What is the opto electronic transfer function, and how do I calculate that for an image, to get back my linear RGB values?

[s***@gmail.com]

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!

[Phil Hobbs]

Post by s***@gmail.com
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

[s***@gmail.com]

Post by Phil Hobbs

Post by s***@gmail.com
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?

[Phil Hobbs]

Post by s***@gmail.com

Post by Phil Hobbs

Post by s***@gmail.com
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

[s***@g.rit.edu]

Post by s***@gmail.com
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