AGS new cut grade system early 2005

[Garry H (Cut Nut)]

Just spoke with Marty.
These two views of the same diamond with a 15 degree rotation are an attempt to describe the variations in light return that result from different view points.

With various degrees of roation of the diamond, or by moving my viewing position from facing the girdle to facing the table - the two different charts show the effect.
There fore marty likes the GIA averaging approach.

 

[adamasgem]

Date: 11/21/2004 8:19:18 PM
Author: Garry H (Cut Nut)
Just spoke with Marty.
These two views of the same diamond with a 15 degree rotation are an attempt to describe the variations in light return that result from different view points.

With various degrees of roation of the diamond, or by moving my viewing position from facing the girdle to facing the table - the two different charts show the effect.
There fore marty likes the GIA averaging approach.

Good presentation Gary.. shows the idea and the difference in billiance depending on the wiewing azimuth for the same tilt..

I wantto make it clear that I liked the ORIGINAL GIA approach. I don''t like the limited overhead viewpoint that GIA is currently proposing..

 

[adamasgem]

Sergey

Are you able to qualitatively verify my findings regarding tilt angle using current DiamondCalc or a modification to it..

Note that a larger TOA will smooth out some of the apparent sharp variations in my data due to the 1 degree solid angle quantization in my data..

 

[Serg]

Date: 11/25/2004 2:24:39 PM
Author: adamasgem
Sergey

Are you able to qualitatively verify my findings regarding tilt angle using current DiamondCalc or a modification to it..

Note that a larger TOA will smooth out some of the apparent sharp variations in my data due to the 1 degree solid angle quantization in my data..

Marty,

I checked RD 11.

Mono crown static view =0.72
Mono crown Tilt 30 view =0.83
LrMono=0.81

 

[Serg]

Marty,

Should I do something more? Please clarify you task.

 

[Garry H (Cut Nut)]

i.e. Marty write in English (Sergey can translate it, and others can comprehend the conversation)

 

[adamasgem]

Date: 11/26/2004 4:18:57 AM
Author: Serg
Marty,

Should I do something more? Please clarify you task.

If you can run the metrics for RD01 for tilts ranging from 25 to 35 degrees, instaed of 30 degrees, in one degree increments, it should show the effect.

Did you take a look at the spreadsheet I sent you where the data were grouped in one degree increments for tilt versus azimuth..

 

[adamasgem]

Sergey, Here is a subset of data from the Tolkowsky spread sheet I sent you and Gary for tilts 25 to 38 degrees, refrected rays only.

I thickened the curves for the tilts which had the wide variations in average refracted light within the 1 degree windows. Note the symmetry of the data versus Azimiuth, as well as the phase shift from one tilt to another as to where the minimums occur..

 

[adamasgem]

Sergey..

The observability of these type of effects will be greater as you move your viewpoint out, as your angular range for data collection narrows..

Because you collect rays over a larger window, given pupil size, stone diameter amd viewer distance, there will be some smoothing of these type of phenomena.

 

[adamasgem]

Probably the major issue to discuss is the Lighting environment used to generate a metric..

1) Hemispherical ,low angle equal intensity lighting, overweights the importance of light return from low angle lighting

2) NO lighting from above (black, BIG head model in the case of GIA) ignores the FACT that the face will reflect 50%
or more of incident light.. The GIA hemisphere is not a realistic everyday environment, even for simulating the laboratory or dealer grading environment, let alone the typical consumer viewing environment. It is great for a controlled model verification, but little else..

 

[Serg]

Date: 11/30/2004 7:35:59 AM
Author: adamasgem
Probably the major issue to discuss is the Lighting environment used to generate a metric..

1) Hemispherical ,low angle equal intensity lighting, overweights the importance of light return from low angle lighting

2) NO lighting from above (black, BIG head model in the case of GIA) ignores the FACT that the face will reflect 50%
or more of incident light.. The GIA hemisphere is not a realistic everyday environment, even for simulating the laboratory or dealer grading environment, let alone the typical consumer viewing environment. It is great for a controlled model verification, but little else..

re:NO lighting from above (black, BIG head model in the case of GIA) ignores the FACT that the face will reflect 50%

Marty,

I have small task for you:

One small source light with brightness 100.

Distance from human face to light source:
1) 1 meters
2) 3 meters

In both cases faces reflect 50% of incident light.

What brightness should you use for face in your ray tracing software:
1)?
2)?

 

[adamasgem]

Date: 11/30/2004 8:22:44 AM
Author: Serg

Date: 11/30/2004 7:35:59 AM
Author: adamasgem
Probably the major issue to discuss is the Lighting environment used to generate a metric..

1) Hemispherical ,low angle equal intensity lighting, overweights the importance of light return from low angle lighting

2) NO lighting from above (black, BIG head model in the case of GIA) ignores the FACT that the face will reflect 50%
or more of incident light.. The GIA hemisphere is not a realistic everyday environment, even for simulating the laboratory or dealer grading environment, let alone the typical consumer viewing environment. It is great for a controlled model verification, but little else..

re:NO lighting from above (black, BIG head model in the case of GIA) ignores the FACT that the face will reflect 50%

Marty,

I have small task for you:

One small source light with brightness 100.

Distance from human face to light source:
1) 1 meters
2) 3 meters

In both cases faces reflect 50% of incident light.

What brightness should you use for face in your ray tracing software:
1)?
2)?

Sergey, No trick questions

Your problem is underdefined, I believe, for the purposes of this discussion.

What is the distance from the diamond to the light source and the diamond to the human face
and what is the intensity of the spot at the diamond that you use.?

What is the beam spread angle of the spot source, and the position of the spot relative to the face and the diamond?

In general, one could consider 1/r^2 falloff for a point source radiating in all directions, but that is not what you are talking about, is it?

 

[Serg]

Date: 11/30/2004 10

6:23 AM
Author: adamasgem

Date: 11/30/2004 8:22:44 AM
Author: Serg

Sergey, No trick questions

Your problem is underdefined, I believe, for the purposes of this discussion.

What is the distance from the diamond to the light source and the diamond to the human face
and what is the intensity of the spot at the diamond that you use.?

What is the beam spread angle of the spot source, and the position of the spot relative to the face and the diamond?

In general, one could consider 1/r^2 falloff for a point source radiating in all directions, but that is not what you are talking about, is it?

Marty,
What is underdefined problem? Sorry I can not translate.

re: What is the distance from the diamond to the light source and the diamond to the human face

Do you use these distance in your software for calculation brightness of diamond facets?

re: What is the beam spread angle of the spot source, and the position of the spot relative to the face and the diamond?

for example it is old simple bulb.

re:In general, one could consider 1/r^2 falloff for a point source radiating in all directions, but that is not what you are talking about, is it?
My statement : The Face contribution to brightness is much mo less than "50%".

 

[Garry H (Cut Nut)]

As we discussed Marty - the face is looking down at the ring.

only a portion of the illumination can light the face - so 50% is not realistic - maybe the head should be modeled as 10%white/90%black - but even this is too simple.
The main head impact is simply blocking strong lights - and strong lights can be blocked by cyclops eye - but one or other eye can see nost lights that cyclops can not - and the way the brain works - one sparkle = sparkle - 2 eyes do not need to see sparkle to make strong sparkle.

 

[adamasgem]

Date: 11/30/2004 1:54

4 PM
Author: Garry H (Cut Nut)
As we discussed Marty - the face is looking down at the ring.

only a portion of the illumination can light the face - so 50% is not realistic - maybe the head should be modeled as 10%white/90%black - but even this is too simple.
The main head impact is simply blocking strong lights - and strong lights can be blocked by cyclops eye - but one or other eye can see nost lights that cyclops can not - and the way the brain works - one sparkle = sparkle - 2 eyes do not need to see sparkle to make strong sparkle.

Gary We''re not talking about strong sources, we are talking about the uniform diffuse illumination chosen by GIA with 100% head blockage as representative of typical viewing conditions..

 

[adamasgem]

Date: 11/30/2004 10:30:49 AM
Author: Serg

Date: 11/30/2004 10

6:23 AM
Author: adamasgem

Date: 11/30/2004 8:22:44 AM
Author: Serg

Sergey, No trick questions

Your problem is underdefined, I believe, for the purposes of this discussion.

What is the distance from the diamond to the light source and the diamond to the human face
and what is the intensity of the spot at the diamond that you use.? 

What is the beam spread angle of the spot source, and the position of the spot relative to the face and the diamond?

In general, one could consider 1/r^2 falloff for a point source radiating in all directions, but that is not what you are talking about, is it?

Marty,
What is underdefined problem? Sorry I can not translate.

re: What is the distance from the diamond to the light source and the diamond to the human face

Do you use these distance in your software for calculation brightness of diamond facets?

re: What is the beam spread angle of the spot source, and the position of the spot relative to the face and the diamond?

for example it is old simple bulb.

re:In general, one could consider 1/r^2 falloff for a point source radiating in all directions, but that is not what you are talking about, is it?
My statement : The Face contribution to brightness is much mo less than ''50%''.

Look Sergey The intensity at 3 meters is 1/9 the intensity at 1 meter for a point source radiating in all directions your simple old bulb.. If you have a spot light that focuses energy with a reflector, typical of store lighting then you need to know the beam spread to do you calculation. If your head is blocking the bulb, it might also be blocking the diamond from direct rays.. if it isn''t then the bulb to diamond and bulb to face distance are not much different, and the head is usually closer to the unblocked bulb than the diamond..

The face reflects about 50% or greater of incident light, and probably can be treated like a diffuse reflector.., but it has a large area relative to the size of a bulb, so it is collecting and reflecting a lot more energy than the diamond is collecting (solid angle) and as a diffuse reflector will put lot of energy from all the "face sources", in my opinion. Look how a H&A scope lights up the arrows just by the small amount of non colored light entering from above..

In a store, one spot may be blocked by the head while another may hit the face dead on.. as well as the background. or outside in a cloud covered sky or in the shade. If the diamond is in direct sunlight, then the direct solar irradition swamps every thing else out.

High angle lighting appears to have a significant efficiency advantage over low angle lighting, like two to one, and low angle lighting is typically much dimmer than high angle lighting (3 to 1 for a cloud covered sky)

 

[Serg]

Marty,

I have task for you:

One small source light with brightness 100.

Distance from human face to light source:
1) 1 meters
2) 3 meters

In both cases faces reflect 50% of incident light.

What brightness should you use for face in your ray tracing software:
1)?
2)?

of course you need one more parameter. But you can use any real bulb for example.

 

[adamasgem]

Date: 12/1/2004 9

0:24 AM
Author: Serg

Marty,

I have task for you:

One small source light with brightness 100.

Distance from human face to light source:
1) 1 meters
2) 3 meters

In both cases faces reflect 50% of incident light.

What brightness should you use for face in your ray tracing software:
1)?
2)?

of course you need one more parameter. But you can use any real bulb for example.

Sergey..

If the bulb is treated as a point source then, for a 100 units per sq cm, with the 100 level/cm2 BEING DEFINED for convenience at 1/3 of a meter (roughly a foot) then at one meter for the face you would have an intensity of 1.23/cm2 and at 3 meters 0.137/cm2.. the same as if the diamond were at the same distances..
Then apply 50% reflectance of the face to get a radiating level for the face of 0.615/cm2 or 0.0685/cm2

Then it gets complicated to treat the integral source from the face to the diamond, I''d have to think about it.
It depends on the aspect angle also as if you were only illuminating one side of the face or the entire face.

Almost simpler to measure it..

 

[adamasgem]

Date: 12/1/2004 10:26:47 AM
Author: adamasgem

Date: 12/1/2004 9

0:24 AM
Author: Serg

Marty,

I have task for you:

One small source light with brightness 100.

Distance from human face to light source:
1) 1 meters
2) 3 meters

In both cases faces reflect 50% of incident light.

What brightness should you use for face in your ray tracing software:
1)?
2)?

of course you need one more parameter. But you can use any real bulb for example.

Sergey..

If the bulb is treated as a point source then, for a 100 units per sq cm, with the 100 level/cm2 BEING DEFINED for convenience at 1/3 of a meter (roughly a foot) then at one meter for the face you would have an intensity of 1.23/cm2 and at 3 meters 0.137/cm2.. the same as if the diamond were at the same distances..
Then apply 50% reflectance of the face to get a radiating level for the face of 0.615/cm2 or 0.0685/cm2

Then it gets complicated to treat the integral source from the face to the diamond, I''d have to think about it.
It depends on the aspect angle also as if you were only illuminating one side of the face or the entire face.

Almost simpler to measure it..

Sergey

I stood about 6 feet away from a bulb in a dark room, basically horizontal aspect, and measuring using a Minolta ChromaMeter II (CL100) got chromaticity coordinates (Y,x,y) of (50, 0.498, 0.409) and then measured the reflectance off of my face, at about 1 foot away from my face, looking up at my face from about 30 degrees so I wasn''t blocking the incident light,and got (9.3,0.537,0.404)

I don''t have a high ceiling room so I can''t get the overhead aspect ..

 

[Serg]

Date: 12/1/2004 10:26:47 AM
Author: adamasgem

Sergey..

If the bulb is treated as a point source then, for a 100 units per sq cm, with the 100 level/cm2 BEING DEFINED for convenience at 1/3 of a meter (roughly a foot) then at one meter for the face you would have an intensity of 1.23/cm2 and at 3 meters 0.137/cm2.. the same as if the diamond were at the same distances..
Then apply 50% reflectance of the face to get a radiating level for the face of 0.615/cm2 or 0.0685/cm2

Then it gets complicated to treat the integral source from the face to the diamond, I''d have to think about it.
It depends on the aspect angle also as if you were only illuminating one side of the face or the entire face.

Almost simpler to measure it..

Marty,

1) How did you get 1.23/cm2 ? Did you push X^2 two times?
2) One small source light with brightness 100. The bulb is not point. And I ask about brightness. You are speaking about illumination.

 

[Serg]

Date: 12/1/2004 10:48

8 AM
Author: adamasgem

Date: 12/1/2004 10:26:47 AM
Author: adamasgem

Sergey

I stood about 6 feet away from a bulb in a dark room, basically horizontal aspect, and measuring using a Minolta ChromaMeter II (CL100) got chromaticity coordinates (Y,x,y) of (50, 0.498, 0.409) and then measured the reflectance off of my face, at about 1 foot away from my face, looking up at my face from about 30 degrees so I wasn''t blocking the incident light,and got (9.3,0.537,0.404)

I don''t have a high ceiling room so I can''t get the overhead aspect ..

perfect.

Could you recalculate for with case the brightness of bulb and the brightness your of face for your ray tracing calculations? ( ratio of brightness is enough too)

Is good question?

 

[Garry H (Cut Nut)]

actually Marty - on further reflection (pun intended) the illumination from the head would make a greater contribution than I thought,

Even a 10% comparative intensity of illumination is precieved as being more than that by our eyes - as is represented by this Chart of Sergey''s

 

[adamasgem]

Date: 12/1/2004 11

2:16 AM
Author: Serg

Date: 12/1/2004 10:48

8 AM
Author: adamasgem

Date: 12/1/2004 10:26:47 AM
Author: adamasgem

Sergey

I stood about 6 feet away from a bulb in a dark room, basically horizontal aspect, and measuring using a Minolta ChromaMeter II (CL100) got chromaticity coordinates (Y,x,y) of (50, 0.498, 0.409) and then measured the reflectance off of my face, at about 1 foot away from my face, looking up at my face from about 30 degrees so I wasn''t blocking the incident light,and got (9.3,0.537,0.404)

I don''t have a high ceiling room so I can''t get the overhead aspect ..

perfect.

Could you recalculate for with case the brightness of bulb and the brightness your of face for your ray tracing calculations? ( ratio of brightness is enough too)

Is good question?

Sergey I don''t know what you need.. I guess I gave you before, the "brightness" of my face at 20%, using the CL100

I had the reflectance of the human hand measured to get the 50% number I quoted from the spectral data,

I measured about 20% of incident luminance reflected a foot away from the face for the situation I described

The problem arises is that if I get any closer I''m probably blocking some of the incident light with a meter..
I measured off of a bigger target, my pasty white stomach, and I get Y/Y0 ratios of 20% which are Lux ratios, I guess from the CL100 manual

 

[adamasgem]

Date: 12/1/2004 6:42:43 PM
Author: Garry H (Cut Nut)
actually Marty - on further reflection (pun intended) the illumination from the head would make a greater contribution than I thought,

Even a 10% comparative intensity of illumination is precieved as being more than that by our eyes - as is represented by this Chart of Sergey''s

OK Gary I''m lost..
Could you explain to me Sergey''s graph, in English please

 

[adamasgem]

Should have looked in Wyszecki & Stiles first..
My friend Johns reflectance data shows higher numbers, with the same shape, probably because he wound up having his hand closer to the probe than when he took a reference white trace off off NIST standard spectralon

There can''t be much argument with these published data, now how to apply them for our modeling problem.. I say that the black in the GIA and AGS uniform diffuse hemisphere models be replaced by the average caucasian skin model. I don''t realy like the uniform hemisphere model, as it doesn''t represent a cloud covered sky.. The intensity variation should be replaced by the Moon and Spencer Intensity model

L(theta)=Lx(1+2 sin(theta))/3, Lx the luminence at the zenith and theta the angle from the horizon,
and the intensity of the face be based on the skin reflectance model and the average intensity intensity in other than the head obscuration area. That seems to match an observer under a cloud covered sky, which incidently is the D6500 spectral model used..

I still have SERIOUS problems with GIA''s black hole at the girdle plane.

I would replace the girdle plane with a skin reflectance model

Now we have a physically realizable viewing condition that makes sense to calculate "brightnes" or "brilliance" or whatever you want to call it to get "proprietary rights"

Basing a diamonds performance on calculations based on the GIA modeled hemisphere with 40 degree solid angle head obscuration, a condition NEVER attained, is pure consumer deception..

 

[Serg]

Marty,

re:Sergey I don''t know what you need.. I guess I gave you before, the "brightness" of my face at 20%, using the CL100
I ask about ratio between the brightness of bulb and brightness of your face. This information is necessary for your ray tracing software.
Do you agree?

This ratio is much more less than 20%(0.2)

Do you agree?

Your are speaking about reflection function of face only.

 

[adamasgem]

Date: 12/2/2004 4:49:22 AM
Author: Serg


Marty,

re:Sergey I don't know what you need.. I guess I gave you before, the 'brightness' of my face at 20%, using the CL100


I ask about ratio between the brightness of bulb and brightness of your face. This information is necessary for your ray tracing software.
Do you agree?

This ratio is much more less than 20%(0.2)

Do you agree?

Your are speaking about reflection function of face only.

Sergey What you want to know is the relative intensity of the illumination of the diamond from both the face and the bulb, a geometry related problem, and if the diamond and the face are at similiar distances from the face, depending on the aspect angles the 20% numbers look reasonable. Also consider that when you are talking about a "bulb" you are talking about blackbody irradiators of 2800 degrees Kelvin of so, where the energy concentration is in the red end of the spectrum and where the reflectivity of the face is greater than 20%, more like 50 or 60%.. See the data I posted..

 

[Serg]

re: Sergey What you want to know is the relative intensity of the illumination of the diamond from both the face and the bulb, a geometry related problem, and if the diamond and the face are at similiar distances from the face, depending on the aspect angles the 20% numbers look reasonable.

No, No, No, No, No,

I ask about brightness source light for your ray tracing software. I suppose You want use face like source light. I think it is one way to consider light from face in your software.

 

[Serg]

Marty,

Could you use two light source with different brightness at one time in your software?

 

[adamasgem]

Date: 12/2/2004 12:50:39 PM
Author: Serg
Marty,

Could you use two light source with different brightness at one time in your software?

Sergey Right now I can''t but, I''m setting it up to use up to 10 spots but haven''t finsihed the software mods yet, and won''t be able to get to it for a week or so..