Light Return. Is maximization really the answer?

[Karl_K]

Date: 5/8/2010 10:18:33 AM
Author: oldminer
If one is going to ''measure'' light return and light performance, one must uise a tool which is sensitive over the entire potential range of light return, from total dark to maximum concentrated light. In order to do this, one must use only enough light that no matter how much is refracted and concentrated back to the measuring sensor, that the sensor will not become overexposed and beyond its capacity to measure the amount of returning light. This means then that the lighting used to measure the effectiveness of cut cannot be super strong as the maximum returned must not exceed the ability fo the measuring sensor to differentiate that maximum from amounts below the maximum amount. Too much light used will make less than a maximum return potentially measure the identically as a greater amount returned to the sensor. Overwhelming the measuring sensor leads to improper assessment of the effectiveness of the cut and the light return.


Selecting a proper standardized lighting environment is critical to making such assessments in a repeatable and meaningful way. Using strong lighting which blows out the ability of the sensor to discriminate at the top end will create errors in which diamond cut has the greatest light return capability. The greatest light return capability does not automatically equate to the best cut or the best diamond. But, it is a solid, objective measure, which can be counted on when a grading scale is created based on human preferences.

measuring the light is not a huge issue.
The issue with any machine that says it measures diamond performance is the type of lighting.
diffused lighting? Many small light points? A mix of the 2? How much of a mix? Maybe a white dome with some black? maybe a 2 colored dome? 3 colored? 10 colored? back light?
Which is the right lighting to use?
There are literally millions of different lighting conditions in the real world.
Any diamond will have different looks to some degree in each of those lighting conditions.
In which one should diamond light performance be measured?

 

[Serg]

Date: 5/8/2010 10:18:33 AM
Author: oldminer
If one is going to ''measure'' light return and light performance, one must uise a tool which is sensitive over the entire potential range of light return, from total dark to maximum concentrated light. In order to do this, one must use only enough light that no matter how much is refracted and concentrated back to the measuring sensor, that the sensor will not become overexposed and beyond its capacity to measure the amount of returning light. This means then that the lighting used to measure the effectiveness of cut cannot be super strong as the maximum returned must not exceed the ability fo the measuring sensor to differentiate that maximum from amounts below the maximum amount. Too much light used will make less than a maximum return potentially measure the identically as a greater amount returned to the sensor. Overwhelming the measuring sensor leads to improper assessment of the effectiveness of the cut and the light return.


Selecting a proper standardized lighting environment is critical to making such assessments in a repeatable and meaningful way. Using strong lighting which blows out the ability of the sensor to discriminate at the top end will create errors in which diamond cut has the greatest light return capability. The greatest light return capability does not automatically equate to the best cut or the best diamond. But, it is a solid, objective measure, which can be counted on when a grading scale is created based on human preferences.

Dave,

re:In order to do this, one must use only enough light that no matter how much is refracted and concentrated back to the measuring sensor, that the sensor will not become overexposed and beyond its capacity to measure the amount of returning light. This means then that the lighting used to measure the effectiveness of cut cannot be super strong as the maximum returned must not exceed the ability fo the measuring sensor to differentiate that maximum from amounts below the maximum amount.

You can work with very big range brightness for lights source during direct measurement
you can use any standard light for direct measurement without problem with overexposed sensor ( blooming )
you need use very old idea HDRI( high dynamic range imaging)

"In image processing, computer graphics, and photography, high dynamic range imaging (HDRI or just HDR) is a set of techniques that allow a greater dynamic range of luminances between the lightest and darkest areas of an image than standard digital imaging techniques or photographic methods. This wider dynamic range allows HDR images to more accurately represent the wide range of intensity levels found in real scenes, ranging from direct sunlight to faint starlight.[1]"



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


History of HDR photography

[edit]1850
The idea of using several exposures to fix a too-extreme range of luminance was pioneered as early as the 1850s by Gustave Le Gray to render seascapes showing both the sky and the sea. Such rendering was impossible at the time using standard techniques, the luminosity range being too extreme. Le Gray used one negative for the sky, and another one with a longer exposure for the sea, and combined the two in a single picture in positive.[15]
[edit]1930
High dynamic range imaging was originally developed in the 1930s and 1940s by Charles Wyckoff. Wyckoff''s detailed pictures of nuclear explosions appeared on the cover of Life magazine in the mid 1940s. Wyckoff implemented local neighborhood tone remapping to combine differently exposed film layers into one single image of greater dynamic range.
[edit]1980
The desirability of HDR has been recognized for decades, but its wider usage was, until quite recently, precluded by the limitations imposed by the available computer processing power. Probably the first practical application of HDRI was by the movie industry in late 1980s and, in 1985, Gregory Ward created the Radiance RGBE image file format which was the first (and still the most commonly used) HDR imaging file format.
Wyckoff''s concept of neighborhood tone mapping was applied to video cameras by a group from the Technion in Israel led by Prof. Y.Y.Zeevi who filed for a patent on this concept in 1988.[16] In 1993 the first commercial medical camera was introduced that performed real time capturing of multiple images with different exposures, and producing an HDR video image.[17]
Modern HDR imaging uses a completely different approach, based on making a high-dynamic range luminance or light map using only global image operations (across the entire image), and then tone mapping this result. Global HDR was first introduced in 1993[18] resulting in a mathematical theory of differently exposed pictures of the same subject matter that was published in 1995 by Steve Mann and Rosalind Picard.[19] In 1997 this global-HDR technique of combining several differently exposed images to produce a single HDR image was presented to the computer graphics community by Paul Debevec.
This method was developed to produce a high dynamic range image from a set of photographs taken with a range of exposures. With the rising popularity of digital cameras and easy-to-use desktop software, the term HDR is now popularly used to refer to this process. This composite technique is different from (and may be of lesser or greater quality than) the production of an image from a single exposure of a sensor that has a native high dynamic range. Tone mapping is also used to display HDR images on devices with a low native dynamic range, such as a computer screen.
[edit]1996
Steve Mann developed and patented the global-HDR method for producing digital images having extended dynamic range at the MIT Media Laboratory.[20] Mann''s method involved a two-step procedure: (1) generate a single floating point image array by global-only image operations (operations that affect all pixels identically, without regard to their local neighborhoods); and then (2) convert this image array, using local neighborhood processing (tone-remapping, etc.), into an HDR image. The image array generated by the first step of Mann''s process is called a "lightspace image", "lightspace picture", or "radiance map". Another benefit of global-HDR imaging is that it provides access to the intermediate light or radiance map, which has been used for computer vision, and other image processing operations[20].
[edit]1997
In 1997 this technique of combining several differently exposed images to produce a single HDR image was presented to the public by Paul Debevec.
[edit]2005
Photoshop CS2 introduced the Merge to HDR functio

 

[oldminer]

Would you commit yourself to using HDRI, a complex tool, or do you possibly agree that a simpler possibly more practical everyday solution is to just use sufficent lighting to always be able to measure pixels and fractional pixels with 256 gray scale measurement without exceeding the amount of light that can be so readily differentiated? A failed apporach already in the market uses so mugh lighting that reults are compromised at the top of the grading scale due to overexposure from so much more than enough lighting.

I understand that for making lighting displays and comparison of diamonds in a store or on-line, a multitude of lighting scenarios may be a superb way to show diamonds to consumers. If this is your goal, then it is a very important contribution. Also, your goal appears to allow cutters to define new and varied ways to make diamonds beautiful yet quite different from one another as they might be designed with certain light sources and lighting models in mind. We all agree that variety and added choices will help widen the market.

My issue remains that "grading" done from measurements is best done from one "normal", standardized mode of lighting so that the result makes sense, is repeatable and consistent. That lighting model must give results which human perception can appreciate and people should see the differences in the grades not only by the reported measurements, but to a great extent simply by looking at the supplied images in comparison to one another.

 

[Serg]

Date: 5/12/2010 12:17:32 PM
Author: oldminer
Would you commit yourself to using HDRI, a complex tool, or do you possibly agree that a simpler possibly more practical everyday solution is to just use sufficent lighting to always be able to measure pixels and fractional pixels with 256 gray scale measurement without exceeding the amount of light that can be so readily differentiated? A failed apporach already in the market uses so mugh lighting that reults are compromised at the top of the grading scale due to overexposure from so much more than enough lighting.


I understand that for making lighting displays and comparison of diamonds in a store or on-line, a multitude of lighting scenarios may be a superb way to show diamonds to consumers. If this is your goal, then it is a very important contribution. Also, your goal appears to allow cutters to define new and varied ways to make diamonds beautiful yet quite different from one another as they might be designed with certain light sources and lighting models in mind. We all agree that variety and added choices will help widen the market.


My issue remains that ''grading'' done from measurements is best done from one ''normal'', standardized mode of lighting so that the result makes sense, is repeatable and consistent. That lighting model must give results which human perception can appreciate and people should see the differences in the grades not only by the reported measurements, but to a great extent simply by looking at the supplied images in comparison to one another.

Dave,
HDRI has method to receive 4096 or even more gradation during measurement light( instead 256 gradation grayscale.
BTW RAW format or a lot of technical cameras have 12-14 bit instead 8 bit( 256 gradation grayscale). So overexposure is not problem at all

I do not see real connection between your last post and my answer for overexposure problem. Could you give more simple explanation? without connections to "for making lighting displays and comparison of diamonds in a store or on-line,"?

 

[oldminer]

My two comments we not related and I was not talking about overexposure when I referring to what your goals of making a light box and what the benefits might be to the trade and consumers.

I am aware of more than 256 grayscale with higher bit camera sensors, yet the top measure of each one is pure white and bright and the bottom of each is black and dark. If a diamond is lit with too much light, the sensor, no matter how many bits it is will be overexposed by the way light is concentrated by the flashes diamonds produce back to the sensor. The failure to discriminate meaningfully at the top levels of light return is a failure of proper lighting model design and causes such a system to tell the user that one diamond is the same as another when in actuality one of them does a better job of light return. If the lighting model is carefully designed, such a controlled lighting environment will never exceed the ability of the sensor to measure meaningfully on the available grayscale. Higher than 256 bits will work just fine, but if the top 10 levels of light return all read at the absolute top of the sensor, then there is too much light going into the diamond and the tool will be less useful to all of us.

 

[Serg]

Date: 5/12/2010 4:19:11 PM
Author: oldminer
My two comments we not related and I was not talking about overexposure when I referring to what your goals of making a light box and what the benefits might be to the trade and consumers.


I am aware of more than 256 grayscale with higher bit camera sensors, yet the top measure of each one is pure white and bright and the bottom of each is black and dark. If a diamond is lit with too much light, the sensor, no matter how many bits it is will be overexposed by the way light is concentrated by the flashes diamonds produce back to the sensor. The failure to discriminate meaningfully at the top levels of light return is a failure of proper lighting model design and causes such a system to tell the user that one diamond is the same as another when in actuality one of them does a better job of light return. If the lighting model is carefully designed, such a controlled lighting environment will never exceed the ability of the sensor to measure meaningfully on the available grayscale. Higher than 256 bits will work just fine, but if the top 10 levels of light return all read at the absolute top of the sensor, then there is too much light going into the diamond and the tool will be less useful to all of us.

Dave,
1) 256 gradations is not enough to measure Brilliance and Scintillation for real light conditions . You need much bigger Dynamical range. HDRI is standard and simple solution for it.
2) of course camera exposure should been synchronized with average diamond brightness. Is it really important issue for discussion?. I do not see any problems and questions here. very simple issue. But 256 via 4096 gradations is important point if you want measure Brilliance instead average LR.

 

[Garry H (Cut Nut)]

Hi Dave,
This lighting is based on a HDR series of photos taken in my store with a 180 degreee fish eye lens with each set of photos (about 6 from memory) taken straight up and straight down to the near black desk.
(Jess is the standard observer ''inside'' DiamCalc).

Each one of those photo''s independantly makes for a different appearance in the diamond because the exposures varied from just being able to see the lights, all the way to seeing the detxture of a wall or the desk top.
No single image - nor the mid exposure - shows enough detail.
Our eyes cn see all these lighting effects because we have amazing adaption capacity that the camer still does not.

 

[Garry H (Cut Nut)]

Here is an example Dave - not the one used, and not as many images as I remember - but cant find the other one and dont have the software to seperate the images from the huge HDR file:

 

[Garry H (Cut Nut)]

oops

 

[Serg]

Garry, thanks

Now everyone can compare brightness and angular sizes for Tube lamps, halogen lights and Windows.

where are most important lights here? are they green or red in ASET?

 

[Karl_K]

Date: 5/13/2010 4:32:25 AM
Author: Serg
Garry, thanks


Now everyone can compare brightness and angular sizes for Tube lamps, halogen lights and Windows.


where are most important lights here? are they green or red in ASET?

halogen lights: brightest, small angular size (red)
Windows: second brightest potential, large angular size but always off axis! (green to low red in ASET)
Tubes: least brightness potentual, huge angular size one direction, less the other. Even less if they are modified accoring to Garry's patent. They are mostly on axis lighting as installed in a typical office and are heavily diffused. (red in ASET, sparkles from secondary lighting in the green zone such as a desk lamp or window))
However when they are mounted high up in a warehouse type store with no or little diffusion they can cause a lot of fire and sparkle. (red in ASET)

The higher they are the less angular size they have.

Would a good rule be if the angular size is larger than the area the diamond is drawing from only brightness is seen if there are no bright secondary light sources?

Another rule would be angular size decreases with distance.

Off axis decreases the angular size but can increase the area of diamond it is striking.

What would be interesting is do an hdr shot of Garry's store at night with all the lights on but the windows dark.
Then compare the effects in DC.

 

[Garry H (Cut Nut)]

Date: 5/14/2010 2:20:34 AM
Author: Karl_K

Date: 5/13/2010 4:32:25 AM
Author: Serg
Garry, thanks


Now everyone can compare brightness and angular sizes for Tube lamps, halogen lights and Windows.


where are most important lights here? are they green or red in ASET?

halogen lights: brightest, small angular size (red)
Windows: second brightest potential, large angular size but always off axis! (green to low red in ASET)
Tubes: least brightness potentual, huge angular size one direction, less the other. Even less if they are modified accoring to Garry''s patent. They are mostly on axis lighting as installed in a typical office and are heavily diffused. (red in ASET, sparkles from secondary lighting in the green zone such as a desk lamp or window))
However when they are mounted high up in a warehouse type store with no or little diffusion they can cause a lot of fire and sparkle. (red in ASET)

The higher they are the less angular size they have.

Would a good rule be if the angular size is larger than the area the diamond is drawing from only brightness is seen if there are no bright secondary light sources?

Another rule would be angular size decreases with distance.

Off axis decreases the angular size but can increase the area of diamond it is striking.

What would be interesting is do an hdr shot of Garry''s store at night with all the lights on but the windows dark.
Then compare the effects in DC.

Karl it is many shots in the HDR in DiamCalc. That one was never used - it was a test only - and was taken where the windows are mainly blocked by a column.
Maybe Sergey - you might have the individual photo''s from the one below? We have deleted them from arthur''s server.
Here the windows are brightest, then the metal halide in the center of the ceiling and then the halogens.
(the red dot is top dead center)

 

[Serg]

re:halogen lights: brightest, small angular size (red)

In Garry shop halogen lights have less brightness then tubes and windows.

 

[Rockit]

David Atlas, thank you for this thread. I''ve long thought that a diamond''s "performance" is best considered in ways that a report, statistics, or measurement for light return, and etc., can not completely cover. For me, it is the magic mix of science, craft and art that make a gem beautiful and desirable.

By the same token, I understand the need for criteria to judge merchandise that is for sale online and can''t be judged IRL. And, there will always be new methods to define what is best or most desirable... isn''t that the very nature of marketing?

Again, the conversation has taken a technical bend,so I continue to read, learn, and appreciate the talking points. I look forward to more discussion.

 

[oldminer]

I think we can see there are two general reasons for investigating, measuring and grading of Light Performance wihen it comes to diamonds. No everyone wants to do all three things. There are valid reasons why having tools to display and predict light performance and stone appearance in variable lighting conditions works great for marketing and designing of diamond cuts. There are also valid reasons to look for the most elegant, simplest practical solution for measuring and grading of light performance for those who want to have objective measures and repeatable results to compare apples to apples.

No one lighting scenario will be the "perfect" one. However, in order to grade diamonds for light return, a single lighting scenario makes sense. We grade the color in one light and from the side for the near colorless variety. We grade clarity at 10X. Both are arbirary, imperfect choices, but it is our standard practice. We should hope to do the same for lighting and measuring light return. Selecting a model which works is crucial. Such a model must meet human perception choices and give the ability to measure all diamonds in one environment with no particular shape or style having an unfair advantage or exceeding the limits of the measuring tool.

We may choose to say someday that the finest cut diamonds return a bit less than the maximum theoretically possible to design into a cut. They would be the finest if the eyes of numerous human graders decided that a certain range looked best which happened not to include the most light return stones. Right now, we sort of assume that the most light return adds up to a better cut, but it might be premature to make that judgment. We know low light return does not equate to a fine cut, but the total opposite may not be as true. High light return is a positive thing, but maximization, that''s still yet another thing unto itself.

 

[Karl_K]

Date: 5/26/2010 3:39:29 PM
Author: oldminer
We may choose to say someday that the finest cut diamonds return a bit less than the maximum theoretically possible to design into a cut. They would be the finest if the eyes of numerous human graders decided that a certain range looked best which happened not to include the most light return stones. Right now, we sort of assume that the most light return adds up to a better cut, but it might be premature to make that judgment. We know low light return does not equate to a fine cut, but the total opposite may not be as true. High light return is a positive thing, but maximization, that''s still yet another thing unto itself.

The maximum light return is not the best diamond if it as the expense of contrast and light draw.
The problem is with how contrast is currently defined does not take into account a huge part of what produces contrast in a diamond.
Then you have to consider where the diamond is drawing light from.
The wider area you can make a virtual facet draw light from the more chance it has of producing a sparkle.
That has to be balanced against where the brightest light is coming from, and the direction it returns it.
All of the current models of diamond performance are incomplete.
There is no way that can be denied.

Where the future of high performance diamonds is hiding is in getting a better understanding of human vision, and lighting dynamics/interaction with virtual facets.

 

[diagem]

Date: 5/26/2010 3:39:29 PM
Author: oldminer


We may choose to say someday that the finest cut diamonds return a bit less than the maximum theoretically possible to design into a cut. They would be the finest if the eyes of numerous human graders decided that a certain range looked best which happened not to include the most light return stones. Right now, we sort of assume that the most light return adds up to a better cut, but it might be premature to make that judgment. We know low light return does not equate to a fine cut, but the total opposite may not be as true. High light return is a positive thing, but maximization, that''s still yet another thing unto itself.

Dave..., you are touching a ''grey'' area!!
If its premature to make a judgement that ''most'' LR is ''better cut'', it would be premature as well to say ''low'' LR does not equate to a fine cut.

Again..., are we touching an objective or subjective issue?
When you say ''fine cut'', what do you mean? The faceup appearance due to the cut? Or could there be other factors that can set the bar for "fine" cut?

 

[oldminer]

I meant that the common person here assumes "more is better" and that may not be correct. I agree that there are possible ways to cut a diamond which give so much light back we''d lose the necessary contrast and sparkle components. We definitely know that lots of light return will win over minimnal light return when eventual "grading" takes place. I am sure that "more" is in Karl''s mind when he designs, not way less.

We will need to set some single viewing position for grading someday. I think perpendicular to 15 degrees from perpendicular to the table may be in the agreed model for grading. As far as designing goes, I don''t want to limit choices. Maybe someday we''ll have a design which looks wonderful from the top all the way down to 90 degrees from perpendicualr to the table. However, if the diamond does not look its best near the face-up view, it won''t easily become a factor in the overall market scheme.

We can argue over fine points, but we cannot change the simple desires of regular people who see a beautiful object and want to make it their own.