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currobegbeg
Currently Being Moderated

8 and 16 bits in grayscale alpha channel

Aug 20, 2012 4:43 AM

Tags: #grayscale #alpha_channel #8_bits_per_channel #16_bits_per_channel

Hello.

When I have an image in 8 bits per channel, its grayscale alpha channel is in 8 bits (256 levels).

But when I have an image in 16 bits per channel, is its grayscale alpha channel in 16 bits (32.768 levels)? They are a lot to make a selection...

 
Replies
  • Currently Being Moderated
    Aug 20, 2012 5:40 AM   in reply to currobegbeg

    Be aware that Selections are 8bit.

     

    Edit: Which means that you will get differnt results

    • if you load the Channel as a Selection and apply it as a Layer Mask and

    • if you copy the Channel’s content and paste it into a Layer Mask –

    though the difference may seem imperceptible.

     
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  • Noel Carboni
    23,469 posts
    Dec 23, 2006
    Currently Being Moderated
    Aug 20, 2012 6:40 AM   in reply to currobegbeg

    currobegbeg wrote:

     

    grayscale alpha channel in 16 bits (32.768 levels)

     

    Just to be numerically accurate, it's 0x0000 through 0x8000, so it's really 32,769 levels including pure black and max white.

     

    -Noel

     
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  • Currently Being Moderated
    Aug 20, 2012 6:45 AM   in reply to currobegbeg

    No, an Alpha Channel in a 16bit image is also 16bit, a Selection is 8bit.

    So if you store a Selection you are storing 8bit data in a 16bit Channel.

     
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  • Currently Being Moderated
    Aug 20, 2012 7:31 AM   in reply to currobegbeg

    Why do alpha channels in 16 bits exist if they are not real?

    They are real, you can copy and paste them into a Layer Mask for example instead of loading them.

     

    http://forums.adobe.com/message/4597174#4597174

     
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