Definitions of Brilliancy, Sparkle and Intensity

We are constantly asked for these and thought it would be good to post these most updated definitions:
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Light Behavior, The Imagem Definitions, both simple and more complex:

Three simple definitions:

Brilliance: a measure of a stone’s overall strength of light return that represents its average light return in the face-up position. This measure is arrived at by computing the mean gray-scale value of all pixels within the girdle portion of a diamond.

Sparkle: a measure of those spangle-like flashes of reflected and refracted light that gives diamonds what might be called “kick”. The greater the number of these flashes, the higher a stone’s sparkle. This measure is arrived at by measuring the standard deviation in the gray-scale value of the light return within the girdle image. (Note: Do not confuse sparkle, which is observed when the diamond is held stationary, with scintillation, which is observed when a diamond is moved about.)

Intensity: a measure of the number and strength of contrasting light-dark areas in the girdle portion of a diamond that give it vitality and character. The greater the stone’s symmetry the higher its intensity will be. .This measure is arrived at by calculating a ratio of bright pixels to the total number of pixels within the girdle.
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The more technical definitions:

1.  ImaGem uses direct measurement of light returned from a diamond.
Measurements are repeatable within margins of error.

2.  Three measures of light behavior are used to represent the beauty and the quality of a diamond.  These are: Brilliance, Sparkle, and Intensity.  Combinations of these measures represent levels of beauty in diamonds.

Brilliance represents "average light return."  It is measured as the average of gray scale values of pixels within the girdle area.  This value can range from 0 to 255 as a property of the measuring device.  For the standard lighting level used this value is purposely kept low to prevent saturation.  Higher value on Brilliance represents: more brilliant, brighter, excellent cut stone, more efficient stone returning more of the incident light back.

Sparkle represents "variation" in light return.  It is measured as a variation in the gray scale values of pixels within the girdle area. Theoretical maximum standard deviation for 40 pixels is about 129. Sparkle represents the degree to which a diamond is lively, dynamic, and responsive to kinetic behavior. Higher the value, more lively, more dynamic a stone is likely to appear to a viewer.

Intensity is measured as a ratio of pixel areas with high levels of light return to the total area within a girdle.  In theory this value can be as high as 1000, but under selected lighting condition the value has not exceeded 500 yet.  Intensity level represents well defined areas of contrast and pattern and hence gives a stone a "pleasing visual definition", "interest" and "mystique."  Stones with high levels of optical symmetry score very high on this scale.  But other types of cut may score well on this scale as well.

Garry Holloway FGAA DipDT

HCA and Ideal-scope developer

http://www.ideal-scope.com and
http://www.HollowayDiamonds.com.au

Hi Dave

A few questions if they are not top secret

Does Imagem pixel count like BS.

If so do you use known good performing dimensions/scans to create the original pixel maps to be used as benchmarks.
Does the software calculate deviations from these benchmarks?

Johan

Diamond Exchange Ltd. (Australia)

David S. Atlas

GG(GIA), ASG, Sr. Mbr. NAJA

www.datlas.com

Here is what Dr. Aggarwal, founder of ImaGem, has responded:

"The first question is hypothetical and does not represent reality.  One will
be hard pressed to get two stones that are identical let alone get three
stones of any size that are identical. Factors like color, clarity,
fluorescence, faceting and graining among others may contribute to
differences between stones and affect light behavior."

Dave Atlas' edit: For clarity's sake, I would then add to Garry:  Three diamonds of three diferent weights will NOT react the same to light..  There seems to be no point to be made.  Diamonds of differnet sizes are "different" and light will be differenly altered.

To Johan, Dr. Aggarwal has responded:

"Direct measurement of light behavior by ImaGem takes these and other factors automatically in to account in the measurement of brilliance, sparkle and intensity.  The form factor of pixels and scaling are carefully considered by ImaGem as part of its calibration routines."

Dave Atlas' edit: For clarity's sake, I would then add to Johan:  ImaGem is "counting pixels" but not "like" Gemex.  There is a very distinct difference in methodology, but there is counting going on.  The end results are not like Gemex.  ImaGem results are repeatable, and scientifically solid.

David S. Atlas

GG(GIA), ASG, Sr. Mbr. NAJA

www.datlas.com