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Thread: Alpha Channel

  1. #1
    Join Date
    Mar 2002
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    Alpha Channel

    hey can any one tell me that what is alpha chanel and where and why we use them ?

  2. #2
    Join Date
    Mar 2002
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    Orlando, FL
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    in simple words.. if there is an alpha channel, then the background is going to be cut out of the picture...I'll try to show you an example:

    here is a ZIP file with 2 exact pictures but one is with and other is without an alpha
    Attached Files Attached Files

  3. #3
    Join Date
    Mar 2002
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    just to add to this, an alpha channel is a grayscale image which dictates which part of you original image will be 'cut out' when you composite the pic on top of something else, so you can get nice edges around the part of the pic you want to use.
    You can create an alpha channel in PS just by saving a selection or making a copy of your Quickmask or various other ways. Not all file formats will save the alpha info.
    Targa is the one I use (32 bit) you can then use the alpha channel in other programs (eg Premiere, Combustion etc) HTH

  4. #4
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    just a quick addition. for web pages you can use a gif or png type file. gif only has one level of transparency and png has 256 levels of transparency. for games work its either targa -tga or one of those nifty Direct X exporter utility file types. for print work use tif type files.

  5. #5
    laz0r's Avatar
    laz0r is offline = teh woot—call me laz :D
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    you can also use the alpha channel to create more depth into your pictures (instead of using layer styles)

    i usually use gif for simple webgraphics, but jpg is better for more detailed pics

  6. #6
    Join Date
    Mar 2002
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    Just as a quick comment, as of this moment I wouldn't recommend using PNG with alpha on websites because of one single reason. Internet Explorer doesn't fully support it, and that (at least for me) would be a reason to not use it (at least not with the alpha) broadly, since it is, by far, the most used internet browser. As a test, check this website. On internet explorer, the suposedly transparent section will show as either pink or light grey and the last four images will just now show at all.
    "If you put together all the work I did on "Shrek", I would say I have spent more time promoting it in the last three days than I did actually working on it... When you compare that to the amount of work that the animators and producers put into it, I’m embarrassed to get all the attention and praise for it." - JOHN LITHGOW
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