Why is the Pass through layer mode changing this image?

[gasMask]

Hi,
I am using GIMP 2.10.38 on Windows 10.

I'm having difficulty understanding GIMP's group layer mode, “Pass through”. I assume that its influence is limited to the group layer's 'Opacity' and 'Mode' settings. However, my assumption is incorrect because I am getting two different outcomes as shown with this comparison image. So, my question is: why are there two different outcomes, or I could ask, what is happening here?
 
In this comparison image, there are two rows depicting the two outcomes. In the first row, the “Burn” layer is inside the “Pass through” layer group. In the second row, I have dragged the “Burn” layer out of the “Pass through” layer group.

   

Here is the XCF file in question: 
  pass-through.xcf (Size: 752.74 KB / Downloads: 203)

[PixLab]

Yeah.. it says that pass through should pass through and not compute the group before going below/next, thus we think it does act like there is NO group, but there is...

Put the layer group a 3% opacity, and the burn layer 3% inside the group at 100%, like that it will pass through the burn at 3%
(EDIT humm... not sure I understand myself with this explanation)

[gasMask]

Patrice, that is a solution I might be able to use. The problem I'm facing is greater in scale. What I want to do is move group layers out of a complex Layers tree on to the trunk. These layer groups might have multiple layers with random layer modes. All of the layer groups are 'Pass through 100% opacity'. It was working (the moving layers), but then this problem showed up, and I'm still confused about "Pass through" layer mode's role and behavior.

This is Pass through documentation on GIMP's website.

[Ofnuts]

Normally, layer modes define how a layer blends with whatever is under it with in the same "scope", except the bottom layer in the scope which is always treated as in Normal mode.

When you have groups, groups are scopes, so layer modes blend with other other layers in the group. The result is a "virtual" layer (thumbnail of the group) which is applied to the rest of the image using the group blend mode.

Since your "Burn" layer is alone in its group it has no image to apply to so the blend mode doesn't apply and the layer is merely a hardly visible, low opacity version of itself.

Putting the group in Pass-through mode removes the scope (the scope in then the level above, image or parent group), so in that mode your "Burn" layer applies to other layers in the image, in other words in behave as if it were outside the group.

"Pass-through" groups are mostly useful to keep together layers that you want to handle as a unit, even if their blend mode apply to the rest of the image. They are more "management" groups than "effect" groups.

[PixLab]

Now it's bugging me!!!
I mean seriously, because if you have different layers opacity in the group, that will not work. I mean different layers with different opacities, this will not work THAT way.

As Ofnuts excellent explanation from its POV (witch I agree), I feel like > I don't know, because this very xcf you uploaded for us to test never happens to me (1 layer in a group with a mode), and it's a very good example that can be shown to the GIMP team.

Thus I'm sorry, but I don't have an answer, as a matter of fact, I'm kind of flabbergasted by your XCF, I would ask the GIMP team what is happening just to have a different point of view (I mean Ofnuts is right from my POV) and this XCF is perfect to get some answers from the GIMP's team POV.

[gasMask]

Thank you guys for your help! I really appreciate it.

It's strange that I can reproduce this Pass through layer mode behavior with only two blend modes, Burn and Divide.

I think Ofnuts exclamation has led me to a solution to the moving layer problem I was facing. The problem is that the layer in the group is alone. The solution, to moving a lone layer out of a Pass through layer group, is to merge the layer group and then change merged layer back to it's original layer mode and opacity (Burn, 3%). Then the output is the same.

[gasMask]

(07-02-2024, 03:08 PM)gasMask Wrote: I think Ofnuts exclamation has led me to a solution to the moving layer problem I was facing. The problem is that 

I meant to say "explanation".

[Ofnuts]

(07-02-2024, 07:34 PM)gasMask Wrote:

(07-02-2024, 03:08 PM)gasMask Wrote: I think Ofnuts exclamation has led me to a solution to the moving layer problem I was facing. The problem is that 

I meant to say "explanation".

Of course!!!!