Grayscale PDFs for print, dot gain and profiles

Question

Hi, I work on a lot of books for print that just are K plate only. So far I've generally been asked by various printers to manually prevent TAC going over 80–95% depending on the images and the press, and I've  always done this using curves in Photoshop on a grayscale image with max + min highlight / shadow. Is there a better way than doing this manually?!… I haven't read a lot on here about people working in black and white so much but there must be lots in the same situation as me. I believe that InDesign just ignores whatever profiles are attached to a grayscale image when it's imported, but you can still export to greyscale with whatever dot gain you want – is that going to be better / worse / more / less work than tweaking things in Photoshop? Thanks! I would ask the printer but … they are quite rarely clear or helpful on profiles.

rob day · Accepted Answer

which I've also been told can be caused by too high an ink density. Total Ink drying problems are only a problem with 4-color printing—there’s no way black only at 100% should cause drying problems—if it did you wouldn’t be able to print 4-colors. CMYK profiles limit ink on a color conversion—typically coated sheetfed profiles limit total ink to between 300% and 350%. US Sheetfed is 350%, US Web Coated SWOP is 300%. Uncoated profiles are usually less, Uncoated GRACoL is 280%. The limit is only enforced on a color conversion—you can color correct a CMYK image and force the total ink over the limit. Also, InDesign does ignore embedded Gray profiles, and with Overprint Preview turned on, InDesign displays the grayscale as it would print on the CMYK black plate—the preview of a grayscale would change depending the ID document’s CMYK profile, and how the profile is soft proofing the black plate, but the gray output values do not change. If you are color correcting to Gray Gamma 2.2 in Photoshop, the soft proof of the grayscale is going to change when it is placed in a document with the default US Web Coated SWOP and Overprint turned on. Gray Gamma is a Display class profile, not a press output profile. It might coincidentally profile the press, but it’s not an Output profile for any press.

rob day · Answer

So far I've generally been asked by various printers to manually prevent TAC going over 80–95% Limiting the grayscale black point percentage tops my list of printer’s advice to ignore. That conventional wisdom originates from the 90s when there was no reliable way to soft proof profiled grayscale images. The idea is you can prevent images from going too dark from dot gain or "filling in", but all you are really doing is limiting the already limited dynamic range of a black only image printing on an offset press. Dot gain is most noticeable in the mid range values, and a Gray profile will soft proof the gain through out the scale. Consider this scan of a black only image printed on coated stock from a 4-color press running to the Coated GRACoL CMYK profile:  The patches at the bottom are in 5% increments. There’s plenty of range between 80 and 100%, and there is a clear difference between the 95% and 100% patch. Limiting the black point of this image to 85% would only wash it out   Which gets to the other printer problem: I would ask the printer but … they are quite rarely clear or helpful on profiles. In fairness to the printers, most probably don’t know what the profile for a black only press run is—the profile could change depending on the amount of ink density the press person decides to run. But the Gray profile you assign to a Grayscale image in photoshop soft proofs dot gain so there’s no need to put a limit on the black point. Black Ink profiles tend to be more accrate through out the scale:  Black Ink - US Sheetfed Coated compensates for more gain than Black Ink GRACoL Coated, or Dot Gain 20% More on Black Ink profiles herehttps://community.adobe.com/t5/indesign-discussions/exporting-rgb-cmyk-and-grayscale-to-print-pdf/m-p/10990825#M179498

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