Super noob about optics, so forgive me if I make any mistakes. But I have images from smartphones which have a color checker in them. I wish to calculate the opto electronic function(can i use color checker for this?) so that I can map my processed RGB
values onto linear scale ( rgb values before smartphone camera applies processing).

any advice/answer to clear what this is would tremendously help me out. thanks!

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On 9/20/18 3:21 PM, [email protected] wrote:

Super noob about optics, so forgive me if I make any mistakes. But I have images from smartphones which have a color checker in them. I wish to calculate the opto electronic function(can i use color checker for this?) so that I can map my processed RGB

values onto linear scale ( rgb values before smartphone camera applies processing).

any advice/answer to clear what this is would tremendously help me out. thanks!

The apparent colour of a matte surface depends on the product of the illumination intensity and the surface reflectance, both as a function
of wavelength. (There are fine points, e.g. the reflectance can be a
function of angle as well, but that's not too important most of the time.)

The classical method is to get a Macbeth colour checker, <https://en.wikipedia.org/wiki/ColorChecker>. That'll correct for the illumination as well.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

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On Thursday, 20 September 2018 16:19:17 UTC-4, Phil Hobbs wrote:

On 9/20/18 3:21 PM, [email protected] wrote:

Super noob about optics, so forgive me if I make any mistakes. But I have images from smartphones which have a color checker in them. I wish to calculate the opto electronic function(can i use color checker for this?) so that I can map my processed

RGB values onto linear scale ( rgb values before smartphone camera applies processing).

any advice/answer to clear what this is would tremendously help me out. thanks!

The apparent colour of a matte surface depends on the product of the illumination intensity and the surface reflectance, both as a function
of wavelength. (There are fine points, e.g. the reflectance can be a function of angle as well, but that's not too important most of the time.)

The classical method is to get a Macbeth colour checker, <https://en.wikipedia.org/wiki/ColorChecker>. That'll correct for the illumination as well.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

hello!
thanks for the response...but I don't understand how opto electronic transfer function is related to what you've said? Is there an equation I could use to get the transferred picture?

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On 9/20/18 7:04 PM, [email protected] wrote:

On Thursday, 20 September 2018 16:19:17 UTC-4, Phil Hobbs wrote:

On 9/20/18 3:21 PM, [email protected] wrote:

Super noob about optics, so forgive me if I make any mistakes. But I have images from smartphones which have a color checker in them. I wish to calculate the opto electronic function(can i use color checker for this?) so that I can map my processed

RGB values onto linear scale ( rgb values before smartphone camera applies processing).

any advice/answer to clear what this is would tremendously help me out. thanks!

The apparent colour of a matte surface depends on the product of the
illumination intensity and the surface reflectance, both as a function
of wavelength. (There are fine points, e.g. the reflectance can be a
function of angle as well, but that's not too important most of the time.) >>
The classical method is to get a Macbeth colour checker,
<https://en.wikipedia.org/wiki/ColorChecker>. That'll correct for the
illumination as well.

hello!
thanks for the response...but I don't understand how opto electronic transfer function is related to what you've said? Is there an equation I could use to get the transferred picture?

"Optoelectronic transfer function" is not a term I'm familiar with. The ColorChecker gives you a bunch of known reflectances, so you can take
the RGB values from your camera, convert to whatever colour space the ColorChecker is calibrated in, and then use something like
singular-value decomposition to get the least-squares optimum
transformation from your image data to true reflectance.

SVD is a super-useful technique for this sort of thing--have a look at
the second edition of Numerical Recipes in C for an excellent discussion
of how to use it. (The C++ edition isn't as good in my opinion.)

There's an enormous amount of jargon and obfuscation in photometry,
which (as far as I can tell) is mostly intended to promote the job
security of photometrists. Sorry about that!

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

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On Thursday, September 20, 2018 at 3:21:29 PM UTC-4, [email protected] wrote:

Super noob about optics, so forgive me if I make any mistakes. But I have images from smartphones which have a color checker in them. I wish to calculate the opto electronic function(can i use color checker for this?) so that I can map my processed RGB

values onto linear scale ( rgb values before smartphone camera applies processing).

any advice/answer to clear what this is would tremendously help me out. thanks!

thanks a lot! that made things clear!

Sincerely
Shashi

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