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Alpha in Targa, not transparency - Adobe Photoshop 7, CS, CS2 & CS3

Running PS 7.0.1 on Win NT. I want to "key" names/titles over video through a Panasonic MX-70 switcher, which requires 32-bit Targa format w/ alpha channel for its MX-NAVI software. When I save a PS image as a Targa, I get just white bg, not transparent, and it comes back as just one layer of course. The Adobe site says I don't need the Targa alpha channel plug-in for 7.0.1 The NAVI won't load a "psd" file and I am one stumped puppy....

  1. #1

    Default Alpha in Targa, not transparency

    Running PS 7.0.1 on Win NT. I want to "key" names/titles over video through a Panasonic MX-70 switcher, which requires 32-bit Targa format w/ alpha channel for its MX-NAVI software. When I save a PS image as a Targa, I get just white bg, not transparent, and it comes back as just one layer of course. The Adobe site says I don't need the Targa alpha channel plug-in for 7.0.1 The NAVI won't load a "psd" file and I am one stumped puppy.
    Ken Warren Guest

  2. #2

    Default Re: Alpha in Targa, not transparency

    Photoshop 7 shipped using transparency for Targa files -- but that confused too many video users. So 7.0.1 changed back to using an alpha channel with Targa files. Also see the downloads section for Photoshop 7 that has the targa alpha channel version of the plugin available separately.

    So, it depends on exactly which version you're using as to what you need to save in the Targa file.

    BMP has always used an alpha channel, since the format does not support transparency.
    Chris Cox Guest

  3. #3

    Default Re: Alpha in Targa, not transparency

    All right - so I create an image with transparent bg (leave the alpha channel alone). When I save it as a Targa, it comes back with white, not transparent, as the bg. What step am I missing? Do I need to mask the bg and paint it black? I want just the title information to be over video, not the whole image.
    Ken Warren Guest

  4. #4

    Default Re: Alpha in Targa, not transparency

    Ken - again, which version of the plugin are you using?

    It sounds like you're using the alpha channel version. What you saved was flattened, and you didn't add an alpha channel.
    Chris Cox Guest

  5. #5

    Default Re: Alpha in Targa, not transparency

    I'm using PS 7.0.1 w/no plug-ins (that I'm aware of - I'm a capital-R rookie - I haven't added any). My understanding is that 7.0.1 has the alpha channel in Targa (instead of the transparency in 7.0) - when I've added an alpha channel, it's full-screen and I have not been able to modify it to "un-alpha" my text. You don't use the fill tool , do you?
    Ken Warren Guest

  6. #6

    Default Re: Alpha in Targa, not transparency

    with OpenEXR it is standard practice to interpret the "A"
    channel as pre-multiplied alpha. Compositing a foreground
    layer over a background layer is correctly done like this

    composite = foreground + (1-alpha) * background

    Programs that read and write OpenEXR files generally adhere
    to this convention. I don't know how transparency works in
    Photoshop; your message suggests that PS transparency is not
    the same as alpha. This would imply that PS should not treat
    OpenEXR's alpha channel as if it was transparency. Of course,
    PS could add transparency channels as needed when it writes
    OpenEXR files.
    [url]http://www.trainingintambaram.in/informatica-training-in-chennai.html[/url]
    Vignesh Waran is offline Junior Member
    Join Date
    Sep 2015
    Posts
    3

  7. #7

    Default Re: Alpha in Targa, not transparency

    with OpenEXR it is standard practice to interpret the "A"
    channel as pre-multiplied alpha. Compositing a foreground
    layer over a background layer is correctly done like this

    composite = foreground + (1-alpha) * background

    Programs that read and write OpenEXR files generally adhere
    to this convention. I don't know how transparency works in
    Photoshop; your message suggests that PS transparency is not
    the same as alpha. This would imply that PS should not treat
    OpenEXR's alpha channel as if it was transparency. Of course,
    PS could add transparency channels as needed when it writes
    OpenEXR files.
    [url]http://www.trainingintambaram.in/informatica-training-in-chennai.html[/url]
    Vignesh Waran is offline Junior Member
    Join Date
    Sep 2015
    Posts
    3

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