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JC de Blok
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Adjusting alpha levels

May 2, 2013 11:57 PM

Tags: #alpha #levels #adjust

I have a 3d render that has some semi transparent areas (shadows on matte objects) I want to get rid off. In AE a can simple adjust the alpha levels and set everything under 25 to be 0 for example.

 

In PS the entire alpha channel seems to be out of reach.. it's not in the Channels tab?  I can add one but  PS fills it with an B&W version of my RGB image.. What trick I'm a missing here?

 
Replies
  • Currently Being Moderated
    May 3, 2013 12:10 AM   in reply to JC de Blok

    Could you please post a screenshot with the Layers and Channels Panels visible?

     

    It seems you might be misunderstanding what Transparency and Channels in Photoshop mean.

     

    In PS the entire alpha channel seems to be out of reach.. it's not in the Channels tab? 

    Have you tried Layer > Layer Mask > From Transparency?

     
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  • Currently Being Moderated
    May 3, 2013 10:18 AM   in reply to JC de Blok

    Yeah, you're confusing transparency (a specific subset of possible alpha channels) with alpha channels (the superset, which are just any additional channels beyond the color data).

     
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  • Currently Being Moderated
    May 3, 2013 3:30 PM   in reply to JC de Blok

    PNG has transparency (specifically straight color, not premultiplied transparency), not arbitrary alpha channels.

    And the transparency is in the image, where it belongs, and is used to composite the image layer.

     

    Again, you are getting transparency and alpha channels confused.

     
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  • Currently Being Moderated
    May 3, 2013 9:57 PM   in reply to JC de Blok

    Well, this is the Photoshop forum, and we only deal with Photoshop.

     

    It would behoove you to use proper Photoshop terminology when seeking help here.

     

    Personally, I don't give a rat's *** as to how "AE, Premiere, Nuke, 3dsMax etc" may do it as I never go near one of those appications, and you're not helping the discussion by bringing up those other apps here.

     
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  • Currently Being Moderated
    May 3, 2013 10:39 PM   in reply to JC de Blok

    That quote gets it kinda wrong.  And the wikipedia article is talking about alpha compositing - where alpha is a mathematical symbol, not the name of a channel (but that's why people get it wrong).

     

    Again, you are confusing transparency (a specialized subset of possible channels that is tightly coupled to the color channes) with alpha channels (the superset of all possible extra channels that generally are not coupled with the color channels).

     

    Image files can have multiple alpha channels, but only one transparency channel per image layer.

    Some file formats support transparency, but not alpha channels.

    Some file formats support alpha channels (or just one extra channel that is not transparency), but not transparency.

    And some file formats support both.

     

    Yes, video and some 3D applications tend to get the concepts confused (even though many of them allow multiple alpha channels).

     
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  • Currently Being Moderated
    May 3, 2013 11:01 PM   in reply to JC de Blok

    JC de Blok wrote:

     

    …this frustrates you somehow?

     

    No frustration here, "irritate" would be more appropriate than frustrate.  What might irritate me would be your Blok-headed stubbornness in not realizing you're confused and your refusal to use correct terminology.

     

    It's not just about you but about the future readers of this thread who will be confused by your repeated misuse of simple terminology.

     
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  • Currently Being Moderated
    May 4, 2013 2:18 AM   in reply to JC de Blok

    JC de Blok wrote:

     

    …I guess you wouldn't know about that since you only live in PS world…

     

    That's a very presumptuous statement, mijnheer de Blok.  You have zero idea what worlds (plural) I live in, just like I would not presume to know what world you live in.

     

    Just carefully re-read post #10 by guru Chris Cox, a senior Adobe engineer who has been writing Photoshop's code for something like 17 years or so.

     
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  • Currently Being Moderated
    May 4, 2013 2:20 AM   in reply to JC de Blok

    By the way, it's called transparency, not "transparancy".

     
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  • Currently Being Moderated
    May 4, 2013 1:07 PM   in reply to JC de Blok

    JC de Blok wrote:

     

    You are not getting it I guess…

     

    You guess completely wrong and you are the one who doesn't grasp the issue.

     

     

    JC de Blok wrote:

     

    …again PS does it one way, other software the other way…

     

    But Mr. Cox has already explained to you that those "other software" applications are using incorrect terminology:

     

    Chris Cox wrote:

     

    Yes, video and some 3D applications tend to get the concepts confused (even though many of them allow multiple alpha channels). 

                    [emphasis added]

     

    Read the entire text of his posts.  It seems that you took some speed-reading course that is impairing your comprehension.

     

     

    If you want to remain perennially ignorant, that is fine with me.  As I told you before, my concern is for future readers of this thread.  They should not be misled by your ill-considered, wrong-headed posts so far.

     
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  • Currently Being Moderated
    May 4, 2013 2:38 PM   in reply to station_two

    Look, he had it confused, but now he's got it figured out enough to accomplish his task (even if still not getting it all quite right).

     

    Let it go.

     

    If he wants to learn more, figure out why file formats have different transparency capabilities, figure out why so many apps mess up transparency handling, etc. -- he can come back and ask.

     

    Until then, just let it go.

     
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  • Currently Being Moderated
    May 4, 2013 4:52 PM   in reply to Chris Cox

    Absolutely.  I had no plans to address the OP directly anymore.

     

    As I said I was only concerned with future readers getting confused by his posts, but I believe there are more than enough caveats on the thread for the future readership to grasp the issue.

     
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