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Clipping Path vs Alpha Channel

Mar 11, 2010 8:44 PM

Not sure if this is the right place to ask, but wondering which is better for outlined images (no soft transitions, just hard outline.)

 

I've used both and don't see an advantage to either EXCEPT when converting an InDesign file to PDF. Files with PSDs with clipping paths seem to make much larger pdfs than same file using PSD with alpha channel. Not important for a final press file, but when I have to email screen proofs, then it's a big deal.

 

Anyone care to weigh in? Thanks.

 

Ringo

 
Replies
  • Currently Being Moderated
    Mar 12, 2010 7:11 AM   in reply to Artdirectorringo

    Here's a suggestion.

     

    Let's say you have a simple flat image. In Paths window in Photoshop, a path is defined as a clipping path. The image is saved as a PSD and placed in InDesign.

     

    InDesign of course recognizes the clipping path. Export a PDF, you end up with a hard vector edge, but a cumbersome PDF (which is unfortunate but normal).

     

    1. Back to Photoshop. Duplicate the background layer. Click on the clipping path in Paths panel. Layer: Vector Mask: Current Path. Save and close.

     

    2. Back to InDesign. Update the image. Object: Clipping Path: Options. Change Type to None, enter. Object: Object Layer Options. Hide the background layer.

     

    3. Output a new PDF, you have an Alpha mask instead of hard edge. Even though it is defined as a vector mask in Photoshop, InDesign treats it as soft mask because the image is saved in PSD format (as opposed to EPS or PDF).

     

    To get the hard edge back again, just reverse the InDesign procedure (step 2), no need to go back to Photoshop.

     
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  • Currently Being Moderated
    Mar 12, 2010 9:44 AM   in reply to Artdirectorringo

    If you need crisp edges (shapes, boxes, rules etc), then vector output is best. But if you silhouette a person, you need a soft mask to get semi-transparent edges.

     

    Certain RIPs and trapping engines can have trouble with complex vector output from Photoshop. The reason is that it is not fully vector. The fill is raster and the mask is vector. The same is true with Photoshop text.

     

    For artwork type designs, especially those with text, it is much better to build it in Illustrator or InDesign, where you have true, clean vector. Then the PDF output is much more streamlined and screen redraw is faster.

     
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  • Currently Being Moderated
    Mar 30, 2010 9:45 AM   in reply to Artdirectorringo

    Hi, there,

     

    I found this discussion during a search for alpha channels vs. clipping paths for clipping (for a job I'm working on), and thought I'd offer my own feedback based on my own experiences w/ similar files. I can't really offer a printer perspective, however, although we do work closely with many and also print film fairly regularly for local printers who are not yet Direct-To-Plate.

     

    For what it's worth, I use paths, myself, and save the file as a TIFF. Then I use the Object: Clipping Path menu in InDesign to select the path (I don't specifically designate a path as an actual clipping path in Photoshop anymore, as sometimes an image will have more than one path to isolate different elements).

     

    I find that alpha channels don't look very good when used in InDesign. They're just not that smooth/precise, in my admittedly limited use.

     

    I've uploaded a quick sample to http://i486.photobucket.com/albums/rr222/Xiebinrui/Alpha_vs_Clipping.j pg -- it's pretty self-explanatory, but the left side shows the bottom of an image using an alpha channel created from the original clipping path (cmd-click on the path to create a selection and then click the "create channel" button in the Channels tab, which automatically creates an "Alpha 1" channel), with the original clipped version on the right. I've tried adjusting the threshold and tolerance in InDesign, but it just always looks bad.

     

    I also haven't used the behemoth Photoshop EPS format since my QuarkXPress/Mac OS 9 days (even then, it eventually became possible to use TIFFs w/ clipping paths -- I could finally see my photo correctly instead of with the horrible Quark EPS preview).

     

    Anyway, re: alpha channels, maybe it's just that I don't know the right way to use them, but they don't seem to be very smooth when importing into InDesign (I was working on a job yesterday and today for which I had to download hi-res images from the client -- many of which used alpha channels instead of actual paths, but they're used on white backgrounds in InDesign, so I just didn't use the channels).

     

    So, anyway, I personally use and recommend paths (vector masks, as Artdirectorringo mentioned, seem to work fine, too) as opposed to standard pixel-based alpha channels, in general, if you're going to be placing the file into InDesign.

     
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  • Currently Being Moderated
    Mar 30, 2010 10:05 AM   in reply to BriGuyAG

    BriGuyAG wrote:

     

     

    I've uploaded a quick sample to http://i486.photobucket.com/albums/rr222/Xiebinrui/Alpha_vs_Clipping.j pg -- it's pretty self-explanatory, but the left side shows the bottom of an image using an alpha channel created from the original clipping path (cmd-click on the path to create a selection and then click the "create channel" button in the Channels tab, which automatically creates an "Alpha 1" channel), with the original clipped version on the right. I've tried adjusting the threshold and tolerance in InDesign, but it just always looks bad.

     


    When you create a mask from an Alpha channel in InDesign the result is a clipping path, not a soft mask. To get a true soft mask you have to create the mask in Photoshop using layers.

     
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  • Currently Being Moderated
    Mar 30, 2010 10:38 AM   in reply to Printer_Rick

    Ohhh, OK. Thanks!

     

    Oh, and "...(vector masks, as Printer_Rick mentioned, seem to work fine, too)" -- that's what I meant (fixed credit). Oops!

     

    I couldn't go back in and edit my original post from earlier.

     
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  • Currently Being Moderated
    Mar 30, 2010 11:31 AM   in reply to Artdirectorringo

    Cool, I'm glad you got something working for you.

     

    I'm not sure if I was totally clear, but I don't actually create the paths in InDesign -- I use the pen tool in Photoshop and save the path there as "Path 1" or whatever I feel like naming it.

     

    Then, in InDesign, I place the photo and select the path I want to use from the Clipping Path menu -- in there I select "Photoshop Path" from the "Type" drop-down and "Path 1" from the "Path" drop-down (InDesign CS2).

     
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  • Currently Being Moderated
    Mar 30, 2010 12:53 PM   in reply to Artdirectorringo

    I don't have any issues w/ clipping paths, it was just the alpha channel method of "clipping" in the sample that looked wrong (the left). I think Printer_Rick nailed it in that InDesign is essentially trying to turn a raster mask into a vector clipping path and it just doesn't work the same way as importing an already-vector clipping path (or vector mask -- his vector mask procedure worked for me, as well).

     

    My display is always set to High-Quality Display (a PDF/X-1a of the sample looks bad, too -- or rather the alpha mask version on the left does; the clipping path on the right looks fine).

     

    Message was edited by: BriGuyAG

     
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  • Currently Being Moderated
    May 11, 2010 12:44 PM   in reply to Artdirectorringo

    Is there any way in InDesign to mask several objects into one frame?

     
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  • Currently Being Moderated
    May 11, 2010 3:09 PM   in reply to Peggie Wiechman

    Sure. Group all the items you want masked. Copy. Draw the container and Paste Into.

     
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    May 12, 2010 5:53 AM   in reply to Printer_Rick

    Yep, thanks...I finally figured it out!

     

    Do you know how to unmask items?

     

    The only way I found to do it was to use the white arrow and dbl/triple

    click on item inside of mask and delete?

     

    Is this the only way?

     

    Thanks so much,

    Peggie

     
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  • Currently Being Moderated
    May 12, 2010 6:29 AM   in reply to Peggie Wiechman

    Peggie Wiechman wrote:

     

    Is there any way in InDesign to mask several objects into one frame?

    As you are stepping into a specific application question instead of the broad print design topic already in progress, it may be ideal for you to be asking this in the InDesign forum.

     
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  • Currently Being Moderated
    May 12, 2010 6:57 AM   in reply to Peggie Wiechman

    Select contents, cut, paste in place.

     
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  • Bernie X
    91 posts
    Feb 20, 2002
    Currently Being Moderated
    May 23, 2010 12:55 AM   in reply to Artdirectorringo

    Sorry if I am rehashing, but PSDs don't include a clipping paths, they do have alpha channels and regular paths.  Thus a PDF of an INDD file with a clipping path would be larger because there's more information in the file.

     
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  • Currently Being Moderated
    Aug 21, 2010 1:32 PM   in reply to Artdirectorringo

    thanks for helpful information. need good quality clipping path service follow me.

     
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