3 Replies Latest reply on May 5, 2014 7:17 AM by rob day

    Problems with placed PDF bit depth

    Optima-OGC

      4bitrgb.PNG

       

      The left image is a view in Acrobat Pro of an original file. This also appears correctly inside the Indesign document in high-res preview. The right shows the result after an export to PDF of this ID document.

       

      The colored background in the original image is a 4-bit RGB bitmap image; on the right, Acrobat Pro claims it's now "24-bit". The original image cannot be edited through TouchUp with Photoshop (it claims it's an "Unsupported color space"); refrying the original by printing it again to PDF does not work either, as the image stays unchanged. Changing the color space inside the original PDF leads to the same result (the color space changes but the bit depth stays the same). Opening the entire PDF in Photoshop gives the same result as shown on the right (because apparently PS cannot handle this 4-bit color space).

       

      The only way of fixing the color space that worked so far is to open the entire PDF in Illustrator and saving it again as AI. However, Illustrator converts *some* text to outlines (without specifying why, as it's all Arial).

       

      Any suggestions on how to fix this while maintaining the original vector data?

       

      ****

       

      (OT, but worth mentioning anyway: I had to log in (wait), browse to ID forum (wait again), find a "Post" button that worked (wait again), and attempt to write this mail in 3 different browsers. IE does not work -- you cannot insert an image and expect to be able to type text. Firefox took so long to even load the text editor that I gave up. Chrome works -- slowly. Definitely room for improvement there.)

        • 1. Re: Problems with placed PDF bit depth
          rob day Adobe Community Professional & MVP

          edited through TouchUp with Photoshop (it claims it's an "Unsupported color space");

           

          That's right Photoshop has the 1-bit Bitmap Mode, and the 8-bit Grayscale, Duotone, and Index Color modes with nothing in between.

           

          I assume you tried exporting with compression and down sampling turned off?

          • 2. Re: Problems with placed PDF bit depth
            Optima-OGC Level 1

            Rob Day wrote:

             

            I assume you tried exporting with compression and down sampling turned off?

             

            I did not ... but indeed this "solves" this particular issue! So thanks for pointing this out; the problem is not the image itself, but ID's internal sub-standard sub-sampling algorithm.

             

            However, I insist on "solves" between quotes because it may only move the problem "down the production line". The rescaled, not-resampled image now has a resolution of 495 ppi in the final PDF. That is too much for offset printing, so one way or the other this image is going to be downsampled. Much as I'd like to leave this to the printer (and so let him solve it if it goes wrong again at his end), I'd rather take responsibility to provide a correct file.

             

            I guess there is no chance Adobe is going to provide a fix for this for my trusty old CS4.

            • 3. Re: Problems with placed PDF bit depth
              rob day Adobe Community Professional & MVP

              ...now has a resolution of 495 ppi in the final PDF. That is too much for offset printing, so one way or the other this image is going to be downsampled.

               

              Sampling down certainly isn't going to improve an image and whether it gets sampled down at output is up to the printer.

               

              It would be possible to have a CMYK image with no halftone dot (colored line art) so an image to line screen rule of thumb wouldn't apply. In that case 495 might not be enough.