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

Discussion in 'Photoshop Tutorials' started by Dale Glaser, Jun 19, 2004.

  1. Dale Glaser

    Dale Glaser Guest


    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 Glaser, Jun 19, 2004
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  2. Dale Glaser

    V1nc3nt Guest

    That's a lot you're asking. I'd say RTFM
    V1nc3nt, Jun 19, 2004
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  3. Dale Glaser

    Hecate Guest

    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.
    Hecate, Jun 20, 2004
  4. Dale Glaser

    Dale Glaser Guest


    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 Glaser, Jun 22, 2004
  5. Dale Glaser

    Mike Russell Guest

    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.
    Mike Russell, Jun 23, 2004
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