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InDesign black actually 91%K

Jan 19, 2013 6:11 PM

Tags: #pdf #black #export #indesign #print

Hi all,

I've seen this discussed in many forums, but I have yet to come across a satisfying solution, so I thought I'd try to find an answer.

 

The problem seems simple:

 

For the sake of discussion let's imagine a single page in inDesign with one word or graphic shape in the middle, set in black, using the default indesign 'black' swatch. This is a greyscale document, and will be sent to an off-set press for printing with no colour signatures. Just a black plate.

 

I export this page as a PDF and view it on screen: the text doesn't show black, but more of a grey. I thought no problem, it's just showing me an approximation or a proof black that shows how it will be on paper (if it is set in RGB, it comes out nice and black).

 

So to test, I open the PDF in photoshop to check the levels. Lo and behold, the black is not 100%, but 91%K.

 

Why is the black not black? And should I worry about this? (Images with a 100 seem to come out black just fine).

 

Anyone any thoughts?

 

Thanks in advance.

 

eu.

 
Replies
  • Currently Being Moderated
    Jan 19, 2013 7:16 PM   in reply to temple_of_doom

    First of all, you should not open the PDF file in Photoshop to accurately assess colors since by definition, Photoshop will do color conversions when opening a PDF file for objects for which the color space in the PDF file does not match the default color space of Photoshop.

     

    You can readily determine the actual colors in Acrobat Pro itself using the Output Preview=>Separations  function (typically under Print Production). Move the cursor to the “black” object and see what it says about the values of CMYK. Pure black should be (0,0,0,100).

     

    If Acrobat doesn't show (0,0,0,100) for the CMYK values, you would need to look at your export settings and make sure that the CMYK output color space matches the CMYK color space of the document itself and that you are making no color conversions during the export process. For example, if your default/document CMYK color space is US Web Coated SWOP and you are exporting to Fogra, you could readily expect changes in the colors.

     

              - Dov

     
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  • Currently Being Moderated
    Jan 20, 2013 4:22 AM   in reply to temple_of_doom

    There's another way I can think of to get 100% K to convert to 90-something % black in the PDF, and that's to do a conversion to a grayscale profile. Prior to CS6 it was not possible to export to grayscale, though you could print to postscript/distill, but in CS6 you can now select a grasycale profile on export.

     

    My understanding is that rich blacks (Blacks with cmy components, or rgb), which are darker than 100% K, are mapped to the 100% value in the grayscale conversion, and in order to maintain the relative darkness the 100% K in the original is mapped to a screened value in the output. To avoid this you can change your settings in the Appearance of Black preference item. Choose Display All Blacks Accurately and Output All Blacks as Rich Black. This will NOT have any adverse effect on exporting PDF to a non-grayscale space.

     
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  • Rob Day
    3,138 posts
    Oct 16, 2007
    Currently Being Moderated
    Jan 20, 2013 2:30 PM   in reply to temple_of_doom

    Why is the black not black?

     

    If you print the black separation of your default black object it will output as 100% as long as the destination is document CMYK. If you make a color conversion from CMYK to grayscale the resulting gray value will depend on the source CMYK profile and the destination gray profile. The US Prepress Default color setting converts 0|0|0|100 CMYK to 91% grayscale.

     

    Here PS Info is set to Actual Color (CMYK) on the left and grayscale on the right—the K value will change if I change profiles

     

    PhotoshopScreenSnapz001.png

     
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  • Rob Day
    3,138 posts
    Oct 16, 2007
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    Jan 21, 2013 5:27 AM   in reply to temple_of_doom

    interesting that the US prepress default exports to 91%.

     

    You get 91% if you make a conversion to grayscale and the grayscale profile is 20% dot gain. A conversion may or may not happen during export.

     

    ID doesn't have a grayscale space, so if you want to build a 1-color document you should use black only and output the black separation.

     

    The grayscale numbers you get on a conversion depend on the source and destination profiles. If you assign the CMYK source as Photoshop 5 Default and the gray destination as Dot Gain 20%, black only CMYK values will convert unchanged to grayscale.

     

    Message was edited by: Rob Day

     
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  • Currently Being Moderated
    Jan 21, 2013 5:31 AM   in reply to temple_of_doom

    As I said, if you set your Appearance of Black preference as I indicated, this will not happen.

     
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  • Rob Day
    3,138 posts
    Oct 16, 2007
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    Jan 21, 2013 6:32 AM   in reply to Peter Spier

    As I said, if you set your Appearance of Black preference as I indicated, this will not happen.

    That forces 0|0|0|100 to 100% grayscale, but doesn't match other values. So if the source is the default US SWOP and destination is 20% Dot Gain, 0|0|0|95 converts to 90%, 0|0|0|90 converts to 82%, etc.

     

    Here I'm sampling what was 0|0|0|90 in ID converted to 20% dot gain:

     

     

    AcrobatScreenSnapz001.png

     
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  • Currently Being Moderated
    Jan 21, 2013 6:53 AM   in reply to Rob Day

    That's quite true, but the result is that you are spreading the entire 0-100% tonal range over 0-100% output and maintaining the relative values rather than clipping off the full black and rendering screened type. In my opinion it's more important to render a solid black and keep the relationships between the shadows and the midtones than it is to preserve absolute percentage values.

     
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  • Rob Day
    3,138 posts
    Oct 16, 2007
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    Jan 21, 2013 7:50 AM   in reply to Peter Spier

    In my opinion it's more important to render a solid black and keep the relationships between the shadows and the midtones than it is to preserve absolute percentage values.

     

    But that doesn't happen if you export from SWOP to 20% Dot Gain and the appearance of black set to rich. You do preserve 100% black, but you don't preserve all the other relative values—the shadows get lighter and the highlights get darker than the original.

     

    Look at these PDFs and you'll see the problem—the swatch labels are the starting CMYK black values.

     

    This is a Photoshop5 to 20% dot gain conversion:

     

    http://www.zenodesign.com/forum/PS5-20.pdf

     

    Here's SWOP to 20% with rich black turned on:

     

    http://www.zenodesign.com/forum/SWOP-20-RichBlack.pdf

     

    Here's a capture from Acrobat. The SWOP conversion is on the right—the image tonal range is flattened and the blend bands in th shadow end

     

    Screen shot 2013-01-21 at 10.25.14 AM.png

     
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  • Currently Being Moderated
    Jan 21, 2013 8:15 AM   in reply to Rob Day

    You're right. I misspoke. You are expanding the output across the entire tonal range of the output device, which does, indeed lower the contrast and flatten the image slightly.

     

    I don't normally export to grayscale except when I need a conversion from full color and don't want to do the image conversions independently (which is really only for the student newspaper I advise where it's essential that no RGB or CMYK content make it's way into a page and the staff mostly lacks the training to even begin to do a grayscale conversion in Photoshop).

     
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  • Rob Day
    3,138 posts
    Oct 16, 2007
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    Jan 21, 2013 8:34 AM   in reply to Peter Spier

    The reason the PhotoShop 5 Default CMYK profile works is because first generation profiles were curve based and that profile has the black channel at 20% dot gain:

     

    Screen shot 2013-01-21 at 10.55.21 AM.png

     

     

    I still think the better approach is to use an appropriate CMYK press profile like US Sheetfed Coated and don't do any grayscale conversion.

     
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  • Currently Being Moderated
    Jan 21, 2013 8:45 AM   in reply to Rob Day

    Rob Day wrote:

    I still think the better approach is to use an appropriate CMYK press profile like US Sheetfed Coated and don't do any grayscale conversion.

    In general I agree. It's best to use a CMYK profile for the document that matches the output condition and to do the grayscale conversion in photshop to match. But users have long requested the ability to do a grayscale conversion on export, and I think that in that scenario -- moving a color document into grayscale directly during the conversion process -- the output as rich black is a very good option since it keeps the type solid. My presumption is that the conversion of images is of less importance in that scenario than maintaining a solid black. If it were not, I think, the user would be doing grayscale conversions on the images individually.

     
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