Applying Halftone Curves To Images For Print Production?

Question

I know what you see on a computer screen, comes out darker in actual print form. I contacted a vendor and he told that to compensate for this, I need to apply halftone curves to my photos. Unfortunately, I don't know if I properly applied them and Google isn't any help.

Here’s my current process when preparing photos for print, right or wrong:

The vendor requirements were Highlight 3% / Shadow 90%

I first convert the images to either CMYK or Grayscale
I get the pictures all cleaned up, color corrected, etc.
I apply an adjustment layer of Curves.
Within Curves, I set the Highlight eyedropper to the print vendor’s setting.
Within Curves, I set the Shadow eyedropper to the print vendor’s setting.
- The vendor says to then hit “Auto” and adjust manually until I get the desired look, but this completely messes up the photo, so I set the highlight and shadow eyedroppers and don’t touch anything else in Curves.
I then apply a Levels layer
Within Levels, I move the Shadow slider to 8 (approx 3%)
Within Levels, I move the Highlight slider to 229 (approx 90%)
Within Levels, I adjust the midtone, if needed
Next, apply any additional adjustment layers as needed.
Save

Is this the right process? Am I doing steps wrong, missing steps, have too many steps…?

Any help would be appreciated!

D Fosse · Answer

This sounds like a printer from the last century, before color management was invented. They should just give you a CMYK profile to convert to, done. I'd turn right around and go elsewhere.

There are two things to consider.

The darkening the printer refers to here is known as dot gain, caused by ink spreading in the paper. This makes the halftone dots larger than intended. Dot gain can be a fairly complex curve, which is compensated in modern CMYK profiles.

A CMYK profile is always press/paper/ink specific. The profile describes the final output given a certain input. Presses are calibrated to standards that vary regionally, so that they behave predictably. This reduces the variables, so that in practice, different CMYK profiles correspond to different paper types, in different geographic regions.

But there's one other thing.

If your screen is too bright, the print will be too dark. You need to calibrate your screen to get a visual match. You need to set monitor white so that it is a close visual match to paper white. This is important! You should "see" paper white on screen. It makes perfect sense: the color of the paper is not adjustable, it is what it is. So that has to be your reference, and you adjust your monitor - which after all is just a proofing device - to match that.

You can do all this in the monitor's OSD controls, it should be done before running any calibration software. Since your perception will be heavily influenced by your working environment, this is a purely visual process - just tweak until it looks right. Numbers are secondary to irrelevant (other than as reference)

If you do this with some care, what you see is what you get. You'd be surprised how close it's possible to get, especially if you also adjust the black point in the same way.

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