Color Change in Identical Pictures of CC Gemstones
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Author:  valeria102 [ Fri Jul 24, 2009 11:46 am ]
Post subject:  Re: Perfection with color in photography can be difficult

brucetourm wrote:

I have asked experts why there were color problems and this is their explanation. The mind's/eye's interaction with light in the blue/purple area of the spectrum is very complex.

A tourmaline of extraspectral purple? 8) [excuse to link up to a rather good book... that stumbles upon some gem color issues from a different point of view: the page linked there also comes up with a quip about the quirks of 'red' - a rather more sung color. 'Doubt the author ever heard of 'pidgen blood' unless he's into cooking a great deal!]

Oh well...

Author:  anitame [ Fri Jul 24, 2009 12:12 pm ]
Post subject: 

There's a thread somewhere around here about alexandrite rough, where the person can see the green, but when photographed it is only red. Imagine if you were trying to photograph that for your website!

"Trust me, you can't see it but there's green in there..."

Author:  Swishman [ Fri Jul 24, 2009 12:26 pm ]
Post subject: 

The color problem in digital is not digital, but actually the Bayer based sensor used in most digital cameras. I can NOT capture all 3 colors(rgb) in each photosite(pixel to keep it simple). Each photosite captures a single color and then uses the other photosites around it to guess/interpolate the other two colors that it could not capture. Also the Bayer based sensor has another large fault which is the red channel, it can not capture reds properly nor much detail within the red channel.

The above is why cameras with the FovenX3 sensor are the best choice for gemstone photography. Because each photosite actually captures rgb and there is no guessing involved. They also have no issues at all capturing reds nor details in the red channel.

As for touching base on the printers, that is a prime example why I seldom use a home inkjet based printer. If one has a color calibrated monitor and color profiled and calibrated printers/developers there is no problem with color reproduction aside from that noted above. I get my digital prints done through a professional printing house that actually develops and "prints" them the same way film is done, in fact, they are done on the same machine film prints are done on. :).

I have found three digital cameras that work the best to reproduce accurate colors, in order from best to worst:
1. Sigma SD14 or SD15
2. Panasonic LZ series(but limitations in functions holds me back from recommended only to experienced shooters typically)
3. Panasonic FZ series
4. Pentax K10D/K20D/K7

Even though the Panasonic and Pentax cameras use the Bayer based sensors, their on board processing chips, accurate white balance settings, and accurate and more advanced metering allows them to come close ad produce more natural colors.

Author:  mhuynh [ Fri Jul 24, 2009 12:44 pm ]
Post subject: 

This thread was started with my naïve question. But it is turning into an informative technological thread. Very interesting. I like it. :D

anitame wrote:
"Trust me, you can't see it but there's green in there..."

anitame, here's one for you.

I happen to be able to read Japanese. The Japanese version of the ID report also says: Pleochroism; three colors, strong (green, yellowish green, brownish red). :wink:


Note: Italic part edited.

Author:  anitame [ Fri Jul 24, 2009 1:09 pm ]
Post subject: 

For such a big stone and for your $1.5 million you'd think they could have gotten a little bit better cut - the window is massive! Ugly cut, and color change or not, ugly color (IMO). I'm not sure even Photoshop could help that... :wink:

Author:  Alberto [ Fri Jul 24, 2009 1:23 pm ]
Post subject: 

maybe you've missed it but that report (released in 1980) is signed by Dr. Gubelin & Dr, Schiffmann :shock:
Have a look, it worth a read.

Author:  gingerkid [ Fri Jul 24, 2009 3:23 pm ]
Post subject: 

:?: how large is this stone? 141,92ct? or 141.92ct?

are there commas inserted in the report where there should be decimal points for measurement purposes?

i could understand if the stone is the "largest alexandrite chrysolberyl of this clarity we have encountered..." why the stone is faceted with a terrible window.

hey alberto, i checked out the "english" copy of the gem report. is it a fake gem report?

Author:  bruce_tourm [ Fri Jul 24, 2009 5:33 pm ]
Post subject:  A bit more

A bit more on what I was told by the researcher from Kodac and others. The CIELAB color space (developed by an historic international group to present and handle color information) is well behaved and nearly uniform except for two areas of the color space, orange/red and purple/blue. In these areas the mind/eye is actively attempting to maintain color consistency and existing mathematic models that try and permit the interpolation of color points fails to perform adequately. The way Kodac end up handling the complexity of the interpolation was the development of Look Up Tables. All the new wide gamut monitors strongly press how accurate (how many bits of information they contain) their tables are. All this would be transparent to the user as long as his work does not demand greater accuracy then the look up tables can provide. This still does not solve the problem of having colors in gems that can not be render on the monitors or reproduced by even the best photographic media.


Author:  JB [ Fri Jul 24, 2009 5:39 pm ]
Post subject: 

Oh, for christsake, buy the gem on memo and look at it. :lol:

Love you Bruce. :)

Author:  Brian [ Fri Jul 24, 2009 5:58 pm ]
Post subject: 

gingerkid wrote:
:?: how large is this stone? 141,92ct? or 141.92ct?

are there commas inserted in the report where there should be decimal points for measurement purposes?

In many countries, it is common to use commas for decimals, and maybe vice versa.

Author:  bruce_tourm [ Fri Jul 24, 2009 6:59 pm ]
Post subject:  JB a straighter arrow has never been shot.

I love color and tourmaline and pictures and the ability to share, but if I ever bought an expensive cut gem, I would need time alone with it to be sure that my love was for real. When I finish cutting a gem, I take it for a walk. I see it under as many different light sources and times of the day as I can. I have been surprised many times by the dynamic color of tourmaline that can be very personal. My three kids keep me on the ground when I glow too much the color of my newest catch.

Thanks again for the bull's eye.


Author:  gingerkid [ Fri Jul 24, 2009 7:18 pm ]
Post subject: 

since valeria posted a link to the book, "perception of the visual environment," i have a difficult time telling the difference between black and navy and some other colors as well. does anyone else have this or a problem distinguishing any colors?

Author:  Swishman [ Sat Jul 25, 2009 1:17 am ]
Post subject: 

As promised as well, here is an Animated GIF. It flashes back and froth between both images. You can see that everything is identical! Again, this is possible to do, but is unlikely. Also, if you look closely, there are lots of blue blotches in the "red" image, which is typically due to not properly switching the entire hue of the color being replaced.

The hex of the files are not identical though, but this could be caused by simple editing, the part that counts, the headers(what identifies each image) are identical, screen capture supplied as well. Compare the green highlighted areas.

Author:  bruce_tourm [ Sat Jul 25, 2009 6:48 am ]
Post subject:  Normal differences

In the quest to spread the beauty of tourmaline I have shown my gems to many people. I usually start out by asking them if they have ever heard of tourmaline. I would say that upwards of 90 per cent in the Pittsburgh Pa area have never heard of it. Then I show them one of my beauties. Differences in color perception soon become apparent. How much green is in yellow and purple is in red are areas of difference that come to mind. I am sure that everyone I asked had normal color perception, but it does vary between people and changes with age. Of course you have to be careful of the quality of your light source or the comparison is not valid. I have read that the scientist can look into a health eye and see the color receptors. Large differences between the eyes of people with normal color vision have been observed, which helps explain normal differences in people. I find that for myself the quality of light makes a big difference in differentiating between navy and black, especially if I do not have a black available for comparison with the navy.


Author:  valeria102 [ Sat Jul 25, 2009 7:14 am ]
Post subject: 

Same & not fun when navy is a favorite (just try to match any in store lighting!).

I believe low saturation or extreme dark / light tones are always senzitive to lighting conditions - they ought to be.

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