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View Full Version : Film knockout errors. Where does it happen.




dogbone
Sep 19, 2006, 03:28 AM
Sorry for the confusing title. I've just had a look at a job I did as it was being run out. To my horror some black type on an light ochre background had the ochre knocked out. That is the black was printing on white.

Fortunately it printed OK as the printing gods were happy today. However I want to locate where this problem occurred.

I checked the separations in the original Indesign document and they look good. I then checkecd the seps on the pdf's that were sent to the filmakers, in Acrobat, and the seps look good there too. So I know that the cock up has happened at the film setters.

I want to talk to them tomorrow to avoid this happening again but I don't know how film makers work with a pdf file. I always thought that a pdf file was to avoid precisely these sorts of problems. If Acrobat is telling me that the magenta and yellow plates have no knockout then how the hell does the platemaker somehow add knockout to the pdf file?

Do the platemakers use some sort of software that takes a pdf and reprocesses it before sending it to the filmsetter? Or what. How would others here deal with this problem.

Thanks.



leumluath
Sep 19, 2006, 08:13 AM
To output your job to film, a program called a RIP (raster image processor) converts your PDF into instructions the imagesetter understands. And yes, Postscript instructions can be added for output. This is where the knockout is being controlled, overriding your file settings.

Talk to your printer (as you're already planning.) I install and train on the PrePRESS Panther RIP at newspapers, and knocking out undercolors is standard behavior. However, postscript instructions can be added to the job to make it overprint rather than knock out. You don't say what RIP or imagesetter your printer is using, but they probably have a similar function available.

Sorry for the confusing title. I've just had a look at a job I did as it was being run out. To my horror some black type on an light ochre background had the ochre knocked out. That is the black was printing on white.

Fortunately it printed OK as the printing gods were happy today. However I want to locate where this problem occurred.

I checked the separations in the original Indesign document and they look good. I then checkecd the seps on the pdf's that were sent to the filmakers, in Acrobat, and the seps look good there too. So I know that the cock up has happened at the film setters.

I want to talk to them tomorrow to avoid this happening again but I don't know how film makers work with a pdf file. I always thought that a pdf file was to avoid precisely these sorts of problems. If Acrobat is telling me that the magenta and yellow plates have no knockout then how the hell does the platemaker somehow add knockout to the pdf file?

Do the platemakers use some sort of software that takes a pdf and reprocesses it before sending it to the filmsetter? Or what. How would others here deal with this problem.

Thanks.

dogbone
Sep 19, 2006, 09:00 AM
leumluath, thanks for that useful reply. I'll find out tomorrow about their rip.

If this is standard behaviour can you enlighten me as to the reason. I would have thought that a low res ouput like a newpaper with higher dot gain would be even less likely to want to knock out undercolours for black type.

It can't be for ink build up because black type is only ever going to go on top of a relatively light background.

leumluath
Sep 20, 2006, 08:12 AM
The primary reason is to avoid picking up the undercolor in the black and giving it a color cast. Excessive ink density would be another reason.

The downside would be that the knocked out job would be more critical to register, and the counter to that is trapping.

leumluath, thanks for that useful reply. I'll find out tomorrow about their rip.

If this is standard behaviour can you enlighten me as to the reason. I would have thought that a low res ouput like a newpaper with higher dot gain would be even less likely to want to knock out undercolours for black type.

It can't be for ink build up because black type is only ever going to go on top of a relatively light background.