precisely what the conditions are, it's not possible.

Its even less complex than that. You only need to match the luminance of the display to the luminance of the viewing conditions next to it. If the print is hanging in a different room, if that room is 20 feet or 20 miles away, the display is out of the equation.

You can adjust the white point of prints (the print ICC profile) to that of the print viewing conditions (a gallery) but this has nothing to do with the print to display match.
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Andrew Rodney
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walter.sk
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« Reply #48 on: June 07, 2010, 10:19:28 AM »
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Quote from: digitaldog
You can adjust the white point of prints (the print ICC profile) to that of the print viewing conditions (a gallery) but this has nothing to do with the print to display match.

Thank you, Andrew.  This statement brings us back to what I understand as the main reason for softproofing, calibration and profiling in the first place, which seems to get lost in all of the discussion:

Unless you have a consistent way of viewing what is on screen and comparing it to what is on your print, in your studio or workroom, *you don't know how to adjust the color and tone of the image you are working on.*


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