# Need explanation on parameters for freqency separation with 16 bits image.

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Feb 23, 2021 Feb 23, 2021

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Parameters of "Apply Image" : blending operation/scale/offest are never explained in tutorials on Frequency Separation

I understand that for image 8bits (luminance R/V/B coded from 0 to 255),  to get high frequencies (structure) we substract low pass image from original, then the result values are from -255 to + 255, so we use a scale of 2 to reduce values to -128 to +127 and then an offset of 128 to get a final 8bits value from 0 to 255.

For 16bits images (luminance R/V/B coded from 0 to 65535) all tutos use without explanation : Addition with inversion of low pass layer, scale 2 , offset 0. I don't understand how it works ?

Furthermore using substract without inversion seems to give the same result (seems to me normal since addition of the inverse is equivalent to a substract),  so what is the reason of this choice ?

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Feb 23, 2021 Feb 23, 2021

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New Here ,
Feb 23, 2021 Feb 23, 2021

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I use Photoshop 22.2.0 for frequency separation method with  "Image/Applys Image..."

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Feb 23, 2021 Feb 23, 2021

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For 16 bpc, one should introduce a 128 offset with subtract, which leads to a lossy conversion (for what that may matter).

The "standard" 16 bpc method produces a lossless conversion, depending on why one is using frequency separation, this may or may not have a critical affect.

Let me dig up a link for you...

EDIT: There are 26 pages in the topic thread, here is page 1 –

https://www.modelmayhem.com/forums/post/439098

Here is my action:

https://www.dropbox.com/s/7sf1xcijtzdygyh/Frequency%20Splitter%20v4%20Conditional.zip?dl=0

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