Peculiar Distiller CS behaviour

[Foamcow]

Hi,

I noticed something odd in a PDF I made the other day.

I made a Press Quality PDF of an ad. I then tried the flightchecking capability of Distiller 6 (version shipped with Adobe Creative Suite) and saw that the main image used in the ad seemed to be at 150dpi.

I checked the original Quark artwork and the TIFF file used and noted that the image was 300dpi and was placed into the artwork at a reduced size of 40%.
Now to my mind this meant that it have an effective resolution HIGHER than 300dpi. But for some reason it was being sampled down to 150dpi. I was using the "out of the box" Press Job Options, which shouldn't sample images down to 150dpi no matter what.

Further tests showed that this happened to images when reduced in size in Quark picture boxes. But if the same image was placed at 100% then it's resolution remained at (or was sampled down to) 300dpi.

I did discover that clicking "Full resolution TIFF output" in the print dialogue when making the postscript file seemed to get around the problem.
This may well be the "correct" thing to do. But I have been creating Press PDFs in this way for 3 years plus and never had to worry about doing this.

I intend to perform some further tests and write up the results properly but I wondered if anyone else had observed this behaviour?
Indeed, does anyone else have any comments on this behavior? Does it seem normal?

 

[tgreer]

You've stumbled upon an important issue when working in a "quality critical" environment with Acrobat.

The Distiller settings cannot "fix" the underlying PostScript code. It's the garbage in, garbage out truism at work. Also, Distiller only processes PostScript, not Quark or InDesign or Word native files.

Something has to generate that PostScript, even if you never see it. Quark doesn't generate the PostScript, it uses the PostScript printer driver. If that driver is downsampling images, there is nothing Distiller can do.

Your fix is the correct one, fix it at the point where it goes wrong: the print dialog.



Thomas D. Greer

http://www.tgreer.com

Providing PostScript & PDF
Training, Development & Consulting

 

[Foamcow]

The postscript file is fine.
Well, I did the following test anyway.

Create a ps file (using Adobe PS 8.5 driver).
Make a Press PDF from that file.

Rasterise both the PS and PDF in Photoshop at 300dpi@their actual size.

In the rasterised PS file, the image looks fine and dandy as you would expect.
In the rasterised PDF file, the image is obviously of lower quality.

This lead me to the conclusion that the PS file contains the image at a higher resolution that what is being produced in the PDF.
The difference in image quality is noticable.

 

[tgreer]

Thinking that through, that seems like a valid test. Maybe. I'm not sure what Photoshop might be doing.

Could you post a link to the PostScript in question? I'd like to investigate a little bit. Extract the image directly, see what it is.

Or you can email me, my address is on my website.



Thomas D. Greer

http://www.tgreer.com

Providing PostScript & PDF
Training, Development & Consulting

 

[Foamcow]

If you rasterise a PS file that was generated with "Full resolution TIFF output" on, or where the image wasn't reduced in size then it looks fine.

I'll put up some test files when I get back to work.