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jf83971618
Participating Frequently
April 17, 2019
解決済み

how to stop downsample of images when exporting to print ready CMYK pdf

  • April 17, 2019
  • 返信数 5.
  • 9500 ビュー

Hi,

I'm trying to save a pdf as a print ready (colour) CMYK PDF using acrobat pro.  I've worked out all things except how to stop it downsizing / sampling the images in the original file. Each time I try the images come out slightly pixelated & I have looked online & these forums for an answer to this but can't seem to find one.

to clarify: all I want to do is 'turn off' any downsampling or resizing of images so that the outputted pdf (CMYK) has the same sharp high res images as a normal pdf (RGB)

thanks.

    このトピックへの返信は締め切られました。
    解決に役立った回答 Dov Isaacs

    At this point, a numbers of excellent responses have been provided vis-à-vis conversions of RGB imagery to CMYK and lossiness of such conversions.

    On behalf of Adobe:

    (1) There will be extra lossiness in performing a conversion of an image from RGB to CMYK if this conversion is done post PDF creation. If you really believe you need a PDF file totally in CMYK, that should be accomplished when the PDF file is created, not afterwards if you wish to avoid any lossiness.

    (2) The simple act of converting RGB to CMYK either in PDF creation or afterwards in Adobe Acrobat Pro will not be so lossy that you end up with pixelation where you had sharp imagery before. Such pixelation would occur if you are simultaneously significantly downsampling the image such as 300dpi to 72dpi or even 100dpi. Converting color spaces of JPEG images after-the-fact in Acrobat will also incur some lossiness (although typically not pixelation) – why? The image has to be decompressed from JPEG, converted, and then converted back to JPEG which by definition adds more lossiness! That's exactly why any color changes should occur either when creating the PDF or better, where it belongs, at the RIP/DFE!

    To answer the specific question, the color conversion functionality of Adobe Acrobat Pro does not do any image downsampling! Such downsampling does occur if you try to combine color conversions with other operations.

    (3) Modern PDF print publishing workflows absolutely do not require conversions of content from RGB to CMYK. The ISO PDF/X-4 standard provides for printing from ICC color managed PDF exported/saved from any modern publishing/illustration software. All RIPs/DFEs produced over the last decade should be able to handle PDF/X-4 files at least as well if not much better than any PDF/X-1a or totally-CMYK PDF (with flattened transparency) from original RGB content. Any print service provider that tells you otherwise is either (a) burdened with antique production software, (b) ignorant, (c) a Luddite, or (d) some combination of these. A print service provider that insists that all transparency be flattened and that all content be converted to CMYK as a prerequisite for their printing a job is a good indication that you should consider looking for an alternative print service provider!

              - Dov

    返信数 5

    Dov Isaacs
    Dov Isaacs解決！
    Legend
    April 17, 2019

    At this point, a numbers of excellent responses have been provided vis-à-vis conversions of RGB imagery to CMYK and lossiness of such conversions.

    On behalf of Adobe:

    (1) There will be extra lossiness in performing a conversion of an image from RGB to CMYK if this conversion is done post PDF creation. If you really believe you need a PDF file totally in CMYK, that should be accomplished when the PDF file is created, not afterwards if you wish to avoid any lossiness.

    (2) The simple act of converting RGB to CMYK either in PDF creation or afterwards in Adobe Acrobat Pro will not be so lossy that you end up with pixelation where you had sharp imagery before. Such pixelation would occur if you are simultaneously significantly downsampling the image such as 300dpi to 72dpi or even 100dpi. Converting color spaces of JPEG images after-the-fact in Acrobat will also incur some lossiness (although typically not pixelation) – why? The image has to be decompressed from JPEG, converted, and then converted back to JPEG which by definition adds more lossiness! That's exactly why any color changes should occur either when creating the PDF or better, where it belongs, at the RIP/DFE!

    To answer the specific question, the color conversion functionality of Adobe Acrobat Pro does not do any image downsampling! Such downsampling does occur if you try to combine color conversions with other operations.

    (3) Modern PDF print publishing workflows absolutely do not require conversions of content from RGB to CMYK. The ISO PDF/X-4 standard provides for printing from ICC color managed PDF exported/saved from any modern publishing/illustration software. All RIPs/DFEs produced over the last decade should be able to handle PDF/X-4 files at least as well if not much better than any PDF/X-1a or totally-CMYK PDF (with flattened transparency) from original RGB content. Any print service provider that tells you otherwise is either (a) burdened with antique production software, (b) ignorant, (c) a Luddite, or (d) some combination of these. A print service provider that insists that all transparency be flattened and that all content be converted to CMYK as a prerequisite for their printing a job is a good indication that you should consider looking for an alternative print service provider!

              - Dov

    - Dov Isaacs, former Adobe Principal Scientist (April 30, 1990 - May 30, 2021)
      T
      Test Screen Name
      Legend
      April 17, 2019

      You know what? I'm not interested in helping you any more. You know so much more than us, I wouldn't dare to try.

      J
      jf83971618作成者
      Participating Frequently
      April 17, 2019

      that's ok with me. I asked a simple question & you weren't prepared to answer it, instead trying to get me to answer questions that had nothing to do with it. The question was nothing to do with what program I was using to create the pdf in the first place or about what printers ask for but simply how to turn off downscaling.

        T
        Test Screen Name
        Legend
        April 17, 2019

        So, your quality is reduced but you have not actually checked the resolution. Please do so and tell us the before and after poi, so we can see if your poor quality is really the result of downssmpling, or something else like over-heavy JPEG compression.

        If if you aren’t able to do this, please share before and after files.

        J
        jf83971618作成者
        Participating Frequently
        April 17, 2019

        does anyone at all reading this thread understand that I am asking, again & again, how to turn off the downscaling ?

        the only thing that is altered going through the process of converting the PGB pdf to CMYK via acrobat are that the images are reduced in size & resolution. As its a pdf I can't then select one of the images to check for its res stats.

        seriously, all I want to know is IS IT POSSIBLE TO TURN OFF DOWNSCALING / RESAMPLING ETC OF IMAGES & SIMPLY EXPORT THE PDF AS A CMYK ONE WITHOUT ANY ADJUSTMENT TO THE IMAGES IN THE PDF AT ALL IN TERMS OF RESOLUTION / SIZE etc. (so the only change is in the colour format not in anything else)

        I don't know how much clearer I can be.

          J
          jf83971618作成者
          Participating Frequently
          April 17, 2019

          jf83971618  wrote

          As its a pdf I can't then select one of the images to check for its res stats.

          You can:


          from the outset I simply asked how to stop acrobat doing anything in terms of resolution / size to the images - that is what I meant by being clear & from that I have been asked all manner of other questions which aren't needed to answer that simple question - the question would still be the same if I was using word or pages or....  

          I am using Adobe Acrobat to convert a pdf in RGB (as that is the only format that mac's output in) to CMYK.

          The screen shot you have included that includes the option not to downscale surely is exactly what I was asking about ? however as to where that screen can be found there is no information.

          you insist that I am not answering the questions I am being asked but that is simply because they are not needed for the answer which was only, how do you turn off...etc.    There is no need to know what size or dpi the photos are after conversion etc. I simply wanted to know how to turn off the default for adobe acrobat which is to downsample images over 300dpi.

          I have no idea how to get to the screen you have included & have spent hours looking for such a screen / option before asking.

            Abambo
            Community Expert
            AbamboCommunity Expert
            Community Expert
            April 17, 2019

            So again:

            If I use save in my Acrobat to save the PDF it does neither modify the colour model nor does it down-sample the images.

            So, if you want an answer, you should answer my question that you simply try to ignore for the second time in a row.

            (may I refer you to your point 1)

            Your second point is information from 20 years ago. When I started in this business 30 years ago, I needed to send over EPS files to my printer (with images uncompressed and in CMYK).

            Then they started accepting PDF files but still data in CMYK and no support for transparency.

            The now current standard is PDF X4:2008, and that should be accepted from printers around the world. That's an additional information I gave you and is not the answer to your question. An answer to your question will be given as soon as I understand ​what your doing and how your doing it and I want to add: with what tools (name and version) your doing it.​

            ABAMBO | Hard- and Software Engineer | Photographer
            J
            jf83971618作成者
            Participating Frequently
            April 17, 2019

            seriously, why do you find this so hard to answer.

            I have the original artwork in pages. The printer wants it in PDF  (btw PDFx4 is a CMYK format !). With a mac you can't save a project as a pdf on CMYK. Hence I upload it to Acrobat (which is a recommended bit of software for adjusting pdf's) & then convert to CMYK. Doing so downsizing / downsamples / resizes all images meaning they do not have the original resolution. This is fact - this is what acrobat does to any pdf as it clearly states.  I am simply asking for a way to turn off that system which adjusts all images above 300dpi.

            I have been totally clear from the outset but you have continued to ask for information that has nothing to do with what I need to do. Sorry to sound frustrated but this is why forums are so problematic.

              T
              Test Screen Name
              Legend
              April 17, 2019

              How do you know that doing this reduces the image resolution? Have you measured it?

              Abambo
              Community Expert
              AbamboCommunity Expert
              Community Expert
              April 17, 2019

              First of all:

              If your printer is able to accept PDF X4 files, there is no need any more to convert to CMYK, avoiding an additional step. The RIP will take care of this.

              Second:

              Saving does not modify to CMYK. So I wonder what steps exactly your taking.

              Third:

              Consider using Preflight for the RGB to CMYK conversion.

              ABAMBO | Hard- and Software Engineer | Photographer
              J
              jf83971618作成者
              Participating Frequently
              April 17, 2019

              thanks for the reply but this kind of is similar to some of the other online replies to this simple problem & doesn't actually answer it.

              all I want to know is how to stop acrobat doing anything to the images when converting to CMYK from RGB. supplying a pdf to the printer it needs to be in CMYK & when doing that conversion acrobat rescales the images & the come out pixelated.

                Abambo
                Community Expert
                AbamboCommunity Expert
                Community Expert
                April 17, 2019

                jf83971618  wrote

                thanks for the reply but this kind of is similar to some of the other online replies to this simple problem & doesn't actually answer it.

                Well, if it is similar it may be the correct answer or you were looking at my answers to similar questions

                all I want to know is how to stop acrobat doing anything to the images when converting to CMYK from RGB.

                .Changing RGB images to CMYK images is a huge modification of the image, resulting in some loss of information. You can't simply take a RGB image and convert to CMYK and convert back to RGB and getting the same image than the starting image. You are doing a lossy operation with irreversible information change.

                This said, I assume you only want to change RGB to CMYK and then print. That's OK, but there is a loss in information.

                supplying a pdf to the printer it needs to be in CMYK

                That's assertion was true twenty years ago.

                when doing that conversion acrobat rescales the images & the come out pixelated.

                So please answer this question:

                Second:

                Saving does not modify to CMYK. So I wonder what steps exactly your taking.

                Tell me what exact step you take when you save your PDF file.

                ABAMBO | Hard- and Software Engineer | Photographer
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