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digitaldog

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« Reply #20 on: September 04, 2009, 01:45:40 pm »

Quote from: James R
Cut him a break.  Brightness is perceived not measured.  Reducing luminance gave him the perception that the LCD was less bright.  The results are the same, his prints were spot on.   Nothing about the monitor affects the print; but, it can affect how we adjust the image file, which has an effect on the print.  Isn't that why one should make image adjustments on a properly calibrated monitor?

No, Luminance, which is what we set is not brightness! Luminosity is a measure of the total radiant energy from a body. It has nothing to do with what a human observer perceives but rather describes the total radiant energy, such as watts/second of a source (the surface of a radiating object like a display).  So what values is he describing other than the luminance values of the target he's supposedly calibrating to with said software?

Lightness is a perceptually scaled component of color, the axis seen in Lab (Lstar) from light to dark. It IS the L in HSL.
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« Reply #21 on: September 04, 2009, 01:49:01 pm »

Quote from: JeffKohn
He didn't say anything about cd/m2, at least not in the quote above. I would assume  that the 98/47 numbers are the numeric brightness setting of his LCD, probably on a scale that goes to 100.

That's possible but it would be far more useful to supply actual target calibration aim points using cd/m2 since the scale of the buttons on a display are meaningless.
Quote
If I had to work on a display calibrated to 150 or even 120 cd/m2, it wouldn't just make getting a match with prints more difficult - it would make me miserable due to the eye strain.

All depends on the viewing booth. On my GTI booth, dimmed to 50%, I'm getting screen to print matching with a target calibration of 150cd/m2. I could lower the booth (and the display) but with at least this unit, going below about 120cd/m2 introduces the dimming in the panel and not via the actual Fluorescent backlight. And no eyestrain here.
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James R

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« Reply #22 on: September 04, 2009, 02:20:40 pm »

Quote from: digitaldog
No, Luminance, which is what we set is not brightness! Luminosity is a measure of the total radiant energy from a body. It has nothing to do with what a human observer perceives but rather describes the total radiant energy, such as watts/second of a source (the surface of a radiating object like a display).  So what values is he describing other than the luminance values of the target he's supposedly calibrating to with said software?

Lightness is a perceptually scaled component of color, the axis seen in Lab (Lstar) from light to dark. It IS the L in HSL.

I believe you are taking this too far for the average or above average photographer, without a PHD in the related field.  I understand luminance as a measure of the visual perceived brightness of an object.  Here is abstract from a paper  written by 3 medical doctors/researchers:

"Brightness—the perception of an object's luminance—arises from complex and poorly understood interactions at several levels of processing1. It is well known that the brightness of an object depends on its spatial context2, which can include perceptual organization3, scene interpretation4, three-dimensional interpretation5, shadows6, and other high-level percepts. Here we present a new class of illusion in which temporal relations with spatially neighbouring objects can modulate a target object's brightness. When compared with a nearby patch of constant luminance, a brief flash appears brighter with increasing onset asynchrony. Simultaneous contrast, retinal effects, masking, apparent motion and attentional effects cannot account for this illusory enhancement of brightness. This temporal context effect indicates that two parallel streams—one adapting and one non-adapting—encode brightness in the visual cortex."

I guess this clears it up.  Life is too short, I'll continue using the definition I was given years ago.
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digitaldog

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« Reply #23 on: September 04, 2009, 02:23:27 pm »

Quote from: James R
I guess this clears it up.  Life is too short, I'll continue using the definition I was given years ago.

Brightness SEE:
http://www.crompton.com/wa3dsp/light/lumin.html

A photometer and a pilot's eyes are receiving light from the same point on a display' s screen ( SEE cover photo). Measuring the luminance of the light from that point is straightforward and highly repeatable We can go a step further and take a second measurement at a different point on the screen. We can then calculate the contrast between the two points. The pilot's perception of brightness, however, is complicated by human visual phenomena such as time-dependent light and dark adaptation, simultaneous contrast, lateral inhibition (Mach effect), dazzle (contrast overload), and color. The pilot's perception of display contrast is intimately related to his perception of brightness .

The concept that is now known as "luminance " was for many years designated by the term "brightness. " This led to much confusion between the objective concept of "brightness" as intensity per unit of projected area, and' the subjective concept of "brightness" which referred to a sensation in the consciousness of a human observer. The newer term "luminance" was adopted to avoid this confusion. - from Optics by Francis Weston Sears (Addison-Wesley, 1949)

Is there enough of a difference between luminance and brightness to justify the distinction? Has there ever been a case where a display had an incorrect specification, didn't perform properly, or cost too much because somebody said "brightness" when he or she should have said "luminance"? Many professionals in the display community say that they say "brightness" because many people don't know what "luminance" is. But to believe that the words brightness and luminance are essentially interchangeable ignores the clear distinction in the definitions of these two words, and the differing realities behind the words. If the luminance of a viewed light source is increased 10 times, viewers do not judge that the brightness has increased 10 times. The relationship is, in fact, logarithmic: the sensitivity of the eye decreases rapidly as the luminance of the source increases. It is this characteristic that allows the human eye to operate over such an extremely wide range of light levels ( SEE Fig. 4).

Also see:http://en.wikipedia.org/wiki/White%27s_illusion
White's illusion is an optical illusion illustrating the fact that the same target luminance can elicit different perceptions of brightness in different contexts.Brightness (also called effulgence) is an attribute of visual perception in which a source appears to emit a given amount of light. In other words, brightness is the perception elicited by the luminance of a visual target. This is a subjective attribute/property of an object being observed.

As the Chinese proverb says: The first step towards genius is calling things by their proper name.
« Last Edit: September 04, 2009, 02:24:11 pm by digitaldog »
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« Reply #24 on: September 04, 2009, 04:53:02 pm »

Quote from: James R
Cut him a break.

The results are the same, his prints were spot on.

How can this be so? His post is so confusing as he first writes:
Quote
I’ve been profiling with the EyeOne for years now and it always did a great job. It always set my 21UXs brightness near the max though which always bugged me, but the color was for the most part spot on.

Then after dialing down the Luminance he says:
Quote
OK, I’ll process a new file from NEF to 24×30 print using my usual workflow. If the Munki is right, the print will be spot on. If my logic is right, the print will be dark. My jaw hit the floor as the print coming out of the Epson 7900 (great printer!) was spot on! Damn, it was gorgeous!

Can this be explained?
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« Reply #25 on: September 04, 2009, 05:42:51 pm »

Quote from: digitaldog
Brightness SEE:
http://www.crompton.com/wa3dsp/light/lumin.html

A photometer and a pilot's eyes are receiving light from the same point on a display' s screen ( SEE cover photo). Measuring the luminance of the light from that point is straightforward and highly repeatable We can go a step further and take a second measurement at a different point on the screen. We can then calculate the contrast between the two points. The pilot's perception of brightness, however, is complicated by human visual phenomena such as time-dependent light and dark adaptation, simultaneous contrast, lateral inhibition (Mach effect), dazzle (contrast overload), and color. The pilot's perception of display contrast is intimately related to his perception of brightness .

The concept that is now known as "luminance " was for many years designated by the term "brightness. " This led to much confusion between the objective concept of "brightness" as intensity per unit of projected area, and' the subjective concept of "brightness" which referred to a sensation in the consciousness of a human observer. The newer term "luminance" was adopted to avoid this confusion. - from Optics by Francis Weston Sears (Addison-Wesley, 1949)

Is there enough of a difference between luminance and brightness to justify the distinction? Has there ever been a case where a display had an incorrect specification, didn't perform properly, or cost too much because somebody said "brightness" when he or she should have said "luminance"? Many professionals in the display community say that they say "brightness" because many people don't know what "luminance" is. But to believe that the words brightness and luminance are essentially interchangeable ignores the clear distinction in the definitions of these two words, and the differing realities behind the words. If the luminance of a viewed light source is increased 10 times, viewers do not judge that the brightness has increased 10 times. The relationship is, in fact, logarithmic: the sensitivity of the eye decreases rapidly as the luminance of the source increases. It is this characteristic that allows the human eye to operate over such an extremely wide range of light levels ( SEE Fig. 4).

Also see:http://en.wikipedia.org/wiki/White%27s_illusion
White's illusion is an optical illusion illustrating the fact that the same target luminance can elicit different perceptions of brightness in different contexts.Brightness (also called effulgence) is an attribute of visual perception in which a source appears to emit a given amount of light. In other words, brightness is the perception elicited by the luminance of a visual target. This is a subjective attribute/property of an object being observed.

As the Chinese proverb says: The first step towards genius is calling things by their proper name.

I thought we had agreement. Life is easier knowing that there are many factors that effect one's perception of brightness, but, not needing to dissect the factors every time you talk about a monitor's brightness. A reality check is needed before criticizing a photographer for not understanding the science or finding it necessary to explain the science behind the subject.  Surprisingly, most photographers take pictures and leave the science to others.  I don't think science motivates people to read photographer's blogs.  They just want to learn how to take better pictures.  

We can agree upon one thing, this dead horse has been beat enough.
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digitaldog

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« Reply #26 on: September 04, 2009, 05:53:26 pm »

Quote from: James R
I thought we had agreement.

We agree that Brightness is a perceptual human visual phenomena, I'm not sure we agree that Luminance is a different term and condition. The two are not the same.

Quote
A reality check is needed before criticizing a photographer for not understanding the science or finding it necessary to explain the science behind the subject.

Who criticized who for what? I'm not at all sure what Moose is saying, its very unclear, down to the values he's talking about (one could reasonably assume 98 is 98cd/m2 but again, the copy of the blog is so unclear, I'm not sure what his point is). If someone can clarify this, great. If there is criticism, its only due to a lack of proper communication. Considering how many people find the task of properly calibrating their LCD displays (my prints are too dark), what values to hit and why, I think its a disservice to muck up the discussion with blog posts like this.
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« Reply #27 on: September 04, 2009, 06:45:45 pm »

Quote from: digitaldog
We agree that Brightness is a perceptual human visual phenomena, I'm not sure we agree that Luminance is a different term and condition. The two are not the same.



Who criticized who for what? I'm not at all sure what Moose is saying, its very unclear, down to the values he's talking about (one could reasonably assume 98 is 98cd/m2 but again, the copy of the blog is so unclear, I'm not sure what his point is). If someone can clarify this, great. If there is criticism, its only due to a lack of proper communication. Considering how many people find the task of properly calibrating their LCD displays (my prints are too dark), what values to hit and why, I think its a disservice to muck up the discussion with blog posts like this.

My understanding is luminance is one factor that can affect one's perception of brightness.  Guess I need to go back and read your book, it does sits near my computer.  BTW, I read Moose's comment with an assumption of his intent, not as a learning opportunity.  

Thanks for taking the time to discuss this topic.
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