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Would Like to Clarify Ops of some Functions in the Calculations Command in Ps

Engaged ,
Jun 06, 2024 Jun 06, 2024

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Hi, I’m hoping someone with Ps expertise (or, an Adobe Ps product mgr.) can help me better understand a few of the settings options in the Image > Calculations pop-up box.

 

I can play with the settings visually, but hoped if I understood a few functions, generally, it might help me be more effective/efficient using Calcs.

 

Okay, here are the settings I hoped to clarify or get a general understanding of:

  • Does the Blending Mode in the Calcs Cmd apply to the doc./channel selected for Source 2?

  • What does Scale do for me - I know it runs from 1-2 but what does it help me achieve (for making masks/selections) if I move the numbers along that spectrum?

  • What is Invert inverting? Again, is it preferable to only invert either Source 1 or Source 2? Is Invert only useful when using a Subtract blending mode?

  • What does clicking the Mask option do? Why wouldn’t we just return whatever we come up with in the Calcs Cmd to an alpha channel then make it usable as a mask in the Ps layers stack? Does Mask achieve the same thing, but more directly? If yes, is any flexibility lost wrt how the mask can be used vs going the alpha channel to mask route?

 

I’m not a math-y person. But I’d like to understand the logic so that I’m not just bumbling around. But, if it is all just trial & error, I’m okay with that too if that's just how it is!

 

Thx in advance to anyone who can help.

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correct answers 2 Correct answers

Community Expert , Jun 06, 2024 Jun 06, 2024

To start:

 

https://helpx.adobe.com/au/photoshop/using/channel-calculations.html

 

The old bible on CHannel OPerationS was:

 

Photoshop Channel Chops

By Bert Monroy; Mark Christiansen; David Biedny; Nathan Moody

ISBN 13 / ISBN 10: 9781562057237 / 1562057235

 

https://www.amazon.com.au/Photoshop-Channel-Chops-David-Biedny/dp/1562057235

 

The $46-$390 USD Amazon pricing reflects its status as an out-of-print collectable!  :]

 

P.S. The following Biblio pricing may be more reasonable:

 

https://biblio.com.au/search.php?stage=1&title=photoshop+channel+chops

...

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Community Expert , Jun 06, 2024 Jun 06, 2024

I think that it is easier to learn calculations by first learning to use the Apply Image command, which simplifies and clarifies the process and concepts.

 

quote
  • Does the Blending Mode in the Calcs Cmd apply to the doc./channel selected for Source 2?


By @Fotomaker01RA

 

The blending mode applies to the result of the operation between source 1 and source 2. If you swap the source around with the same blending mode etc., you get the same result (swapping source 1 for source 2 and source 2 for sou

...

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Adobe
Community Expert ,
Jun 06, 2024 Jun 06, 2024

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To start:

 

https://helpx.adobe.com/au/photoshop/using/channel-calculations.html

 

The old bible on CHannel OPerationS was:

 

Photoshop Channel Chops

By Bert Monroy; Mark Christiansen; David Biedny; Nathan Moody

ISBN 13 / ISBN 10: 9781562057237 / 1562057235

 

https://www.amazon.com.au/Photoshop-Channel-Chops-David-Biedny/dp/1562057235

 

The $46-$390 USD Amazon pricing reflects its status as an out-of-print collectable!  :]

 

P.S. The following Biblio pricing may be more reasonable:

 

https://biblio.com.au/search.php?stage=1&title=photoshop+channel+chops

 

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Engaged ,
Jun 21, 2024 Jun 21, 2024

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Thx again. I got the book and it was just what I needed. It answered my questions. It was $8 used.

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Community Expert ,
Jun 06, 2024 Jun 06, 2024

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I think that it is easier to learn calculations by first learning to use the Apply Image command, which simplifies and clarifies the process and concepts.

 

quote
  • Does the Blending Mode in the Calcs Cmd apply to the doc./channel selected for Source 2?


By @Fotomaker01RA

 

The blending mode applies to the result of the operation between source 1 and source 2. If you swap the source around with the same blending mode etc., you get the same result (swapping source 1 for source 2 and source 2 for source 1). From the behaviour of the related Apply Image command, I would say that it's calculated from source 1.

 

 

quote
  • What does Scale do for me - I know it runs from 1-2 but what does it help me achieve (for making masks/selections) if I move the numbers along that spectrum?

 

Offhand, the most common example of using the scale and offset feature for Add or Subtract blending that I can think of is in Frequency Separation.

 

When creating the high-frequency layer, working in 16 bpc mode for a mathematically lossless conversion, a scale of 2 is used in the Add blend, darkening the result to create a "neutral" mid-grey result for blending the resulting layer in Linear Light blend mode.

 

If working in 8 bpc for a mostly visually lossless conversion,  a scale of 2 and a rounded offset of 128 (mid-grey) is often used and set to Subtract blend mode.

 

quote
  • What is Invert inverting? Again, is it preferable to only invert either Source 1 or Source 2? Is Invert only useful when using a Subtract blending mode?

 

Invert simply provides on-the-fly flipping of the values of the pixels in either source channel. White becomes black, black becomes white, 75% becomes 25% and 50% remains the same. It is useful when it is useful, as it all depends on what you are doing. That's not intended as a glib reply!  :]

 

 

quote
  • What does clicking the Mask option do? Why wouldn’t we just return whatever we come up with in the Calcs Cmd to an alpha channel then make it usable as a mask in the Ps layers stack? Does Mask achieve the same thing, but more directly? If yes, is any flexibility lost wrt how the mask can be used vs going the alpha channel to mask route?

 

Mask gives the user the flexibility to use a primary or alpha channel from any supported open document during the creation of the channel (or selection or doc). Black hides, white reveals. This is a useful and powerful feature, with or without Layers. Before Photoshop 3.0 in 1994, there were no layers, only a temporary floating selection with pixel content that was merged afterwards! The Apply Image and Calculations commands pre-date Layers.

 

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Engaged ,
Jun 07, 2024 Jun 07, 2024

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Thx for taking the time to explain. It helps!

 

Like with my Blending Mode question.  I just didn't know if the Sources were being treated like subsequent layers (1 below 2) in a layers stack and therefore whether the blend mode was being applied to whichever layer (ie in the Cmd context, Source) came last. I'll have to check out the links in the 1st post too. Thx again. 

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