Tuning Monochrome Output Settings

Paul Gallagher Landscape photographer

The reign of terror started when I casually remarked to the visiting McNamee that while my mono prints (made using the Epson Advanced Black and White setting) matched my screen perfectly, my colour prints were always too dark. A steely look came over his face and by the time he had turned the electrodes up to 300 volts I was singing like a canary:

“No, I didn’t have a calibrated monitor, I’d lost the profile in a disk failure.”
“No, I didn’t know what Dot Gain I was using.”
“No, I didn’t have the Color Management policies turned on.”
“Yes, I was using the setting that Photoshop came on with, when it was installed.”

Eventually he calmed down, detached me from the lie detector, unclipped the electrodes and started muttering about in the Photoshop color settings thingy. The problem had assumed some importance as I had, by now, confessed to writing a book and, as things were, the outcome of the printing looked a little shaky. Here in a nutshell is the problem that we face – and it is based partly around the fact that I was using mixtures of dot gain values.

Dot Gain

Dot Gain is an effect in the printing process in which a blob of ink hits the paper and then expands a little, so that the dot on the page is bigger than the blob of ink. The increase in the size of the mark on the page is termed the Dot Gain. Just to keep everyone on their toes, dot gain is nothing in the pure whites (no ink to spread or gain) and nothing in the pure blacks (no uncovered space for the ink to go into). The dot gain values are thus largest at the 50% grey point (the 18% grey mid-tone out in the real world of the camera).

Now clever little Photoshop knows all about this and bulges out the tone curve to lighten the ink coverage by the expected amount that it will darken due to the dot gain. Hence if you set up for bigger dot gains than you actually get, you end up light and vice versa. This only happens if you tell Photoshop about it, by turning the colour management on and obeying the rules. Monochrome dot gain settings are just like colour space selection. Incorrectly handling an sRGB file by moving it, in an uncontrolled way, to ProPhoto RGB will create a change in saturation; doing the same thing with a monochrome by moving it, in an uncontrolled way, from one dot gain to another, will produce a change in the tone values.

The rules for handling both mono and colour profiles are, however, the same

1. In Photoshop’s Color Settings use a consistent Gray Dot Gain setting. This is normally 15% in Europe, 20% in the USA and 20%, by default, as Photoshop is installed.

2. Set the Color Management Policies to “Preserve Embedded” for all options and “ask when opening” for all options – that way you cannot be fooled by images from strangers.

3. When you open a file made by somebody else and you are warned that there is a profile mismatch, click the “Use Embedded Profile” option. When you paste a rogue file into another you get the option to “Preserve Color Appearance” or “Preserve Color Numbers” – use preserve appearance. If the pasted pixels are not rogues (ie that have the same profile) then they paste without the warning appearing.

If you do all these things you might just stop McNamee calling – he knows where we all live you know!

ABOVE: The image from the opening spread was adjusted, dodged and burned with a dot gain setting of 20%. In the composite image above, all the available default dot gain settings have been assigned along with the two additonal options of gamma 1.8 and gamma 2.2. The variation across the set is considerable and represents the drift that might be obtained with un-colour managed output. The values in white are the nominal luminance values from exactly the same part of each sub image and show that the mid tones vary between 38% and 59%. Gamma values are normally used for mono images to be displayed on the web

Post Script

Why did my screen match my ABW Epson prints? My uncalibrated screen was too light. The Epson ABW setting produces light prints and so the two actually matched. However, when printing using colour settings and an RGB profile, the printer produced the correct tone but this was darker than the screen. Experience has taught us that you need to reduce the density of the print by between 9 and 11% when using ABW, by dialling that amount out in the setting (see diagram on the opposite page). We often add back about 6% contrast as well. As with all these things there is scope for tweaking and interpretation, never mix up what you like the look of with what a set of numbers might demand! However, consistency is the key to repeatability and accurate reproduction.

“Can I take the electrodes off now Mike?”

ABOVE: Mike McNamee’s analysis of prints made from the Groynes image shows the lightening effect of using the Advanced Black and White setting on the Epson 7800. The bowing out of the curve from the straight line shows the mismatch between the expected and actual values. This may be overcome by tweaking the settings of the ABW driver (see previous page)

Photo Quote: There are no rules and regulations for perfect composition. If there Were we would be able to put all the information into a computer and Would come out with a masterpiece. We know that's impossible. You have To compose by the seat of your pants. - Arnold Newman