This topic contains 0 replies, has 0 voices, and was last updated by  Andrew Rydzewski 9 years, 1 month ago.

Viewing 2 posts - 1 through 2 (of 2 total)
  • Author
    Posts
  • #202876

    kepler
    Member

    Hi, firstly I want to thank you Ron for your great work with this second volume. It’s a great source that I read and reread lots of times.

    Well, what I want to ask and comment here is what I find a really confusing topic among diferent sources: the gamma correction.

    First I’ve read a number of explanations about the topic and I find that the explanation given in the book isnt accurate and contradictory to another ones like the Wikipedia one in http://en.wikipedia.org/wiki/Gamma_correction

    In the page 424 in the Video Gamma section is said that video images are encoded when captured with a 2.2 gamma and consequently they would display brighter.

    About the brighter image, it would be darker cause the x=y^2.2 gamma function is a convex one so dark values are darker.

    If a video monitor has a Gamma of 2.2 , why the video captured image would need the same Gamma?

    It’s said at the end “It may be easier to adjust the viewing device (computer monitor) so that is darkened by a gamma of 0.45”

    Well, computer monitors dont have a 0.45 gamma but a 2.2 normally so I think that here is a confussion being the encoding a 0.45 gamma to compensate with the standard 2.2 of a video monitor.

    Also I cant understand why if the Human eye has a Gamma of approximatelly 0.45 (http://www.poynton.com/PDFs/GammaFAQ.pdf) so when decoding the image to linearize it the eye gamma would make nonlinear again the image so it would be brighter, I’m wrong?

    Maybe I’m wrong but I would like to clarify this one.

    Thank you.

    #217889

    @kepler 28117 wrote:

    About the brighter image, it would be darker cause the x=y^2.2 gamma function is a convex one so dark values are darker.

    The gamma function is actually raised to the inverse of 2.2: y=x^(1/n), so a gamma of n=2.2 would look brighter.

Viewing 2 posts - 1 through 2 (of 2 total)

You must be logged in to reply to this topic.