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  • What is the opto electronic transfer function, and how do I calculate t

    From shashidhar.nagabandi@gmail.com@21:1/5 to All on Thu Sep 20 12:21:27 2018
    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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  • From Phil Hobbs@21:1/5 to shashidhar.nagabandi@gmail.com on Thu Sep 20 16:19:31 2018
    On 9/20/18 3:21 PM, shashidhar.nagabandi@gmail.com 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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  • From shashidhar.nagabandi@gmail.com@21:1/5 to Phil Hobbs on Thu Sep 20 16:04:20 2018
    On Thursday, 20 September 2018 16:19:17 UTC-4, Phil Hobbs wrote:
    On 9/20/18 3:21 PM, shashidhar.nagabandi@gmail.com 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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  • From Phil Hobbs@21:1/5 to shashidhar.nagabandi@gmail.com on Thu Sep 20 20:03:19 2018
    On 9/20/18 7:04 PM, shashidhar.nagabandi@gmail.com wrote:
    On Thursday, 20 September 2018 16:19:17 UTC-4, Phil Hobbs wrote:
    On 9/20/18 3:21 PM, shashidhar.nagabandi@gmail.com 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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  • From sn6582@g.rit.edu@21:1/5 to shashidhar...@gmail.com on Fri Sep 21 07:12:13 2018
    On Thursday, September 20, 2018 at 3:21:29 PM UTC-4, shashidhar...@gmail.com 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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