What are these different kinds of masks and how are they used?

Hi,

I have been studying the topic of masks, and in my information
gathering have come across reference to many different kinds of masks.
Could someone summarize what these masks are, how to create them and
how and why to use them?

While layer and gradient masks are perhaps more familiar to people I
have included them just to keep my list complete.

I got started on this topic when I came across a keyboard equivalent
for selecting the luminosity of a layer (Cmd-Opt-~/Ctrl-Alt-~). I
began to wonder what the difference was between using the Magic Wand
and using this luminosity mask equivalent, and this led to gathering
this list

layer mask
gradient mask
blend mask
edge mask
midtone mask
luminosity mask
highlight mask
contrast mask
shadow mask
density mask

Thanks for any help,

Dale

 

That's a lot you're asking. I'd say RTFM

 

Get a good book and learn how to use Photoshop. Try Photoshop Artistry
for whatever version of PS you have. it covers what you've asked in
about 5 or 6 chapters.

 

Mike,

Thanks for the response...

Couple of questions related to your post...Actually as I wrote this
the questions kept increasing. I think there is a major philosophical
principle of PS going here that I am not getting and maybe you can
ferret it out.

When you talk about a shadow mask being "a mask with max value in the
shadows", what do you mean? I assume that a shadow mask masks the
shadows so that everything else shows through, but I am having trouble
wrapping myself around the "maximum value in the shadows" statement.

In an RGB image, are "maximum values" the blacks with lower rgb
values, or the whites or higher rgb values. I assume the latter. This
maximum value thing confuses me because I tend to think of whites as
no pixels, gray as 50%, and black 100% pixels, which I think is true
with CMTK but the opposite with RGB. Do you see my confusion here?

This leads to some much larger questions that I put at the top of my
original post:

What is the difference in what is happening between using the Magic
Wand in a layer vs. a channel.

And what is actually happening when you Cmd/Ctrl-click in a mask or a
channel. As with any selection, are you selecting all pixels with at
least 50% of white value. But then different things happen when you do
that in each of the channels. So then...in a green channel, do white
pixels represent more green in the image than black pixels?

If you use the magic wand in a layer you are selecting by color I
think, but I have never been clear about what that actually means. But
if you use the magic wand in a channel or on a layer mask, I think you
are selecting based on brightness value, or luminecence.

I came across a keyboard command Cmd-Opt/Ctrl-Alt-~ which "loads
composite as selection". What does THAT mean. Or Cmd/Ctrl-~ will
"load composite channel". What does that mean?

Help! If you could answer even one of my confusions here, I would
appreciate it. Or figure out the larger principle at foot here that
would be great.

As for permission to make a page up about different masks, go for it,
and send me the link!

Dale

 

It means that the layer or effect controlled by the mask has a max
(nominally 255) value for the shadows. For example, using the Dust and
Scratches filter with a shadow mask will remove noise from the shadows only,
and leave detail in the brighter parts of the image, the midtones and
highlights, alone.

In curves it's true with either one, depending on how you set your curve
axis. RGB folks think of 255 as bright, 0 as black. For print folks, 0 is
white, 100 is max ink. Internally, Photoshop stores 100% ink as zero.

Similar concepts, in that the selection created by the magic wand will limit
any subsequent filter or other image operations to the selected area, just
as a layer max will limit them to the areas with nonzero mask values. A
selection is temporary, and not associated with a layer. A layer mask is
permanent, and stays with the layer.

The cmd/ctrl click loads a the image data or mas as a selection.

If the magic wand is clicked on a color image, then the color and brightness
are used to determine the resulting selection. In a monochrome image,
channel, or mask, the pixel values are used directly.

That does a per pixel brightness calculation based on the color image, and
loads that as a selection.

Try reading Alvy's article on the alpha channel. I like that article
because it describes the original problem that the alpha channel solved,
which was to emulate the masking operation use in film for compositing movie
images. Photoshop was developed at ILM, and Alvy I'm sure had a hand in
getting the alpha channel concept into Photoshop - everyone was using it.

If that doesn't ring a bell, do a google search for alpha channel, and
"layer mask" and find something that makes sense. And play with the stuff.
It's free after all. Make an image with several layers, and play with
selections and layer masks.

Cool!