P: LAB values in not reflect image colors from Selective Adjustments to Monochrome images

[Carefree_user15D5]

See screenshot.

(1) The cursor was on the sky (trust me!). You can see that the LAB values for the A and B channels (shown below the histogram are zero (as they are throughout the image) - not surprising because the image has been changed to B&W. But the histogram and the image clearly show a blue sky. (It's blue because I've applied a mask for the sky with a curves adjustment in the Red and Green channel which makes it blue).  But why do the LAB values (which are zero in A and B) not reflect the histogram and the image?

(2) Why would LR allow colour in a B&W profile? I would have expected that applying such a profile would remove all colours?

Educate me please! 

P.S. I'm wasn't trying to create this blue sky. It's just a hangover from the original colour edit after applying the monochrome profile. And yes, I know how to get rid of it.

.

LR Classic 13.0.1. on Mac Mini 2018

[Rikk Flohr: Photography]

For Item 1: I cannot replicate - supplying color via Color Swatch or Tone Curve does represent as color in LAB mouse over.

For item 2: Colors applied via Local Adjustment tools are treated as overlays, not image data.  Many people use this to create warm or cool-toned monochromatic versions. 

[Carefree_user15D5]

Thanks @Rikk Flohr: Photography . To replicate (1) try this:

In an unedited RAW file Create new mask > Select Sky > Apply a curve to the green channel (for example) within the mask.

Then exit the mask and apply the Adobe Monochrome profile by clicking the B&W button (between Auto and HDR in the Basic panel).

If you had the LAB (rather than RGB) data displayed underneath the Histogram you should see A and B values of zero even though the sky has a colour applied as confirmed by the histogram.  The RGB values do reflect the 

coloured sky but the LAB values don't.

On (2). Thank you. That makes sense.

[Bob Somrak]

@Rikk Flohr: Photography 

I can duplicate what the OP is showing.  If the histogram is set for RGB the color values are reflected correctly but in LAB the A/B values are always zero.

[Rikk Flohr: Photography]

I see correct values for A and B that match expectations for a Color Swatch or a Single Color Channel Tone curve. 

There must be a missing piece of information in your reproduction steps.  @Bob Somrak  Can you add any commentary since you can repro? 

 

[Bob Somrak]

@Rikk Flohr: Photography 

Start with Color image

Select B&W

 

Add Sky Mask and use both Red and Green curves to make sky blue.  Then EXIT mask mode

With cursor over blue sky and histogram in RGB mode the values indicate a color blue

is under cursor

Switch histogram to Lab Color and with cursor over blue the A/B values are zero

 

Lab and RGB shoud both be indicating color but only RGB does.

 

 

[richardplondon]

to the second question in the OP title, a monochrome profile strips off all hues on the input side (so, deriving from the imported file) and tells the Basic panel adjustments to treat the image in a B&W manner.

But this does not prevent non-neutral RGB values from arising during other postprocessing, that will show on the output side. Perhaps the clearest example of this is Grading, formerly named Split Toning, which could never have e.g. achieved a sepia tinted or cyanotype 'effect', if denied the ability to vary a monochrome image away from its neutral hue.

[Rikk Flohr: Photography]

Thanks, Bob,

With your instructions, it fails as described. It also fails in Camera Raw. I will convert this to a Camera Raw post and file the bug there as it is the underlying engine - not LrC that is failing. 

Afterwards, I will move the post back for the sake of greater traffic LrC vs CR Forums.

[Rikk Flohr: Photography]

Bug logged with Camera Raw team - thanks for the report and the help!

[Rikk Flohr: Photography]

@Bob Somrak 

I note that until you close the Mask panel, the color does read in LrC but does not in CR. 

[Carefree_user15D5]

Thanks @richardplondon . On the second question (which is now off-topic since the topic has moved!). Yes, I was aware of the post-input colour grading, and the process of colour-toning a B&W image is logical. 
I guess what was surprising for me is that creating a virtual copy of a colour image then converting the copy to B&W can still leave colour in the image.  I would have expected that the input would be the act of creating a virtual copy (to your point about the profile stripping the colour on input).
Thanks anyway.  I'm a little wiser.  

[richardplondon]

yes, a bit OT but a new virtual copy is no different than the first copy - the two can even switch places - and in this nondestructive environment the selection of a monchrome profile can simply be reconsidered in either one, and a full colour profile selected instead.

My own habit is to make a B&W treatment by lowering the saturation to 0 across all the HSL colour ranges, so am always conscious of dealing with a colour image even so (continues to use a colour profile as it happens). And when externally editing I will leave myself the full colour there, and defer any B&W treatment(s) to be only applied onto the image that returns into the Catalog from PS. For the most freedom to vary that B&W conversion.

[Rikk Flohr: Photography]

Greetings all, 

Updates for the Adobe Photography Products have been released.  The May 2024 updates contain an update for this issue. 

If you do not see the update in your Creative Cloud Application, you can refresh it by hitting [Ctrl/Cmd]+[Alt/Opt]+[ R ].

Note: It may take up to 24 hours for your update to be available in your Creative Cloud app.

Thank you for being so patient.