PDF ink coverage?

[leonardr]

Obviously, all the color images in your PDF file must be CMYK or they must be converted into CMYK, before they can be printed.

This is not true in many cases.

1 - Images comes in all sorts of forms that can be output on a CMYK device w/o conversion. For example, Black&White, Grayscale, Spot Colors or DeviceN.

2 - Not all printers are CMYK. Many include other colors than just those - especially inkjets. And, again, let us not forget about spot colors.

Unfortunately all images that come from a scanner or from a digital camera are RGB until they will be converted into CMYK. Maybe, some day, cars will be able to fly to the moon but there will never, ever be a scanner or a camera that directly catches pictures in CMYK mode.

Actually, there have been "CMYK scanners" - but in general, yes, I agree.

Another complicated thing is the fact that there are different places where the RGB to CMYK conversion can be done. It can be done in Photoshop, then you have a technique which is called Early Binding. It can be done while the PDF file is exported, then you have a technique called Intermediate Binding. It can also be done by the print shops prepress in the PDF file, this technique is called Late Binding.

Actually, you missed one of the most common ones in use today - automatic handing in the RIP. In which case the PDF containing RGB images is sent to the printer/RIP and it handles it during the printing process.

There are several ways to change the ink coverage even when a PDF already is CMYK. For example you can convert the file from CMYK into RGB and then back into another CMYK profile or you can directly convert it into CMYK by using a special Device Link Profile.

While such things would have worked in the dark ages of print production, in the world of PDFs containing live transparency, such as with PDF/X-4, color conversion is a BAD IDEA.

 

[ASchuett]

Hi leonardr,
thanks for your answer.

Photoshop is NOT a PDF RIP.

You're right! Photoshop is NOT a PDF RIP-Software and Photoshop is NOT a software for PDF editing. And in my post I am NOT suggesting to use it as such. I am suggesting to use Photoshop as a quick and dirty way to get an idea if the PDF will consume a little, a medium or a high amount of ink.

Actually, there have been "CMYK scanners"

There have been scanners that gave you CMYK files in the past, that's true. But even these had to scan in RGB first and then the scan software made the CMYK conversion.

1 - Images comes in all sorts of forms that can be output on a CMYK device w/o conversion. For example, Black&White, Grayscale, Spot Colors or DeviceN.

You're not completely right! I am talking about COLOR images and i am answering to a question about OFFSET printing. You definitely cannot print any color images without Conversion, not in CMYK, not in Hexachrome, nor in Spot Color. Digital printers are not subject of my post. But even though some of these can do the conversion internally, it still is a conversion.

Actually, you missed one of the most common ones in use today - automatic handing in the RIP. In which case the PDF containing RGB images is sent to the printer/RIP and it handles it during the printing process.

InRip conversion IS one of several late binding techniques and I only mentioned late binding in form of PDF conversion. So, thank you for this point, i did not think about this.

While such things would have worked in the dark ages of print production, in the world of PDFs containing live transparency, such as with PDF/X-4, color conversion is a BAD IDEA.

Maybe. But where, exactly, do i recommend to use such techniques without background knowlede and care?

Although I do not completely agree with your points, I think we both share the common view that one should be really, really careful and aware of such things.