How to export grayscale image as grayscale in PDF?

Steps:

1. Open the attached document in Xara Designer Pro X11. The included image has no color information. It is purely gray scale.
2. Export as PDF for commercial printing.
3. Extract the image from the PDF, e.g. using pdfimages: pdfimages grayscale.pdf img
4. Open the exported image in Xara or e.g. the Gimp.
5. With the color picker inspect the gray areas. They contain color information now. For example, what was #999999 in the original Xara document is now #8e8582.

The problem is that the colors do appear in print, as an undesired tint.

How do I properly export a PDF with all images as grayscale? In the actual document, only text has color.

Xara products have no concept of grayscale. All gray images are converted to RGB, generally maintain appearance very well, and are exported to the appropriate profile upon PDF export. To an RGB profile, those gray images will/should maintain their RGB values, to CMYK they will be an appropriate CMYK mix.

This has been a long-standing request--to handle gray images.

One can use Acrobat to convert gray images to K only.

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Originally Posted by mwenz

One can use Acrobat to convert gray images to K only.

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Thanks for clarification! Any alternative to $$$ Acrobat? I’m fine with command line tools.

Update: Discovered a tool myself, A-PDF Black/White. The suggested use case is minimizing file size by converting PDF files to gray scale. Via settings it is possible to specify that only images, i.e. not text, should be converted. That seems to do the trick, although I haven’t yet verified the output thoroughly.

Not that I am aware of. One version back of Acrobat is generally available from some (valid) retailers if one looks hard enough. Still there is a cost. But I cannot imagine doing commercial print without Acrobat. It's not like, at least on Windows, there is need to always update it. I know shops running version 9 still. In fact, version 9 is probably the last "near perfect" version

While I don't need to mix CMYK and gray images--if there is a gray image typically the whole thing is gray--unlike some other applications, I also cannot choose a non-CMYK or RGB ICC/ICM profile for PDF generation. So, for instance, I cannot choose a gray, or B/W, PDF profile from inside XDP. Nor, like other applications, is there an in-built option for choosing Grayscale, or B/W, as a valid output color model.

While the above doesn't help in your case of mixed gray images with colored elements that need to remain colored, it would be nice to at least have the option. I suspect the PDF library Xara uses has that option, just not as an option within Xara applications.

Mike

Reimport your PDF into Xara and check your text values on grayscale as Xara likes to give Rich Black instead of a % of K. If it had done this just move the K slider one way and then adjust the K value to the % that you want and then resave the PDF then all is sorted.
I agree with Mike here, if you're going to send more than 1 file a month for print it is really worth your while to buy a copy of Acro Pro. For people who use print it's the best tool in your bag.

Don't reimport the pdf to check the result...it will recovery it. If you want to check the output, upload a sample and I'll check in Acrobat.

I have long used A-PDF's various utilities. But not this particular one. To check that text remains text is easy enough. See if you can select the text after a conversion.

Mike

Thanks for the suggestions. Some notes:

• Text stays text with A-PDF. I would be surprised if it doesn’t, since the advertised use case of the tool is to shrink PDF size. Only – as I wrote – one needs to check an option in order to prevent colored text from being turned into grayscale.
• There is no grayscale text in my document. Only black and orange.

Concerning Acrobat: Asides from converting images to gray scale, what use cases are there when preparing Xara documents for printing?

I guess Acrobat’s standard version is sufficient. XI Standard can be found for less than a hundred bucks on eBay, for example. The pro versions seem to add features such as multimedia and 3D, which I don’t need.

It's not just an issue of preparing Xara PDFs for print. I use it on every job regardless of what I am using at the time to create the PDFs.

I have no idea what Acrobat versions do what. I have always used the Pro version--once upon a day, there wasn't the Standard/Pro distinction. One thing to check for would be whether the "Print Production" tools are in the Standard version and what those tools are comprised of (compare to the Pro version if you can find a comparison chart). One can transform just about anything in at least the Pro version. I often need to convert text that is rich black to 100%k--and vice versa depending on the point size. I often need to flatten transparency but keep text live text, the list of how I use Acrobat can go on.

I also don't know whether plug-ins are available in the Standard version. I use two different plug-ins and while the maker released a stand-alone version of one of them, the other will likely always be a plug-in.

As for buying off of eBay, you do know the risks of whether a computer application can be registered, whether it is a legitimate copy, etc., right?

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Originally Posted by mwenz

Not that I am aware of. One version back of Acrobat is generally available from some (valid) retailers if one looks hard enough. Still there is a cost. But I cannot imagine doing commercial print without Acrobat. It's not like, at least on Windows, there is need to always update it. I know shops running version 9 still. In fact, version 9 is probably the last "near perfect" version

While I don't need to mix CMYK and gray images--if there is a gray image typically the whole thing is gray--unlike some other applications, I also cannot choose a non-CMYK or RGB ICC/ICM profile for PDF generation. So, for instance, I cannot choose a gray, or B/W, PDF profile from inside XDP. Nor, like other applications, is there an in-built option for choosing Grayscale, or B/W, as a valid output color model.

While the above doesn't help in your case of mixed gray images with colored elements that need to remain colored, it would be nice to at least have the option. I suspect the PDF library Xara uses has that option, just not as an option within Xara applications.

Mike

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Mike,
How do I convert a color png to a grayscale png in Acrobat 9 Standard? I can't figure it out.

Don't think Acro Pro could handle that Ron needs to be done in PS/Gimp. Mind you my copy of Acro Pro is old it's CS3 so don't know if you can with more recent versions or not and there could be now plugins available for the job.

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Originally Posted by Ron Duke

Mike,
How do I convert a color png to a grayscale png in Acrobat 9 Standard? I can't figure it out.

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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

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.

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Originally Posted by mwenz

Convert Colors is the dialog you want. Let me know if you have that panel/dialog box.

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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).

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.

Quote:

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Originally Posted by mwenz

But it would seem to me that triple-processing you show in that link is a fault in work-flow.

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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?

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I would leave the image in XDP (or whatever you are using) as an RGB.

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It’s a grayscale scan. Only Xara exports it as RGB.

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10% dot gain if going to print digital

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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.

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.

Attachment 112179

Mike

Quote:

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Originally Posted by mwenz

In acrobat, converting it to grayscale yet again is another processing.

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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:

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Originally Posted by feklee

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.

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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.

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.

Quote:

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Originally Posted by mwenz

There is no need to replace the image in Acrobat.

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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.

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.

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.

You are not doing anything wrong as regards the so-called shades of Black on the default color line. It is that the help file is a bit mis-leading. Yes, they will be "quality printed grays." But that doesn't mean they won't be a mix of CMYK or RGB values (depending upon the output intent).

Make all your text 100% K. Now, there is a lomg-standing bug in Xara products that can catch one out. That is, if one has an object defined as RGB of 0,0,0 and switches to the CMYK color model in the Color Editor, it will show as 100% K. It most definitely is not 100% K. It is a rich black composed of X amounts of CMY plus a high percentage of Black (if not 100% sometimes).

But with such an object selected, if you make the CMY sliders 0% if not already, then slide the K slider down a bit and back up it should work.

I use my own palette that avoids this issue.

It's a feature! See my advice on #5 on this thread as I was thinking that you had a bitmap with text. This has always been one of the silly quirks of Xara. Just re-import your PDF and adjust K value and resave. For any bitmap that you want to be commercially printed you should start this process off in a Bitmap editor. You can use Grayscale or Lab but the best way is to using the "channel mixing" route. Just do a quick search "colour to BW + channel mixing". The reason for using this method you have much more control of the output and therefore better definition. Here a tut for P/Shop but I am sure that you could do the same in Gimp which is free to download: http://www.photoshopessentials.com/p...olor-channels/

mwenz, Albacore, thanks a lot for all the advice!