How to export grayscale image as grayscale in PDF?

[mwenz]

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

[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. This is unexpected to me. For details, see my question in Graphic Design Stack Exchange.

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).

[mwenz]

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.

[feklee]

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.

[mwenz]

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.



Mike

[feklee]

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:

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.

[mwenz]

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.