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Does alpha channel really need 8-bits?

  1. Jan 10, 2018 #1
    Hi,

    I am looking for the differences between 16-bit, 24-bit and 32-bit colors for a while. I saw that actually 32-bit color is also like 24-bit color but plus 8-bit alpha channel. Since 8-bit information represents 256 possible values for each color channel, what does 8-bit do exactly for alpha channel to store color or transparency info?

    I hope I didn't ask a stupid thing. Thanks a lot!
     
  2. jcsd
  3. Jan 10, 2018 #2

    berkeman

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    Staff: Mentor

    For those folks (like me) who had no idea what you are asking about, here is a link: https://en.wikipedia.org/wiki/RGBA_color_space

    Are you asking specifically about Photoshop? This thread probably belongs in one of the technical forums -- Physics or Computing?

    EDIT -- Thread moved by the Mods to Computing. :smile:
     
    Last edited: Jan 10, 2018
  4. Jan 10, 2018 #3
    Ah, ok I got my answer. It holds the percentage information of the alpha channel. This makes sense. Otherwise 8-bit channel badwidth wouldl be very unneccesarry if it was only holding transparent or not. Thanks a lot!
     
  5. Jan 10, 2018 #4

    berkeman

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    Staff: Mentor

    Hey, always happy to help... :wink:
     
  6. Jan 10, 2018 #5
    It's exactly the same as the other components, why would it be any different? r is a 0-255 value for how intense the red part of the color is, a is how intense the alpha is.
     
  7. Jan 10, 2018 #6
    The alpha channel could use any depth from not existing, 1 -bit and up depending on you needs.
     
  8. Jan 10, 2018 #7
    You can’t use 1 bit for alpha. That’s not alpha, that’s masking. 1 bit would give you the option of having the pixel fully there or not at all, no transluscency at all.
     
  9. Jan 11, 2018 #8
    Yes, in this case I must agree with @newjerseyrunner because alpha must able to have at least 101 value in order to represent transparency percentage.
     
  10. Jan 11, 2018 #9
    Yeah, but because engineers tend to think in base 16 rather than base 10, 100 would be completely arbitrary. Thinking of parts per 256 is simply easier when you do base 16 stuff all day.
     
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