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i_am_jim
i_am_jim
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Multiple Levels Adjustments

Aug 20, 2012 3:12 PM

Question 1:  If I create two levels layers and, adjusting the center slider, I enter 1.5 of lightening on one and .5 darkening on the other, and then flatten the image do the two equal and opposite adjustments cancel each other without altering the image?

 

Question 2:  Assuming the answer to Question 1 is yes, there's no alteration to the image -- if I adjust the first to 1.5 and the other to .6 does this create the same effect and using only one layer with an adjustment of 1.10?

465 Views   4 Replies   Latest reply: c.pfaffenbichler, Aug 20, 2012 11:22 PM
 
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  • Chris Cox
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    1. Chris Cox,
    Aug 20, 2012 3:37 PM   in reply to i_am_jim
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    No, because of quantization.  (the pixel values only have discrete values, not infinitely precise values)

     

    And the middle slider is a gamma factor.  x = y^gamma or x = y^(1/gamma) depending on how you look at it.

     
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  • i_am_jim
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    2. i_am_jim,
    Aug 20, 2012 4:45 PM   in reply to Chris Cox
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    Thanks.  I don't really understand that but it sounds like there would be less image distortion doing this if in a 12 bit image.

     
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  • conroy
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    3. conroy,
    Aug 20, 2012 5:52 PM   in reply to i_am_jim
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    Jim, just remember that gamma(x) followed by gamma(y) is equivalent to gamma(x times y).

     

    To reverse a gamma(x) adjustment, apply gamma(1 divided by x).

     

    Work in 16-bit mode for greater precision than 8-bit mode. (Infinite precision would be required for perfect reversal of gamma adjustments but 16 bits will be good enough for most purposes.)

     
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  • c.pfaffenbichler
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    4. c.pfaffenbichler,
    Aug 20, 2012 11:22 PM   in reply to conroy
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    And with multiple stacked Adjustment Layers even just changing an 8-bit image to 16-bit (without having access to the raw data) can alleviate some quantization effects somewhat.

     
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