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  #1  
Old May 26th, 2011, 06:56 PM
Doug Kerr Doug Kerr is offline
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Default Photoshop - Clipping masks and clipped adjustment layers

Hey, Photoshop experts,

I need help dealing with some overlapping language in Photoshop.

There are two "constructs" that both involve the word "clip". As I understand, this is the deal:

Clipping mask - An otherwise "ordinary" layer can be given a special power; wherever its content is not (fully) transparent, the pixels in the layer above have their normal opacity (typically 100%). Wherever its content is (fully) transparent, the pixels of the layer above are given a opacity of 0%.

Clips to the layer below - When an adjustment layer "clips to the layer below", it only affects the layer immediately below it; when it "does not clip to the layer below", it affects all layers below it.

I have been trying to find some relationship between these two concepts, but so far I haven't found it.

And that's OK. Indeed, in English, "clipping" (as in "clipping my hair") isn't necessarily related to "clip" ("clip your check to your application").

Of course, it is unfortunate that the names have the same root, if in fact the terms as used here have nothing to do with each other. ("Oh, you said 'illuminance'. I thought you said 'luminance'.")

But now we find another funny thing.

If I right click on the layer control bar for an adjustment layer, I find on the context menu "Create Clipping Mask". If I click on it, it makes the adjustment layer be clipped to the layer below.

If I right click on the layer control bar for an image layer, I find on the context menu "Create Clipping Mask". If I click on it, it makes the image layer below into a clipping mask.

If I right click on the layer control bar for an adjustment layer that clips to the layer below, I find on the context menu "Release Clipping Mask". If I click on it, it makes the adjustment no longer clipped to the layer below.

If I right click on the layer control bar for an image layer having a clipping mask below it , I find on the context menu "Release Clipping Mask". If I click on it, it makes the layer below no longer a clipping mask.


Is this because menu strings cost $5.00 apiece, and Abobe was too cheap to make these menu items say what they do in each case?

Or is there in fact some equivalence between "an adjustment layer being clipped to the layer below" and "a clipping mask" that I haven't recognized?

Best regards,

Doug
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  #2  
Old May 26th, 2011, 07:57 PM
Asher Kelman Asher Kelman is offline
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Doug,

I must admit I too have been confused to the extent that I never use "clipping" masks, or I don't think I do. But with your description of the definitions I'm now wondering. Maybe, after all, I've been using them.

To me, it's nomenclature is confusing and I've not ventured there. I do know about the pen tool that creates clipping paths!

Asher
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  #3  
Old May 26th, 2011, 09:16 PM
Doug Kerr Doug Kerr is offline
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Hi, Asher,

Quote:
Originally Posted by Asher Kelman View Post
I must admit I too have been confused to the extent that I never use "clipping" masks, or I don't think I do. But with your description of the definitions I'm now wondering. Maybe, after all, I've been using them.
Maybe so.

Quote:
To me, it's nomenclature is confusing and I've not ventured there.
Indeed.

Quote:
I do know about the pen tool that creates clipping paths!
It is baffling to me that almost every tutorial on the use of clipping paths for masking (including in the Photoshop Help) omits the critical step, after one has made a path and saved its as a clipping path, of making a vector mask based on it (on the layer you want "clipped/masked").

Or is there some way that the clipping path does its work without that?

Best regards,

Doug
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Old May 27th, 2011, 01:22 AM
Joachim Bolte Joachim Bolte is offline
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I think about the word 'clipping' as in paperclip. A device to bind together two things. Depending on what you bind together, the effect will change.

First I'll teach you a shortcut that is way easier than the menu. If you press and hold the Alt-key and leftclick in between two layers (of any kind), the upper one will be clipped to the lower one.

The properties of the upper one will be applied to the lower one, and only to that. If the upper layer is in 'normal' blend mode, and the lower one has transparent parts, the content of the upper layer will replace the non-transparent content of the lower layer. If you lower the opacity of the upper layer, the content of the lower one will start showing through.
Same with adjustment layers, they will apply to the visible parts of the lower layer, and can have their own blend mode.

You can see an example of this in the polaroid-collage thread, where I put my layer setup next to the picture of the horse. For making the polaroid frame I clipped the horses image to a gray square that has the same size as the polaroids image-field. And then to alter the horses image I clipped an adjustment layer to it. That adjustment will only apply to the horses picture, because the polaroid frame itself is not in the clipping stack. It is below it, but it is linked to the clipping mask layer so they always move together. You can make this link by selecting both layers, and clicking the shackles-icon on the bottom of the layers-palette

And for the paths thing using the pen tool... A path is just like any other object, and it is quite similar to a vector shape or a text. You can clip other layers to these in exactly the same way as you would do with pixel-images. An example of this can be found in the thread with the picture of the little boy.
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Old May 27th, 2011, 08:45 AM
Asher Kelman Asher Kelman is offline
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Quote:
Originally Posted by Joachim Bolte View Post
I think about the word 'clipping' as in paperclip. A device to bind together two things. Depending on what you bind together, the effect will change.
Joachim,

Now that makes sense! Thanks for the clear and helpful contribution.

Asher
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  #6  
Old May 27th, 2011, 09:01 AM
Doug Kerr Doug Kerr is offline
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Ji, Joachim,

Quote:
Originally Posted by Joachim Bolte View Post
I think about the word 'clipping' as in paperclip. A device to bind together two things. Depending on what you bind together, the effect will change.

First I'll teach you a shortcut that is way easier than the menu. If you press and hold the Alt-key and leftclick in between two layers (of any kind), the upper one will be clipped to the lower one.
Yes, I had learned of that through the PS Help.

Quote:
The properties of the upper one will be applied to the lower one, and only to that. If the upper layer is in 'normal' blend mode, and the lower one has transparent parts, the content of the upper layer will replace the non-transparent content of the lower layer. If you lower the opacity of the upper layer, the content of the lower one will start showing through.
Same with adjustment layers, they will apply to the visible parts of the lower layer, and can have their own blend mode.
That discussion has helped me to better understand the "clipping mask" behavior.

Your passage I have made blue was one of the keys. Let me try to elaborate a little on it.

For simplciity's sake, I will assume that all material on the upper layer is fully opaque.

Then, one way to describe what happens is this:
Considering the composite result of the two clipped-together layers, each pixel of the lower layer has the color of the upper layer and the opacity of the lower layer.
Now, if we allow variable opacity of the upper layer, the familiar "blending" of the upper and lower layer colors comes into play. I won't right now attempt to expand the above formal description to reflect that, and it isn't really necessary for our purposes here.

This behavior, however, cannot be explained wholly by reliance on the concept that the presence of a "clip" means that the impact of the upper layer of the pair is only on its lower mate, not on any layer lower yet.

To probe that a little bit, suppose we "release the clip", but there is no third layer below which the upper layer could affect. Then it would seem that releasing the clip would not change the composite image. But it does.

In contrast, where the upper layer of the pair is an adjustment layer, in the case where there are no further layers below, applying and releasing the clip seems to have no effect on the overall result (as we might expect from the definition).

So I'm not completely to my goal, which is to see if there is a consistent definition of the effect of the "clip" that fits both the behavior where the upper later is an image layer and where it is an adjustment layer.

I will apply a little relentless reverse engineering to some layer stacks and see what further clues come from that.

You have helped by a lot in this matter.

Thanks.

Best regards,

Doug
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  #7  
Old May 27th, 2011, 01:45 PM
Joachim Bolte Joachim Bolte is offline
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did some reading up, and it seems to me that it is a two-way thing. The bottom layer can act as a mask, and the upper layer can inherit this mask through the clip. At the same time, the upper layer can act as an adjustment (like the normal situation), and the bottom layer will inherit these adjustments. Because of the clip, ONLY the bottom layer will be affected, not the layers below that.

So you could use a clip in two ways. As a specific adjustment tool or as a masking tool (or of course a combination of the two).

Then your interpretation of the word 'clipping' like in cutting would also make some sense
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Old May 27th, 2011, 03:35 PM
Doug Kerr Doug Kerr is offline
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Hi, Joachim,

Quote:
Originally Posted by Joachim Bolte View Post
did some reading up, and it seems to me that it is a two-way thing. The bottom layer can act as a mask, and the upper layer can inherit this mask through the clip.
Yes.

Quote:
At the same time, the upper layer can act as an adjustment (like the normal situation), and the bottom layer will inherit these adjustments. Because of the clip, ONLY the bottom layer will be affected, not the layers below that.
I assume you mean in a situation where the "clipping mask" notion is in effect - where the upper layer is an image layer. (We do not have the clipping layer behavior when the upper layer is an adjustment layer "with a paperclip"- the image layer below it does not act like a mask on its adjustment behavior.) How would such an upper image layer act as an adjustment layer, acting upon the lower layer (or all layers, depending on whether or not there was a paperclip)?

Quote:
So you could use a clip in two ways. As a specific adjustment tool or as a masking tool (or of course a combination of the two).
Yes, and I can't see how to consider those two behaviors the same notion as it plays in two different situations. They seem to be two quite separate notions, joined only by a common root in their names (which is sad).

Even sadder is that the menu items to put both of them them into effect are the same, carrying the specific name of one of them (the clipping mask).

Best regards,

Doug
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  #9  
Old May 28th, 2011, 04:31 AM
Joachim Bolte Joachim Bolte is offline
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Quote:
Originally Posted by Doug Kerr View Post
... (We do not have the clipping layer behavior when the upper layer is an adjustment layer ...
Might be because the adjustment layer contains no pixels to mask. But is that so? What would happen if you put a mask onto a clipped adjustment layer? Would the mask be applied only to the non-transparent parts of the bottom layer? In that case the behaviour is identical, but it's not pixels being masked but an effect.

And how about you adjust a picture not by an adjustment layer, but by giving the upper layer a different blend-mode? The properties would work down only to the non transparent parts of the clipped bottom-layer...

A little test I did now:


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  #10  
Old May 28th, 2011, 06:03 AM
Doug Kerr Doug Kerr is offline
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Hi, Joachim,

Quote:
Originally Posted by Joachim Bolte View Post
Might be because the adjustment layer contains no pixels to mask.
Let me interrupt here to make a point that may be of no importance.

I like to take the view that in fact an adjustment layer contains pixels: a duplicate of the pixels of the layer below, but with the defined "adjustment" applied to them all-over. We of course cannot look at this "secret content".

The "adjustment" to our work then occurs through the ordinary participation of the "secret content" of the adjustment layer in the image buildup. This outlook can help us understand how, for example, using a non-Normal blend mode for the adjustment layer works.

Just a thought. I haven't yet figured out how it might apply to the rest of your thoughts here!

Quote:
But is that so? What would happen if you put a mask onto a clipped adjustment layer? Would the mask be applied only to the non-transparent parts of the bottom layer? In that case the behaviour is identical, but it's not pixels being masked but an effect.
A good question. And perhaps what I said above would help support that conclusion - it is pixels being masked (the "secret content" of the adjustment layer).

Quote:
And how about you adjust a picture not by an adjustment layer, but by giving the upper layer a different blend-mode? The properties would work down only to the non transparent parts of the clipped bottom-layer...

A little test I did now:
You use so many clever tricks in this composition that it makes it hard for me to follow what happens with respect to our issue here.

For example, where does the "stone" pattern come from? Is it on the layer "Layer 2" (I can't see from the thumbnail).

If so, then it suggest to me that Layer 2 is not working as a "clipping mask", since ordinarily there the varying colors of the non-transparent part are not visible. (I am in fact about to post a further analysis of that behavior.)

But I will do some testing here to pursue your lines of inquiry.

By the way, the result of your test is a very nice work!

Thanks much.

Best regards,

Doug
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  #11  
Old May 28th, 2011, 06:33 AM
Joachim Bolte Joachim Bolte is offline
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The layer with the eagle is the clipping mask, it defines the area the clipped layers should work on. To the eagle-layer I clipped two layers, one B&W adjustment with a mask and some layer effects, and one stone texture. They BOTH work down on the eagle layer.

Stone texture is on layer 2, and it stretches from left to right across the whole picture. Becuase that layer is clipped to the layer the eagle is on, it will only show up across the eagle picture, and not on the green parts of the background layer. I changed the blending modus of layer 2 to Overlay, so you can see that the properties of layer 2 work down to the clipping mask, overlaying a brick pattern on the eagle image.

If you want to, you can pick up the PSD of this on ftp://FTPuser:userFTP@217.122.170.96/share, it's called clipping.psd. I made it a bit different to see if the clipping used the combination of a layer and it's mask, rather than only the layer content.
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Old May 28th, 2011, 06:42 AM
Doug Kerr Doug Kerr is offline
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Hi, Joachim,

A test just now done here:

At the top of the layer stack I have an adjustment layer (X).

Just beneath it is an image layer with a transparent ground but some opaque object (Y).

Beneath that is an image layer with some scene (Z).

I apply a paperclip (to use our "universal" term) to the adjustment layer (X).

Then the opacity of Y does not mask the effect of X (the "clipping mask" behavior). Rather, X affects (by applying its "adjustment" to) the content of Y, but not to Z as well.

Y (as modified by X) participates in the overall image buildup in the usual way.

If I then release the paperclip, now X affects both Y and Z. Both (as modified by X) participate in the overall image buildup in the usual way.

This is consistent with the definition of the role of "an adjustment layer clipped to the layer below".

It does not, in any way I can yet see, relate at all to the concept of a clipping mask, which is what we get when we apply the "paperclip" to an image layer and the image layer below.

I believe that the only relationship between those two concepts is that they have:

descriptions with a common root ("clip")
a common indicator on the upper of the two layers involved (the bent arrow)
are enabled/disabled by the identical mouse maneuver (Alt-click on the boundary between the two layers involved)
are enabled/disabled by the identical menu item (Create/Release Clipping Mask).

If these really are two cases of the same concept, it eludes me!

Best regards,

Doug
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Old May 28th, 2011, 07:14 AM
Joachim Bolte Joachim Bolte is offline
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What would be the difference between an adjustment layer and a pixel layer in a certain blend mode? They both tell PS to do 'something' to the layers below, in a slightly different way offcourse, but they both alter the state of layers below.

With the clipping mask you can confine this effect to one specific layer. If that one layer has transparency in it, it is logical that on these parts stay transparent even after appliance of the linked layers. What you see on screen is that the clipping only has effect on visible parts of the picture.

Using the normal blend mode you just tell PS to replace every visible part of the base layer with the clipped layer.
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Old May 28th, 2011, 08:10 AM
Doug Kerr Doug Kerr is offline
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Hi, Joachim,

Let me now make more general my discussion of the interaction of two "image" layers clipped together.
The result below is predicated on the blending mode being based on the gamma in force, not based on "gamma 1.00". This is the "default" mode of Photoshop, and the math is quite simple under that condition.

To adapt my expression of the algorithm to the "linear light blend" situation would make it much more complicated, and I believe thus obscures the principle.
The situation: We have two "image" layers (that is, neither is an adjustment layer), clipped together.

The two layers, working together in the "clipping mask" mode, act together like a single layer in which:

The color* is that of the the colors of the two layers blended in accordance with the opacity of the upper layer (just as in an ordinary blend in the Normal blend mode).

The opacity is the opacity of the lower layer. [This is the unique aspect of the "clipping mask" mode.]
*Note that, as in any case of a layer with semitransparency, this not necessarily the color that we "see" looking at our layer (in this case, the equivalent layer produced by the two layers working together under the "clipping mask" doctrine); that would be affected by the color of the next layer down. Rather, it is the equivalent of the "coded" color in a regular layer, whose values would be read by the Info panel if there were no layer below.
In the common situation where the upper layer is all fully-opaque, that devolves to what I had expressed earlier: the two layers, working together, act like a layer in which:

The color is that of the upper layer of the pair.

The opacity is that of the lower layer of the pair.

Best regards,

Doug
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Old May 28th, 2011, 08:25 AM
Doug Kerr Doug Kerr is offline
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Hi, Joachim,

Now we move to the situation in which we have two image layers "clipped together" (so as to produce the "clipping mask" construct) and the blend mode of the upper of those layers is set to Screen rather than Normal.

Here is the result:

The two layers, working together in the "clipping mask" mode, act together like a single layer in which:

The color is that of the the colors of the two layers blended in accordance with the opacity of the upper layer (just as in an ordinary blend in the Screen blend mode).

The opacity is the opacity of the lower layer.

A corresponding thing seems to occur with the blend mode set to Multiply.

How about that!

Best regards,

Doug
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Old May 28th, 2011, 09:46 AM
Doug Kerr Doug Kerr is offline
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At the head of this thread I called attention to two Photoshop "functionalities" with similar names (and which share some User Interface doodads).

I then asked were these related in any other way. Perhaps, they might be the manifestations of a common concept in two different situations. I have come to a conclusion in that regard: they are actually not related at all.

The two functionalities are:

Clipping an adjustment layer to the image layer below

This means that the adjustment layer affects that adjacent layer only, not all image layers below, which would otherwise be the case.

Clipping mask

This arrangement, invoked on behalf of an image layer, it and the image layer immediately below collaborate in a special way, in effect becoming a layer in which:

The color at any point is the composite of the colors of the two layers at that point, blending in the ordinary way in accordance with the blending mode in effect for the upper layer.

The opacity at any point is the opacity of the lower layer.

Thus, if the lower layer has only fully transparent and fully opaque regions (and if the blending mode for the upper layer is Normal), where the lower layer is opaque the stuff on the upper layer participates in image buildup in the usual way; where the lower layer is transparent, the stuff on the upper layer does not participate (as if it were itself fully transparent).

Thus the lower layer becomes in effect a mask interposed in the stack.

In these circumstances, the actual color of the opaque pixels in the lower layer is of no consequence.

Note that the Photoshop documentation is ambiguous as to exactly what the "Clipping Mask" is. My preferred interpretation is that the lower layer, when in this mode, is a "clipping mask", "clipping out" (for inclusion in the composite image) part of the upper layer.

How are these related?

Their names both include the root "clip".

They can both be put into play or taken out of play by Alt-clicking on the boundary between the layer control bars for the two layers involved.

They can both be put into play or taken out of play by choosing Create Clipping Mask or Release Clipping Mask on the "right-click" menu for the upper layer control bar.

For either, the fact that it is in effect is indicated by a left-then-down bent arrow on the layer control bar for the upper layer.

That's it.

So does that mean if I have an adjustment layer, right click on the layer control bar, and click on Create Clipping Mask, I have made the layer below into a Clipping Mask? No.

In other words, they are related about like mineral spirits and animal spirits are related.

Create

By the way, when we take an adjustment layer, right click on its layer control bar, and select Create Clipping Mask, is a new layer created? No. The image layer below is given unique powers, so it becomes a Clipping Mask.

("Create" is used rather as the British use the term when speaking of conferring a title on a person. When Prince William was recently created Duke of Cambridge, Earl of Strathearn and Baron Carrickfergus, it's not that William was "created" in the sense of being brought into existence. He was just made to be the Duke of Cambridge etc.)

Best regards,

Doug
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