Color density in photoshop

One of the advantages some of you have, living on the other side of the pond, is that you have the opportunity to take the first bite out of some juicy posts such as this one.  

As a result I had to content myself with a leftover: trying to come up with a valid reason for the number 240 to be appropriate anywhere at all in the graphic arts.

I came up almost empty and now submit my findings. If you can add to the list I will be forever grateful.

1. Before the industry settled into the custom of considering a  ream of paper to be 500 sheets (now sometimes called a long ream) it amounted to only 480 sheets (you guessed it: called a short ream by the printing nerds) and half of a short ream is 240 sheets.  

2.  I was lucky enough to have been around when densitometers were introduced into pressrooms. They were clunky devices with potentiometers (we called them “pots” ) that were both magical and inconsistent.  One day I took a machine home from our printing plant to test and determine the d/max of each of the papers I used in the darkroom.  That was ages ago but for some reason I can still recall that Polycontrast developed in Dektol, when dried, measured a density of 2.4. I admit that 2.4 is not 240 but give me a break.

3. As a  lithographer I included myself in the list.  I was married at 24. Let’s say that counts because I just celebrated my sixty-ninth anniversary. (Do the math.) Since you didn’t send a gift please allow the number 24 to be a valid entry. After all, 2.4 made the cut. 

And make sure to embed the RGB Profile when saving the file. 

240% TAC – is that for a newspaper? 

These are mutually exclusive requirements. Are you sure they really know what they're doing?

"maximum color density of 240"

That sounds like the CMYK ink limit, known in the trade as Total Area Coverage (TAC). That's the maximum amount of total ink before you risk ink smearing and drying problems. The thing about TAC is that it's built into all CMYK profiles. If you convert from RGB to any specific CMYK profile, TAC is automatically applied and that's the deepest black you get. It can't go over the limit. This limit is normally in the 270-320% range, and 240 is on the low side.

Any CMYK profile represents a particular printing process; a press calibrated to a certain standard, a certain set of inks used, on a certain paper stock. There is no such thing as a generic CMYK. You always need to know which CMYK profile to use. The Photoshop default (US web Coated SWOP) probably doesn't apply, it's just there because there has to be some default.

TAC does not apply to RGB.

The long and short of it is that these instructions you got are incomplete and problematic from the start. They haven't given you the information you need. If this is an important job, I'd call this an emergency and demand to get through to them. They need to give you a CMYK profile to use. If they don't, you can't do a proper job.

The alternative is to go guessing. You can probably do some research and find a CMYK profile that seems to be commonly used in your part of the world, with a 240% TAC, and hope it's not too far off. Or you can find a profile that seems to match what you know about the actual printing process, regardless of TAC - and then manually check in the info panel that you don't go over anywhere.

RGB files cannot have density because they are not based on ink simulation. Whoever fired this nonsensical requirement at you probably doesn't know what they are talking about. That being the case, you need to get on the phone with someone who actually understands the issue. Ideally you would obtain a color profile that simulates the printed output that already accounts for ink densities and based on that you could tweak your RGB artwork. Everything else just doesn't make any sense, at least not on a mundane standard RGB to CMYK print workflow. If there is anything more involved like e.g. using dedicated spot colors or "photo inks" in on-demand-printing inkjet machines than that's a whole different thing and cannot be handled wit hso little info and basic adjustments. Again, you need to talk to someone who actually knows what is required.

Mylenium