Characterizing the Inks

Characterizing the Inks (actually a specific ink/paper combination) is a two step process. This process is made quite easy by QTRgui, since it one does not even need a curve to perform this step. Using QTRgui, select menu item Options/Calibration Mode.

Once you select this option QTRgui will automatically select the Ink Separation Test Page as the image to be printed and set the Ink Limit and Gamma adjustments to 0. Make sure the other settings (Dither, Resolution, and Speed) are as you would normally use them.

To print the first Ink Separation Test Page, place a piece of the paper for which the curve will be designed in the printer, make sure the calibration slider is all the way to the left (100) and click the print button.

Hardware Ink Limit Calibration

It’s a good idea to let the printed page sit for a while to let the inks stabilize. Next figure out the overall hardware ink limit for the printer. This can be done visually by just looking at the test print and deciding where the inks seem to max out -- i.e. fill the patch.

Ink Density Calibration

The next step is to print out the Ink Separation Test Page again setting the calibration slider to this limit.

Now measure the density of each ink in terms of the darkest ink. The nice thing about this is that the numbers are not important, you just have to match one patch with another one. You are also deciding the order of the inks to be used during this process. Determine the darkest ink (probably black) then the next darkest, etc. that will be used for gray ink (or toner).

The darkest ink limit will be called 100. Now match the density of the limit for the next lighter ink with the matching density of a percentage of darkest ink. You can measure this with a densitometer but it's easy to do this with a scanner as well. If you do use a scanner, open the scanned image in your image editor (e.g. Photoshop) without color managing it and use the info palette with 5x5 sampling. If the density fits between two black patches, interpolate the value.

This process is repeated for each lighter ink, comparing it to the next darker ink, calculating its density relative to that ink and then converting it to a density relative to the darkest ink. Record these values in the appropriate ink density box.