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  1. #11

    Default Re: How to export grayscale image as grayscale in PDF?

    Quote Originally Posted by Ron Duke View Post
    Mike,
    How do I convert a color png to a grayscale png in Acrobat 9 Standard? I can't figure it out.
    Hi Ron,

    I don't know if one can with the Standard version or not. I'll post some screen shots in a bit if needed--and Adobe changed the look of some of the ways one goes about getting to the tools.

    In short, if you have a tools panel, open it. Look for the Print Production tools. Convert Colors is the dialog you want. Let me know if you have that panel/dialog box.

    Mike

  2. #12

    Default Re: How to export grayscale image as grayscale in PDF?

    Just playing with the test version of Acrobat. It's relatively simple to replace an image with its full-resolution grayscale version. Only, then there is loss of contrast. This is unexpected to me. For details, see my question in Graphic Design Stack Exchange.

    Quote Originally Posted by mwenz View Post
    Convert Colors is the dialog you want. Let me know if you have that panel/dialog box.
    Indeed, it's possible to convert color images to grayscale, but again there is the issue with loss of contrast: An existing RBG encoded grayscale image washes out when processed with the Print Production tool. This happens with both conversion profiles that I tried, Gray Gamma 1.8 and Gray Gamma 2.2.

    I am preparing a document for digital print (laser).

  3. #13

    Default Re: How to export grayscale image as grayscale in PDF?

    They seem washed out on-screen. But I think you'll find that a properly prepared image in any color space will do fine on paper.

    But it would seem to me that triple-processing you show in that link is a fault in work-flow. I would leave the image in XDP (or whatever you are using) as an RGB. If you must/desire to at least see it as a "gray" image, use the Saturation tool to desaturate it. Export your PDF. The image appears gray, obviously still an RGB image.

    Use the Convert Colors to change it. Set the Object Type to "Image." Set the "Conversion Profile" to say a 10% dot gain if going to print digital, perhaps higher if using offset (typical would be 15 to 20% depending upon the press). Click OK.

    Now look at the saturation.

  4. #14

    Default Re: How to export grayscale image as grayscale in PDF?

    Quote Originally Posted by mwenz View Post
    But it would seem to me that triple-processing you show in that link is a fault in work-flow.
    Read it more like a bug report, with steps specifically targeted at illustrating an issue that I don’t understand: Why does saturation of grayscale images change on import?

    I would leave the image in XDP (or whatever you are using) as an RGB.
    It’s a grayscale scan. Only Xara exports it as RGB.

    10% dot gain if going to print digital
    Isn’t it possible to convert to grayscale without any contrast adjustment? I could imagine it’s best to leave the image at maximum contrast and let the printer take care of further processing. Maybe I’ll ask the printer, BOD.

    In the first test print, I left the image completely untouched. But then there were color artifacts because of Xara embedding grayscale images as RGB images. In fact the color artifacts are in the generated PDF. They can be seen with the color picker. That's why I want to convert images to grayscale.

  5. #15

    Default Re: How to export grayscale image as grayscale in PDF?

    But you are at least triple-processing anyway.

    Your scanner when scanning to grayscale is applying a dot gain profile and likelya gamma curve to the image.
    You bring it into Xara wherein it is converted to an RGB image.
    Depending on what type of PDF you are producing, you are possibly processing it again at PDF output time. If you are using a CMYK profile, it is now being converted to CMYK. Yet another processing.
    In acrobat, converting it to grayscale yet again is another processing.

    Each time it is processed, you are changing the pixels. Not a good work-flow.

    I have attached the test image from the Wiki page. I placed it into XDP as an untouched, "original" RGB image. I exported to PDF. Whether I use a CMYK or an RGB output profile doesn't matter, the result is identical. I then used the process in Acrobat I described.

    In short, scanning to gray, etc., has only detriment--there is no reason to do so if using an application like an Xara product.

    Click image for larger version. 

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    Mike

  6. #16

    Default Re: How to export grayscale image as grayscale in PDF?

    Quote Originally Posted by mwenz View Post
    In acrobat, converting it to grayscale yet again is another processing.
    I’m fully aware of this, and that’s why I intend to replace the image in the PDF with the original grayscale image from the scan. Of course, the scan has already been converted from RGB as the scanner is an RGB device – thanks for pointing that out. Also I stretched the histogram to give maximum contrast.

    When attempting to replace the image, I ran into something that I didn’t understand:

    Quote Originally Posted by feklee View Post
    Just playing with the test version of Acrobat. It's relatively simple to replace an image with its full-resolution grayscale version. Only, then there is loss of contrast.
    Thanks to shettler’s answer on Graphic Design Stack Exchange, I now understand what is happening. The RGB image is separated into all four CMYK channels. In fact this can be verified using Output Preview in Acrobat’s Print Production tool. The result is a rich black but possibly with a color shift, which in fact is visible in the test print that we ordered. The grayscale image is mapped to the K channel, avoiding the color shift and – I can imagine – rendering to nicer gradients in print.

  7. #17

    Default Re: How to export grayscale image as grayscale in PDF?

    There is no need to replace the image in Acrobat. Your work-flow is an amazingly convoluted one.

    But I'll leave you alone to go about this however you want.

    Good luck.

  8. #18

    Default Re: How to export grayscale image as grayscale in PDF?

    Quote Originally Posted by mwenz View Post
    There is no need to replace the image in Acrobat.
    The alternative would be to convert to grayscale using Acrobat's Print Production tool, i.e. to move image data from all CMYK channels to the K channel. That's definitely no less effort than simply replacing the image, which is extremely easy in Acrobat. If there are many images, things may be different, but in my case, it's only one.

    As for scanning to RGB (48 bit) and letting Acrobat to the conversion to grayscale: Depends on the task, I presume. Converting to grayscale as part of image post processing in a bitmap software gives more control. For example, one may want to use color filters, especially when converting a full-color image.

    In either case, post processing the PDF is necessary, as in Xara it's simply not possible to assign a grayscale image to the K channel only. As far as I understand it, Xara documents are always RGB.

  9. #19

    Default Re: How to export grayscale image as grayscale in PDF?

    No, Xara documents are not all rgb. You can design in cmyk, I do. It is true that they are not a color managed application.

    Using Convert Color under print production one can just choose to convert images, as well as what color space those images are in. Converting everything to use just the K channel can have the effect of lowering/altering the K of non-images, but it doesn't have to with the correct settings. As well, one can create a preflight to do this.

    Adjusting the images (in your case just one evidently) as rgb properly will can result in the same luminance once converted using Convert Colors on just images. But yes, one can have more control over luminance in a decent photo editor. Whether one needs to do so depends on the image. This can all be done in a decent editor using adjustment layers even though the image remains in the rgb color space. I do it almost every day.

  10. #20

    Default Re: How to export grayscale image as grayscale in PDF?

    Just realized that in the PDF, black text, in addition to K, also has components in the C, M, and Y channels. Indeed in the test print I realized that there are slight color fringes, which I originally blamed on the thick lamination.

    Quote from Xara’s documentation on color separating: “When creating documents based on the default templates designed to be printed, such as US Letter or A4, then the shades of gray defined on the Color Line are defined to be tints of pure "K" black. So if you use these gray colors from the Color Line, you will get quality printed grays.”

    I tested this with a new A4 document, and a rectangle, filled with Black from the Color Line. When exporting to PDF, I selected the Commercial Printing preset. When checking in Acrobat I see that the black box has components in the C, M, and Y channels.

    Am I doing something wrong, or is this a bug / feature?

    Workaround: PANTONE Process Black C maps to only the K channel.

 

 

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