Rich, if those plates are blank, it’s expected behavior. If there’s something on them, then come on back.
Bob
There is something on them Bob.
Printing the plates and viewing on the seperations preview in ID and Acrobat shows the pdf image has converted to CMYK, Image data on all 4 plates. When I save a grayscale pdf from v 7 and turn off the black plate, everything disappears from the seperations preview.
It happens on 2 computers here.
Just tested it here and it looks like you found yourself a bug. The grayscale definitely converts to 4 color.
Bob
I was afraid of that. This one is a pretty major deal to printers 🙁
I discovered it in a Photoshop pdf file sent to me from a customer. I had him send me tif files to get around it, but I can see this being a major issue.
I get a t-shirt or something right 🙂
I get a t-shirt or something right 🙂
Yeah, it’s coming along with mine for finding the ID bug which incidently also deals with problems with grayscale graphics.
Depending on what you need to do with those Photoshop PDFs save as PSD, place in InDesign and create a PDF from there.
Bob
Yeah, that will work.
I can get around it easily in-house. I generally place PSD files in ID. I am more worried about customers sending files to me from the Mac side and running into font issues. It can be worked around by rasterizing the text, but I don’t want to look incompentant by not being able to use a customer supplied pdf, when they created it correctly.
Well, you can still open it in Photoshop and it will retain the grayscale. So, you can still use your client’s files and just save them out as PSDs yourself.
Bob
Yes, that’s true. Mac font issues are a concern though.
Indeed, but can’t they be converted to vectors?
Bob
Sure they can, it’s just a step I wouldn’t want to have to require my customers to do. Hopefully the first patch will clear up the problem. I submitted a bug report
I wasn’t talking about your clients doing it. I thought even without the fonts. PS maintains the vector info in case the fonts aren’t there.
Not sure but worth checking out.
Bob
Oh, I wasn’t thinking along that line. I’ll check that out tomorrow.
Thanks Bob.
Rich,
1. A grayscale is a grayscale in PostScript and in PDF,
It´s not separated (Color Space Device Gray).
This is a piece of the PDF code:
/Type /XObject
/Subtype /Image
/Interpolate false
/Filter /DCTDecode
/Width 3008
/Height 2000
/BitsPerComponent 8
/ColorSpace /DeviceGray
/Length 11 0 R >>
stream
For separations the image has to be converted to CMYK.
2. Using any CMYK profile delivers rich black CMYK (all plates).
3. Using any CMYK profile with custom settings GCR, Black Generation Max. delivers three empty plates CMY and the grayscale on the K plate.
The PDF contains exactly the respective informations:
1. Gray
2. Rich Black
3. K-only
Version 1 doesn´t contain informations about the intended printing process, whereas for 2,3 a profile including dot gain was chosen.
The RGB to grayscale conversion is independent of CMYK profiles.
Tested by PhS6 and Distiller 5. It´s probably the same in newer versions.
Best regards –Gernot Hoffmann
Tested by PhS6 and Distiller 5
Hi Gernot,
It works correctly in PS 7 also. When you save the PDF from CS and place it into ID (or open it in Acrobat) the grayscale has now become CMYK (or possibly rich black) with image data on all 4 CMYK plates.
Saving using the same method in PS 7, all the grayscale image date stays on the K plate only, as it should.
Rich
Tested by PhS6 and Distiller 5. It´s probably the same in newer versions.
Gernot,
You went to a lot of trouble for nothing. We already established that it works in earlier versions. It doesn’t work in the current version.
Rich points out that this happens when placing in ID but the bug is in Photoshop since it shows as 4 colors in Acrobat 6 professional.
Bob
Rich,
in your original post you are saying that the image is "grayscale". The interpretation of a grayscale in CMYK values is undefined (depends entirely on the active CMYK profile).
Or do you mean that the grayscale was already converted to K-only in advance to Distilling ? IMO, that´s the only correct method.
For further tests I would download the free trial version of "Quite a box of tricks" by <
http://www.quite.com> This programs shows how the images in the PDF are coded.
Another question in this context:
The K-only version of a grayscale shows the "composite CMYK preview", which uses three empty plates and K, as expected, but the K-plate alone looks much lighter. This seems to be a preview of the positive K-plate which is lighter because of the dotgain compensation. Is this correct ?
Best regards –Gernot Hoffmann
Bob,
I have read the whole thread once again.
A grayscale was packed into a PDF. There is IMO no guarantee how this grayscale appears on plates.
A grayscale in a PDF is in DeviceGray, not in CMYK. That´s so for PhS6, can be tested for PhS7 if necessary.
Best regards –Gernot Hoffmann
Gernot,
You are exposing my lack of specific details about Photoshops inner workings 🙂
What I’m doing is taking a CMYK image, and converting it to grayscale (image>mode>grayscale) and clicking ok when asked to discard color information. I would assume then that this image should be all on the black channel.
When saved as psd or tif, the color information works as expected when opened/placed in another application. All image data remains on the K plate. When saved as a pdf however, the image data is now on all 4 CMYK plates.
The PDF works as expected in Photoshop 7.
Gernot,
While I would not want to match my limited knowlege of color with yours, I can confidently tell you that you are way over analyzing this.
It’s grayscale which means there’s only one channel–BLACK. The graphic is on one black plate in earlier versions of Photoshop.
When saved as PDF from PS 7.0 and earier, the entire image remains just shades of black. When you do this with PS CS it separates into 4 colors.
IT’S A BUG!
Bob
Rich, Bob,
thanks for the feedback.
Aha, the workflow was CMYK–Grayscale–PDF.
Now tested by PhS7: it´s the same for RGB–Grayscale–PDF: The PDF uses in both cases the colorspace DeviceGray,
instead of DeviceCMYK.
The interpretation as separations is then up to the program which reads the PDF.
Perhaps there is a hidden parameter which allows to pack the grayscale into the PDF as K-plate in DeviceCMYK .
Are the global Distiller Job-Options valid for PhS ?
Best regards –Gernot Hoffmann
It’s a native save in Photoshop. It has nothing to do with distiller.
I know you want to find something here, but there’s nothing to find.
It’s a bug! Now let’s move on… Please. 🙂
Bob
Rich,
I am an engineer responsible for the PDF code in Photoshop, and cannot reproduce this problem. The PDF I generate has only /DeviceGray image data, and when using Acrobat Separation Preview, the image only appears in the K channel, as it should.
Are you by any chance using Automate > PDF Presentation to save the PDF, or are you using the standard "Save as PDF"? What other options are you setting when you save the PDF? If you have a small example file, I’m happy to take a look at it.
Paul
Paul,
I’ve duplicated Rich’s problem here. Would you like me to e-mail you a file?
Bob
Hi Paul,
I am using the standard Save As, with the default settings. Encoding Zip, save transparency checked.
The file I have is about 1.2 MB. I will be glad to e-mail it to you if that size is small enough.
I have reproduced it on 2 machines here, Bob was able to reproduce it, as well as my customer who sent me a pdf.
I appriciate you looking into this.
Rich
Trying to get my T-shirt Bob 😛
(g,r,& d)
You can email the files to me at ferguson (@adobe.com) If you can crop the documents down so they are smaller (I usually test on 8×8 pixel images), that would be better; it shouldn’t affect the problem, but does make it easier to examine the PDF contents. If you could send both the original PSD and the resulting PDF that would be helpful.
Ok, I cropped the origional psd down and saved it and a pdf version. They are on the way to you. I checked the pdf, and this one also has image data on the CM and Y plates when viewed in ID and Acrobat seperations preview.
Thanks Paul.
There’s one on it’s way from me also.
About 100 k total between the two files. Please let us know what you find.
Bob
Got the images, and it appears this is related to color profiles. If you don’t embed the color profile by unchecking Embed Color Profile in the Save As dialog, then the separations only show image data in the K channel. With a profile assigned (I’ve tried 20% dot gain and sGray), I am seeing the separation behaviors you reported. However, the image data in the PDF generated by Photoshop is /DeviceGray in all cases; Photoshop is not writing CMYK to the PDF.
Interesting. It seems that v7 works this way as well. It just happened that the file I tested with did not have the ICC profile checked by default when I saved.
Do you know what would cause the ICC profile to check by default, or not check by default? Why would the profile cause the pdf to convert to CMYK? It’s strange that I have never seen this happen before now.
Also, the color profile does not seem to change anything for PSD and TIF files
Paul,
very interesting.
A CMYK device interprets DeviceGray as pure K if no profile is embedded. If a profile is embedded (dot gain) then it should be the same, but in this case the profile is understood as a full CMYK profile and therefore all plates are con- cerned or affected. Right ?
If we convert RGB (or CMYK) to grayscale then we dont´t SEE any difference in the monitor preview, whatever dot gain (or gamma) is assigned in Color Settings. Does this mean that the file is MODIFIED for the chosen dot gain, but the modification is not shown ?
And why are the grayscale dot gain settings not the same as the dot gain settings for CMYK ?
I suspect that this is caused by the uncertainty of the destination – at the time of the conversion it´s not yet defined whether the grayscale is intended for RGB (gamma=2.2) or for K printing (dot gain as in CMYK profile, IMO).
Best regards –Gernot Hoffmann
Same here. Odd behavior. And IMO incorrect behavior.
Bob
Gernot,
I am no color expert, but here’s an interesting experiment to try: Create a new grayscale document in Photoshop (to keep things simple, specify no color management). Then create a gradient from white to black across the image, and convert the image to CMYK. Examine the resulting CMY channels and the K channel; you’ll see that the gray gradient you created has been split between CMY and K as the gradient changes from white to gray to black.
I suspect what is happening in Acrobat and InDesign is that if it finds a color profile with a grayscale image, it uses that to separate the gray image data in a similar fashion. If no profile is present, it takes a more conservative approach of not assuming anything about the grayscale image and just puts the whole thing into the K channel. Perhaps one of the more knowledgable folks on this forum can shed more light on this…
When saving a grayscale PDF in CS, the resulting pdf is somehow getting converted to CMYK. I checked the seperations in InDesign and Acrobat. Both show CMYK plates.
OK, you guys got me lost here. You have declared this a bug but where is this bug?
I save Grayscale image as PDF in PS CS. It opens as Grayscale image in PS CS. Where does it get converted to CMYK? If another Application converts it to CMYK how is this Photoshop bug?
Gentlemen,
it´s perhaps more a missing insight into the actual state of the rendering process than a bug.
Profiles (for printing) use CIELab as profile connection space. A grayscale profile is merely a tone reproduction curve (gamma or dot gain curve). If an embedded or assigned grayscale profile is applied then the intermediate output is CIELab.
The three numbers L,a and b are inputs for a CMYK look-up table which delivers CMYK, based on definitions for black generation. All plates contain data. The original information "K-only" is lost.
I think this is a reasonable explanation, because I get just the same effect by a large format RIP if the input profile is Any CMYK profile instead of No CMYK profile: K-only images are printed CMYK then.
IMO, Grayscale (represented by DeviceGray in PostScript), is an ill-defined color space. One has to find a solution for a specified workflow (above for the PDF, as explained by Paul: no use of a grayscale profile).
There is no guarantee that grayscales are printed by all PostScript devices by K-only: (Lexmark 4079 prints always CMYK, QMS Magicolor 6100 prints K-only if the file is Indexed Color Gray, RIP Postershop prints K-only if it´s a CMYK K-only file and no input profile is chosen. RIP Best Colorproof prints K-only if it´s a CMYK K-only file, even with assigned input profile) . All tests by packing the images in PDFs. No experience with imagesetter RIPs.
Best regards –Gernot Hoffmann
If another Application converts it to CMYK how is this Photoshop bug
I don’t know this is a Photoshop bug for sure, but something is not correct in my opinion.
If a grayscale tif or psd file seperates correctly in another application, I would expect a pdf to do the same.
If I need to uncheck color profiles for pdf’s to get correct seperations, I would expect to have to do the same for tif and psd. And embedding the profile should not be checked by default if this is going to cause problems when it gets to the final output destination.
I just think the steps needed to save should work the same for all the format options. I have customers sending me files for printing. They do not have Gernot’s very impressive understanding of how color works. Nor do the necessarily understand all the options in the save dialog. They just want a photograph printed in one color.
