Doug Kerr
Well-known member
A very useful functionality of Photoshop is the clipping mask. But it took me a while to figure out exactly how it works. The Photoshop Help for it just makes my head hurt.
How it works and what it does
A clipping mask is a "normal" (content) layer that has been given a special power. Its own pixel content is not normally seen, and does not normally ever enter into the image buildup.
But the opacity of this layer, pixel-by-pixel, is conferred on the content layer above.
Wherever the special layer is 100% opaque, the layer above acts as if it is 100% opaque. Thus, its pixels participate in the image buildup; they will "cover up" the pixels of a layer below the special layer.
Wherever the special layer is 0% opaque, the layer above acts as if it is 0% opaque. Thus, its pixels do not participate in the image buildup; they will "cover up" the pixels of a content layer below the special layer.
Wherever the special layer is (for example) 30% opaque, the layer above acts as if it is 30% opaque. Thus, its pixels participate in the image buildup at "30% of par"; they will "30% cover up" the pixels of a content layer below the special layer (such that they participate in the image buildup at 70% of par.
Note that the pixel colors in the special layer have no effect on this, only their transparency.
Setting this up
To put this deal into effect, we can:
• Right click on the control bar for the layer above the one to be made a clipping layer (the layer whose content is to be affected by the clipping mask); click on Create Clipping Mask.
or
• Alt-click on the boundary between the "layer to be governed" and "the layer to be made a clipping mask".
Once we have done this, the layer to be governed shows a "left then down" bent arrow. That says, "look down there: that is my boss".
An alternate description
There is an alternate way to describe what happens here:
• The pixels on the layer above the special layer never appear in the image buildup.
• The pixels of the special layer are replaced by the pixels of the layer above with respect to pixel color, but retain the opacity of the original inhabitants of the special layer. Those immigrant pixels then participate in the layer buildup in the usual way.
Thus, only where those immigrant pixels have an opacity greater than 0% (which is where the original content of the special layer had an opacity greater than 0%) will they be seen.
Best regards,
Doug
How it works and what it does
Note that in the basic story here, no layer masks are involved.
A clipping mask is a "normal" (content) layer that has been given a special power. Its own pixel content is not normally seen, and does not normally ever enter into the image buildup.
But the opacity of this layer, pixel-by-pixel, is conferred on the content layer above.
Assume for simplicity's sake in the following that the basic opacity of the content layer above, and of the pixels of its content, is 100%.
Wherever the special layer is 100% opaque, the layer above acts as if it is 100% opaque. Thus, its pixels participate in the image buildup; they will "cover up" the pixels of a layer below the special layer.
Wherever the special layer is 0% opaque, the layer above acts as if it is 0% opaque. Thus, its pixels do not participate in the image buildup; they will "cover up" the pixels of a content layer below the special layer.
Wherever the special layer is (for example) 30% opaque, the layer above acts as if it is 30% opaque. Thus, its pixels participate in the image buildup at "30% of par"; they will "30% cover up" the pixels of a content layer below the special layer (such that they participate in the image buildup at 70% of par.
Note that the pixel colors in the special layer have no effect on this, only their transparency.
Setting this up
To put this deal into effect, we can:
• Right click on the control bar for the layer above the one to be made a clipping layer (the layer whose content is to be affected by the clipping mask); click on Create Clipping Mask.
or
• Alt-click on the boundary between the "layer to be governed" and "the layer to be made a clipping mask".
Once we have done this, the layer to be governed shows a "left then down" bent arrow. That says, "look down there: that is my boss".
An alternate description
There is an alternate way to describe what happens here:
• The pixels on the layer above the special layer never appear in the image buildup.
• The pixels of the special layer are replaced by the pixels of the layer above with respect to pixel color, but retain the opacity of the original inhabitants of the special layer. Those immigrant pixels then participate in the layer buildup in the usual way.
Thus, only where those immigrant pixels have an opacity greater than 0% (which is where the original content of the special layer had an opacity greater than 0%) will they be seen.
Best regards,
Doug