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Mustafa Umut Sarac
06-23-2013, 06:17 AM
All I know about dyes is about their color spectrums. I want to know is it possible to calculate the dyed starch grains reaction to the different light temperatures ? Or does color spectrum change with light ? Or does it require experiments ?

Umut

Photo Engineer
06-23-2013, 10:26 AM
Umut;

AFAIK, it cannot be calculated. It must be measured with a spectrophotometer.

PE

Mustafa Umut Sarac
06-23-2013, 12:50 PM
PE,

Do spectrophotometers have a ability to create different temperature lights in to starch grains or do we need a light source ?
Does China produce these test devices , what size do they come with ? What is the cheapest ones price ?
I am receiving dye quatations from china and most expensive one 1 gram / 10 dollars range to 25 cent range for Autochrome.
Still waiting the monday.

Umut

Photo Engineer
06-23-2013, 01:09 PM
Testing for hue shifts involves a different type of test method IIRC.

You would make up a color patch and expose it to daylight and tungsten (as an example) while reading the spectrum at a distance with a spot reader and scanning the density at different wavelengths.

This is a characteristic of dyes known as Metamerism. And with any dye you can have a hypsochromic or bathochromic shift in hue (]t shorter or longer wavelengths).

PE

E76
06-23-2013, 09:25 PM
Umut;

AFAIK, it cannot be calculated. It must be measured with a spectrophotometer.

PE

Not true! The appearance of dyes under different light sources can be easily calculated, so long as you know the spectral reflectance of the dye (as measured with a spectrophotometer), as well as the spectral power distribution (PSD) of the source. Multiplty these functions together, then multiply by each of the CIE standard observer color matching functions. The integral of these results will give you the XYZ tristimulus values, from which you can calculate the chromaticity coordinates, L*a*b* values, and so on.

Photo Engineer
06-23-2013, 10:21 PM
Wonderful. Happy tobe corrected.

When I worked on it, there was no "cure".

PE

Tom1956
06-23-2013, 10:39 PM
Now that this miraculous color technology has been buggy-whipped by digital, it begs the question whether the R&D on this kind of thing can now be considered as stalled.

Mustafa Umut Sarac
06-24-2013, 06:42 AM
Not true! The appearance of dyes under different light sources can be easily calculated, so long as you know the spectral reflectance of the dye (as measured with a spectrophotometer), as well as the spectral power distribution (PSD) of the source. Multiplty these functions together, then multiply by each of the CIE standard observer color matching functions. The integral of these results will give you the XYZ tristimulus values, from which you can calculate the chromaticity coordinates, L*a*b* values, and so on.

Is there anywhere, any database , I can ask for an spectral reflectance of one of six spectral dye reflectance record ? I can pay for the papers also.

Umut

Photo Engineer
06-24-2013, 10:40 AM
Not true! The appearance of dyes under different light sources can be easily calculated, so long as you know the spectral reflectance of the dye (as measured with a spectrophotometer), as well as the spectral power distribution (PSD) of the source. Multiplty these functions together, then multiply by each of the CIE standard observer color matching functions. The integral of these results will give you the XYZ tristimulus values, from which you can calculate the chromaticity coordinates, L*a*b* values, and so on.

Thinking about this makes me wonder. At present, the new EK POD units produce color images with a huge amount of metamerism between daylight and tungsten. So, someone there doing R&D has not gotten the word on this method, or they are ignoring it, or they have note even tested for it. It is truly amazing. We used to do these tests without computers and thus without the intense calculations you describe. Being in the Flower City yourself, you must have some experience with this yourself.

One of our great EK color engineers died last week BTW.

PE

E76
06-26-2013, 07:10 PM
That is interesting. The method I described is hardly new. It was defined completely, along with the rest of the CIE XYZ color space, by Wright and Guild in 1931 and is used extensively in color science. Anyone with a basic background in color science would have knowledge of this, especially today, as it is a critical part of digital color management.

Mustafa, if you are interested in learning more about color science you may find Principles of Color Technology by Roy Berns a helpful resource.

Photo Engineer
06-26-2013, 07:48 PM
E76, I was not a color engineer, I was a system engineer designing products after the best of the best couplers were picked, so I really am not an expert in this even though I took 2 courses from Bob Hunt (OBE).

Our real expert unfortunately, died 2 weeks ago and I am saddened by his loss. He was a member of the ANSI committee on color photography and color television.

PE

E76
06-26-2013, 09:15 PM
No worries—very few people are experts in the field! I'm no expert color scientist eithe, which makes me all the more surprised to hear that Kodak couldn't get their new printer right.

I'm sorry to hear about your friend. :(

Tom1956
06-26-2013, 09:17 PM
E76, I was not a color engineer, I was a system engineer designing products after the best of the best couplers were picked, so I really am not an expert in this even though I took 2 courses from Bob Hunt (OBE).

Our real expert unfortunately, died 2 weeks ago and I am saddened by his loss. He was a member of the ANSI committee on color photography and color television.

PE

Kind regards for the loss of the co-worker.