Dot terminology

[Gregg]

When someone mentions that they are having their press fingerprinted and that dots are being measured what is the proper term for dot measurement?

I know in digital printing they use the term picoliters (at least I read that somewhere).

Is the same measurement term used for offset?

Thank you in advance.

[bluekivi]

"Dot Gain" would be the term we use. The dots in offset printing usually gain a nominal amount when transfering from plate to blanket to paper. Also, the stock used will affect the amount of gain. Uncoated gains more than coated stock.

[Gregg]

Yes, I understand Dot gain (well to some degree), but how is it measured. Meaning, how do you determine that your press, using a matte coated stock is going to produce a 15% dot gain?

My phrasing of the question may be wrong. But I'm thinking there is a unit of measurement used to measure a dot, correct?

[MarkTonk]

Gregg,

Picoliters is a term used to describe the smallest size an ink droplet is on a inkjet printer and is not used in describing a halftone dot. Measurement of a dot is referred to as dot percentage i.e 49% dot, 2% dot.

You need a densitometer that can be programmed to read "dot percentages" on the press sheet. Typically when finger printing, first make sure the plate has the proper exposure on the CtP. Then output plates with a test chart (if it is a 4 color press, out put the chart on each color, make sure they do not over print each other, you want to be able to read each color on the printed sheet). The test chart will have different steps with dots, for example 2, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 95, 100. Have the pressman hang the plates and run to his standard densities. Make sure the sheet has also even densities across. Now read each color with the densitometer reading dot percentages and this will tell you you dot gain. The 50% may read 68% (the dot gained from 50 to 68) and this would be very acceptable for sheetfed on a good coated stock. Any way, once you know where you dot gain is, you now have the option of increasing or decreasing it to match your ideal target for gain. This requires knowing what you want the gain to be, it could be based on SWOP or GRACol, or others. If you output dot gain does not match your target, then your rip should have software that allows you to change it so it will. On Heidelberg's MetaDimension, we call this software Process Calibration.

Regards,

Mark

[Gregg]

Thank you. Good info. I appreciate it.

[madhura mahajan]

When we say it is 20 % dot it means 20% dot and 80 %paper. So if there is dot gain then automatically 80% paper becomes less depending upon how much the dot gain was..