Does alpha channel really need 8-bits?

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Discussion Overview

The discussion revolves around the necessity and function of an 8-bit alpha channel in color representation, particularly in the context of 16-bit, 24-bit, and 32-bit color formats. Participants explore the implications of using different bit depths for the alpha channel in terms of transparency and color representation.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions the role of the 8-bit alpha channel in storing transparency information, suggesting it holds percentage information for transparency.
  • Another participant asserts that the alpha channel functions similarly to color channels, with values ranging from 0 to 255 representing intensity.
  • Some participants propose that the alpha channel could theoretically use varying bit depths, but emphasize that a 1-bit alpha channel would not allow for translucency, only masking.
  • There is a contention regarding the minimum bit depth required for the alpha channel, with one participant arguing that at least 101 values are necessary to represent transparency percentages effectively.
  • A later reply discusses the preference for base 16 over base 10 in engineering contexts, suggesting that using 256 parts is more intuitive for those familiar with hexadecimal systems.

Areas of Agreement / Disagreement

Participants express differing views on the necessity of an 8-bit alpha channel and the implications of using lower bit depths. There is no consensus on the minimum requirements for effective alpha channel representation.

Contextual Notes

Some participants reference specific applications, such as Photoshop, and the discussion may be influenced by varying definitions of alpha channel usage across different contexts.

Flashbond
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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!
 
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Flashbond said:
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!
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:
 
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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!
 
Hey, always happy to help... :wink:
 
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.
 
The alpha channel could use any depth from not existing, 1 -bit and up depending on you needs.
 
glappkaeft said:
The alpha channel could use any depth from not existing, 1 -bit and up depending on you needs.
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.
 
newjerseyrunner said:
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.
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.
 
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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